Compositionally Distinct Renal Lipid Droplets Form in Response to Different Stimuli

Background: Acute kidney injury (AKI) affects roughly 1 in 5 hospitalized patients and if left untreated can lead to chronic kidney disease and death. Lipid droplet (LD) accumulation occurs after AKI, but whether LDs are part of tissue pathology or a pro-survival response is unknown. To address this, we sought to identify unique AKI-associated LD pathways. We profiled the lipidome, proteome and spatial distribution of accumulated LDs in renal ischemia/reperfusion injury (IRI), a mouse model of AKI. We hypothesized that IRI-induced LDs would be distinct from LDs formed in the kidney under nutritional fasting, another stress condition which induces LD accumulation. Methods: Male C57BL/6J mice were either fed or fasted; or underwent sham or bilateral renal IRI surgery. Kidneys were harvested 24 hours later and tissue processed for high resolution microscopy, lipidomics, and proteomics. Results: Following IRI stress, proximal tubules in the corticomedullary junction, an injury susceptible region of the kidney, becomes decorated with large and morphologically heterogenous LDs, whereas fasting forms more uniform and smaller LDs in proximal tubules across the kidney cortex. Lipidomic profiling reveals that kidney LDs formed in response to IRI display distinct lipid and protein signatures associated with turnover of polyunsaturated fatty acids, which are particularly susceptible to oxidative damage. IRI-stressed kidney tissue shows an increase in arachidonic acid (AA)-containing LD phospholipids compared to fasting kidney tissue, as well as AA-derived prostaglandin PGF1α. In line with this, proteomics of IRI and fasting LDs show an enrichment of several enzymes linked to AA processing on IRI-induced LDs, including cPLA2G4A, MBOAT7, and ACSL4. Furthermore, lipidomic profiling shows an increase in the AA precursor, linoleic acid (LA), as well as the oxidized form of LA in the neutral lipid LD core. Conclusion: Collectively, we propose that the kidney produces compositionally unique LD populations in response to specific stress cues, and that IRI-induced LDs are enriched in proteins dedicated to converting AA into signaling molecules and preferentially sequester LA in the neutral lipid core of the LD to limit cellular lipid peroxidation. Funding: NIDDK Support - NIDDK Support, NIDDK Support