With age, hematopoietic stem cells (HSCs) lose their ability to regenerate the blood system, and promote disease development. Autophagy is associated with health and longevity, and is critical for protecting HSCs from metabolic stress. Here, we show that loss of autophagy in HSCs causes accumulation of mitochondria and an activated metabolic state, which drives accelerated myeloid differentiation mainly through epigenetic deregulations, and impairs HSC self-renewal activity and regenerative potential. Strikingly, the majority of HSCs in aged mice share these altered metabolic and functional features. However, ~ 1/3 of aged HSCs exhibit high autophagy levels and maintain a low metabolic state with robust long-term regeneration potential similar to healthy young HSCs. Our results demonstrate that autophagy actively suppresses HSC metabolism by clearing active, healthy mitochondria to maintain quiescence and stemness, and becomes increasingly necessary with age to preserve the regenerative capacity of old HSCs.

While young blood can restore many aged tissues, its effects on the aged blood system itself and old hematopoietic stem cells (HSCs) have not been determined. Here, we used transplantation, parabiosis, plasma transfer, exercise, calorie restriction, and aging mutant mice to understand the effects of age-regulated systemic factors on HSCs and their bone marrow (BM) niche. We found that neither exposure to young blood, nor long-term residence in young niches after parabiont separation, nor direct heterochronic transplantation had any observable rejuvenating effects on old HSCs. Likewise, exercise and calorie restriction did not improve old HSC function, nor old BM niches. Conversely, young HSCs were not affected by systemic pro-aging conditions, and HSC function was not impacted by mutations influencing organismal aging in established long-lived or progeroid genetic models. Therefore, the blood system that carries factors with either rejuvenating or pro-aging properties for many other tissues is itself refractory to those factors.

PURPOSE Despite the widespread use of the taxanes paclitaxel and docetaxel for a variety of cancers and their well-known association with hypersensitivity reactions (HSRs), there is still significant variation in the prescribing practices of steroids for premedication. Premedication almost always includes dexamethasone, which can be associated with multiple adverse effects if taken for extended periods of time. This study reviews the pattern of steroid premedication in patients who received paclitaxel or docetaxel at Stanford Cancer Institute between January 2010 and June 2020. METHODS We used an electronic query of the electronic medical record followed up with a manual review of patient charts to ask whether we could find a correlation between steroid premedication dosing and the incidence or severity of HSRs with the first taxane dose. Variables considered included steroid dose and route, dose and type of taxane, clinical cancer group, sex, and race. RESULTS Five thousand two hundred seventeen patients were identified as having received paclitaxel or docetaxel, and 3,181 met criteria for our analysis. There were 264 (8.3%) HSRs. In adjusted multivariate analysis, we found no correlation of HSR rate or severity among any of the variables evaluated except gynecology oncology clinic patients, who had an increased risk (hazard ratio [HR] 1.34) of HSRs overall and high-grade HSRs (HR 2.34), and female patients, who had a higher rate of HSRs overall (HR 1.26), but not high-grade HSRs. CONCLUSION Neither dexamethasone dose nor route correlated with subsequent HSRs. Given the potential for adverse events from repeated high-dose steroids, our findings suggest that routine use of lower doses, such as a single 10 mg dose of dexamethasone, as premedication for taxanes to prevent HSRs is preferable to the current prescribing guidelines.