Accumulating evidence indicates a strong association between diabetic status and degenerative brain disease, including cognitive impairment. Here we hypothesized that although insulin is not necessary for glucose metabolism in brain, like in skeletal muscle insulin is critical for mitochondrial function in brain. We measured oxygen consumption rate (OCR), maximal ATP production rate (MAPR), and reactive oxygen species (ROS) production in isolated brain mitochondria of streptozotocin (STZ) diabetic mice. STZ mice deprived of insulin treatment for 96 hours (D-I), in comparison to nondiabetic mice (ND) showed a significant reduction in State 3 MAPR [1.77±0.14 vs. 2.35±0.27 (pmol/s/ug)], phosphorylation efficiency [0.42±0.04 vs. 0.54±0.07 (mol ATP produced/mol of oxygen consumed)] and respiratory control ratio [2.95±0.16 vs. 3.12±0.18] indicating reduced mitochondrial coupling efficiency during insulin deprivation. Citrate synthase and cytochrome c oxidase activities were significantly decreased in the hypothalamus of D-I compared ND. Surprisingly, no significant differences in ROS emission were detected between ND and D-I suggesting additional factors, potentially elevated ketone bodies, may protect against increased oxidative stress in the D-I brain. Proteomics analysis of the cerebrum found post-translational modification involving oxidative damage of several mitochondrial proteins that potentially cause tau phosphorylation and neurofibrillary degeneration in D-I vs. ND. In STZ mice with continued insulin treatment (D+I), state 3 OCR, MAPR, and phosphorylation efficiency were comparable to ND, demonstrating the restorative effects of insulin and euglycemia on brain mitochondrial function. We conclude that insulin deprivation and hyperglycemia significantly alter brain mitochondrial function. Insulin treatment and control of glycemia could have salutary effects on these parameters.
G. Ruegsegger: None. M. Shankarappa: None. P. Summer: None. S. Gopala: None. P. Zabielski: None. K. Klaus: None. S. Dasari: None. I.R. Lanza: None. K. Nair: None.