Mitochondrial Dysfunction and Disorganized Microtubules in Duchenne Muscular Dystrophy are Not Related to Altered α Tubulin‐Voltage Dependent Anion Channel (VDAC) 2 Interactions
Authors: Ramos Sofhia V , Hughes Meghan C , Bellissimo Catherine A , Perry Christopher GR 
Published: June 2021

Rationale

In Duchenne muscular dystrophy (DMD), a genetic mutation results in a loss of dystrophin which leads to microtubular disorganization, cellular degeneration and muscle weakness. However, a mechanism by which microtubule disorganization contributes to muscle weakness in DMD has not been established. We considered a model that proposes tubulin, the structural component of microtubules, may directly bind VDAC2 on the outer mitochondrial membrane and alter its permeability to ADP import. Given ADP stimulates oxidative phosphorylation and attenuates H2O2 emission through modulation of membrane potential, the model predicts that tubulin‐VDAC interactions may be a novel regulator of cellular energy and redox homeostasis. Furthermore, as VDAC is also thought to be involved in formation of the mitochondrial permeability transition pore (mPTP) in response to calcium stress – a phenomenon that occurs in DMD – tubulin‐VDAC interactions may also influence the maximal mitochondrial calcium retention capacity (CRC) required to trigger cell death. Considering these relationships between VDAC and bioenergetic control, we hypothesized that the disorganized microtubule network in DMD would be linked to impairments in ADP's control of bioenergetics and mPTP formation through altered tubulin‐VDAC binding.

Methods

Permeabilized fibre bundles and single fibers from 4 week old wildtype (WT) and D2.mdx (DMD mouse) were prepared from extensor digitorum longus (EDL) muscles and used for mitochondrial bioenergetic and histological assessments.

Results

D2.mdx EDL demonstrated impaired ADP‐stimulated respiration at a range of ADP concentrations (−37–43% at 25mM, 100mM, 500mM and 5mM ADP, p<0.003) and an impaired ability of ADP to attenuate H2O2 emission (71% increase in H2O2 at 500mM ADP, p=0.04) despite similar CRC. There were no differences in the protein content of electron transport chain complex subunits (Complexes I to V) or VDAC2 despite significantly decreased adenine nucleotide translocase (ANT) (p=0.03). a‐tubulin–VDAC2 interactions were unchanged despite alterations to a‐tubulin network in D2.mdx fibers.

Conclusions and Discussion

Disorganized microtubules in EDL from D2.mdx mice are related to mitochondrial dysfunction, but this is not due to altered a‐tubulin–VDAC2 interactions. It remains to be determined if interactions between other tubulin or VDAC isoforms are altered in DMD and contribute to impaired VDAC‐dependent bioenergetics. In addition, reduced ANT content may partially explain impaired mitochondrial function in dystrophic EDL.

Support or Funding Information

Funding was provided to C.G.R.P. by National Science and Engineering Research Council (#436138‐2013) with infrastructure supported by Canada Foundation for Innovation, Ontario Research Fund and the James H. Cummings Foundation. S.V.R was supported by Ontario Graduate Scholarship.

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.