Jennifer Robinson - US grants

The long-term objective of the proposed work is to determine the role of estrogen and the mechanical microenvironment on meniscus health and regeneration to reduce osteoarthritis onset and progression. Knee osteoarthritis is a major cause of global disability resulting in over $6,000 in annual healthcare costs per patient. Meniscal tears are the most prevalent intra-articular knee injury and pose significant risk in the development of OA. Recent studies have shown that adult males experience greater tear complexity and have a reduced repair rate compared to females suggesting that sex hormones, including estrogen, may play a role in protecting the menisci from tear and promote repair. However, the differential role of estrogen and the mechanical environment on regional transcriptional changes, cell phenotype, and mechanotransduction have not been determined. Thus, this proposal aims to tackle this overarching question by evaluating the effect of estrogen treatment and substrate modulus on meniscal fibrochondrocytes in 2D and 3D. The hypothesis that physiological estrogen treatment and substrate modulus will promote an increase in meniscal extracellular matrix production and regeneration will be investigated in the following aims: 1) Elucidate the role of estrogen via estrogen receptor alpha on meniscal fibrochondrocyte proliferation and extracellular matrix production 2) Determine impact of substrate modulus on fibrochondrocyte migration, mechanotransduction, and phenotype in the presence of estrogen in 2D and 3D Deciphering the mechanism by which estrogen promotes meniscal fibrocartilage homeostasis is a vital first step in patient-specific repair and regeneration to reduce osteoarthritis progression and alleviate the corresponding pain and discomfort.

PROJECT SUMMARY An individuals? biological sex significantly affects their ability to repair and regenerate tissue. A clear example of this is the reduced ability for women to heal and regenerate new, healthy tissue after menopause, which results from a significant loss of sex hormone signaling. This reduction in hormone levels disproportionately enhances the risk for many degenerative diseases including osteoporosis, osteoarthritis, cardiovascular disease, and degenerative brain diseases in which the rate of tissue breakdown exceeds the rate of tissue repair. While it is known that several factors contribute to sex differences in tissue repair including biomechanics, nutrition, physical activity level and sex hormones, the interplay between these parameters is not well understood. Specifically, it is unknown how the native sex differences in tissue structure and the resulting differences in mechanical function dictate cell phenotype and behavior and how this effect interacts with estrogen signaling to overall control tissue repair. Thus, a fundamental, mechanistic understanding of how a cell responds to the spatial and mechanical cues of its environment while mediating estrogen signaling is critical to understand why sex differences occur in tissue repair and homeostasis and for future patient-centered repair and regeneration strategies. The overall goal of our research program aims to develop biomaterial tools to interrogate sex differences in tissue repair and homeostasis. Theme 1: Do male and female MSCs respond to spatial and mechanical properties of the cell microenvironment differently? There is evidence in many tissues that extracellular matrix structure, organization, and resulting function differs between age-matched males and females. However, there are no studies showing how this affects cell response. Biomaterials engineered to mimic both the fibrous properties of structural collagens and the viscoelastic properties of proteoglycans in the native extracellular matrix will be used to assess sex differences in cell response to controlled changes in matrix properties. Theme 2: How does estrogen presentation to the cell affect downstream transcription and behavior? While estrogen is known to play a role on cell processes, these results are dependent on the concentration and the temporal presentation of estrogen to the cell. To address this limitation, we will use concentration gradient generator microchips to quickly and accurately determine the effect of estrogen concentration and timing on cell transcriptional activity. Theme 3: Can we engineer biomaterial systems to control release and presentation of estrogen to the cells? Release rates in a range of hours to months will be controlled by modulating diffusion out of the biomaterials via material chemistry and architecture. The ability to control the rate of release and localize to a specific tissue in the body is critical to promote the estrogen effects at the site while reducing the negative and potentially deadly off-target effects. Results from these studies will provide future avenues of study to understand how estrogen and the cell microenvironment drive sex differences in stem cell behavior which is critical for tissue repair and homeostasis in both women and men.