Minocycline Treatment Reduces Mass and Force Output From Fast-Twitch Mouse Muscles and Inhibits Myosin Production in C2C12 Myotubes.

Leonit Kiriaev,Ben D Perry,Stewart I Head,David A Mahns,John W Morley,Peter J Shortland,Asma Redwan

doi:10.3389/fphys.2021.696039

Abstract

Minocycline, a tetracycline-class of antibiotic, has been tested with mixed effectiveness on neuromuscular disorders such as amyotrophic lateral sclerosis, autoimmune neuritis and muscular dystrophy. The independent effect of minocycline on skeletal muscle force production and signalling remain poorly understood. Our aim here is to investigate the effects of minocycline on muscle mass, force production, myosin heavy chain abundance and protein synthesis. Mice were injected with minocycline (40 mg/kg i.p.) daily for 5 days and sacrificed at day six. Fast-twitch EDL, TA muscles and slow-twitch soleus muscles were dissected out, the TA muscle was snap-frozen and the remaining muscles were attached to force transducer whilst maintained in an organ bath. In C2C12 myotubes, minocycline was applied to the media at a final concentration of 10 μg/mL for 48 h. In minocycline treated mice absolute maximal force was lower in fast-twitch EDL while in slow-twitch soleus there was an increase in the time to peak and relaxation of the twitch. There was no effect of minocycline treatment on the other contractile parameters measured in isolated fast- and slow-twitch muscles. In C2C12 cultured cells, minocycline treatment significantly reduced both myosin heavy chain content and protein synthesis without visible changes to myotube morphology. In the TA muscle there was no significant changes in myosin heavy chain content. These results indicate that high dose minocycline treatment can cause a reduction in maximal isometric force production and mass in fast-twitch EDL and impair protein synthesis during myogenesis in C2C12 cultured cells. These findings have important implications for future studies investigating the efficacy of minocycline treatment in neuromuscular or other muscle-atrophy inducing conditions.

Highlights

MATERIALS AND METHODSMinocycline is part of the tetracycline family of broad-spectrum antibiotics
In the fast-twitch Extensor digitorum longus (EDL) muscle, minocycline treatment reduced the mass of the muscle by 8%, and not statistically significant (MD −1,09, 95% CI [−2.417, 0.2372], P = 0.102), the distribution of the 95% confidence intervals and proximity to statistical significance strongly suggests the EDL mass was lowered with minocycline treatment, while in the slow-twitch soleus muscle the mass was unaffected by minocycline treatment (Table 1)
Minocycline treatment in C2C12 myotubes reduced both protein synthesis and myosin heavy chain content, myosin heavy chain content analysis of the Tibialis anterior (TA) muscle showed no effect of minocycline treatment

Summary

Introduction

MATERIALS AND METHODSMinocycline is part of the tetracycline family of broad-spectrum antibiotics. In addition to the well-established antibacterial clinical uses of minocycline, it has gained interest as a possible treatment for neuromuscular disorders, in part because of its improved lipid solubility and uptake into cerebrospinal fluid compared to other tetracyclines (Richards et al, 1981; Orsucci et al, 2009). While many studies have reported the potential benefit of minocycline treatment in neuromuscular conditions such as amyotrophic lateral sclerosis (Kriz et al, 2002), neuropathies and muscular dystrophies (Orsucci et al, 2012), there is evidence that in some instances minocycline treatment may have detrimental clinical outcomes or physiological outcomes; for example, despite promising findings in animal studies, a phase III clinical trial of minocycline in ALS patients found it worsened clinical deterioration (Gordon et al, 2007). In a clinical case-study, Bokuda et al (2012) reported skeletal muscle pigmentation, autophagic vacuoles, and scattered atrophic fibres in a 75-yearold patient who had been prescribed minocycline for several years. In C. elegans, minocycline treatment increased lifespan, it reduced protein synthesis rate (Solis et al, 2018), consistent with findings in minocycline-treated cancer cells (Jung et al, 2014)

Objectives

Results

Conclusion