Pulmonary inflammation-induced loss and subsequent recovery of skeletal muscle mass require functional poly-ubiquitin conjugation

Abstract

BackgroundPulmonary inflammation in response to respiratory infections can evoke muscle wasting. Increased activity of the ubiquitin (Ub)-proteasome system (UPS) and the autophagy lysosome pathway (ALP) have been implicated in inflammation-induced muscle atrophy. Since poly-Ub conjugation is required for UPS-mediated proteolysis and has been implicated in the ALP, we assessed the effect of impaired ubiquitin conjugation on muscle atrophy and recovery following pulmonary inflammation, and compared activation and suppression of these proteolytic systems to protein synthesis regulation.MethodsPulmonary inflammation was induced in mice by an intratracheal instillation of LPS. Proteolysis (UPS and ALP) and synthesis signaling were examined in gastrocnemius muscle homogenates. Ub-conjugation-dependency of muscle atrophy and recovery was addressed using Ub-K48R (K48R) mice with attenuated poly-ubiquitin conjugation, and compared to UBWT control mice.ResultsPulmonary inflammation caused a decrease in skeletal muscle mass which was accompanied by a rapid increase in expression of UPS and ALP constituents and reduction in protein synthesis signaling acutely after LPS. Muscle atrophy was attenuated in K48R mice, while ALP and protein synthesis signaling were not affected. Muscle mass recovery starting 72 h post LPS, correlated with reduced expression of UPS and ALP constituents and restoration of protein synthesis signaling. K48R mice however displayed impaired recovery of muscle mass.ConclusionPulmonary inflammation-induced muscle atrophy is in part attributable to UPS-mediated proteolysis, as activation of ALP- and suppression of protein synthesis signaling occur independently of poly-Ub conjugation during muscle atrophy. Recovery of muscle mass following pulmonary inflammation involves inverse regulation of proteolysis and protein synthesis signaling, and requires a functional poly-Ub conjugation.Electronic supplementary materialThe online version of this article (10.1186/s12931-018-0753-8) contains supplementary material, which is available to authorized users.

Pulmonary inflammation-induced alterations in key regulators of mitophagy and mitochondrial biogenesis in murine skeletal muscle

“…Moreover, the activation of inflammatory NF-κB signalling has been described in the skeletal muscle of this model [27]. These data are in line with the inflammatory profile reported in the current study, as we previously reported inflammatory cell recruitment, and increased gene-expression of pro-inflammatory cytokines and chemokines in these IT-LPS instilled lungs [33], and we now report increased levels of inflammatory gene expression in the gastrocnemius muscle of these mice.…”

“…These changes were not associated with pronounced differences in skeletal muscle mitochondrial content. The currently reported changes in mitophagy-and mitochondrial biogenesis-associated signalling are associated with increased atrophysignalling that was previously described in this study by our group [33].…”

“…Moreover, we describe associations between changes in the processes of autophagy/mitophagy and mitochondrial biogenesis, but the causality of these associations remains unclear in our study. In addition to the known decrease in physical activity, it has been shown that food intake is reduced in this model [33]. As decreased physical activity and food intake both have been shown to be able to modulate mitophagy and mitochondrial biogenesis in muscle [55,56], a potential contribution of these aspects to the changes we observed in muscle of IT-LPS-instilled animals cannot be discarded.…”

“…The presented murine data concerns data from the genetic control group, expressing 6xhis/GFP-tagged ubiquitin on a FVB/N background (kindly provided by Douglas Gray [32]), of a larger research project concerning multiple unrelated hypotheses [33], in order to reduce number of laboratory animals used. The mice were owned and bred by the animal care facility at Maastricht University.…”

“…A small proportion of data included in this manuscript (i.e. proportions of LC3B and SQSTM1 protein and mRNA expression data in the time-course study) has been previously published in a research project concerning unrelated hypotheses [33].…”