Glial Growth Factor 2 Regulates Glucose Transport in Healthy Cardiac Myocytes and During Myocardial Infarction via an Akt-Dependent Pathway.

Shanell Shoop,Allison Campolo,Pamela Lovern,Zahra Maria,Dominic Martin,Véronique A. Lacombe,Nabil Rashdan

doi:10.3389/fphys.2019.00189

Shanell Shoop, Allison Campolo + Show 5 more

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https://doi.org/10.3389/fphys.2019.00189

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Abstract

Neuregulin (NRG), a paracrine factor in myocytes, promotes cardiac development via the ErbB receptors. NRG-1β also improves cardiac function and cell survival after myocardial infarction (MI), although the mechanisms underlying these cardioprotective effects are not well elucidated. Increased glucose uptake has been shown to be cardio-protective during MI. We hypothesized that treatment with a recombinant version of NRG-1β, glial growth factor 2 (GGF2), will enhance glucose transport in the healthy myocardium and during MI. Cardiac myocytes were isolated from MI and healthy adult rats, and subsequently incubated with or without insulin or GGF2. Glucose uptake was measured using a fluorescent D-glucose analog. The translocation of glucose transporter (GLUT) 4 to the cell surface, the rate-limiting step in glucose uptake, was measured using a photolabeled biotinylation assay in isolated myocytes. Similar to insulin, acute in vitro GGF2 treatment increased glucose uptake in healthy cardiac myocytes (by 40 and 49%, respectively, P = 0.002). GGF2 treatment also increased GLUT4 translocation in healthy myocytes by 184% (P < 0.01), while ErbB 2/4 receptor blockade (by afatinib) abolished these effects. In addition, GGF2 treatment enhanced Akt phosphorylation (at both threonine and serine sites, by 75 and 139%, respectively, P = 0.029 and P = 0.01), which was blunted by ErbB 2/4 receptor blockade. GGF2 treatment increased the phosphorylation of AS160 (an Akt effector) by 72% (P < 0.05), as well as the phosphorylation of PDK-1 and PKC (by 118 and 92%, respectively, P < 0.05). During MI, cardiac GLUT4 translocation was downregulated by 44% (P = 0.004) and was partially rescued by both in vitro insulin and GGF2 treatment. Our data demonstrate that acute GGF2 treatment increased glucose transport in cardiac myocytes by activating the ErbB 2/4 receptors and subsequent key downstream effectors (i.e., PDK-1, Akt, AS160, and PKC). These findings highlight novel mechanisms of action of GGF2, which warrant further investigation in patients with heart failure.

Highlights

Heart failure is a complex syndrome that develops over months to years and affects approximately 5 million people in the United States (Writing Group et al, 2016)
Similar to the effects of insulin, we demonstrated that glial growth factor 2 (GGF2) significantly increased protein kinase B (Akt) phosphorylation at both T308 and S473 sites, in addition to an increase of total Akt protein expression
Since activation of Akt phosphorylates AKT substrate at 160 kDa (AS160), we investigated whether GGF2 regulates glucose trafficking through an AS160 dependent pathway in the healthy heart

Summary

Introduction

Heart failure is a complex syndrome that develops over months to years and affects approximately 5 million people in the United States (Writing Group et al, 2016). In light of the fact that glucose uptake is crucial to proper cardiac function, metabolic therapy has emerged as a promising new therapeutic avenue for patients affected by HF. Only the β isoform is biologically active on cardiac myocytes (Marchionni et al, 1993). NRG1β signaling, via its ErbB2 and ErbB4 receptors, is crucial for proper function of the adult heart (Marchionni et al, 1993; Tania et al, 2014). Blunted expression of ErbB2 or ErbB4 receptors in vivo led to mortality in utero in knockout models, due to the failure of cardiac development of the endocardial cushions and trabeculae (Gassmann et al, 1995; Lee et al, 1995; Meyer and Birchmeier, 1995)

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