Date Published: January 18, 2017
Publisher: Public Library of Science
Author(s): Harumasa Nakazawa, Kyungho Chang, Shohei Shinozaki, Takashi Yasukawa, Kazuhiro Ishimaru, Shingo Yasuhara, Yong-Ming Yu, J. A. Jeevendra Martyn, Ronald. G. Tompkins, Kentaro Shimokado, Masao Kaneki, Partha Mukhopadhyay.
Inflammation and apoptosis develop in skeletal muscle after major trauma, including burn injury, and play a pivotal role in insulin resistance and muscle wasting. We and others have shown that inducible nitric oxide synthase (iNOS), a major mediator of inflammation, plays an important role in stress (e.g., burn)-induced insulin resistance. However, it remains to be determined how iNOS induces insulin resistance. Moreover, the interrelation between inflammatory response and apoptosis is poorly understood, although they often develop simultaneously. Nuclear factor (NF)-κB and p53 are key regulators of inflammation and apoptosis, respectively. Sirt1 inhibits p65 NF-κB and p53 by deacetylating these transcription factors. Recently, we have shown that iNOS induces S-nitrosylation of Sirt1, which inactivates Sirt1 and thereby increases acetylation and activity of p65 NF-κB and p53 in various cell types, including skeletal muscle cells. Here, we show that iNOS enhances burn-induced inflammatory response and apoptotic change in mouse skeletal muscle along with S-nitrosylation of Sirt1. Burn injury induced robust expression of iNOS in skeletal muscle and gene disruption of iNOS significantly inhibited burn-induced increases in inflammatory gene expression and apoptotic change. In parallel, burn increased Sirt1 S-nitrosylation and acetylation and DNA-binding capacity of p65 NF-κB and p53, all of which were reversed or ameliorated by iNOS deficiency. These results indicate that iNOS functions not only as a downstream effector but also as an upstream enhancer of burn-induced inflammatory response, at least in part, by Sirt1 S-nitrosylation-dependent activation (acetylation) of p65 NF-κB. Our data suggest that Sirt1 S-nitrosylation may play a role in iNOS-mediated enhanced inflammatory response and apoptotic change, which, in turn, contribute to muscle wasting and supposedly to insulin resistance after burn injury.
Metabolic dysfunction in skeletal muscle is a major complication after major trauma, including burn injury, and negatively affects the clinical outcome of patients with major trauma [1, 2]. These metabolic alterations include insulin resistance, hyperglycemia, hypermetabolism, increased lactate production, catabolism and muscle wasting. Inflammatory response plays a critical role in obesity- and stress (e.g., burn)-induced insulin resistance [3–5]. Insulin resistance and apoptotic change contribute to muscle wasting [6–9]. Despite intensive investigation for many years, it is not fully understood how inflammation is initiated and sustained after major trauma and how inflammation causes insulin resistance.
Here, we show that burn injury induced acetylation and activation of p65 NF-κB and p53 at 3 days post-burn, along with iNOS induction and S-nitrosylation of Sirt1 in mouse skeletal muscle. iNOS deficiency prevented these alterations in burned mice. Our data indicate that iNOS induction is required for Sirt1 S-nitrosylation and acetylation of p65 NF-κB and p53 after burn injury. Moreover, the inhibition of acetylation and activation of p65 NF-κB and p53 by iNOS deficiency were associated with amelioration of burn-induced inflammatory response and apoptotic change as well as the prevention of insulin resistance  (Fig 8).