Pioglitazone-induced AMPK-Glutaminase-1 prevents high glucose-induced pancreatic β-cell dysfunction by glutathione antioxidant system
Udayakumar Karunakaran, Suma Elumalai, Jun Sung Moon, Kyu Chang Won
Abstract
Prolonged hyperglycemia plays a major role in the progression of β-cell loss in diabetes mellitus. Here we report an insulin sensitizer thiazolidinedione Pioglitazone selectively preserves the beta cells against high glucose-induced dysfunction by activation of AMPK and Glutaminase 1 (GLS1) axis. AMPK activation increases the stability of Glutaminase 1 by HSP90 family mitochondrial heat shock protein 75 (HSP75/TRAP1). This is associated with an elevation of GSH/GSSG ratio which leads to inhibition of mitochondrial dysfunction by induction of BCL2/BCL-XL in high glucose conditions. Pioglitazone was able to also protect against high glucose-induced elevations in maladaptive ER stress markers and increase the adaptive unfolded protein response (UPR) by inhibiting mTORC1-eEF2 protein translation machinery. Moreover, the pioglitazone effect on AMPK activation was not dependent on the PPARγ pathway. Strikingly, chemical inhibition of AMPK signaling or glutaminase-1 inhibition abrogates the pioglitazone effect on the TRAP1-GLS1 axis and GSH/GSSG ratio linked to mitochondrial dysfunction. Finally, inhibition of AMPK signaling enhanced maladaptive ER stress markers by mTORC1-eEF2 activation. Altogether, these results support the proposal that pioglitazone induced AMPK activation stabilizes a novel interaction of TRAP1/HSP75-GLS1 and its downstream signaling leads to improved β-cell function and survival under high glucose conditions.