A basic feature of multicellular animals is the formation of diverse kinds of tissue, such as skin, blood, or muscle, where cells are organized in specific ways. Cells must also be able to communicate with each other and have markers of individual identity. 

The nature of the physical connections between the cells of a tissue in large measure determines what the tissue is like. Indeed, a tissue’s proper functioning often depedns critically on how the individual cells are arranged within it. 

Most cadherins function as transmembrane adhesion proteins that indirectly link the of the cells they join. This occurs in Cell Junctions like the adherens junctions where the cytoplasmic tails of cadherins interacts indirectly with actin filaments by means of a group of intracellular anchor proteins called “catenins” and with desmosomes where the cytoskeleton is intermediate filaments.

Occluding junctions: include the tight junctions whose role is particularly prominent in the small intestine where they prevent transport proteins at the apical surface of the epithelia cell (surface facing the lumen) from mixing with those in the basolateral surfaces of the cell. In addition tight junctions insure that spaces between epithelia cells are sealed so that transported molecules cannot diffuse back into the gut. Major transmembrane proteins in a tight junction include the claudins and occludins. 

Adherens (Anchoring) junctions: 

Adheres junction connect the cytoskeleton of a cell to the cytoskeleton of other cells using the transmembrane protein cadherin or to the extracellular matrix through the use of the TM protein integrin. In both cases, there is an intracellular coupling to either actin or intermediate filaments depending on the type of intracellular anchor proteins involved. 

Cadherin sueprfamily: is a large family of Ca2+ dependent adhesive moelcuels found in viturally all all metazoan animals. 

Desmosomes: are a cadherin based unciton unique to vertegrates. They contain the cadherins desmocollin and desmoglein, which interact with intermediate filaments of ctoskeletons instead of acin. Desmosomes join adjacent cells. These connections support tissues again mechanical stress. 

Hemidesmosomes and focal adhesions: connect cells to the basal lamins or other ECM. In this calse the proteins that interat with the ECM are integrins. 

Communicating junctions: 

Communicating junctions include the gap junctions which form channels through transmembrane proteins called connexins. 6 connexins are required to form a channel (called a “connexon”) and when the connexons in the PM of 2 cells in contact are aligned, they form a continuous aqueous channel that connects the two cell interiors. These junctions allow communicaiton between cells by diffusion thorugh small openings. Communicating junctions permit small molecuels or ions to pass from one cell to the other. In animals, these direct communicaiton channels are called gap junctions and in plant, plasmodesmata. 

The various anchoring junctions are contained in the chart below:

Cells adhere to each other and to the extracellular matrix through cell surface proteins called cell adhesion molecules (CAMs). Tissue architecture is established and maintained to a large extent by specific affinities of cell surface glycoproteins for molecules in the extracellular matirx or on the surface of adjacent cells. CAMs function not only to fix cells in specific locations within tissues adn regulate their movement but also to translate biochemical information from the extracellular environment through the activation of intracellular signaling pathways leading to specific cell functional resposnes. Some CAMs are Ca2+ dependent whereas others are Ca2+ independent.  Adhesion molecules can be divided into four families: (1) immunoglobulin-like adhesion molecules, (2) selectins, (3) cadherins and (4) integrins.

Cadherins are the major CAMs responsible for Ca2+ dependent  cell-cell adhesion in vertebrate tissues. There are many types of cadherins which make up the cadherin family and cells in culture can sort themselves out according to the type and level of cadherins they express.  Most cadherins are single pass transmembrane glycoproteins that have a large extracellular part of their polypeptide chain folded into 5 or 6 cadherin repeats. Ca2+ ions are positioned between each pair of cadherin repeats. The more Ca2+ ions bound, the more rigid the structure. 

Selectinsarenother major CAM responsible for Ca2+ independent cell-cell adhesion are the selectins which are cell surface carbohydrate binding proteins (lectins) which mediate cell-cell adhesion in the bloodstream. For example, L-selectins are found on lymphocytes which recognize oligosaccharides expressed on endothelial cells in lymphoid organs causing the lymphocytes to become trapped. Conversely, at sites of inflammation, endothelial cells switch on expression of selectins which recognize the oligosaccharides on lymphocytes and platelets. 

Selectins often work together with a third type of cell adhesion molecule called integrins. Selectins and integrins act in sequence to let leave the bloodstream and enter tissues. The selectins mediate a weak adhesion which allows the white blood cell to roll along the surface of the blood vessel propelled by the flow of blood. This rolling continues until the blood cell activates its integrins (cadherins are not involved in leukocyte recruitment) which causes the cell to bind strongly to the endothelial cell surface and to crawl out of the blood vessel between adjacent endothelial cells.

ntegrinsare the principal receptors on animal cells for binding most  like collagens, fibronectin and laminins. Integrins are composed of 2 noncovalently associated transmembrane glycoprotein subunits called alpha and beta. The binding to their ligands depend on extracellular divalent cations like Ca2+ reflecting the presence of divalent cation binding domains in the extracellular part of the subunits. Integrins bind to a matrix protein outside the cell and to the  via an anchor protein inside the cell. The binding to their ligands is of low affinity but high capacity. (binding depends on a large number of weak adhesions). The clustering of integrins at sites of contact with the matrix can activate intracellular signaling pathways. Many of the signaling functions of integrins depend on a cytoplasmic protein tyrosine kinase called focal adhesion kinase (FAK). When integrins cluster at sites of cell-matrix contact, FAK is recruited to focal adhesions by intracellular anchor proteins such as talin or paxillin. The clustered FAK molecules cross phosphorylate each other on a specific tyrosine for members of the Src family of cytoplasmic . A cell can also control integrin ligand interactions from within (inside out signaling) which allows regulated adhesion. This is important for example with T lymphocytes where the weak binding of a T lymphocyte to its specific antigen on the surface of an antigen presenting cell triggers intracellular signaling pathways that activate its integrins. The activated integrins enable the T cell to remain in contact long enough to become fully stimulated.

Whereas cadherins, slectins and integrins all depend on extracellular Ca2+ to function in cell adhesion, a major CAM which is Ca2+ independent are the N-CAMs or “neural cell adhesion molecules” which are expressed in a variety of cells including most nerve cells. 

Most cadherins function as transmembrane adhesion proteins that indirectly link the of the cells they join. This occurs in Cell Junctions like the adherens junctions where the cytoplasmic tails of cadherins interacts indirectly with actin filaments by means of a group of intracellular anchor proteins called “catenins” and with desmosomes where the cytoskeleton is intermediate filaments.

• Occluding junctions: include the tight junctions whose role is particularly prominent in the small intestine where they prevent transport proteins at the apical surface of the epithelia cell (surface facing the lumen) from mixing with those in the basolateral surfaces of the cell. In addition tight junctions insure that spaces between epithelia cells are sealed so that transported molecules cannot diffuse back into the gut. Major transmembrane proteins in a tight junction include the claudins and occludins.

• • Anchoring junctions: connect the cytoskeleton of a cell to the cytoskeleton of other cells using the transmembrane protein cadherin or to the extracellular matrix () through the use of the TM protein integrin. In both cases, there is an intracellular coupling to either actin or intermediate filaments depending on the type of intracellular anchor proteins involved. The various anchoring junctions are contained in the chart below:

  Cell-Cell	TM protein	Extracellular Ligand	Intracellular Ligand	Intracellular anchor proteins
  Adherens junction	cadherin	cadherin in other cell	actin filaments	? actinin, catenins, more
  Desmosome	cadherin	desmogleins & desmocolins	intermediate filaments	desmoplakins
  Cell-Matrix
  Focal adhesion	integrins	extracellular matrix proteins	actin filaments	? actinin, more
  Hemidesosome	integrins	extracellular matrix proteins	intermediate filaments

  • Communicating junctions: include the gap junctions which form channels through transmembrane proteins called connexins. 6 connexins are required to form a channel (called a “connexon”) and when the connexons in the PM of 2 cells in contact are aligned, they form a continuous aqueous channel that connects the two cell interiors.

CIRM  US Stem cell  NIH  NOVA   International Society for Stem Cell Research

Aging and Brain Repair (USF Health)

Companies: Stem Genomics

Introduction:

A stem cell is defined by its ability to undergo asymmetric division, whereby one daughter cell differentiates and the other daughter cell is still a stem cell. The stem cell status of an HSC depends on its niche, which includes bone marrow stromal cells, the extracellular matrix and the local levels of cytokines. (Risitano “Advances in understanding the pathogenesis of acquired aplastic anaemia” 2018)

Types of Stem Cells

Due to their pluripotency, stem cells show great promise for treatments of many human diseases. Their ability to differentiate into any cell type makes them a valuable resource for research and development of treatments for diseases. Stem cells fall into 4 basic types, with 2 different mechanisms of action. Stem cells can be either pluripotent or multipotent. The two key types currently be pursued are mesenchymal stem cells (MSCs) or induced pluripotent stem cells (IPSCs). MSCs are found in bone marrow, adipose tissue, umbilical cold blood or peripheral blood. These cells can become new bone or carliage, fat, muscle or pancreatic beta cells. These cells, like iPSCs, have differentiation potential, meaning that they can turn into any type of cell. IPSCs have various sources and can become any adult cell type.

The majority of approve stem cell therapies use mesenchymal stem cells. These stem cells can differentiate into cell types that form connective tissues such as bone and cartilage and can promote connective tissue formation and repair, and reduce inflammation. Stem cell therapies for teh treatment of the tissue damage caused by heart attacks are moving through clinical trials.

In one type of therpay, induced pluripotent stem cells derived form a patient can have defective genes restored, before reintroduction back into the patient. This is being considered for a number of genetic diseases that result in blindess.

Induced Pluripotent Stem Cells (iPSCs):

In 2006, Keyoto University’s Kazutoshi Takahashi, PhD and Shinya Yamanaka, MD, PhD, reproted that they had used defined factors to reproam differentiated cells to an embryonic like state. This work led to induced pluripotent stem cells (iPSCs) that made it much easier to conduct stem cell research.

iPSCs are obained form adult donor somatic cells. The cells are reprogrammed to pluripotency using a combination of genetic elements devlivered into the cells by viral or other means. IPSCs proliferate indeifnitely and maintain the potential to differentiate to nearly any funcitonal cell type in the body. Thus, the cells can be gene edited, expanded and characterized to create master cell banks that can be used for every prouct batch. Because of those attributes, IPSCs have become one of the preferred starting materials for cell therpay development.

Cord Blood Stem Cells: Placental tissue is discarded routinely. It is very devoid of infectious pathogens. Companies involved in cord blood stem cells include Americord

Embryonic stem cells: The two most widely studies embryonic stem cell types are mouse enbroyonic stem cells (mESC) and human embryonic stem cells (hESC). Maintenance of the undifferentiated state and pluripotency in mESC requires the presence of mouse fibroblast feeder layers (mEFs) or activation of STAT3 with leukemia inhibitory factor (LIF). Likewise, hESC are typically cultured on mEFs or in media obtained from growth of fibroblasts.

Hematopoietic stem cells: Pluripotent stem cells in the bone marrow of mammals have the potential to give rise to different types of blood cells which circulate in the peripheral blood. The pluripotent stem cells differentiate into various cell lineaages through multiple maturatational stages, thereby giving rise to committed blood cell types. Hematopoietic stem cells can be enriched by a procedure developed by I.L. Weissman and colleagues. In this procedure, a bone marrow sample is reacted with fluorescent monoclonal antibodies specific for antigens expressed on mature red and white blood cells. The labeled cells are then removed by flow cytometry with a fluorescence activated cell sorter leaving a number of stem cells in the sample. To further enrich the stem cells they can be incubated with various antibodies raised against cells likley to represent early differentiation stages in hematopoiesis (for example raised against antigen stem-cell antigen 1 in mice or CD34 which is present on 1-3% of hematopoeitic cells that can reconstitute the entire hematopoietic system in humans.) CellPro Inc. has reported successfull enrichment of CD34 stem cells using affinity chromatography. Such CD34 stem cells can be enriched and then engineered to replace any defective genes and then reintroduced back into the body. If some of the engineered stem cells are pluripotent, then all blood cells originating from those cells should have the healthy gene. In theory, patients would only need a single injection of the stem cells whereas if mature cells were used, multiple injections would be required.

–Markers:

—–CD34: serves as a valuable tool for identifying and isolating cruial cell populations, Its discovery has played a pivotal role in advancing understanidng of hematopoiesis, improving characterizqtion and manipulation of HSCs. Fiedorowicz, “Analytical considerations for gene-modified hematopoietic stem and progenitor cell therapies” Part 1- In-process drug substances and drug products, Bioprocess Interantional, 22(5), May 2024).

–Genome-modified hematopoietic stem and progenitor cells (GM-HSPC):

GM-HSPC therapies represent a significant frontier in the realm of personalized medicine, holding the promise of targeted interventions for a spectrum of disorders far beyond hematological conditions. The journey toward gene edited stem cell therapies begain with the work of E. Donnall Thomas during the 1950s and 1960s which demonstrated regenerative potential of HSC grafts transplanted into recipients. The 1970s brought a shift toward allegeneic HSC transplants. During the 1980s significant strides were made in improved conditioning regimens, optimizing the success of HSC grafts. These regimens involved pretransplant chemotherapy or radiation to create a conductive envionment for donor cell engraftment, which helped improved patient outcomes. The understanding about CD34 as a cell surface antigen and marker for hematopoeitic stem and progentior states was a significant milestone. (Fiedorowicz, “Analytical considerations for gene-modified hematopoietic stem and progenitor cell therapies” Part 1- In-process drug substances and drug products, Bioprocess Interantional, 22(5), May 2024). 

–Applications of CD34 stem cells:

After AMI, damaged tissue secretes a complex blend of cardioactive chemokines that recruits and stimulated CD34+ cells, when then travel form bone marrow to periopheral blood. Post AMI peripheral blood concentrations of cD34+ cells correlated significantly with heart regeneration and functional improvement. CD34+ cells promote cardiac repair by releasing soluble paracrine factors and exosomes containing microRNA 9miRNA) molecules that induce antiogenesis and revascularization of damaged tissue. Those paracrine factors also enhance proliferation of resident cardiomyocytes, reducing fibrosis and attentuating remodeling effects. Scar-assocaited chemokines attract CD34+ cell to the ischemic zone and induce their committment into endothelial pathways. CellProthera, a French clinical stage biotechnology company develops cell based therapies for ischemic diseases and has demosntrated the feasibility of intramyocardial injection of cluster of differentiation 34 (CD34) positive stem cells in patients who experienced acute myocardial infarcion. (Garitaonandia “Regenerative Medicine for Cardiovascular Disease”” BioProcess International, 22(4), April 2024)

Liu, (“Cytokine polarized, alternatively activated bone marrow neutrophils drive axon regeenration” Research Square) describe novel populations of BM dervied myeloid cells possessing neuroprotective and pro-regenerative properties. These cells were generated in vitro via short term culture of human CD34+ BM stem cells, with a combination of recombinant IL-4 and G-CSF. The findings suggested that fundamental characteritics of IL-4/G-CSF polarized neuro-regenerative myeloid cells cells. Wehther o mouse or human origin, these polrized cells, responsible for triggering axon regrowth, have a cell surface phenotype and transcriptomic signature consistent with immature, alternatively activated neutrophils. Both the mouse and human myeloid subseets epxressed eGFR ligands (HB-EGF for mice and TGFalpha for human), along with a panoply of other neuroprotective agetns and grwoth factors, that oculd contribute to their reparative functions.

Hepatic stellate cells (HSC): are the major profibrogenic cells in the liver. During liver injury, HSC are activated to a myofibrolastic phenotype. Together with protal fibroblasts and septal myofibroblasts of bone marrow origin, activated HSC produce most of the collagen matrix in injured livers.

Mesenchymal stems cells (MSCs): MSCs are multipotent adult stem cells that have been found in several different tissues, including umbilical cord blood, amniotic fluid and adipose tissue, as well as bone marrow. MSCs can self renew and have the multi lineage potential of differentation into a variety of cell types, including osteoblasts, chondrocytes, myoctes and adipocytes and also several different types of stromal cells, incluidng muscle, cartilage, marrow stroma and fibroblasts. MSCs have also been reported to have another unique characteristic (tropism migration) which facilitates migration to damaged tissue sites, such as sites with inflammation or wounds and sites with cancer cells. Cho (Gynecologic Oncology, 123 (2011) 379-386. Only MSCs posses the immunobmodulatory ability and are well tolerated during allogenic transplantation.

Over 900 clinical trials involving MSCs are listed on ClinicalTrials.gov but no MSC based therapics have been aproved in the US. (Kimbrel “Next-generation stem cells — ushering in a new era of cell-based therapies” Nature Reviews: Drug Discovery, 19, July 2020).

–Orbital fat-dervied stem cells (OFSCs): are MSCs isolated form human orbital fat tissue. They lack immunogenecity, and the safety and immunomodulatory ability of systemic OFSC transplantation has been demonstrated. In addition, OFSCs possess the osteogenic, chondrogenic and adipogenic differentiation capacity , and may differentiate into cornal epithelial cells upon contact with human corneal epithelial cells (Lin, Stem cell Research & therapy 2013, 4 72)).

Mesenchymal stromal cells (MSCs): are multipotent, self-renewing progenitor cells that can differentiate into adipocytes, chondrocytes and osteocytes. Cultured MSCs are plastic-adherent and spingle-shaped, and they express cell-surface markers CD44, CD73, CD90 and CD105, but not CD14, CD34, CD45, CD11b, CD79a, CD19 or HLA-DR. First isolated from bone marrow, human MSCs have been investigated extensively in clinical studies. MSCs also have been isolated from adiope tissue and peripheral blood. Perinatal organs and tissues such as aminiotic membrane, placenta, and umbilical cord also have been shown to be rich source of MSCs. The ability of MSCs to secrete high levels of proangiogenic and antinflammatory cyotkines has been shown to enhance wound healing. (Phan, “Deriving messenchymal stromal cells from umbilical cord lining and Wharton’s Jelly”, Bioprocess Technical Journal, 2022).

A formulation developed from skin regeneration technology, CALECIM® is a product that encourages skin to regain its youthfulness. CellResearch Corporation’s, CALECIM® Cosmeceuticals Pte Ltd, has formulated CALECIM® into a range of skin care products.

The International Society for Cell & Gene Therapy (ISCT®) Mesenchymal Stromal Cell (ISCT MSC) committee states that the term mesenchymal stem cell is not equivalent or interchangeable with mesenchymal stromal cell (MSC). The former refers to a stem cell population with demonstrable progenitor cell functionality of self-renewal and differentiation, whereas the latter refers to a bulk population with notable secretory, immunomodulatory and homing properties. The ISCT’s MSC committee further issued a minimal criteria to define multipotent MSCs as being plastic adherent, expressing CD73, CD90 and CD105, lacking the expression of hematopoietic and endothelial markers CD11b, CD14, CD19, CD34, CD45, CD79a and HLA-DR and capable of in vitro differentiation into adipocyte, chondrocyte and osteoblast lineages. (Sensebe, “Mesenchymal stem versus stromal cells: International Society for Cell & Gene Therapy (ISCT®) Mesenchymal Stromal Cell committee position statement on nomenclature” Cytotherapy, 2019).

MSCs have garnered extensive attentaion becasue of their unique properites, including their multilineage differentation and immunomodulatory effects. To date, 474 clinical trails ahve been completed using MSCs to treat an array of diseases, such as acute myocardial infarction, knew osteoarthritis, rhematoid arthritis and diabetes. Despire the widespread interest in MSCs, they are scarce in humans, constituting just 0.01% and 0.005% of the bone-marrow mononucleated cells population for males and femailes. With such low cell counts, large volumes of bone-marrow aspirate and extended culture times are needed for sufficient MSC expansion in downstream processing and therapeutic applciations. 

Production of Stem Cells

Under normal conditions, stem cells are anchored to the bone marrow at least in part through a bond between a particular receptor (CXCR-4) located on the stem cell and a protien (SDF-1) produced in the bone marrow. Plerixafor releases the stem cells into the bloodstream by disrupting that bond.

US Patent No. 7,897,590 discloses a method to obtain progenitor and/or stem cells by adminsitering G-CSF to a subject, administering plerixafor or a pharmaceutically acceptable salt in an amount effective to mobilize the progenitor and/or stems cells and harvesting the progenitor and/or stem cells.

Within the bone marrow, all blood cells originate from a single type of unspecialized cell called a stem cell. When a stem cell divides, it first becomes an immature red blood cell, white blood cell, or platelet-producing cell. The immature cell then divides, matures further, and ultimately becomes a mature red blood cell, white blood cell, or platelet. The rate of blood cell production is controlled by the body’s needs. Normal blood cells last for a limited time (ranging from a few hours to a few days for white blood cells, to about 10 days for platelets, to about 120 days for red blood cells) and must be replaced constantly. Merk Manual

Erythrocytes (Red Blood Cells): are the most common type of cell in the blood. They are packed full of hemoglobin and contain practically none of the usual cell organelles. Erythrocytes have an average life span of 120 days before being phagocytosed and digested by macrophages in the spleen. A lack of oxygen or shortage of erythrocytes stimulates cells in the kidney to synthesize and secret erythropoietin in the blood which stimulates the production of more erythrocytes.

RBCs fill a critical role by transporting oxygen and metabolic waste between the lungs and other cells and tissues. This role has been optimized by the unique features of RBCs, which lack nuclei, mitochondria, Golgi, the endoplasmic reticulum (ER), and most other major organelles so as to maximize oxygen-carrying capacity. Nonetheless, RBCs respond actively to changing tissue environments and dynamically alter their cell shapes on short timescales in order to thread narrow capillary networks and splenic tissues. (Marcotte, “The protein organization of a Red Blood cell” Cell Reports 40(3), 2022)

Endothelial cells: line the blood vessels and mediate rapid responses to neural signals for blood vessel dilation by releasing NO to make smooth muscle relax in the vessel wall.

Keratinocytes: differentiated activity is the synthesis of intermediate filament proteins called keratins, which give the epidermis its toughness. As keratinocytes mature, they produce keratin hyaline granuleswhich release their contents into the cytoplasm as the cell dies and lamellar bodies which are involved in the formation of the water barrier in .

Melanosomes: are located in the basal layer of the  and are of  original rather than ectoderm as with the epithelium. Melanosomes produce melanin which help protect developing keratinocytes from DNA damages due to UV light.

Langerhands Cells are phagocytic cells found in the epidermis and develop from bone marrow cells, as do most . They process antigens and present them to lymphocytes.

Merkel Cells also reside in the epidermis and function as mechanoreceptors. Nerve endings are closely associated with these cells to transmit the sensory signal.

Platelets are another name for thrombocytes and are miniature cells without a nucleus. They circulate in the blood and help stimulate blood clotting at sites of tissue damage. Plates can be identified by staining for CD61 and CD62P.

Platelets secrete a called platelet derived growth factor (PDGF) which stimulates cell division. When blood clots, platelets incorporated in the clot are triggered to release PDGF. The serum of a cell which is prepared by allowing blood to clot and taking the cell free liquid that remains contains this PDGF. Compare the term “plasma” which is prepared by removing cells from blood without allowing clotting to occur.

Type I alveolar cells cover most of the wall of alveoli. They are squamous (thin and flat) to allow gas exchange.

Type II alveolar cells are interspersed among type I alveolar cells and secret surfactant which is a phospholipid rich material that forms a film on water surfaces thereby reducing surface tension.

Hepatocytes of the liver play a central part in carbohydrate and lipid metobolism of the body. They remain connected with the lumen of the gut via a system of small channels and larger ducts and secrete waste products of their metabolism and an emulsifying agent, bile, which helps in the absorption of fats.

Skeletal muscle cells are often referred to as muscle fibers because of their elongated shape. Each one is a syncytium, containing many nuclei within a common cytoplasm. Myoblasts are the precursor cells to skeletal muscle fibers. They differentiate and fuse with one another to form multinucleate skeletal fibers. Humans do not usually generate new skeletal muscle fibers but small inactivate cells lying in close contact with the muscle cell called satellite cells can be activated to proliferate and fuse to repair damaged muscle.

–Satellite cells: The normal mechanisms involved in muscle tissue regeneration initially invovles the recruitment of satellite cells. Muscle Satellite cells are a distinct lineage of myogenic progenitors which are located between the basal lamina and sarcolemma of mature myofibers. During the regeneration cycle, satellite cells are activated and migrate from the myofibers to the site of regeneration to give myoblasts. Most of the poriferating myoblasts differentiate into myotubes. The myotubes mature and are incorporated into muscle fibres. The remamaining myoblasts return to the myfibers to renew the satelllite cell population and thus the capactiy to continue the regneration cycle. (WO2006/083183).

Smooth muscle cells are non-striated spindle shaped cells that have one central nucleus.

Heart muscle cells like smooth muscle cells are single cells with one nucleus but they resemble skeletal muscle cells in that they appear striated.

–Cardiospheres are undifferentiated cardiac cells that grow on self-adherent clusters as described in WO 2005/012510 and Messina et al. “Isolation and expansion of adult cardiac stem cells from human and murine heart” Circulation Research, 95: 911-921 (2004). For example, CDCs can be generated by plating cardiospheres on a solid surface which is coated with a substance which encourages adherence of cells to a solid surface of a culture vessel, e.g., fibronectin, a hydrogel, a polymer, laminin, serum, collagen, gelatin or poly-D-lysine and expanding the same as an adherent monolayer culture. (Hemmati, US 2019/0099370). Kreke (US 2018/0169150) disclsoes methods for preparing cardiosphere dervied cells (CDCs) suitable for allogeneic cardiac stem cell therapy that includes receiving donar cardiac tissue from a subject, processing the piece of donor cardiac tissue into a plurality of tissue explants, enzymatically digesting the explants, culturing the explants area until cells migrate from teh explant, collecitng the cells that migrate from the explant, culturing the collected cells in order ot generate CDCs, harvesting teh CDCs, filtering the harvested CDCsto remove particles greater than about 50 um.

Fibroblasts are dispersed in connective tissue through the body where they secrete a nonrigid  that is rich in type I and/or type III collagen.

Fibrocytes: are a CD45-positive hematopietic stem cells. These cells can be detected in tissue sections by colocalization of reactivity for collagen and CD45.

Stromal cells are found in the bone marrow.

Cells of the Bone Tissue

Living bone tissue exhibits a dynamic equilibrium between formation of bone, which is called deposition, and break-down of bone, which is called resorption. Three types of cells found in bone, osteocytes, osteoblasts and osteoclasts, are involved in this equilibrium. Osteoblasts promote formation of bone tissue whereas osteoclasts are associated with resorption (dissolution of bone matrix and mineral). Resorption is a fast and efficient process compared to bone formation and can release large amounts of mineral from bone.

Osteoblasts: are devied form mesenchymal stem cells. They produce the bone matrix which consists of collagenous and non-collagenous proteins (sucha s type I collagen and osteocalsin, respectively) and control its subsequent mineralisation that is the deposition of hydroyapatite. Thus, the rate of bone formation will depend upon individual osteoblast activity, their lifespan and the number of precursor cells recruited. Parathormone (PTH) and PTH related protein (PTHrp), the only other known ligand of the PTH receptor, increase the lifespan of mature osteopblasts by reducing their rate of apptosis, which explains their anabolic effects on bone. Teh calcium-sensing receptor (CaR) which is located on the surface of the parathyrodoid gland senses extracellular levels of ionised calcium and controls calcium homeostasis by regulating the release of PTH.

Osteoclasts demolish old bone matrix. Osteoclasts are capable of tunneling deep into bone, forming cavities which are then lined by a blood capillary. The walls of the tunnel become lined with a layer of osteoblasts. Resorption is stimulated by the secretion of parathyroid hromone in response to decreasing concentration of calcium ion in extracellular fluids. Inhibition of resorption is a funciton of calcitonin. The metabolites vitamin D alter the responsiveness of bone to parathyroid hormone and calcitonin. Osteoprotegerin ligand (OPGL) is a member of the TNF family of cytokines which promotes formation of osteoclasts through bidning to the receptor activator NF-kappaB. Osteoprotegerin (OPG), on the other hand, inhibits the formation of osteoclasts by sequestering OPGL and preventing OPGL associaiton with ODAR (US2004/0033535).

Osteoclasts are issued form haemopoietic stem cells and are formed by the fusion of cells form the monocyte-macrophage cell line. Osteoclastogenesis requires the presence of rANKL (Receptor Activator of Nuclear facto kappabea ligand), a member of the TNF cytokines and M-CSF (macrophage-colony stimulating factor). Once RANKL is epxressed by the osteoblasts, it activates its receptor RANK on the cells of the osteoclast lineage leading to their proliferation, maturation, activation and survival, ultimately resulting into increased bone resorption.

Osteoblasts deposit new bone matrix.

Cells of the Nervous System

Nerve cells or neurons have an extended shape with a long axon and branching dendrites connecting it through synapses to other cells. Most neurons consist of three parts: a cell body, dendrites and an axon. The cell body contains the nucleus. Dendrites are thin, highly branched extensions that receive incoming stimulation and conduct electrical impulses to the cell body. The axon is a single extension of cytoplasm that conducts impulses away from the cell body. most axons and dendrites can be measured in millimeters, but some can be quite long. For example, the cell bodies of neurons that control the muscles in your feet lie in the spinal cord, therefore, their axons may extend over a meter.

Teh brain and spinal cord form the central nervous system (CNS) of vertebrates and sensory and motor neurons from teh peripheral nervous system (PNS). Sensory neurons of the peripheral nervous system carry information about the environment to the CNS. Interneurons in teh CNS provide links between sensory and motor neurons. Motor neurons of teh PNS system carry impurlsesto muslces and glands.

Glial cells create an enclosed protective environment in which neurons can function. Neuroglia or glial cells do not conduct implsses. They function to lend support, aid in nourishment and provide protection for neurons. They are also intrumental in the regulation of neurotranons. Glial cells and neurons of the central nervous system in vertebrates derive from the part of the ectoderm that rolls up to form the neural tube, while those of the peripheral nervous system derive mainly from the neural crest.

Retinal ganglion cells are neurons that transmit signals from the  to the brain.

Olfactory Sensory Neurons have a single axon extending form their basal end toward the brain and contain oderant receptor proteins.

Over 200 different cell types in the human are known. The most numerous are the red blood cells, then platelets/thrombocytes and 3) white blood cells or leukocytes. These cells form a variety of different tissues. Blood can be separated in a centrifuge into a fluid and a cellular fraction. The fluid fraction is the plasma which contains all of the soluble small molecules and macromolecules of blood like fibrin and other proteins required for the formation of blood clots. If blood or plasma is allowed to clot, the fluid phase that remains is called serum (the liquid, noncellular component of coagulated blood).

Human blood serum is a very complex fluid containing many thousands of proteins representing nearly all human protein families. Most serum proteins are present in concentrations at least 8-10 orders of magnitude less than the hihgly abudnant proteins such as albumin, immunoglobulines, transferrin and haptoglobin which compose more than 90% of the total serum proteome.  Antibodies reside in the serum. About half of the serum proteins have a molecular mass below 45kDA (i.e., the kidney size cutoff). Such molecules can only exist in the circulation for a limited time. However, if a small protein is associated with a larger protein molecule (such as immunoglobulins), it can persist for a relatively long time. For example, IgG molecules have a long half-life of about 23 days in serum. Complexes of IgG molecules involved in interactions with the C domains of the IgG molecules are oftein designated as “non-immune” complexes (non-IC), as distinct from “immune” complexes (IC) formed by the antigen-combining sites located in V domains (Nezlin, Immun. Lett., 122, 2009, 141-144)

The cellular fraction of blood contains 1) red blood cells or erythrocytes, 2) white blood cells or leucocytes, 3)platelets and 4) plasma.

Peripheral blood mononuclear cells (PBMCs) are a mixed population consisting of several cell types: CD4+ and CD8+ T-lymphocytes (70%), B-lympohocytes (15%), natural killer cells (10%), monocytes (5%), and dendritic cells (<1%), each expressing a unique set of genes. 

Hematopoiesis

Cells of the body are formed and developed in a process referred to as hematopoiesis. Every mature blood cell is derived from a common stem cell which is pluripotent or able to differentiate along a number of pathways. Early in hematopoiesis, a pluripotent stem cell differentiates along 1 of 2 pathways, giving rise to either a common lymphoid progenitor cell or a common myeloid progenitor cell. Myeloid stem cells generate progenitors of red blood cells (erythrocytes), many of the various white blood cells (neutrophils, eosinophils, basophils, monocytes, mast cells, dendritic cells) and platelets. A lympohoid progenitor becomes a lymphoblast and then one of the 3 types of lymphocytes (white blood cells), a B lymphocyte, a T lymphocyte or a natural killer cell (NTK) 

In the adult, hemopoietic stem cells are found mainly in bone marrow and they grow and mature on a meshwork of stromal cells which include fat cells, endothelial cells, fibroblasts, and macropages. Progenitor committment depends on various growth factors called “cytokines”. In the absence of infection, bone marrow stromal cells are the major source of hematopoietic cytokines. In the presence of infection, cytokines produced by activated macrophages and induce additional hematopoietic activity resulting the the rapid expansion of the WBC population that is necessary for fighting infection.

Various growth factors are required for the survival, and maturation of hematopoietic cells in culture. These hematopoietic cytokines include the colony-stimulating factors (CSFs) which induce the formation of distinct hematopoietic cell lines. Another important cytokine is erythropoietin (EPO) which is produced by the kidney and induces the terminal development of erythrocytes and regulates the production of red blood cells. The ability of a given  to signal growth and differentiation is dependent upon the presence of a receptor for that cytokine on the surface of the target cell.

The regulation of hematopoiesis is quite complex. For example, the binding CSF to its receptor causes some of the receptors to be internalized by the cells which serves to down modulate receptor expression by the cell. Steady state hematopoisis is also regulated by cell apoptosis or death. Abnormalities in the expression of hematopoietic cytokines or their receptors may result in some leukemias.

Plant Cells:

Vacuoles: Plant cells have specialized membrane bounded structures called vacuoles. The most conspicuous example is the alrge centrl vacuole seein in most plant cells. The membrane surrounding this vacuole is called the tonoplast because it contains channels for water that are used to help the cell maintain its tonicity, or osmotic balance. 

The centrol vacuol is important for a number of roles. The water channels in the tonoplast maintain the tonicity of the cell, allowing the cell to expand and contract, depending on conditions. The central vacuoles are also invovled in cell growth by occupying most of the volume of the cell. Plant cells grwo by expanding the vacuole, rather than by increasing cytoplasmic volume. 

Vacuoles with a vareity of functions are also fuound in some fungi and protists. 

Chloroplasts: Plant cells and cells of other eukaryotic organisms taht carry out photosynthesis typically contain one to several hundred chloroplasts. Chloroplasts contain the photocsynthetic pigment chlorophyll that gives most plants their green color. 

Cloroplasts, liek their coutnerpart in animal cells for energy metabolism, are surrounded by two membranes. However, choroplasts are larger and more complex than mitochondria. Chloroplasts also have closed compartments of stacked membranes called grana. Each granum may contain from a few to several dozen disk shaped thylakoids. On teh surface of the thylakoids are the light capturing photosynthetic pigments. Surroudning the thylakoid is a fluid matrix called the stroma. The enzyems used to synthesize glucose during photosynthesis are found in teh stroma. 

Like mitochondria, chloroplasts contain DNA but many of the genes that specify chloroplast components are also located in the nucleus. Some of the elemtns used in photosynthesis, including the specific protein components necessary to accomplish the reaciton, are synthesized entirely within the chloroplast. 

Both mitochondria and chloroplasts are thought to ahve arison by endosymbiosis when a free living cell was taken up byt not digested. According to one endosymbiont theory, the engulfed prokaryotes provdied their hosts with certain advantages assocaited with their specific metabolic abilities. Thus, mitochondria are thought to ahve originated as bacterai capable of carrying out oxidative metabolism and chloroplasts are thought to have arose form photsynthetic bacteria. 

Cell Biology is the study of cells such as their structure, property and interactions.