A recent study in our lab showed that senescent mesenchymal stem cells exhibited severe deterioration of oxidative phosphorylation and an increased level of intracellular urea accumulation. In turn high levels of urea inhibited the activity of the electron chain complexes, especially complex IV. Treating senescent stem cells with CB-839, a small molecule inhibitor of glutaminase (GLS1), the key enzyme of glutamine catabolism, showed improved mitochondrial health and increased complex IV activity. Building on these observations, we hypothesized that senescent skeletal muscle (SkM) may depend on glutamine to meet its bioenergetic demands. Indeed, we observed that senescent SkM cells displayed increased glutamine catabolism that was accompanied by significantly elevated levels of intracellular urea accumulation. This in turn contributed to decreased activity of the electron transport chain complexes, indicative of dysfunctional mitochondria. Treating these cells with CB-839 resulted in drastically decreased levels of intracellular urea with significantly increased mitochondrial respiration. Specifically, inhibiting GLS1 increased the oxygen consumption rate (OCR) as measure by Seahorse metabolic analysis. Apart from improving the mitochondrial health, CB-839 treatment reversed several hallmarks of aging such as DNA damage, as evidenced by a decrease in γH2Ax positive cells and ROS accumulation.
To evaluate the effect of GLS1 inhibition on SkM aging in vivo, we employed a mouse model of Hutchinson-Gilford progeria syndrome, carrying a mutation in the nuclear Lamin A gene that leads to premature aging (progeria). We observed that progeria mice exhibited increased reliance on amino acids, particularly glutamine, and inhibition of GLS1 by CB-839 for one month reduced the level of urea and increased the level and activity of the electron chain complexes in the Tibialis Anterior (TA) muscle. In addition to improving mitochondrial health, GLS1 inhibition enhanced the physical performance of SkM as evidenced by a battery of tests such as hang test, grip strength, open field assay and increased the force generation capacity of the dorsiflexor muscles (twitch and isometric tetanic force), as measured by a force transducer following electrical stimulation. Most important, when CB839 was administered for prolonged times, we observed an extension of the mouse lifespan. Specifically, CB-839 extended the median survival by approximately 1.5 months, as compared to untreated mice, while also improving the overall health of the aged mice, as evidenced by a stable body weight, enhanced fur quality and metabolic analysis. Taken together, our data shows that inhibition of glutamine catabolism may be a successful strategy for reversing the aging hallmarks, restoring mitochondrial metabolism, preventing frailty and even extending lifespan.