FAK tyrosine phosphorylation is regulated by AMPK and controls metabolism in human skeletal muscle

David G Lassiter,Rasmus J O Sjögren,Harriet Wallberg-Henriksson,Anna Krook,Erik Näslund,Carolina Nylén,Juleen R Zierath,Alexander V Chibalin

doi:10.1007/s00125-017-4451-8

David G Lassiter, Rasmus J O Sjögren + Show 6 more

Open Access

https://doi.org/10.1007/s00125-017-4451-8

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Abstract

Aims/hypothesisInsulin-mediated signals and AMP-activated protein kinase (AMPK)-mediated signals are activated in response to physiological conditions that represent energy abundance and shortage, respectively. Focal adhesion kinase (FAK) is implicated in insulin signalling and cancer progression in various non-muscle cell types and plays a regulatory role during skeletal muscle differentiation. The role of FAK in skeletal muscle in relation to insulin stimulation or AMPK activation is unknown. We examined the effects of insulin or AMPK activation on FAK phosphorylation in human skeletal muscle and the direct role of FAK on glucose and lipid metabolism. We hypothesised that insulin treatment and AMPK activation would have opposing effects on FAK phosphorylation and that gene silencing of FAK would alter metabolism.MethodsHuman muscle was treated with insulin or the AMPK-activating compound 5-aminoimadazole-4-carboxamide ribonucleotide (AICAR) to determine FAK phosphorylation and glucose transport. Primary human skeletal muscle cells were used to study the effects of insulin or AICAR treatment on FAK signalling during serum starvation, as well as to determine the metabolic consequences of silencing the FAK gene, PTK2.ResultsAMPK activation reduced tyrosine phosphorylation of FAK in skeletal muscle. AICAR reduced p-FAKY397 in isolated human skeletal muscle and cultured myotubes. Insulin stimulation did not alter FAK phosphorylation. Serum starvation increased AMPK activation, as demonstrated by increased p-ACCS222, concomitant with reduced p-FAKY397. FAK signalling was reduced owing to serum starvation and AICAR treatment as demonstrated by reduced p-paxillinY118. Silencing PTK2 in primary human skeletal muscle cells increased palmitate oxidation and reduced glycogen synthesis.Conclusions/interpretationAMPK regulates FAK signalling in skeletal muscle. Moreover, siRNA-mediated FAK knockdown enhances lipid oxidation while impairing glycogen synthesis in skeletal muscle. Further exploration of the interaction between AMPK and FAK may lead to novel therapeutic strategies for diabetes and other chronic conditions associated with an altered metabolic homeostasis.

Highlights

Skeletal muscle is a highly malleable tissue, capable of remodelling physical and biochemical properties to meet changes in cellular and whole-body metabolic demands [1]
AMPactivated protein kinase (AMPK) activation reduces p-FAKY397 Human skeletal muscle strips were incubated in the absence or presence of 120 nmol/l insulin or 2 mmol/l aminoimadazole-4carboxamide ribonucleotide (AICAR), or both, to assess the effects on glucose transport and signal transduction (Fig. 1a–f)
Differentiated primary human skeletal muscle cells were used for p-Focal adhesion kinase (FAK) determination in the absence or presence of serum, and in response to AICAR or insulin stimulation

Summary

Introduction

Skeletal muscle is a highly malleable tissue, capable of remodelling physical and biochemical properties to meet changes in cellular and whole-body metabolic demands [1]. Delineation of signalling pathways emanating from the insulin receptor and AMPactivated protein kinase (AMPK), two major processes controlling glucose and energy homeostasis [4], is central in the efforts to resolve type 2 diabetes pathogenesis. How these signalling networks are kept in homeostatic balance is not completely clear. Examples of common nodes shared by these pathways include two Rab GTPaseactivating proteins, TBC1 domain family member 1 (TBC1D1) and TBC1 domain family member 4 (TBC1D4; known as Akt substrate of 160 kDa, AS160) These proteins respond to AMPK activation and insulin stimulation and are involved in the regulation of glucose transport [2]. Elucidation of other molecular points of crosstalk between AMPK and insulin signalling may reveal how these pathways are coordinated to meet the energy demands of the cell

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