Dual Regulation of Mitochondrial Complexes by H₂S via S-Sulfhydration Controls Respiration in Type 1 Diabetic Hearts

Hydrogen sulfide (H₂S) has been established to regulate mitochondrial respiration and ATP production, but whether the regulation is through S-sulfhydration (-SSH) of mitochondrial complexes is not well understood. Recently, H₂S is known to exert diverse and dose-dependent effects on mitochondrial complexes. However, the involvement of S-sulfhydration of each mitochondrial complex and the activities in diabetic hearts have not been revealed. Here, we conducted comprehensive investigations into S-sulfhydration and the activities of mitochondrial complexes I-V in normal and Streptozotocin (STZ)-induced type 1 diabetic (DM) heart mitochondria. Results showed that proteins of H₂S-producing enzymes were downregulated in DM heart mitochondria, which was accompanied by reduced mitochondrial membrane potential (MMP), greater ROS, and lower complex I and V activities, reduced complex V-SSH in DM. In both groups, supplementation with the H₂S donor NaHS increased the S-sulfhydration of all mitochondrial complexes, and the activities of complexes I-III and V were significantly increased but complex IV activity was reduced. Consequently, mitochondrial MMP, ROS, and ATP production were normalized with NaHS in DM, whereas inhibition of H₂S generation increased mitochondrial ROS and reduced MMP via reducing complex activities in both groups. Ischemic reperfusion did not affect NaHS-increment of S-sulfhydration of complexes I-V, but significantly impaired complex V activity in DM. Collectively, H₂S-dependent S-sulfhydration of mitochondrial complexes I-V in normal and DM heart mitochondria were involved in the activation of mitochondrial complexes I-III/V and the inhibition of complex IV, which control cardiac mitochondrial respiration and ATP production.