Abstract 13646: APOL1 Nephropathy Risk Variant Alters Macrophage Metabolism

Abstract

The common G1 and G2 variants in the APOL1 gene, specific to patients with African ancestry, increase the risk of developing chronic kidney disease and stroke. These variants also confer a survival benefit against African trypanosomiasis, but the effects of G1 and G2 variants on macrophage function remain unclear despite their role in innate immunity. Crucial to both innate immunity and tissue homeostasis, macrophages can promote cardiometabolic disease if dysregulated. Others have shown that metabolic changes can alter macrophage phenotype and function, and the G1 and G2 variants have been linked to mitochondrial dysfunction in epithelial cells. We therefore hypothesize that APOL1 risk variants promote cardiometabolic disease traits by altering macrophage metabolism and, thus, function. To test our hypothesis, we established CRISPR-Cas9 genome-edited induced pluripotent stem cell (iPSC) lines with the G0/G0 (major allele) genotype and the G1/G1 genotype on isogenic backgrounds. We then differentiated these iPSC lines into macrophage-like cells (iPSDMs) and evaluated their phenotype and function at baseline and under stimulation with 5 - 50 ug/mL interferon-γ, a potent inducer of APOL1 expression. We measured inflammatory markers via QPCR and ELISA, mitochondrial oxygen flux with the Agilent Seahorse XF Analyzer, and intracellular hydrophilic metabolites via LCMS. We found that G1/G1 iPSDMs express higher levels of pro-inflammatory markers and exhibited lower basal respiration as well as lower ATP production compared to G0/G0 controls. Because APOL1 risk variants have been linked to defective autophagy and ER stress, we treated the G1/G1 iPSDMs with rapamycin (autophagy inducer) or TUDCA (ER stress inhibitor) but found that they did not abrogate these genotype-specific differences in metabolic flux. Upon examination of metabolomics profiles of G1/G1 vs G0/G0 iPSDMs, differentially abundant metabolites were enriched for SMPDB pathways including spermidine biosynthesis (needed for anti-inflammatory reprogramming), gluconeogenesis, Warburg effect, homocysteine degradation, and fatty acid oxidation. Taken together, G1/G1 iPSDMs exhibit metabolic differences that may contribute to their proinflammatory phenotype.