PPARGC1B and peritonitis: Under the metabolic stress of S. aureus sepsis, Ppargc1a and Ppargc1b are up-regulated synchronously, but independently of Pprc. In peritonitis, Ppargc1a/Ppargc1b mRNA levels increase ∼5-fold in the liver in WT mice, but neither mRNA increases in TLR2−/− mice, and both increase by 10–15-fold in TLR4−/− mice, in part through suppression of microRNA-mediated mRNA degradation [29].