PROJECT SUMMARY/ABSTRACT This proposal’s objective is to determine whether changing the signaling patterns between the skeletal stem cells (SSCs) and hematopoietic stem cells (HSCs) can treat atherosclerotic cardiovascular disease (ASCVD). Previous data from our lab suggests that aging SSCs can cause HSC inflammaging, defined as a skewing of HSC progeny toward myeloid lineages that may be more dysfunctional, leading to the development of vascular disease. Whether rejuvenating the SSCs can be used as a therapy in ASCVD remains unclear. Our long-term goal is to develop novel therapy to reverse age-related ASCVD. Our central hypothesis is that the SSC rejuvenation will rebalance HSCs and improve the function of their progeny that travel to the vasculature in response to injury, preventing the progression of atherosclerosis. The rationale is that previous work by our labs and others: 1) identified and characterized the existence of SSCs in mice and humans, 2) demonstrated that transplantation of SSCs from aged mice cause inflammaging of HSCs in young mice, 3) showed that HSC inflammaging contributes to ASCVD, and 4) observed that activated immune cells, some of which originate from HSCs, contribute to plaque progression. Our work will enhance the understanding of the cross talk between organs that contribute to ASCVD, paving the way for the development of novel strategies for disease treatment. To test our central hypothesis and attain our objective, we propose the following aims: 1. To characterize the effects of SSC aging on the vasculature (including the perivascular fat). We hypothesize that aged SSCs skew HSCs toward dysfunctional myeloid progeny that promote ASCVD. For this aim, we will first perform lineage tracing experiments. The expected outcome from the lineage tracing experiments is that older mice with atherosclerosis have the highest proportion of HSC-progeny in their vasculature. In our second set of experiments for Aim 1, we will determine whether HSC inflammaging induced by aged SSCs contributes to atherosclerosis progression. We hypothesize that 2-month HSCs transplanted into 20-month mice become aged and their progeny then cause atherosclerotic progression in pro-atherogenic mice fed a high fat diet. We will perform cell transplantation studies to determine whether exposure to youthful or aged SSCs affects atherosclerotic progression. We expect that young HSCs exposed to aged SSCs will develop HSC inflammaging and contribute to plaque progression. Finally, we will compare the proteomic and genomic signatures of these multiple organs in humans to confirm that SSC aging also contributes to human atherosclerosis. 2. To determine whether targeted reversal of age-related decreases in BMP2 signaling in SSCs can alter atherosclerosis progression. We hypothesize that BMP2 infusion or application of a BMP2 infused hydrogel to aged bones creates a more balanced HSC progeny, decreasing vascular inflammation and preventing the progression of A...