Lipid Transfer Protein Genes Are Differently Expressed in Rat Soleus Muscle at Early and Later Periods of Muscle Disuse

This work reports analysis of lipid transfer protein (LTPs)mRNA levels in rat soleus muscle after 12-h and 14-day hindlimbsuspension (HS). The LTP genes of interest were as follows: ceramidetransporter 1 (CERT1), ceramide-1-phosphatetransporter protein (CPTP),sphingosine-1-phosphate transporter (Protein spinster homolog 2—SPNS2), four-phosphate adaptor protein2 (FAPP2) transferring glucosylceramide,and oxysterol-binding proteins OSBP and ORP4 (family I of OSBP-related proteins).LTP mRNA expression was analyzed using RT-PCR. Early changes inthe expression of LTP genes after 12-h HS were characterized bythe dramatic decrease in mRNA content of CERT1, CPTP, SPNS2 and ORP4 genes. In contrast, the expressionof the FAPP2 gene was increased,whereas OSBP mRNA content didnot change as compared to the control level. After the 14-day HSonly CERT1 and CPTP mRNA levels remained decreasedwhile expression of other LTP genes did not significantly differ fromthe control values. Clomipramine treatment did not affect sphingolipidtransporters and OSBPs at theearly period of HS, but notably enhanced the expression of CERT1, CPTP, FAPP2, and both OSBPs genesin soleus muscle of rats subjected to 14-day unloading. Our dataindicate that short-term and long-term muscle unloading differentlyaffects the expression of genes encoding LTPs for sphingolipid andcholesterol intracellular transport. Only ceramide and ceramide-1-phosphate transporterswere decreased at both periods of disuse. Taking into account ourprevious data about acid sphingomyelinase (aSMase) and ceramideup-regulation in the unloaded soleus muscle, as well as a normalizingeffect of clomipramine on both high ceramide level and low expressionof its transporters at 14-day HS, we can assume that there mustbe a feedback mechanism in regulation of CERT1 and CPTP genes expression in case ofceramide accumulation caused by disuse.