T-cell development of resistance to apoptosis is driven by a metabolic shift in carbon source and altered activation of death pathways.

Abstract

We developed a model system to investigate apoptotic resistance in T cells using osmotic stress (OS) to drive selection of death-resistant cells. Exposure of S49 (Neo) T cells to multiple rounds of OS followed by recovery of surviving cells resulted in the selection of a population of T cells (S49 (OS 4-25)) that failed to die in response to a variety of intrinsic apoptotic stimuli including acute OS, but remained sensitive to extrinsic apoptotic initiators. Genome-wide microarray analysis comparing the S49 (OS 4-25) with the parent S49 (Neo) cells revealed over 8500 differentially regulated genes, with almost 90% of those identified being repressed. Surprisingly, our data revealed that apoptotic resistance is not associated with expected changes in pro- or antiapoptotic Bcl-2 family member genes. Rather, these cells lack several characteristics associated with the initial signaling or activation of the intrinsic apoptosis pathway, including failure to increase mitochondrial-derived reactive oxygen species, failure to increase intracellular calcium, failure to deplete glutathione, failure to release cytochrome c from the mitochondria, along with a lack of induced caspase activity. The S49 (OS 4-25) cells exhibit metabolic characteristics indicative of the Warburg effect, and, despite numerous changes in mitochondria gene expression, the mitochondria have a normal metabolic capacity. Interestingly, the S49 (OS 4-25) cells have developed a complete dependence on glucose for survival, and glucose withdrawal results in cell death with many of the essential characteristics of apoptosis. Furthermore, we show that other dietary sugars such as galactose support the viability of the S49 (OS 4-25) cells in the absence of glucose; however, this carbon source sensitizes these cells to die. Our findings suggest that carbon substrate reprogramming for energy production in the S49 (OS 4-25) cells results in stimulus-specific recognition defects in the activation of intrinsic apoptotic pathways.