title: Inhibition of Rab1 GTPase and endoplasmic reticulum-to-Golgi trafficking underlies statin's toxicity in rat skeletal myofibers.
abstract: HMG-CoA reductase inhibitor statins are used for the treatment of hypercholesterolemia. However, statins have adverse effects on skeletal muscles with unknown mechanism. We have reported previously that fluvastatin induced vacuolation and cell death in rat skeletal myofibers by depleting geranylgeranylpyrophosphate (GGPP) and suppressing small GTPases, particularly Rab (FASEB J 21:4087-4094, 2007). Rab1 is one of the most susceptible Rab isoforms to GGPP depletion and is essential for endoplasmic reticulum (ER)-to-Golgi trafficking. Here, we explored whether Rab1 and ER-to-Golgi vesicle trafficking were affected by statins in cultured single myofibers isolated from flexor digitorum brevis muscles of adult rats. Western blot analysis revealed that Rab1A protein resided predominantly in membrane but not in cytosol in control myofibers, whereas it was opposite in fluvastatin-treated myofibers, indicating that fluvastatin inhibited Rab1A translocation from cytosol to membrane. GGPP supplementation prevented the effect of fluvastatin on Rab1A translocation. Brefeldin A, a specific suppressor of ER-to-Golgi trafficking, induced vacuolation and cell death in myofibers in a manner similar to that of fluvastatin. Although ER-to-Golgi traffic suppression induces unfolded protein response (UPR) and cell death in some cell types, neither fluvastatin nor brefeldin A up-regulated UPR in myofibers. Immunofluorescence study revealed that the distribution of an ER marker, calnexin, was restricted to the region around nucleus with fluvastatin, suggesting the inhibition of ER membrane traffic by fluvastatin. We conclude that suppression of Rab1 GTPase and the subsequent inhibition of ER-to-Golgi traffic are involved in statin-induced skeletal myotoxicity.
authors.affiliation: Department of Pharmacology, School of Medicine, Fukushima Medical University, Fukushima 960-1295, Japan. kazuho@fmu.ac.jp
authors.forename: Kazuho
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Ikuo
authors.initials: I
authors.lastname: Wada
authors.forename: Junko
authors.initials: J
authors.lastname: Kimura
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D006056:Golgi Apparatus / Q000187:drug effects / Q000201:enzymology*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000633:toxicity*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D020761:rab1 GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D020761:rab1 GTP-Binding Proteins