Complement regulatory protein CD59 involves c-SRC related tyrosine phosphorylation of the creatine transporter in skeletal muscle during sepsis

Background. Myocellular creatine (Cr) uptake is predominantly governed by the creatine transporter (CreaT) and plays a pivotal role in skeletal muscle energy metabolism. The CreaT belongs to a neurotransmitter transporter family that is functionally regulated by protein tyrosine kinase induced tyrosine phosphorylation. Recently, complement regulatory protein CD59 has been found not only to protect host tissue from C5b-9 complex attack that occurs in sepsis but also to initiate the activation of Src family kinase and tyrosine phosphorylation of its downstream proteins. The purpose of this study was to determine the association between myocellular free Cr, c-Src related tyrosine phosphorylation of the CreaT, and CD59 during sepsis. Methods. Male Sprague-Dawley rats (250 to 300 g) were randomized to undergo cecal ligation and puncture (CLP) or sham operation. Fast-twitch gastrocnemius muscles were harvested 24 hours after operation. Myocellular free Cr levels were measured by high-performance liquid chromatography. Combination of protein immunoprecipitation with Western blotting was used to assess tyrosine phosphorylation status of the CreaT and the association between CD59, c-Src, and CreaT. Results. Myocellular free Cr levels were 70% greater after CLP. Tyrosine phosphorylation of the CreaT was significantly increased after CLP as compared to sham operation. Tyrosine phosphorylated c-Src (Tyr-416) in the CreaT-c-Src immune complex was 24% higher after CLP. Sepsis also increased protein expression of tyrosine phosphorylated c-Src (Tyr-416) or CreaT in the CD59-c-Src or CD59-CreaT complex by 20% or 30%, respectively. Conclusions. During sepsis, an increase in myocellular free Cr levels is associated with enhanced tyrosine phosphorylation of the CreaT, which is likely induced by active c-Src. CD59 is physically associated with both c-Src and CreaT, which suggests that CD59 may participate in the regulation of myocellular Cr metabolism via the CreaT during sepsis.