1. Tissue Repair: Cell Regeneration and Fibrosis

2. Tissue Repair Cell regeneration
Growth factors in cell regeneration and fibrosis
Stem cell
Repair by connective tissue (fibrosis)
Wound healing
Pathologic aspects of repair

3. Overview of Repair
Stimuli or stress can lead the cell damage (degeneration and necrosis)
In the same time, injured cells release some soluble factors to star the process of repair
Repair: the process to restore the destroyed cells and tissue by regenerating the same cell type and connective tissue

4. Overview of Repair
A complete restore or incomplete restore of injured tissue depends on
degree of injury (the original framework remains or not)
ability of regeneration of injured parenchymal cells

5. Tissue response to injury
Tissue response to injury. Repair after injury can occur by regeneration, which restores normal tissue, or by healing, which leads to scar formation and fibrosis.
Tissue response to injury. Repair after injury can occur by regeneration, which restores normal tissue, or by healing, which leads to scar formation and fibrosis.

6. Repair Involves
Regeneration of injured tissue by parechymal cells of the same type
Replacement by connective tissue (fibrosis), resulting in a scar
In most cases tissue repair involves both of these two processes.

7. Repair Involves A complete restore is called complete regeneration
A repair with connective tissue is called incomplete regeneration (fibrous repair, scar repair)

8. Normal cell proliferation and cell cycle
Cell-cycle landmarks. The figure shows the cell-cycle phases (G0, G1,G2, S, and M), the location of the G1 restriction point, and the G1/S and G2/M cell-cycle checkpoints. Cells from labile tissues such as the epidermis and the gastrointestinal tract may cycle continuously; stable cells such as hepatocytes are quiescent but can enter the cell cycle; permanent cells such as neurons and cardiac myocytes have lost the capacity to proliferate.

9. Cell Proliferation
Classification of cells by their proliferative potential
Labile (epithelium of skin, respiratory tract, gastrointestinal tract and urinary tract, lymphoid cell, et al)
Stable (parenchymal cells in liver, kidney, pancreas, salivary gland, et al)
Permanent (myocardium, skeletal muscle, neuron)

11. Stable cells (proximal tubule)

12. Mechanisms regulating cell populations
Mechanisms regulating cell populations. Cell numbers can be altered by increased or decreased rates of stem cell input, by cell death due to apoptosis, or by changes in the rates of proliferation or differentiation.

13. Abilities of Regeneration
Potential of regeneration Frameworks Sequelae
Labile cells remained complete regeneration
Labile cells destroyed fibrous repair
Stable cells remained complete regeneration
Stable cells destroyed fibrous repair
Permanent cells remained fibrous repair
Permanent cells destroyed fibrous repair

14. The Processes of Regeneration of Various Tissues
Epithelium
covering epithelium
glandular epithelium
Connective tissue
Bone and cartilage
Blood vessel
Muscle (heart, skeletal, smooth)
Neuron (axon, myelin sheath)

15. The Extracellular Matrix
A dynamic, constantly, remodeling, macromolecular complex
Interstitial matrix
Basement membrane (BM)
Major components
Collagens
Elastic fibers
Fibronectin
Laminin
Proteoglycans

16. Major components of the extracellular matrix (ECM), including collagens, proteoglycans, and adhesive glycoproteins. Both epithelial and mesenchymal cells (e.g., fibroblasts) interact with ECM via integrins. To simplify the diagram, many ECM components (e.g., elastin, fibrillin, hyaluronan, syndecan) are not included.

17. Steps in collagen synthesis

18. Basement membrane

19. The Extracellular Matrix
Roles of ECM
mechanical support for cell anchorage
determination of cell orientation (polarity)
control cell growth
maintenance of cell differentiation
scaffolding for tissue renewal
establishment of tissue microenvironments, storage and presentation of regulatory molecules

20. Summary
Cell growth and differentiation involve at least two types of signals acting in concert.
One derives from soluble molecules such as polypeptide growth factors and growth inhibitors.
The other involves insoluble elements of the ECM interacting with cellular integrins.

21. Mechanisms by which ECM (e. g
Mechanisms by which ECM (e.g., fibronectin and laminin) and growth factors can influence cell growth, motility, differentiation, and protein synthesis. Integrins bind ECM components and interact with the cytoskeleton at focal adhesion complexes (protein aggregates that include vinculin, α-actin, and talin). This can initiate the production of intracellular messengers or can directly mediate nuclear signals. Cell-surface receptors for growth factors may activate signal transduction pathways that overlap with those activated by integrins. Collectively, these are integrated by the cell to yield various responses, including changes in cell growth, locomotion, and differentiation.

22. Stem cells
Stem cell research is one of the most exciting topics in modern-day biomedical investigation and stands at the core of a new field called regenerative medicine
The enthusiasm about stem cell research derives both from data that challenge well-established biological concepts and from the hope that stem cells may one day be used to repair injury in human tissues, including heart, brain, and skeletal muscle

23. Stem cells
Stem cells are characterized by their prolonged self-renewal capacity and by their asymmetric replication
Asymmetric replication describes a special property of stem cells; that is, in every cell division, one of the cells retains its self-renewing capacity while the other enters a differentiation pathway and is converted to a mature, nondividing population

24. Stem cells
This concept has, however, been modified to postulate that asymmetry exists within a whole population of stem cells rather than in every single stem cell division
Thus within a group of stem cells some self replicate and others differentiate

25. Stem cells Embryonic stem cell (ESC) Adult stem cell (ASC) Bone marrow
Tissue

26. The “hot” stem cell research focus on
The identification of stem cells and their niches in various tissues, including the brain
The recognition that stem cells from various tissues and particularly from the bone marrow may have broad developmental plasticity
The realization that some stem cells present in tissues of humans and mice may be similar to embryonic stem cells

27. The “hot” stem cell research focus on
ES cells have been used to study the specific signals and differentiation steps required for the development of many tissues
The production of knockout mice
ES cells may, in the future, be used to repopulate damaged organs, such as the liver after hepatocyte necrosis and the myocardium after infarction.

28. Steps involved in therapeutic cloning, using embryonic stem cells (ES cells) for cell therapy. The diploid nucleus of an adult cell from a patient is introduced into an enucleated oocyte. The oocyte is activated, and the zygote divides to become a blastocyst that contains the donor DNA. The blastocyst is dissociated to obtain ES. These cells are capable of differentiating into various tissues, either in culture or after transplantation into the donor. The goal of the procedure is to reconstitute or repopulate damaged organs of a patient, using the cells of the same patient to avoid immunologic rejection
Steps involved in therapeutic cloning, using embryonic stem cells (ES cells) for cell therapy. The diploid nucleus of an adult cell from a patient is introduced into an enucleated oocyte. The oocyte is activated, and the zygote divides to become a blastocyst that contains the donor DNA. The blastocyst is dissociated to obtain ES. These cells are capable of differentiating into various tissues, either in culture or after transplantation into the donor. The goal of the procedure is to reconstitute or repopulate damaged organs of a patient, using the cells of the same patient to avoid immunologic rejection. (Modified from Hochedlinger K, Jaenisch R: Nuclear transplantation, embryonic stem cells, and the potential for cell therapy. N Engl J Med 349: , 2003.)

29. Roles of stem cells in tissue homeostasis
Liver in the canals of Hering
Brain Neural stem cells singing bird (parrot)
Skeletal muscles satellite cells
Renewal of epithelial tissue

30. Stem-cell niches in various tissues
Stem-cell niches in various tissues. A, Epidermal stem cells located in the bulge area of the hair follicle serve as a stem cells for the hair follicle and the epidermis. B, Intestinal stem cells are located at the base of a colon crypt, above Paneth cells. C, Liver stem cells (commonly known as oval cells) are located in the canals of Hering (thick arrow), structures that connect bile ductules (thin arrow) with parenchymal hepatocytes. D, Corneal stem cells are located in the limbus region, between the conjunctiva and the cornea.

31. Differentiation pathways for pluripotent bone marrow stromal cells
Differentiation pathways for pluripotent bone marrow stromal cells. Activation of key regulatory proteins by growth factors, cytokines, or matrix components leads to commitment of stem cells to differentiate into specific cellular lineages. Differentiation of myotubes requires the combined action of several factors (e.g., myoD, myogenin); fat cells require PPARγ, the osteogenic lineage requires CBFA1 (also known as RUNX2), cartilage formation requires Sox9, and endothelial cells require VEGF and FGF-2.

32. Differentiation of embryonic cells and generation of tissue cells by bone marrow precursors. During embryonic development the three germ layers-endoderm, mesoderm, and ectoderm-are formed, generating all tissues of the body. Adult stem cells localized in organs derived from these layers produce cells that are specific for the organs at which they reside. However, some adult bone marrow stem cells, in addition to producing the blood lineages (mesodermal derived), can also generate cells for tissues that originated from the endoderm and ectoderm (indicated by the red lines).

33. Repair by Connective Tissue (Fibrosis)
Severe or persistent tissue injury destroy
parenchymal cells
stromal framework
incomplete repair by unregenerated parenchymal cells with fibrosis

34. Repair by Connective Tissue (Fibrosis)
Fibrosis consists of four components
formation of new blood vessels (angiogenesis)
migration and proliferation of fibroblasts
deposition of ECM
maturation and reorganization of the fibrous tissue (remodeling)

35. Angiogenesis The procondition of fibrous repair Four steps
proteolytic degradation of the parent vessel BM, allowing formation of a capillary sprout
migration of endothelial cells from the original capillary toward an angiogenetic stimulus
proliferation of the endothelial cells behind the leading edge of migrating cells
maturation of endothelial cells with inhibition of growth and organization into capillary tubes

36. Steps in the process of angiogenesis

37. Angiogenesis by mobilization of endothelial precursor cells (EPCs) from the bone marrow and from pre-existing vessels (capillary growth). EPCs are mobilized from the bone marrow and may migrate to a site of injury or tumor growth (upper panel). The homing mechanisms have not yet been defined. At these sites, EPCs differentiate and form a mature network by linking with existing vessels. In angiogenesis from pre-existing vessels, endothelial cells from these vessels become motile and proliferate to form capillary sprouts (lower panel). Regardless of the initiating mechanism, vessel maturation (stabilization) involves the recruitment of pericytes and smooth muscle cells to form the periendothelial layer.

38. Fibrosis (scar formation)
Granulation tissue is the initial event in the repair of an injury, and consists of richly vascular connective tissue which contains capillaries, young fibroblasts, and a variable infiltrate of inflammatory cells
Do not confuse with GRANULOMA
Granulation tissue: Small, fleshy, bead like protuberances, consisting of outgrowths of
new capillaries, on the surface of a wound that is healing.

39. Student’s soccer injury. An abrasion in the elbow.

40. Bleeding of a deodenal ulcer. Note a ruptured artery in the base of

41. A healed gastric ulcer. Note the radiation of folds from the ulcer.

43. A fresh granulation tissue: Note the fibroblasts, new capillaries
and a few inflammatory cells.

44. Granulation tissue

46. A, Granulation tissue showing numerous blood vessels, edema, and a loose ECM containing occasional inflammatory cells. This is a trichrome stain that stains collagen blue; minimal mature collagen can be seen at this point. B, Trichrome stain of mature scar, showing dense collagen, with only scattered vascular channels.
Granulation tissue

48. Roles of Granulation Tissue in Fibrous Repair
Growth into the necrotic tissue, hemorrhage, thrombi, inflammatory exudate and replace them(organization)
Connect the separated tissue, restore the lost tissue and support them to keep the integrity of body
Protect the wound and anti-infection

49. Scar Remodeling
A scar after surgical operation or trauma will become softer, smaller because of degradation of collagens and other elements of ECM by metalloproteinases (collagenases)
Over growth of scar is called keloid

50. Keloid

51. Definition - Healing
Healing is a response to tissue injury, and represents an attempt by the organism to restore integrity to an injured tissue.
It overlaps the inflammatory process, and it is only for didactic purposes that the two are discussed separately.

52. Wound Healing Induction of an acute inflammatory response
Regeneration of parenchymal cells
Migration and proliferation of both parenchymal and connective tissue cells
Synthesis of extracellular matrix proteins (collagen III)
Remodeling
Collagenization and maturation of wound

53. Wound Healing
The orderly process by which a wound is eventually replaced by a scar
Destruction of epithelium only is termed an erosion, and heals exclusively by regeneration
If destruction of the basement membrane occurs (extracellular matrix), then a scar will form

54. Wound Healing Contraction
Accounts for a reduction in size of the defect primarily by the action of myofibroblasts
This process produces faster healing, since only one-third to one-half of the original defect must be repaired
Myofibroblasts account for contraction, and represent an intermediate type of cell, between a fibroblast and a myocyte

56. Healing of Skin Wound
Primary intention: the usual case with a surgical wound, in which there is a clean wound with well-apposed edges, and minimal clot formation
Secondary intention: when wound edges cannot be apposed, (e.g., following wound infection), then the wound slowly fills with granulation tissue from the bottom up. A large scar usually results.

57. Steps in wound healing by first intention (left) and second intention (right). Note large amounts of granulation tissue and wound contraction in healing by second intention.

58. The Healing in secondary intension Skin Ulcer
Healing of skin ulcers. A, Pressure ulcer of the skin, commonly found in diabetic patients. The histology slides show B, a skin ulcer with a large gap between the edges of the lesion; C, a thin layer of epidermal reepithelialization and extensive granulation tissue formation in the dermis; and D, continuing reepithelialization of the epidermis and wound contraction.
The Healing in secondary intension Skin Ulcer

59. Factors that Influence Wound Healing
Type, size, and location of the wound
Vascular supply (diabetics heal poorly)
Infection - delays wound healing and leads to more granulation tissue and scarring
Movement - wounds over joints do not heal well due to traction
Radiation - ionizing radiation is bad, UV is good

60. Factors that Influence Wound Healing
Overall nutrition: vitamin and protein deficiencies lead to poor wound healing, especially vitamin C, which is involved in collagen synthesis
Age: younger is definitely better!
Hormones - corticosteroids drastically impair wound healing, because of their profound effect on inflammatory cells

61. Complications of Wound Healing
Defective scar formation
Excessive scar formation (keloid)
Contraction
Dehiscence or ulceration is usually due to:
Wound infection (common)
Malnutrition (scurvy - rare)
Hypoxia with ulceration, usually due to inadequate vascularity in a skin flap (common).

62. Dehiscence

63. Excessive Scar Formation
Keloids (hypertrophic scars) are the result of over-exuberant production of scar tissue, which is primarily composed of type III collagen
The cause is thought to be due to genetic factors, perhaps due to lack of the proper metalloproteinases (collagenases) to degrade type III collagen

64. A, Keloid. Excess collagen deposition in the skin forming a raised scar known as keloid.
B, Note the thick connective tissue deposition in the dermis.

65. Keloid (micro)

66. Contraction
Excessive contraction of a wound is known as a contracture. They are a special problem in the treatment of extensive burns
Several diseases of unknown cause are characterized by the formation of contractures
Peyronie disease of the penis
Peyronie was a god in old greece mythos. He had great, firm penis, but it could
not be softing, so he was painful. In the modern medicine, Peyronie’s disease
is fibrous spongiitis leading a firm penis for long time.

67. Scar contracture in a boy after scald

68. Healing in Specific Tissues (heart)
Cardiac myocytes are permanent cells. They do not divide, and the heart thus heals by resolution (dead myocytes are phagocytized by macrophages) and collagenous scar formation.

69. Remote MI (gross)

70. Remote MI (micro)

71. Chronic Pyelonephritis (gross)

72. Cirrhosis (gross)

73. Cirrhosis, trichrome

77. Bony callus

80. Summary of Repair Terms: regeneration, healing, repair
Concept of stem cell
Regenerative abilities of cells
Labile cells Stable cells
Permanent cells
Mechanisms of cell growth
Growth factors (soluble factors)
ECM (insoluble)
Signal transduction pathways (ligand-receptor with intrinsic tyrosine kinase activity)

81. Summary of Repair Fibrous repair Wound healing
Granulation tissue (components, roles)
Scar formation and remodeling
Wound healing
Skin wound healing in first intention
Skin wound healing in second intention
healing of bone fracture
pathologic conditions in wound healing

82. Development of fibrosis in chronic inflammation
Development of fibrosis in chronic inflammation. The persistent stimulus of chronic inflammation activates macrophages and lymphocytes, leading to the production of growth factors and cytokines, which increase the synthesis of collagen. Deposition of collagen is enhanced by decreased activity of metalloproteinases.

83. Repair responses after injury and inflammation
Repair responses after injury and inflammation. Repair after acute injury has several outcomes, including normal tissue restitution and healing with scar formation. Healing in chronic injury involves scar formation and fibrosis (see text).

84. Thank you for your attention!