A role for PKD1 in insulin secretion downstream of P2Y ₁ receptor activation in mouse and human islets

Abstract

Along with insulin, β‐cells co‐secrete the neurotransmitter ATP which acts as a positive autocrine signal via P2Y1 receptors to activate phospholipase C and increase the production of diacylglycerol (DAG). However, the downstream signaling that couples P2Y1 activation to insulin secretion remains to be fully elucidated. Since DAG activates protein kinase D1 (PKD1) to potentiate glucose‐stimulated insulin release, we hypothesized that autocrine ATP signaling activates downstream PKD1 to regulate insulin secretion. Indeed, we find that the P2Y1 receptor agonists, MRS2365 and ATP induce, PKD1 phosphorylation at serine 916 in mouse islets. Similarly, direct depolarization of islets by KCl caused PKD1 activation, which is reduced upon P2Y1 antagonism. Potentiation of insulin secretion by P2Y1 activation was lost from PKD1−/− mouse islets, and knockdown of PKD1 reduced the ability of P2Y1 activation to facilitate exocytosis in single mouse β‐cells. Finally, qPCR analysis confirmed PKD1 transcript (PRKD1) expression in human islets, and insulin secretion assays showed that inhibition of either P2Y1 or PKD1 signaling impaired glucose‐stimulated insulin secretion. Human islets showed donor‐to‐donor variation in their responses to both P2Y1 and PKD1 inhibition, however, and we find that the P2Y1‐PKD1 pathway contributes a substantially greater proportion of insulin secretion from islets of overweight and obese donors. Thus, PKD1 promotes increased insulin secretion, likely mediating an autocrine ATP effect via P2Y1 receptor activation which may be more important in islets of donors who are overweight or obese.

Pharmacogenetics of Type 2 Diabetes—Progress and Prospects

“…Polymorphism located within the fourth intron of PRKD1 gene has found to be closely related to DPP4I treatment efficacy [ 134 ], what can be explained by serine/threonine-protein kinase D1 participation in increasing of insulin secretion in mice and human islets [ 155 ].…”

The role of protein kinase D (PKD) in intracellular nutrient sensing and regulation of adaptive responses to the obese environment

“…Indeed, expression of a non‐phosphorylatable Arfaptin‐1 mutant in INS‐1 rat insulinoma cells severely reduced GSIS, with a similar effect seen with administration of the specific PKD inhibitor CID755673 99 . In humans, GSIS may be more dependent on the PKD1 signalling pathway in obese rather than lean individuals 28 . Khan and colleagues 28 demonstrated a trend ( P = 0.06) for greater inhibition of GSIS in isolated islets from obese compared with lean human donors following exposure to the PKD inhibitor CRT0066101.…”

“…The potentiation of GSIS is also lost upon PKD1 gene deletion in isolated mouse islets, highlighting the requirement of PKD in GPR40 mediated GSIS 97 . In contrast, the initial rapid phase of GSIS is blunted in PKD1 knockdown cells following activation of the purinergic GPCR, P2Y 1 , when compared with control cells 28 . This demonstrates that PKD1 may regulate both exocytosis of immediately available insulin vesicles in the first phase of GSIS and the formation of new insulin vesicles for exocytosis to sustain the second phase of GSIS.…”

“…The best characterized of these processes is the regulation of vesicle transport from the trans‐Golgi network through activation of Golgi phosphatidylinositol 4‐kinase III β 27 . The pancreas provides a key example, where PKD‐mediated Golgi fission in β‐cells leads to the potentiation of glucose‐stimulated insulin secretion (GSIS) 15,28,29 . Other well‐defined biological functions of PKD include stimulation of cell proliferation in multiple cell types (including cancer cells 30,31 ) and cell survival during oxidative stress, where PKD increases the expression of the antioxidant manganese superoxide dismutase in response to elevated levels of reactive oxygen species (ROS) 32,33 …”

“…In humans, GSIS may be more dependent on the PKD1 signalling pathway in obese rather than lean individuals 28 . Khan and colleagues 28 demonstrated a trend ( P = 0.06) for greater inhibition of GSIS in isolated islets from obese compared with lean human donors following exposure to the PKD inhibitor CRT0066101. This greater reliance on pancreatic PKD1 signalling in obesity further highlights the emerging role that PKD plays in the adaptation to the obese environment.…”