Skeletal Muscle PGC-1α Is Required for Maintaining an Acute LPS-Induced TNFα Response

Many lifestyle-related diseases are associated with low-grade inflammation and peroxisome proliferator activated receptor γ coactivator (PGC)-1α has been suggested to be protective against low-grade inflammation. However, whether these anti-inflammatory properties affect acute inflammation is not known. The aim of the present study was therefore to investigate the role of muscle PGC-1α in acute inflammation. Quadriceps muscles were removed from 10-week old whole body PGC-1α knockout (KO), muscle specific PGC-1α KO (MKO) and muscle-specific PGC-1α overexpression mice (TG), 2 hours after an intraperitoneal injection of either 0.8 µg LPS/g body weight or saline. Basal TNFα mRNA content was lower in skeletal muscle of whole body PGC-1α KO mice and in accordance TG mice showed increased TNFα mRNA and protein level relative to WT, indicating a possible PGC-1α mediated regulation of TNFα. Basal p65 phosphorylation was increased in TG mice possibly explaining the elevated TNFα expression in these mice. Systemically, TG mice had reduced basal plasma TNFα levels compared with WT suggesting a protective effect against systemic low-grade inflammation in these animals. While TG mice reached similar TNFα levels as WT and showed more marked induction in plasma TNFα than WT after LPS injection, MKO PGC-1α mice had a reduced plasma TNFα and skeletal muscle TNFα mRNA response to LPS. In conclusion, the present findings suggest that PGC-1α enhances basal TNFα expression in skeletal muscle and indicate that PGC-1α does not exert anti-inflammatory effects during acute inflammation. Lack of skeletal muscle PGC-1α seems however to impair the acute TNFα response, which may reflect a phenotype more susceptible to infections as also observed in type 2 diabetes patients

mRNA expression in adipose tissue and liver from whole body PGC-1α KO mice.

<p>Tumor necrosis factor (TNF)α, TNFα converting enzyme (TACE), interleukin (IL)-6, IL-10, macrophage specific marker (F4/80) mRNA in adipose tissue and liver from whole body PGC-1α knockout (KO) and WT mice, 2 hours after injection with either saline (Sal) as control or lipopolysaccharide (LPS). Values are presented as means ± S.E. with n = 10 in each group.</p><p>*: Significantly different from Sal within given genotype, p<0.05.</p

Plasma IL-6 and IL-10.

<p>Plasma interleukin (IL)-6 and IL-10 from whole body PGC-1α knockout (KO), muscle specific PGC-1α KO (MKO) and muscle specific PGC-1α overexpression (TG) mice and their respective littermate wild type (WT) mice, 2 hours after injection with either saline (Sal) as control or lipopolysaccharide (LPS). Values are presented as means ± S.E. with n = 6–10 in each group, except WT of whole body KO strain injected with saline where n = 3, due to lack of blood.</p><p>*: Significantly different from Sal within given genotype, p<0.05.</p

TNFα mRNA and protein content in quadriceps.

<p>Tumor necrosis factor (TNF)α mRNA and protein in quadriceps muscle from whole body PGC-1α knockout (KO) (A,D), muscle specific PGC-1α KO (MKO) (B,E) and muscle specific PGC-1α overexpression (TG) mice (C,F) and their respective littermate wild type (WT) mice, 2 hours after injection with either saline (Sal) as control or lipopolysaccharide (LPS). Values are presented as means ± S.E. with n = 10 in each group. *: Significantly different from Sal within given genotype, p<0.05. #: Significantly different from WT within given treatment, p<0.05.</p

Plasma TNFα.

<p>Plasma tumor necrosis factor (TNF)α from whole body PGC-1α knockout (KO) (A), muscle specific PGC-1α KO (MKO) (B) and muscle specific PGC-1α overexpression (TG) mice (C) and their respective littermate wild type (WT) mice, 2 hours after injection with either saline (Sal) as control or lipopolysaccharide (LPS). Values are presented as means ± S.E. with n = 6–10 in each group, except WT of whole body KO strain injected with saline where n = 3, due to lack of blood. *: Significantly different from Sal within given genotype, p<0.05. #: Significantly different from WT within given treatment, p<0.05. Notice the bi-sected y-axis.</p

Primer and Taqman probe sequences.

<p>Sequences for forward and reverse primers as well as Taqman probes used. Tumor necrosis factor (TNF)α, interleukin (IL)-6, IL-10, TNFα converting enzyme (TACE), toll-like receptor 4 (TLR4), macrophage specific marker (F4/80).</p

Representative blots.

<p>Representative blot of tumor necrosis factor (TNF)α protein, phosphorylation of p65 protein (p65-p) and phosphorylation of p38 (p38-p) in quadriceps muscle from whole body PGC-1α knockout (KO), muscle specific PGC-1α KO (MKO) and muscle specific PGC-1α overexpression (TG) mice and their respective littermate wild type (WT) mice, 2 hours after injection with either saline (Sal) as control or lipopolysaccharide (LPS).</p