Neuregulins Increase Mitochondrial Oxidative Capacity and Insulin Sensitivity in Skeletal Muscle Cells

Adiponectin is well established to mediate many beneficial metabolic effects, and this has stimulated great interest in development and validation of adiponectin receptor agonists as pharmaceutical tools. This study investigated the effects of ALY688, a peptide-based adiponectin receptor agonist, in rat L6 skeletal muscle cells. ALY688 significantly increased phosphorylation of several adiponectin downstream effectors, including AMPK, ACC and p38MAPK, assessed by immunoblotting and immunofluorescence microscopy. Temporal analysis using cells expressing an Akt biosensor demonstrated that ALY688 enhanced insulin sensitivity. This effect was associated with increased insulin-stimulated Akt and IRS-1 phosphorylation. The functional metabolic significance of these signaling effects was examined by measuring glucose uptake in myoblasts stably overexpressing the glucose transporter GLUT4. ALY688 treatment both increased glucose uptake itself and enhanced insulin-stimulated glucose uptake. In the model of high glucose/high insulin (HGHI)-induced insulin resistant cells, both temporal studies using the Akt biosensor as well as immunoblotting assessing Akt and IRS-1 phosphorylation indicated that ALY688 significantly reduced insulin resistance. Importantly, we observed that ALY688 administration to high-fat high sucrose fed mice also improve glucose handling, validating its efficacy in vivo. In summary, these data indicate that ALY688 activates adiponectin signaling pathways in skeletal muscle, leading to improved insulin sensitivity and beneficial metabolic effects.

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Adiponectin improves insulin sensitivity via activation of autophagic flux

Journal of Molecular Endocrinology ◽

10.1530/jme-17-0096 ◽

2017 ◽

Vol 59 (4) ◽

pp. 339-350 ◽

Cited By ~ 18

Author(s):

Penny Ahlstrom ◽

Esther Rai ◽

Suharto Chakma ◽

Hee Ho Cho ◽

Palanivel Rengasamy ◽

...

Keyword(s):

Insulin Resistance ◽

Skeletal Muscle ◽

Insulin Sensitivity ◽

Er Stress ◽

Western Blotting ◽

Muscle Cells ◽

Dominant Negative ◽

Skeletal Muscle Cells ◽

Dominant Negative Mutant ◽

Autophagic Flux

Skeletal muscle insulin resistance is known to play an important role in the pathogenesis of diabetes, and one potential causative cellular mechanism is endoplasmic reticulum (ER) stress. Adiponectin mediates anti-diabetic effects via direct metabolic actions and by improving insulin sensitivity, and we recently demonstrated an important role in stimulation of autophagy by adiponectin. However, there is limited knowledge on crosstalk between autophagy and ER stress in skeletal muscle and in particular how they are regulated by adiponectin. Here, we utilized the model of high insulin/glucose (HIHG)-induced insulin resistance, determined by measuring Akt phosphorylation (T308 and S473) and glucose uptake in L6 skeletal muscle cells. HIHG reduced autophagic flux measured by LC3 and p62 Western blotting and tandem fluorescent RFP/GFP-LC3 immunofluorescence (IF). HIHG also induced ER stress assessed by thioflavin T/KDEL IF, pIRE1, pPERK, peIF2α and ATF6 Western blotting and induction of a GRP78-mCherry reporter. Induction of autophagy by adiponectin or rapamycin attenuated HIHG-induced ER stress and improved insulin sensitivity. The functional significance of enhanced autophagy was validated by demonstrating a lack of improved insulin sensitivity in response to adiponectin in autophagy-deficient cells generated by overexpression of dominant negative mutant of Atg5. In summary, adiponectin-induced autophagy in skeletal muscle cells alleviated HIHG-induced ER stress and insulin resistance.

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ShRNA-mediated gene silencing of lipoprotein lipase improves insulin sensitivity in L6 skeletal muscle cells

Biochemical and Biophysical Research Communications ◽

10.1016/j.bbrc.2015.04.098 ◽

2015 ◽

Vol 462 (1) ◽

pp. 33-37 ◽

Cited By ~ 2

Author(s):

Majib Jan ◽

Jheem D. Medh

Keyword(s):

Skeletal Muscle ◽

Insulin Sensitivity ◽

Gene Silencing ◽

Lipoprotein Lipase ◽

Muscle Cells ◽

Skeletal Muscle Cells ◽

L6 Skeletal Muscle Cells

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Calcitriol concomitantly enhances insulin sensitivity and alters myocellular lipid partitioning in high fat-treated skeletal muscle cells

Journal of Physiology and Biochemistry ◽

10.1007/s13105-017-0595-8 ◽

2017 ◽

Vol 73 (4) ◽

pp. 613-621 ◽

Cited By ~ 10

Author(s):

Grace E. Jefferson ◽

David M. Schnell ◽

D. Travis Thomas ◽

Lance M. Bollinger

Keyword(s):

Skeletal Muscle ◽

Insulin Sensitivity ◽

Muscle Cells ◽

Skeletal Muscle Cells ◽

High Fat

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Metformin Increases Protein Phosphatase 2A Activity in Primary Human Skeletal Muscle Cells Derived from Lean Healthy Participants

Journal of Diabetes Research ◽

10.1155/2021/9979234 ◽

2021 ◽

Vol 2021 ◽

pp. 1-6

Author(s):

Aktham Mestareehi ◽

Xiangmin Zhang ◽

Berhane Seyoum ◽

Zaher Msallaty ◽

Abdullah Mallisho ◽

...

Keyword(s):

Insulin Resistance ◽

Skeletal Muscle ◽

Insulin Sensitivity ◽

Protein Phosphatase ◽

Human Skeletal Muscle ◽

Muscle Cells ◽

Skeletal Muscle Cells ◽

Human Skeletal Muscle Cells ◽

Phosphatase 2A ◽

Sensitivity Improvement

Context. Skeletal muscle insulin resistance is one of the primary contributors of type 2 diabetes (T2D). Metformin is the first-line drug for the treatment of T2D. The primary effects of metformin include decreasing glucose production in the liver and decreasing insulin resistance in the skeletal muscle. However, the molecular mechanism of metformin’s action in skeletal muscle is not well understood. Protein phosphatase 2A (PP2A), a major serine/threonine protein phosphatase, plays a pivotal role in cellular processes, such as signal transduction, cell proliferation, and apoptosis, and acts through dephosphorylating key signaling molecules such as AKT and AMPK. However, whether PP2A plays a role in metformin-induced insulin sensitivity improvement in human skeletal muscle cells remains to be elucidated. Objective. To investigate if PP2A plays a role in metformin-induced insulin sensitivity improvement in human skeletal muscle cells. Participants. Eight lean insulin-sensitive nondiabetic participants (4 females and 4 males; age: 21.0 ± 1.0 years; BMI: 22.0 ± 0.7 kg / m 2 ; 2-hour OGTT: 97.0 ± 6.0 mg / dl ; HbA1c: 5.3 ± 0.1 % ; fasting plasma glucose: 87.0 ± 2.0 mg / dl ; M value; 11.0 ± 1.0 mg / kgBW / min ). Design. A hyperinsulinemic-euglycemic clamp was performed to assess insulin sensitivity in human subjects, and skeletal muscle biopsy samples were obtained. Primary human skeletal muscle cells (shown to retain metabolic characteristics of donors) were cultured from these muscle biopsies that included 8 lean insulin-sensitive participants. Cultured cells were expanded, differentiated into myotubes, and treated with 50 μM metformin for 24 hours before harvesting. PP2Ac activity was measured by a phosphatase activity assay kit (Millipore) according to the manufacturer’s protocol. Results. The results indicated that metformin significantly increased the activity of PP2A in the myotubes for all 8 lean insulin-sensitive nondiabetic participants, and the average fold increase is 1.54 ± 0.11 ( P < 0.001 ). Conclusions. These results provided the first evidence that metformin can activate PP2A in human skeletal muscle cells derived from lean healthy insulin-sensitive participants and may help to understand metformin’s action in skeletal muscle in humans.

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