Cell-Type-Specific Autophagy in Human Leukocytes

Autophagy is a naturally conserved mechanism crucial for degrading and recycling damaged organelles and proteins to support cell survival. This process slows biological aging and age-related disease in preclinical models. However, there has been little translation of autophagy to the clinic, and we have identified a lack of measurement tools for physiological human autophagy as a barrier. To address this, we have previously developed a direct measurement tool for autophagy in pooled human peripheral blood mononuclear cells (PBMCs) in the context of whole blood. In order to better understand how autophagy behaves and changes in humans, we measured human autophagic flux using flow cytometry in 19 cell subpopulations in whole blood to retain physiological flux. Autophagic flux was different between different cell types, being different within different monocyte, B lymphocyte, natural killer cell, and T lymphocyte subtypes. Autophagic flux also varied with sex, being higher in monocytes in females compared with males. In keeping with previous observations in humans, autophagy also increased with aging at subpopulation levels. Importantly, we found that only monocytes-specifically, nonclassical monocytes-displayed robust increased autophagic flux following amino acid withdrawal, underscoring the importance of population selection for measurement of autophagic flux during nutrient restriction studies in humans. Collectively, these data show PBMC population-level analysis improves sensitivity of human autophagic flux measurement.