Pannexin 1 is required for full activation of insulin-stimulated glucose uptake in adipocytes

Abstract

ObjectiveDefective glucose uptake in adipocytes leads to impaired metabolic homeostasis and insulin resistance, hallmarks of type 2 diabetes. Extracellular ATP-derived nucleotides and nucleosides are important regulators of adipocyte function, but the pathway for controlled ATP release from adipocytes is unknown. Here, we investigated whether Pannexin 1 (Panx1) channels control ATP release from adipocytes and contribute to metabolic homeostasis.MethodsWe assessed Panx1 functionality in cultured 3T3-L1 adipocytes and in adipocytes isolated from murine white adipose tissue by measuring ATP release in response to known activators of Panx1 channels. Glucose uptake in cultured 3T3-L1 adipocytes was measured in the presence of Panx1 pharmacologic inhibitors and in adipocytes isolated from white adipose tissue from wildtype (WT) or adipocyte-specific Panx1 knockout (AdipPanx1 KO) mice generated in our laboratory. We performed in vivo glucose uptake studies in chow fed WT and AdipPanx1 KO mice and assessed insulin resistance in WT and AdipPanx1 KO mice fed a high fat diet for 12 weeks. Panx1 channel function was assessed in response to insulin by performing electrophysiologic recordings in a heterologous expression system. Finally, we measured Panx1 mRNA in human visceral adipose tissue samples by qRT-PCR and compared expression levels with glucose levels and HOMA-IR measurements in patients.ResultsOur data show that adipocytes express functional Pannexin 1 (Panx1) channels that can be activated to release ATP. Pharmacologic inhibition or selective genetic deletion of Panx1 from adipocytes decreased insulin-induced glucose uptake in vitro and in vivo and exacerbated diet-induced insulin resistance in mice. Further, we identify insulin as a novel activator of Panx1 channels. In obese humans Panx1 expression in adipose tissue is increased and correlates with the degree of insulin resistance.ConclusionsWe show that Panx1 channel activity regulates insulin-stimulated glucose uptake in adipocytes and thus contributes to control of metabolic homeostasis.

Pannexin‐1 mediated ATP release in adipocytes is sensitive to glucose and insulin and modulates lipolysis and macrophage migration

“…This insulin-activated PDE3 sig nalling is known in various insulin-sensitive cells, including adipocytes where it inhibits lipolysis. 27 The difference could possibly be explained by the use of different insulin treatment and experimental proce dures to measure extracellular ATP concentration. 49 In another study, on a suspension of visceral adipocytes, con trary to our study, insulin seemed to slightly enhance ATP release.…”

“…35,47,48 Interestingly, in erythrocytes insulin also activates PDE3 and via further regulation of CFTR (and Panx1) inhibits ATP release. However, in that study 27 adipocytes were not adrenergically stimulated and the focus was on the role of Panx1 in insulin-stimulated glucose uptake, while our study focused on adrenergic-puri nergic autocrine and paracrine signalling. 27 The difference could possibly be explained by the use of different insulin treatment and experimental proce dures to measure extracellular ATP concentration.…”

“…Cells were stimulated with control buffer (Ctrl), 5 μmol L −1 phenylephrine (PE), 10 μmol L −1 forskolin (FSK) and 1 μmol L −1 ionomycin (Iono). 27,31 In order to further assess Panx1 activity as a 'pore', 9,33 we monitored ethidium bromide (EtBr) uptake after adrenergic stimulation. C, Quantification of ATP release is in mature adipocytes is shown as a difference between the basal extracellular ATP (before stimulation) and the peak release with the indicated agonist.…”

“…Low extracellular ATP concentra tions (low nM-μM range) are considered physiological and stimulate various P2Y and P2X receptors, while high ATP concentrations (high micromolar to millimolar range) are regarded as danger signals, stimulating P2X7 receptors that mediate pathophysiological processes in, for example, in flammation and cancer. 27 In brown adipose tissue, ATP is released from sympathetic nerves. 1619 Dysregulated white adipocytes could contribute to obesity and low-level chronic inflammation of white adipose tissue character ized by macrophage infiltration.…”

“…One study shows that adrenergic stimulation causes the release of ATP from white adipocytes and that Panx1 might be involved. 27 In brown adipose tissue, ATP is released from sympathetic nerves. 28 VNUT expression was detected by immunohisto chemistry in nerves and brown adipocytes, but not in white adipocytes.…”