Expression of the mitochondrial calcium uniporter in cardiac myocytes improves impaired mitochondrial calcium handling and metabolism in simulated hyperglycemia

Abstract

Diabetic cardiomyopathy is associated with metabolic changes, including decreased glucose oxidation (Gox) and increased fatty acid oxidation (FAox), which result in cardiac energetic deficiency. Diabetic hyperglycemia is a pathophysiological mechanism that triggers multiple maladaptive phenomena. The mitochondrial Ca uniporter (MCU) is the channel responsible for Ca uptake in mitochondria, and free mitochondrial Ca concentration ([Ca]) regulates mitochondrial metabolism. Experiments with cardiac myocytes (CM) exposed to simulated hyperglycemia revealed reduced [Ca] and MCU protein levels. Therefore, we investigated whether returning [Ca] to normal levels in CM by MCU expression could lead to normalization of Gox and FAox with no detrimental effects. Mouse neonatal CM were exposed for 72 h to normal glucose [5.5 mM glucose + 19.5 mM mannitol (NG)], high glucose [25 mM glucose (HG)], or HG + adenoviral MCU expression. Gox and FAox, [Ca], MCU levels, pyruvate dehydrogenase (PDH) activity, oxidative stress, mitochondrial membrane potential, and apoptosis were assessed. [Ca] and MCU protein levels were reduced after 72 h of HG. Gox was decreased and FAox was increased in HG, PDH activity was decreased, phosphorylated PDH levels were increased, and mitochondrial membrane potential was reduced. MCU expression returned these parameters toward NG levels. Moreover, increased oxidative stress and apoptosis were reduced in HG by MCU expression. We also observed reduced MCU protein levels and [Ca] in hearts from type 1 diabetic mice. Thus we conclude that HG-induced metabolic alterations can be reversed by restoration of MCU levels, resulting in return of [Ca] to normal levels.

Restoring mitochondrial calcium uniporter expression in diabetic mouse heart improves mitochondrial calcium handling and cardiac function

“…Recently, the pathophysiological role of MCUC in diabetes has become a topic of investigation. We previously reported that MCU protein levels and [Ca 2ϩ ] m were decreased in diabetic mice (34), and have confirmed these results here. In addi-tion, we observed diminished mitochondrial Ca 2ϩ uptake and mitochondrial Ca 2ϩ content in diabetic CM.…”

“…Our findings show decreased MCU protein levels, corresponding to reduced MCU mRNA levels (Ϫ50%). Hyperglycemia may be a contributing factor to MCU down-regulation in a STZ-induced diabetic model because we have previously demonstrated that exposing cultured neonatal CM to hyperglycemia leads to markedly decreased MCU levels (34).…”

“…The significance of the MCU under in vitro hyperglycemic conditions was tested previously by us (34). Neonatal CM cultured in high glucose media showed decreased [Ca 2ϩ ] m due to decreased MCU protein levels.…”

Why don't mice lacking the mitochondrial Ca2+ uniporter experience an energy crisis?

“…; Diaz‐Juarez et al . ), translational (Zaglia et al . ), and post‐translational regulation (Joiner et al .…”

“…Indeed, the MCU is identified by screening the binding proteins of its regulator, mitochondrial Ca 2+ uptake protein 1 (MICU1), which contains canonical EF-hand Ca 2+ binding domains (Perocchi et al 2010). Regulation of MCU channel activity is mainly achieved by its associated proteins (see below), although transcriptional (Marchi et al 2013;Diaz-Juarez et al 2016), translational (Zaglia et al 2017), and post-translational regulation (Joiner et al 2012;O-Uchi et al 2014) of the MCU have also been reported. The channel activity can be inhibited by Ruthenium Red, Gd 3+ , or site-specific mutagenesis on two residues (D261, E264) in the loop region (De Stefani et al 2011).…”