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Publication
Skeletal muscle autophagy remains responsive to hyperinsulinemia and
hyperglycemia at higher plasma insulin concentrations in insulin-resistant mice.
Authors Ehrlicher SE, Stierwalt HD, Newsom SA, Robinson MM
Submitted By Submitted Externally on 8/20/2018
Status Published
Journal Physiological reports
Year 2018
Date Published 7/1/2018
Volume : Pages 6 : e13810
PubMed Reference 30047243
Abstract Skeletal muscle autophagy is suppressed by insulin, but it is not clear if such
suppression is altered with insulin resistance. We investigated if the
inhibitory action of insulin on autophagy remains intact despite insulin
resistance to glucose metabolism. C57BL/6J mice consumed either a low-fat (10%
fat) diet as control or high-fat (60% fat) diet for 12 weeks to induce insulin
resistance. Following a 5-hour fast, mice underwent either
hyperinsulinemic-euglycemic, hyperinsulinemic-hyperglycemic, or saline infusion
to test the effect of insulin on autophagy markers in the quadriceps muscle
(n = 8-10 per diet and clamp condition). Mice were anesthetized by sodium
pentobarbital for tissue collection after 2 h of infusion. Despite the high-fat
group having lower insulin-stimulated glucose uptake, both low-fat and high-fat
groups had similar autophagosome abundance during hyperinsulinemic conditions.
The lipidation of microtubule-associated proteins 1A/1B light chain 3B
(LC3II/LC3I) was decreased in hyperinsulinemia versus saline control (P < 0.01)
in low-fat (-54%) and high-fat groups (-47%), demonstrating similar suppression
of autophagy between diet groups. Mitochondrial-associated LC3II was greater in
the high-fat compared to the low-fat group (P = 0.045) across clamp conditions,
suggesting a greater localization of autophagosomes with mitochondria. L6
myotubes were treated with insulin and rapamycin to determine the role of
mechanistic target of rapamycin complex-1 (mTORC1) in insulin-mediated
suppression of autophagy. Inhibition of mTORC1 blunted the decline of LC3II/LC3I
with insulin by 40%, suggesting mTORC1 partially mediates the insulin action to
suppress autophagy. Collectively, autophagy remained responsive to the
suppressive effects of insulin in otherwise insulin-resistant and obese mice.




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