Differential Regulation of the PGC Family of Genes in a Mouse Model of Staphylococcus aureus Sepsis

The PGC family of transcriptional co-activators (PGC-1α [Ppargc1a], PGC-1β [Ppargc1b], and PRC [Pprc]) coordinates the upregulation of mitochondrial biogenesis, and Ppargc1a is known to be activated in response to mitochondrial damage in sepsis. Therefore, we postulated that the PGC family is regulated by the innate immune system. We investigated whether mitochondrial biogenesis and PGC gene expression are disrupted in an established model of Staphylococcus aureus sepsis both in mice with impaired innate immune function (TLR2−/− and TLR4−/−) and in wild-type controls. We found an early up-regulation of Ppargc1a and Ppargc1b post-infection (at 6 h) in WT mice, but the expression of both genes was concordantly dysregulated in TLR2−/− mice (no increase at 6 h) and in TLR4−/− mice (amplified at 6 h). However, the third family member, PRC, was regulated differently, and its expression increased significantly at 24 h in all three mouse strains (WT, TLR2−/−, and TLR4−/−). In silico analyses showed that Ppargc1a and Ppargc1b share binding sites for microRNA mmu-mir-202-3p. Thus, miRNA-mediated post-transcriptional mRNA degradation could account for the failure to increase the expression of both genes in TLR2−/− mice. The expression of mmu-mir-202-3p was measured by real-time PCR and found to be significantly increased in TLR2−/− but not in WT or TLR4−/− mice. In addition, it was found that mir-202-3p functionally decreases Ppargc1a mRNA in vitro. Thus, both innate immune signaling through the TLRs and mir-202-3p-mediated mRNA degradation are implicated in the co-regulation of Ppargc1a and Ppargc1b during inflammation. Moreover, the identification of mir-202-3p as a potential factor for Ppargc1a and Ppargc1b repression in acute inflammation may open new avenues for mitochondrial research and, potentially, therapy

Mitochondrial dysfunction and biogenesis: do ICU patients die from mitochondrial failure?

Mitochondrial functions include production of energy, activation of programmed cell death, and a number of cell specific tasks, e.g., cell signaling, control of Ca2+ metabolism, and synthesis of a number of important biomolecules. As proper mitochondrial function is critical for normal performance and survival of cells, mitochondrial dysfunction often leads to pathological conditions resulting in various human diseases. Recently mitochondrial dysfunction has been linked to multiple organ failure (MOF) often leading to the death of critical care patients. However, there are two main reasons why this insight did not generate an adequate resonance in clinical settings. First, most data regarding mitochondrial dysfunction in organs susceptible to failure in critical care diseases (liver, kidney, heart, lung, intestine, brain) were collected using animal models. Second, there is no clear therapeutic strategy how acquired mitochondrial dysfunction can be improved. Only the benefit of such therapies will confirm the critical role of mitochondrial dysfunction in clinical settings. Here we summarized data on mitochondrial dysfunction obtained in diverse experimental systems, which are related to conditions seen in intensive care unit (ICU) patients. Particular attention is given to mechanisms that cause cell death and organ dysfunction and to prospective therapeutic strategies, directed to recover mitochondrial function. Collectively the data discussed in this review suggest that appropriate diagnosis and specific treatment of mitochondrial dysfunction in ICU patients may significantly improve the clinical outcome