McCarthy, Christina B.

Abstract We recently reported normalization of CSF cytokine levels following successful treatment of drug-resistant epilepsy (DRE) with recombinant interleukin-1 receptor antagonist (rIL1RA). To further understand the mechanism of this therapeutic outcome, we interrogated the ability of serum and CSF factors that are elevated in drug resistant-seizure disorders to promote inflammatory responses in astrocytes and human brain microvessel endothelial cells (HBMVECs). We report that CCL2, TNFa, IL6, and CXCL8/1 were strongly induced in 1) astrocytes and HBMVECs stimulated with IL1β (blocked by rIL1RA) and 2) astrocytes but not HBMVECs in response to DRE patient serum but not control serum (partially blocked by rIL1RA). This suggested that other serum factors contribute to astrocyte activation in this DRE. HMGB1 and IL18 were also dysregulated in DRE patient serum; however, IL18 failed to stimulate cytokine secretion from astrocytes. In contrast, HMGB1 induced cytokine secretion from astrocytes, which was blocked by the TLR4 inhibitor TAK242. Remarkably, TAK242 also prevented cytokine production by astrocytes in response to serum from some patients with DRE. Finally, IL1β induced the polarized uptake and secretion of HMGB1 across transwell inserts harboring confluent monolayers of HBMVECs suggesting that IL1b signaling may cause endothelial cells to transport serum HMGB1 into the perivascular space—promoting TLR4-dependent cytokine release from astrocytes. This translation of an “outside” inflammatory signal into an “inside” inflammatory response may underlie seizure disorders that are resistant to anti-seizure drugs.

Insulin resistance associates with increased risk for cognitive decline and dementia; however, the underpinning mechanisms for this increased risk remain to be fully defined. As insulin resistance impairs mitochondrial oxidative metabolism and increases ROS in skeletal muscle, we considered whether similar events occur in the brain, which — like muscle — is rich in insulin receptors and mitochondria. We show that high-fat diet–induced (HFD-induced) brain insulin resistance in mice decreased mitochondrial ATP production rate and oxidative enzyme activities in brain regions rich in insulin receptors. HFD increased ROS emission and reduced antioxidant enzyme activities, with the concurrent accumulation of oxidatively damaged mitochondrial proteins and increased mitochondrial fission. Improvement of insulin sensitivity by both aerobic exercise and metformin ameliorated HFD-induced abnormalities. Moreover, insulin-induced enhancement of ATP production in primary cortical neurons and astrocytes was counteracted by the insulin receptor antagonist S961, demonstrating a direct effect of insulin resistance on brain mitochondria. Further, intranasal S961 administration prevented exercise-induced improvements in ATP production and ROS emission during HFD, supporting that exercise enhances brain mitochondrial function by improving insulin action. These results support that insulin sensitizing by exercise and metformin restores brain mitochondrial function in insulin-resistant states.