A characteristic feature of chronological aging is cline of organ function. Manifestations of this decline in human skin include fragility, impaired wound healing, increased incidence of cancer, reduced elasticity and tone, uneven color, and increased roughness. All of these features are attributable, at least in part, to impairment of the structural integrity of skin connective tissue. The structural component of skin connective tissue is the dermal extracellular matrix (ECM), which is primarily composed of fibrillar type I collagen framework. The structure and function of this type I collagen framework is modulated through direct and indirect interactions with hundreds of additional proteins, which, like type I collagen, are primarily synthesized and secreted by dermal fibroblasts. Fibroblasts adhere to the ECM through integrins, which are a family of specific cell surface ECM receptors. ECM-fibroblast interactions inform and control both ECM and fibroblast functions via integrin attachment sites. These sites regulate function through two interrelated mechanisms: 1) conventional signal transduction, mediated by kinase cascades, and 2) mechanical force transduction, mediated by cytoskeletal machinery and intracellular scaffold proteins. During the aging process, fibrillar type I collagen is fragmented. This fragmentation deleteriously impacts skin health by directly compromising mechanical stability and by destroying ECM sites for fibroblast attachment. Our data indicate that these two factors conspire to reduce mechanical tension within fibroblasts in human skin in vivo. Reduction of mechanical tension manifests as change of fibroblast shape from """"""""stretched"""""""" to """"""""collapsed"""""""". Fibroblast """"""""collapse"""""""" is significant, because a fundamental property of cells is the connection between shape and function. Based on our preliminary data, we hypothesize that fragmented ECM accumulates with aging and causes fibroblasts to """"""""collapse"""""""", resulting in reduced ability to respond to transforming growth factor-beta (TGF-2), which is the primary driving force for ECM production. Reduced collagen production further deteriorates ECM structural integrity, leading to further fibroblast """"""""collapse"""""""", further resistance to TGF-2, and further diminishment of collagen production. This self-perpetuating decline of ECM/fibroblast functions eventuates in thin, fragile skin, characteristically seen in the elderly. To test this hypothesis, Specific Aim 1 will investigate molecular mechanisms by which the fragmented ECM microenvironment regulates TGF-2-dependent collagen production.
Specific Aim 2 will investigate the impact of increasing mechanical tension in the dermis of aged human skin, by injection of space filling material, on fibroblast shape and function.
Specific Aim 3 will delineate mechanisms by which fragmented collagen matrix down-regulates type II TGF-2 receptor.
Specific Aim 4 will investigate mechanisms by which type I collagen-binding integrins sense, signal, and regulate fibroblast shape/mechanical tension in response to fragmented ECM microenvironment. The proposed studies are significant because they will: 1) advance knowledge of molecular mechanisms that are responsible for age-dependent decline of human skin function, 2) provide a new paradigm for understanding the impact of age-dependent ECM alterations on tissue function, and 3) enable development of new modalities to improve the health of the elderly. The proposed studies are novel because they depart from the cellular- centric view of aging to address the role of dynamic interplay between cells and their ECM microenvironment during the aging process.

Public Health Relevance

The primary objective of this proposal is to investigate molecular mechanisms that are responsible for reduction of type I collagen synthesis in chronologically aged human skin. Loss of type I collagen deleteriously alters the structural integrity of skin connective tissue, and thereby impairing skin function and promoting age-related skin diseases. Our findings from the initial grant demonstrate that age-related reduction of type I collagen is mediated by impairment of the TGF-2 pathway in dermal fibroblasts. This proposal builds on our previous findings and will test the hypothesis that accumulation of aged-related alterations of the structural/mechanical/functional properties of the collagenous extracellular matrix in human dermis impairs dermal fibroblast functions, including TGF-2-dependent collagen production. This hypothesis is novel because it focuses on the importance of the extracellular matrix, rather than inherent cellular deficits, as a driving force for the aging process in humans.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Research Project (R01)
Project #
5R01AG019364-09
Application #
8457078
Study Section
Arthritis, Connective Tissue and Skin Study Section (ACTS)
Program Officer
Williams, John
Project Start
2001-04-01
Project End
2015-04-30
Budget Start
2013-07-01
Budget End
2014-04-30
Support Year
9
Fiscal Year
2013
Total Cost
$287,691
Indirect Cost
$101,483
Name
University of Michigan Ann Arbor
Department
Dermatology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Shao, Yuan; Qin, Zhaoping; Alexander Wilks, James et al. (2018) Physical properties of the photodamaged human skin dermis: Rougher collagen surface and stiffer/harder mechanical properties. Exp Dermatol :
Quan, Chunji; Yan, Yan; Qin, Zhaoping et al. (2018) Ezrin regulates skin fibroblast size/mechanical properties and YAP-dependent proliferation. J Cell Commun Signal 12:549-560
Qin, Z; Balimunkwe, R M; Quan, T (2017) Age-related reduction of dermal fibroblast size upregulates multiple matrix metalloproteinases as observed in aged human skin in vivo. Br J Dermatol 177:1337-1348
Shao, Y; He, T; Fisher, G J et al. (2017) Molecular basis of retinol anti-ageing properties in naturally aged human skin in vivo. Int J Cosmet Sci 39:56-65
Fisher, Gary J; Shao, Yuan; He, Tianyuan et al. (2016) Reduction of fibroblast size/mechanical force down-regulates TGF-? type II receptor: implications for human skin aging. Aging Cell 15:67-76
Argyropoulos, Angela J; Robichaud, Patrick; Balimunkwe, Rebecca Mutesi et al. (2016) Alterations of Dermal Connective Tissue Collagen in Diabetes: Molecular Basis of Aged-Appearing Skin. PLoS One 11:e0153806
Quan, Taihao; Fisher, Gary J (2015) Role of Age-Associated Alterations of the Dermal Extracellular Matrix Microenvironment in Human Skin Aging: A Mini-Review. Gerontology 61:427-34
Quan, Taihao; Johnston, Andrew; Gudjonsson, Johann E et al. (2015) CYR61/CCN1: A Novel Mediator of Epidermal Hyperplasia and Inflammation in Psoriasis? J Invest Dermatol 135:2562-2564
Xia, Wei; Quan, Taihao; Hammerberg, Craig et al. (2015) A mouse model of skin aging: fragmentation of dermal collagen fibrils and reduced fibroblast spreading due to expression of human matrix metalloproteinase-1. J Dermatol Sci 78:79-82
Fisher, Gary J (2015) Cancer resistance, high molecular weight hyaluronic acid, and longevity. J Cell Commun Signal 9:91-2

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