Unpolymerized βII Tubulin in Regulation of Mitocondrial Function in Muscle Cells

Abstract

The importance of microtubular system in shaping the organization of intracellular energy metabolism and regulating mitochondrial functioning is becoming increasingly more evident. Our previous studies with cardiac cells have shown that regulation of mitochondrial outer membrane (MOM) permeability for ADP by dimeric αβ-tubulin is important for efficient cross-talk between mitochondria and contraction apparatus through phoshocreatine energy transfer pathway. This regulation was specifically related with tubulin isoform βII after showing its mitochondrial localization in cardiac cells and verifying its concomitant expression with mitochondrial creatine kinase (MtCK). However the exact mechanism of this regulation is still rather elusive and studied mainly in cardiac cells. To determine if βII tubulin expression is specific only to oxidative muscle cells with high MtCK activity and to gain further insight to the role of βII tubulin in energy metabolism, we have analyzed the relationship between βII tubulin expression, mitochondrial respiration regulation and their intracellular positioning in striated muscles with different metabolic phenotype. In this study we provide further proof for the functional importance of βII tubulin in regulation of mitochondrial respiration in striated muscles. We show that both oxidative and glycolytic muscles express βII tubulin, but the presence of unpolymerized βII tubulin is significantly lower in glycolytic muscle cells concomitant with higher MOM permeability for ADP. Analysis of mitochondria and βII tubulin localization reveals that in oxidative muscle cells mitochondria are positioned in close vicinity to βII tubulin with high degree of colocalization which is much less prevalent in glycolytic muscles. Together our results show that βII tubulin displays both structural and regulatory role in striated muscle cells and its distribution and polymerization level has direct impact on regulation of mitochondrial ADP sensitivity and efficiency of mitochondria coupling with contraction apparatus.