Identification of Pro-aging Thrombospondin-1 Producing Cells Within the Bone Marrow Niche - PROJECT SUMMARY The bone marrow (BM) niche is a highly complex microenvironment that houses hematopoietic stem cells (HSCs). These niche cells have been shown to provide instructive cues to HSCs and dysregulation of this signaling due to aging can lead to impaired hematopoietic activity. With our increasingly aging population, understanding and developing therapeutics to combat malignancies associated with an aged blood system is of great importance to both better treat these patients as well as reduce the resulting monetary and healthcare load. This proposal aims to characterize a recent finding in our lab which identifies thrombospondin-1 (Thbs1) as a pro-gerontic factor of HSCs and the BM niche. Thbs1 is a well-studied extracellular matrix protein with notable involvement in age-related changes in other systems, such as the cardiovascular and metabolic systems, but has not been studied within hematopoiesis. Through competitive HSC transplantation assays, we show that HSCs derived from aged global knockout (gKO) Thbs1 murine models have young-like engraftment and lineage potential. Reciprocal transplant assays on these mice also show that intrinsic and extrinsic influence of Thbs1 plays a role in the increased functionality we observe within the global KO. We have since developed a Thbs1- GFP reporter mouse and have identified that endothelial cells (ECs) and megakaryocytes (MKs) produce Thbs1 within the BM niche. My preliminary data suggests that KO of Thbs1 derived from ECs and MKs recapitulates the increased HSC functionality observed in young global KO mice. I hypothesize that age-related dysregulation of cell-specific derived Thbs1 plays a critical role in the aging of HSCs, and, through targeting Thbs1, we can improve HSC functionality. To test this, we will: 1. Identify which cell-specific KOs of Thbs1 recapitulate the global KO phenotype whilst assessing possible alterations in hallmarks of HSC aging, including DNA damage, polarity, and changes in cell cycle, to obtain mechanistic insights. 2. Determine if deletion or inhibition of Thbs1 can enhance the functional capacity of HSCs expanded within a polyvinyl alcohol-based platform to be used within BM transplants. 3. Assess the possible effects Thbs1 has during myelosuppressive insult and determine if targeting Thbs1 can lead to better recovery and preservation of the BM microenvironment and HSC functionality. Results stemming from this proposal will lead to not only a better understanding of the basic biology of Thbs1 within hematopoiesis, but also identify the therapeutic potential of targeting cell-specific Thbs1 to alleviate aged HSC phenotypes.
