Impaired Redox Capacity, Muscle Injury, and Microtubule Alterations Conspire to Impact Skeletal Muscle Function

Abstract

Previously, we linked increases in microtubule (MT) density, MT modification by detyrosination (i.e., deTyr-tub), and NADPH Oxidase 2 (Nox2) expression, to the excess in reactive oxygen species (ROS) and Ca2+ signals responsible for contraction injury in diseased muscle. In the present study, we hypothesized that a reduction in muscle redox buffering, as a result of chronic oxidative stress, is central to the MT changes that impair muscle function. Evidence suggest that oxidative stress is central to MT alterations in disease. Specifically, Nox2 expression precedes MT alterations (Khairallah et al, 2011), and its signaling regulates MT structure (Loehr et al, 2016) in dystrophic muscle. Furthermore, evidence shows oxidative regulation of the tubulin carboxypeptidase responsible for deTyr-tub (Nieuwenhuis et al, 2017). In order to test the contribution of altered redox capacity on MTs and muscle function, we treated adult C57BL/6J mice, with saline, butathione sulfoxamine (BSO; to deplete glutathione), taxol (MT polymerizer, promotes deTyr), or BSO+Taxol for 4 days. We show redox buffer capacity (GSH:GSSG) was significantly reduced with BSO and BSO+Taxol. However, only BSO+Taxol increased MT density and its level of deTyr-tub; a result consistent with BSO promoting Taxol's chemotherapeutic efficacy (Liebmann et al, 1993). With these MT alterations, we show that in vivo gastrocnemius function was unchanged with BSO or Taxol alone, while BSO+Taxol reduced muscle contractility and enhanced muscle contraction injury. Lastly, our examination of gastrocnemius muscle 1 day post contraction injury revealed that BSO treatment yielded a significant increase in MT density and deTyr-tub vs control despite injuring to the same extent. Taken together, we conclude that while decreased redox buffer capacity is insufficient to elicit MT alterations that impact function, it establishes a permissive environment for Taxol or injury to induce these changes.