Recruitment of APOL1 kidney disease risk variants to lipid droplets attenuates cell toxicity

Abstract

Two coding variants in the apolipoprotein L1 (APOL1) gene (termed G1 and G2) are strongly associated with increased risk of nondiabetic kidney disease in people of recent African ancestry. The mechanisms by which the risk variants cause kidney damage, although not well-understood, are believed to involve injury to glomerular podocytes. The intracellular localization and function of APOL1 in podocytes remain unclear, with recent studies suggesting possible roles in the endoplasmic reticulum (ER), mitochondria, endosomes, lysosomes, and autophagosomes. Here, we demonstrate that APOL1 also localizes to intracellular lipid droplets (LDs). While a large fraction of risk variant APOL1 (G1 and G2) localizes to the ER, a significant proportion of wild-type APOL1 (G0) localizes to LDs. APOL1 transiently interacts with numerous organelles, including the ER, mitochondria, and endosomes. Treatment of cells that promote LD formation with oleic acid shifted the localization of G1 and G2 from the ER to LDs, with accompanying reduction of autophagic flux and cytotoxicity. Coexpression of G0 APOL1 with risk variant APOL1 enabled recruitment of G1 and G2 from the ER to LDs, accompanied by reduced cell death. The ability of G0 APOL1 to recruit risk variant APOL1 to LDs may help explain the recessive pattern of kidney disease inheritance. These studies establish APOL1 as a bona fide LD-associated protein, and reveal that recruitment of risk variant APOL1 to LDs reduces cell toxicity, autophagic flux, and cell death. Thus, interventions that divert APOL1 risk variants to LDs may serve as a novel therapeutic strategy to alleviate their cytotoxic effects.

Prevalence of APOL1 Risk Variants in Afro-Descendant Patients with Chronic Kidney Disease in a Latin American Country

“…e APOL1 risk alleles activate the protein kinase R (PKR) which in turn induces glomerular injury and proteinuria [7]. Moreover, the APOL1 may function similarly to the LD-associated protein CIDEA, which has an amphipathic helix that facilitates embedding in the phospholipid monolayer and binding to phosphatidic acid, and altered association of APOL1 with LDs may alter APOL1 delivery to mitochondria, possibly controlling cytotoxicity [8].…”

ProfilingAPOL1Nephropathy Risk Variants in Genome-Edited Kidney Organoids with Single-Cell Transcriptomics

“…We tested whether ER stress could provide a stimulus to alter stress response and cellular phenotypes in the high-risk genotype. ER stress was chosen because ubiquitin D, encoded by UBD, is involved in the ER stress response, and risk-variant APOL1 appears to localize to the ER membrane 30 . Furthermore, ER stress is becoming an increasingly recognized driver of complex diseases, including CKD [31][32][33][34] .…”

Profiling APOL1 Nephropathy Risk Variants in Genome-Edited Kidney Organoids with Single-Cell Transcriptomics

“…We tested whether ER stress could provide a stimulus to alter stress response and cellular phenotypes in the highrisk genotype. ER stress was chosen because ubiquitin D, encoded by UBD, is involved in the ER stress response, and risk-variant APOL1 appears to localize to the ER membrane (36). Furthermore, ER stress is becoming an increasingly recognized driver of complex diseases, including CKD (37-40).…”

“…Unlike prior models (25,45), our model system does not lead to much cell death in the G1 kidney organoids at 24 hours, nor does it activate many proapoptotic genes, consistent with the concept that another stressor is needed to induce a phenotype. We chose ER stress as an experimental condition because previous studies have indicated that risk-variant APOL1 may be regulated by UBD (32), a gene involved in the ER stress response, and that risk-variant APOL1 localizes to the ER rather than to lipid droplets (36). Expression of risk-variant APOL1 alone does not activate a significant unfolded protein response (as seen in Figure 5B), but some differences can be seen for DDIT3, EDEM1, ERN1, GSK3A, and ERP44 upon tunicamycin stimulation, consistent with a second-hit hypothesis.…”