Obesity‐induced and LDL‐mediated NK Cell Function Loss is Accompanied by Proteasome‐dependent induction of Lysophagy in an at‐risk population of African American Women

Abstract

Obesity and related chronic diseases (i.e. cardiovascular disease (CVD) and cancer) disproportionately affect African Americans (AA), shortening life expectancy and impacting quality of life. Life‐long exposure to adverse social determinants of health (SDoH) have been linked to obesity, warranting intensified research to further elucidate the ‘biology of adversity’ or the biologic consequences of adverse social conditions. Evidence suggests that exposure to chronic psychological and environmental stressors as SDoH leads to immune cell dysfunction, particularly for Natural Killer (NK) cells. Therefore, we examined changes in NK cell function in AA women, a group at high risk of Class III obesity (BMI ≥40 kg/m2). We have previously shown that NK cell degranulation is impaired in AA women with Class III obesity accompanied by a decrease in IFNg and TNFa, a loss in function driven by plasma LDL levels (b=‐0.35, p=0.03). A similar phenotype of dysfunctional NK cells could be achieved by overnight LDL treatment (50mg/dl) of healthy donor NK cells. To further determine the underlying signaling pathways, we employed proteomics of control and LDL treated NK cells. Here we identified 18 statistically significant regulated proteins (p<0.05), and 23 proteins approaching significance (p<0.07). Signaling pathway analysis revealed endolysosomal function, actin cytoskeleton regulation, and regulation of innate immune responses as significant pathways. Several proteins associated with autophagy and ubiquitination were also identified. This is of particular importance as LDL treatment of various cell types has been related to damaging lysosomes and a subsequent potential induction of lysophagy. Therefore, we investigated the impact of LDL on NK cell autophagy through western blot analysis of LC3 and p62 and found that enhanced autophagy is present in LDL treated NK cells. By employing the proteasome inhibitor MG‐132, we also found that the LDL‐induced increase in autophagy appears to be dependent on the activation of the 20S proteasome and subsequent ubiquitination of lysosomal proteins which results in depletion of functional lysosomes through lysophagy and is accompanied by NK cell function loss. In summary, we show a novel pathway potentially explaining obesity‐related NK cell function loss as a result of adverse SDoH in a population at highest risk for obesity‐related diseases like CVD and cancer. In the future, more research is needed to further understand the ‘biology of adversity’ and identifying targets for tailored interventions, ultimately reducing health inequities in chronic disease outcomes.