Fatty acid-induced differential regulation of the genes encoding peroxisome proliferator-activated receptor-γ coactivator-1α and -1β in human skeletal muscle cells that have been differentiated in vitro

Abstract

Aims/hypothesis: The transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) enhances metabolically relevant pathways, such as gluconeogenesis, fatty acid oxidation, thermogenesis, oxidative phosphorylation and mitochondrial biogenesis. Since regulation of the expression of the gene encoding PGC-1α (PPARGC1A) by nutrients/metabolites has not been assessed in detail, the aim of this study was to determine whether PPARGC1A (and PPARGC1B) expression is modulated by common plasma fatty acids in human skeletal muscle cells. Methods: Human myotubes that had been differentiated in vitro were treated with 0.5 mmol/l myristate (C14:0), palmitate (C16:0), stearate (C18:0), palmitoleate (C16:1ω7), oleate (C18:1ω9) or linoleate (C18:2ω6). PPARGC1A/B mRNA was quantified by RT-PCR. Mitochondrial activity was determined by formazan formation. Results: Untreated cells expressed 28-fold more PPARGC1B mRNA than PPARGC1A mRNA (13.33±2.86 vs 0.47± 0.08 fg/μg total RNA, n=5). PPARGC1A expression was increased two-to three-fold by all unsaturated fatty acids (UFAs) tested (p<0.05 each, n=5). In contrast, saturated fatty acids (SFAs) did not modulate PPARGC1A expression. Furthermore, the effect of linoleate was not blunted by palmitate. PPARGC1B mRNA expression was not increased by either the UFAs or the SFAs. SFAs reduced PPARGC1B expression (p<0.05 for palmitate and stearate, n=5). Notably, linoleate reversed palmitate's repressive effect on PPARGC1B. Myotube mitochondrial activity was increased by all UFAs (p<0.01 each, n=5), but was impaired by the SFA stearate (p<0.001, n=5). Conclusions/ interpretation: We report here that fatty acids differentially regulated expression of the genes encoding the PGC-1 isoforms. Since these effects were accompanied by significant changes in mitochondrial activity, we suggest that the fatty acid-induced regulation of expression of these genes plays an important role in muscle oxidative metabolism.

Fatty Acid Incubation of Myotubes From Humans With Type 2 Diabetes Leads to Enhanced Release of β-Oxidation Products Because of Impaired Fatty Acid Oxidation

“…In the present study, gene expression of PGC1␣ was increased in response to fatty acids, but the relative response was blunted in diabetic myotubes compared with control cells. In C2C12 myotubes, PGC1␣ expression was enhanced after 4 h but reduced after 16 h of incubation with palmitic acid (35), whereas unsaturated fatty acids like oleic acid and linoleic acid enhanced PGC1␣ expression in human myotubes (36). Our data suggest that the reduced capacity for complete mitochondrial fatty acid oxidation observed for type 2 diabetes myotubes might be related to suboptimal responses in expression of PGC1␣, e.g., when the myotubes are exposed to fatty acids.…”

Excess Lipid Availability Increases Mitochondrial Fatty Acid Oxidative Capacity in Muscle

“…Mice with muscle-specific overexpression of lipoprotein lipase, which increases fatty acid influx into skeletal muscle, display extensive mitochondrial proliferation (32). Fatty acids have also been shown to increase PGC-1␣ expression in muscle cells (33) and ␤-cells (34), and this is associated with increased mitochondrial metabolism (33,35). The fatty acid subtype appears to be important (33), as palmitate alone reduces PGC-1␣ expression (36); however, this may be related to its activation of inflammatory pathways that are known to impact on PGC-1␣ expression (37).…”

“…Fatty acids have also been shown to increase PGC-1␣ expression in muscle cells (33) and ␤-cells (34), and this is associated with increased mitochondrial metabolism (33,35). The fatty acid subtype appears to be important (33), as palmitate alone reduces PGC-1␣ expression (36); however, this may be related to its activation of inflammatory pathways that are known to impact on PGC-1␣ expression (37). The coordinated increase in the activity of ␤-oxidation and trichloroacetic cycle enzymes, along with the increased expression of respiratory chain subunits observed in the current study, suggest that PGC-1␣ is in part mediating the increase in fatty acid oxidative capacity and mitochondrial content by coactivating its known binding partners estrogen-related receptor ␣, PPAR␣, PPAR␦, and nuclear respiratory factor-1 (15).…”

PPARGC1A mRNA levels of in vitro differentiated human skeletal muscle cells are negatively associated with the plasma oleate concentrations of the donors

“…Obese, insulin-resistant and type 2 diabetic states reveal low muscle mitochondrial oxidative capacity, reduced expression of respiratory chain components, and decreased expression of the gene encoding PGC-1α (PPARGC1A) [2,3]. We have recently shown that PPARGC1A expression in in vitro differentiated human skeletal muscle cells (myotubes) is induced by common unsaturated plasma NEFAs, such as palmitoleate, oleate and linoleate, but is not influenced by common saturated NEFAs, such as myristate, palmitate and stearate [4]. In the present study, we investigated (1) whether the basal expression of PPARGC1A and the gene encoding its close homologue, PGC-1β (PPARGC1B) in myotubes derived from metabolically characterised white donors display marked individual variations, and, if so, (2) whether these variations are linked to in vivo metabolic features of the donors, such as adiposity, insulin resistance, total NEFA concentration, or concentration of individual plasma NEFAs.…”

“…Myoblasts were grown from satellite cells obtained from percutaneous needle biopsies performed on the lateral portion of musculus quadriceps femoris and were differentiated into myotubes as described previously [4]. Firstpass cells were used.…”