Abstract 2867: Ceramide-dependent mitophagy leads to metabolic reprogramming in aging T-cells associated with reduced anti-tumor T-cell functions
Authors: Kassir Mohamed Faisal , Lee Han Gyul , Oleinik Natalia , Chakraborty Paramita , Lemasters John J. , Szulc Zdzislaw , Yu Xue-Zhong , Mehrotra Shikhar , Ogretmen Besim 
Published: June 2023

Abstract
Changes in mitochondrial bioenergetics in aging T-cells play a key role in the decrease in T-cell function and tumor resistance with aging. The bioactive sphingolipid ceramide, induced by aging stress, is a major player in these changes, as its accumulation at the mitochondrial membranes of both mouse and human aging T-cells induces ceramide-dependent mitophagy, which decreases T-cell viability, cytokine secretion, and anti-tumor activity. Using knock-out mouse models and pharmacological inhibition, we show that C14-ceramide accumulation in the mitochondria and mitophagy in the T-cells of aging mice are dependent on Ceramide Synthase 6 (CerS6), an enzyme responsible for C14/C16-ceramide synthesis. Interestingly, sphingosine kinase 2 (SphK2), another enzyme involved in ceramide metabolism inhibits HDAC1/2 function in aging T-cells, epigenetically inducing CerS6 expression and the resultant ceramide-dependent mitophagy, which ultimately decreases T-cell anti-tumor function. Both CerS6-/- and SphK2-/- aging T-cells were protected from the reduction in T-cell function, and their anti-tumor function was maintained in adoptive-cell transfer experiments to mice with melanoma. Besides lipid signaling, other metabolic changes associated with this aging-induced process have not been explored, and the utility of correcting these metabolic changes to restore T-cell function has not been evaluated. We studied the total hydrophilic metabolome of aging T-cells undergoing ceramide-dependent mitophagy to assess the metabolic changes occurring in these cells. Our findings show a general depletion of tricarboxylic acid cycle (TCA) metabolites in aging T-cells, with pools of fumarate, malate, and argininosuccinate significantly decreasing in both mouse and human aging T-cells. Interestingly, these changes were mirrored by similar changes in human cancer cells undergoing ceramide-dependent mitophagy, suggesting that these changes might constitute a general metabolic signature for this specific mitophagy process with deleterious effects on anti-tumor functions of aging T-cells. Both in vitro and in vivo supplementation of fumarate to mouse T-cells seemed to correct some of the functional defects observed in aging, with a protection of T-cell viability, cytokine production, and tumor killing capacity in co-cultures with tumor cells. The fumarate supplementation also led to a decrease in ceramide-dependent mitophagy in the aging T-cells, indicating an interplay between ceramide-dependent mitophagy and fumarate metabolism. Overall, these studies help explain the mechanisms behind aging-related dysregulation of T-cell anti-tumor activity, which can be restored by inhibiting ceramide-dependent mitophagy by pharmacological and genetic tools or by reprogramming fumarate metabolism in aging T cells.
Citation Format: Mohamed Faisal Kassir, Han Gyul Lee, Natalia Oleinik, Paramita Chakraborty, John J. Lemasters, Zdzislaw Szulc, Xue-Zhong Yu, Shikhar Mehrotra, Besim Ogretmen. Ceramide-dependent mitophagy leads to metabolic reprogramming in aging T-cells associated with reduced anti-tumor T-cell functions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2867.