Novel redox mechanisms of oxygenated phospholipids in chronic and diabetic kidney disease

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Oxidative stress has long been implicated in the pathogenesis of diabetic and chronic kidney disease (DKD/CKD). Most of the previous studies focused on either a singular concept of oxidative stress vs antioxidant balance, or centered on overproduction of superoxide as a major reactive oxygen species (ROS) and a primary event in DKD/CKD. However, superoxide has major kinetic and biochemical barriers that limit its impacts on biological structures. We propose a key role for less reactive, more specific and membrane diffusible molecules which are also tightly related to changes in cell metabolism – (phospho)lipid peroxides (LOOH). While the basic tenets of lipid peroxidation are established in biology, the molecular entity, modes of action and specific redox signaling ability of LOOH are more enigmatic. This is a critical gap to address because impeding a highly specific form of redox signal at the right timing in disease pathogenesis can prevent renal cell dysfunction. Our central hypothesis is that LOOH are key metabolic signals that transmit an initial redox stress in cells. Furthermore, we propose that diabetes alters the molecular signature of LOOH and that from a myriad of diverse oxidized phospholipids, there are only a few specific ones that dictate the activation of programmed cell death. We focus on proximal tubular epithelial cells (PTC) which comprise ~ 70-80 % of the cortex, where we previously discovered that dysregulation of PTC metabolism potentiates LOOH production. We have a broad array of preliminary data showing that when PTC metabolism is challenged either by lipid overload or by ablating the neutralizing mechanism for membrane peroxides via deletion of glutathione peroxidase 4 (GPx4), LOOH are overproduced and mice develop kidney injury. Using diabetic models, we show that diabetes not only potentiates the formation of LOOH, but also alters the molecular signature of LOOH species in a fashion that oxidized phosphatidylethanolamines (PE) and lysophosphatidylethanolamine (LPE) become abundant. Three aims will test the hypothesis using state-of-the-art biophysical and mass spectrometry imaging methods in combination with pharmacologic and transgenic approaches using both established and newly generated mouse models. In Aim 1, we will test the prediction that changes in PTC metabolic activity regulates the production of LOOH. Aim 2 will explore mechanisms through which diabetes potentiates the production of specific oxygenated phospholipids. In Aim 3, we will test the hypothesis, that selective oxidation of phospholipid species dictates the activation of renal cell death programs. The experimental strategy combines PTC-specific transgenic models, obese CKD and diabetic DKD models, using targeted compounds to delinate originating sources of redox stress and advanced redox phospholipidomics and biophysical approaches. Outcomes from this proposal will establish a new, more specific view of redox stress in CKD/DKD and link specific oxidized (phospho)lipids to PTC injury and demise, paving the way to highly specific anti-apoptotic or anti-ferroptotic interventions in the future.