Reduced Incorporation of Fatty Acids Into Triacylglycerol in Myotubes From Obese Individuals With Type 2 Diabetes

Abstract

Altered skeletal muscle lipid metabolism is a hallmark feature of type 2 diabetes (T2D). We investigated muscle lipid turnover in T2D versus BMI-matched control subjects (controls) and examined whether putative in vivo differences would be preserved in the myotubes. Male obese T2D individuals (n = 6) and BMI-matched controls (n = 6) underwent a hyperinsulinemic-euglycemic clamp, VO 2 max test, dual-energy X-ray absorptiometry scan, underwater weighing, and muscle biopsy of the vastus lateralis.14 C-palmitate and 14 C-oleate oxidation rates and incorporation into lipids were measured in muscle tissue as well as in primary myotubes. Palmitate oxidation (controls: 0.99 6 0.17 nmol/mg protein; T2D: 0.53 6 0.07 nmol/mg protein; P = 0.03) and incorporation of fatty acids (FAs) into triacylglycerol (TAG) (controls: 0.45 6 0.13 nmol/mg protein; T2D: 0.11 6 0.02 nmol/mg protein; P = 0.047) were significantly reduced in muscle homogenates of T2D. These reductions were not retained for palmitate oxidation in primary myotubes (P = 0.38); however, incorporation of FAs into TAG was lower in T2D (P = 0.03 for oleate and P = 0.11 for palmitate), with a strong correlation of TAG incorporation between muscle tissue and primary myotubes (r = 0.848, P = 0.008). The data indicate that the ability to incorporate FAs into TAG is an intrinsic feature of human muscle cells that is reduced in individuals with T2D.

Resistance to the Beneficial Effects of Exercise in Type 2 Diabetes: Are Some Individuals Programmed to Fail?

“…For instance, myotubes derived from obese individuals with T2D retain the impaired mitochondrial function that was observed in vivo (61,62). Consistent with these findings, data from Hulver and colleagues (65), along with some of our own work, have demonstrated that myotubes of nondiabetic individuals with severe obesity and those from obese T2D individuals retained an abnormal lipid partitioning similar to that observed in their muscle tissue (65,66). Work by Nikolic et al (67) demonstrated that chronic low-frequency electrical pulse stimulation was sufficient to induce a more oxidative phenotype in lean myotubes (and hence mimic an exercise contraction)-which is consistent with our previous findings that demonstrated an improved insulin responsiveness and lipid metabolism after a pharmacological exercise mimetic in lean human myotubes (68).…”

Effect of serial cell passaging in the retention of fiber type and mitochondrial content in primary human myotubes

“…A prime example is that of the athlete's paradox , whereby both insulin resistant T2D individuals and endurance trained athletes possess high levels of IMCL in vivo yet differ greatly along the insulin sensitivity spectrum. Prior reports investigating lipid droplet coat proteins comparing myotubes from lean individuals versus those with T2D showed that there was no difference in basal protein levels of perilipin 2, perilipin 3, perilipin 5, or adipose triglyceride lipase (ATGL) . Kitzmann et al showed that there was no difference in basal activity for 5′ adenosine monophosphate‐activated protein kinase (AMPK) or its downstream target acetyl‐CoA carboxylase (ACC) in myotubes taken from controls versus individuals with T2D .…”

In vitro effects of sitosterol and sitostanol on mitochondrial respiration in human brown adipocytes, myotubes and hepatocytes

“…HepG2 cells were grown in MEM supplemented with 10% FCS, sodium pyruvate and non-essential amino acids and pen/strep as described [18]. Collection and differentiation of human primary myotubes have been described previously [19]. Growth and differentiation of human primary differentiated adipocytes have been described before [20], however, modifications have been applied to the original protocol.…”