Author ManuscriptBentov and ReedPageof age-related deficits in angiogenesis, which has an adverse effect on the development of an effective microcirculation38. In an explant model, age-related deficiencies in angiogenesis were reversed, in part, by stimulation with angiogenic growth factors39. IIC. Extracellular matrix and tissue remodeling During the last phase of wound healing, the extracellular matrix begins to remodel and the wound undergoes further contraction. Fibroblasts assume a myofibroblast phenotype characterized by bundles of alpha smooth muscle actin-containing microfilaments. Synchronized collagen reorganization occurs by synthesis and catabolism (although at a much slower rate than in previous Dihexa manufacturer stages), which allows the granulation tissue to turn into a scar. Deposition and remodeling of collagen is slower in aged animals resulting in less scar formation40. Moreover, the collagen deposited has a looser, more disorganized matrix that has decreased tensile strength. The changes in aged collagen matrix reflect decreases in circulating factors, in particular reduced levels of TGF-1 – a potent stimulator of collagen synthesis 41. Of note, dermal fibroblasts from aged and young donors exposed to TGF-1 exhibit similar biosynthetic and contractile properties42. Other matrix components43 that are altered with age (Figure 3C) include: decreased osteonectin (also known as secreted protein acidic and rich in cysteine – SPARC), increases in thrombospondin44 and alterations in fibronectin and laminin45, 46. Non-protein components of the extracellular matrix include glycosaminoglycans, such as hyaluronan, which interact with other matrix components to maintain hydration in the dermis. Hyaluronan is a linear disaccharide polymer that can range from 2?5,000 disaccharides with molecular masses up to 2?04 kDa. Hyaluronan size determines its biologic properties: high molecular weight forms can inhibit proliferation and migration of many cell types, whereas middle and lower molecular weight forms usually promote tissue formation46. Hyaluronan content is maintained in aged wound dermis, but its degradation is reduced47. Wound healing also requires matrix metalloproteinases (MMPs), which promote cell proliferation and vessel ingrowth by degrading the existing extracellular matrix. MMP activity is balanced, in part, by endogenous tissue inhibitors of metalloproteinases. Aged tissues are associated with dysregulation of MMP activity48, with a tendency toward overexpression of MMPs49 and reduced levels of tissue inhibitors of metalloproteinases50. As highlighted above, alterations occur during each stage of wound repair in aging, and many of these changes negatively impact the microcirculation. Nonetheless, given sufficient time aged animals eventually (age related delay is roughly 30?0 ) catch up to their young counterparts with respect to most aspects of tissue repair51.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptIII. The Surgical Context of Wound Repair and AgingMeasures that support the microcirculation improve wound repair, thereby reducing the risk of postoperative dehiscence and infection52. General pre-operative measures such as smoking cessation and optimal management of Crotaline web co-morbid medical conditions have been reviewed in other contexts53, 54. For the purpose of this review, we will focus on interventions in the peri-operative setting. IIIA. Oxygen administration Wound healing is dependent upon adequate levels.Author ManuscriptBentov and ReedPageof age-related deficits in angiogenesis, which has an adverse effect on the development of an effective microcirculation38. In an explant model, age-related deficiencies in angiogenesis were reversed, in part, by stimulation with angiogenic growth factors39. IIC. Extracellular matrix and tissue remodeling During the last phase of wound healing, the extracellular matrix begins to remodel and the wound undergoes further contraction. Fibroblasts assume a myofibroblast phenotype characterized by bundles of alpha smooth muscle actin-containing microfilaments. Synchronized collagen reorganization occurs by synthesis and catabolism (although at a much slower rate than in previous stages), which allows the granulation tissue to turn into a scar. Deposition and remodeling of collagen is slower in aged animals resulting in less scar formation40. Moreover, the collagen deposited has a looser, more disorganized matrix that has decreased tensile strength. The changes in aged collagen matrix reflect decreases in circulating factors, in particular reduced levels of TGF-1 – a potent stimulator of collagen synthesis 41. Of note, dermal fibroblasts from aged and young donors exposed to TGF-1 exhibit similar biosynthetic and contractile properties42. Other matrix components43 that are altered with age (Figure 3C) include: decreased osteonectin (also known as secreted protein acidic and rich in cysteine – SPARC), increases in thrombospondin44 and alterations in fibronectin and laminin45, 46. Non-protein components of the extracellular matrix include glycosaminoglycans, such as hyaluronan, which interact with other matrix components to maintain hydration in the dermis. Hyaluronan is a linear disaccharide polymer that can range from 2?5,000 disaccharides with molecular masses up to 2?04 kDa. Hyaluronan size determines its biologic properties: high molecular weight forms can inhibit proliferation and migration of many cell types, whereas middle and lower molecular weight forms usually promote tissue formation46. Hyaluronan content is maintained in aged wound dermis, but its degradation is reduced47. Wound healing also requires matrix metalloproteinases (MMPs), which promote cell proliferation and vessel ingrowth by degrading the existing extracellular matrix. MMP activity is balanced, in part, by endogenous tissue inhibitors of metalloproteinases. Aged tissues are associated with dysregulation of MMP activity48, with a tendency toward overexpression of MMPs49 and reduced levels of tissue inhibitors of metalloproteinases50. As highlighted above, alterations occur during each stage of wound repair in aging, and many of these changes negatively impact the microcirculation. Nonetheless, given sufficient time aged animals eventually (age related delay is roughly 30?0 ) catch up to their young counterparts with respect to most aspects of tissue repair51.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author ManuscriptIII. The Surgical Context of Wound Repair and AgingMeasures that support the microcirculation improve wound repair, thereby reducing the risk of postoperative dehiscence and infection52. General pre-operative measures such as smoking cessation and optimal management of co-morbid medical conditions have been reviewed in other contexts53, 54. For the purpose of this review, we will focus on interventions in the peri-operative setting. IIIA. Oxygen administration Wound healing is dependent upon adequate levels.
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