Hypothesis: The CD36-SASP Axis as a Sexual Dimorphic Gatekeeper of c-Kit+ Cardiac Progenitor Fate
I propose that the ongoing debate regarding c-Kit+ cardiac cells in the aged heart stems from a fundamental misunderstanding. Rather than failing to differentiate, these cells appear to undergo a sex-specific metabolic reprogramming that pushes them into a senescent, pro-fibrotic state. My hypothesis is that estrogen-dependent regulation of the CD36-mediated fatty acid uptake pathway serves as the mechanistic switch determining whether c-Kit+ cells secrete regenerative signals or a deleterious SASP. I suspect that in males, CD36 hyper-expression triggers lipid-overload-induced p16INK4A activation; conversely, in females, protective estrogen signaling maintains CD36 homeostasis, effectively sequestering the SASP and curbing paracrine senescence.
The current literature suggests that clearing these cells is the only viable path forward (doi.org/10.1111/acel.12931). However, this view ignores the possibility that these cells aren't just "debris," but are functional units gone rogue due to metabolic signaling failure. Drawing from recent work in skeletal muscle regarding SASP modulation versus ablation (pmc.ncbi.nlm.nih.gov/articles/PMC7349658/), it seems clear that total ablation might destroy the very cells that, if metabolically corrected, could help maintain myocardial structural integrity.
I posit that the "regenerative decline" of the c-Kit+ population isn’t an intrinsic failure of lineage potential, but a consequence of chronic lipotoxicity. When fatty acid influx via CD36 outstrips a cell’s oxidative capacity, it triggers mitochondrial DNA damage, which in turn reinforces the senescence phenotype. Given that nearly half of age-related cellular changes are sex-specific (sciencedaily.com/releases/2026/02/260228082717.htm), it is highly likely that estrogen-receptor-alpha (ERα) directly represses CD36 transcription in females. When this mechanism is lost—in males or post-menopausal models—we see the rapid accumulation of dysfunctional c-Kit+ cells.
This hypothesis is testable and falsifiable through three key approaches:
- Transcriptomic Profiling: Perform single-cell RNA-seq on c-Kit+ populations from aged male versus female mice (comparing post-oophorectomy models with controls). I expect to see a clear divergence in the CD36-PPAR signaling axis.
- Pharmacological Modulation: Apply a small-molecule CD36 inhibitor, such as sulfo-N-succinimidyl oleate, to aged male hearts. If I am correct, this should decrease SASP-mediated paracrine toxicity and improve cardiac function without the need to eliminate the c-Kit+ pool entirely.
- Falsification: My hypothesis will be refuted if male c-Kit+ cells show the same senescent trajectory as females under identical metabolic stress, or if CD36 inhibition fails to attenuate the SASP in aged hearts.
By shifting from an "ablation-first" strategy to a "metabolic-reprogramming" model, we can move past the stagnant debate over the "stemness" of c-Kit+ cells and finally address how they actually influence the myocardial microenvironment.