ATP is an essential autocrine factor for pancreatic β‐cell signaling and insulin secretion

Abstract

ATP has been previously identified as an autocrine signaling factor that is co‐released with insulin to modulate and propagate β‐cell activity within islets of Langerhans. Here, we show that β‐cell activity and insulin secretion essentially rely on the presence of extracellular ATP. For this, we monitored changes of the intracellular Ca 2+ concentration ([Ca 2+ ] i oscillations) as an immediate read‐out for insulin secretion in live cell experiments. Extensive washing of cells or depletion of extracellular ATP levels by recombinant apyrase reduced [Ca 2+ ] i oscillations and insulin secretion in pancreatic cell lines and primary β‐cells. Following ATP depletion, [Ca 2+ ] i oscillations were stimulated by the replenishment of ATP in a concentration‐dependent manner. Inhibition of endogenous ecto‐ATP nucleotidases increased extracellular ATP levels, along with [Ca 2+ ] i oscillations and insulin secretion, indicating that there is a constant supply of ATP to the extracellular space. Our combined results demonstrate that extracellular ATP is essential for β‐cell activity. The presented work suggests extracellular ATPases as potential drug targets for the modulation of insulin release. We further found that exogenous fatty acids compensated for depleted extracellular ATP levels by the recovery of [Ca 2+ ] i oscillations, indicating that autocrine factors mutually compensate for the loss of others. Thereby, our results contribute to a more detailed and complete understanding of the general role of autocrine signaling factors as a fundamental regulatory mechanism of β‐cell activity and insulin secretion.

Trace Amines are Essential Metabolites for the Autocrine Regulation ofβ-Cell Signaling and Insulin Secretion

“…This starting point led us to the hypotheses that 1) TAs are produced by β-cells in an autocrine fashion and 2) local TA levels in the islet reach high levels and are quite transient. Therefore, this signaling system might act quasi-autonomous similar to the recently described fatty acid-and ATP-based autocrine regulation systems in the islets of Langerhans [12,17]. This hormone-GPCR signaling system differs significantly from more thoroughly described organism-wide adrenergic and muscarinic signaling.…”

“…Pancreatic β -cells express a multitude of GPCRs [15], such as the fatty acid (FA) receptor GPR40 that was found to mediate the majority of the effects that long-chain FAs have on β -cell activity [16]. In our recent work, we demonstrated the essential role of cellular FAs and ATP for [Ca 2+ ] i oscillations and insulin secretion [12,17]. We found that ATP and endogenous FAs do not only stimulate β -cells, but are secreted by these cells and are required for basal β -cellular activity and insulin secretion [12,17].…”

“…In our recent work, we demonstrated the essential role of cellular FAs and ATP for [Ca 2+ ] i oscillations and insulin secretion [12,17]. We found that ATP and endogenous FAs do not only stimulate β -cells, but are secreted by these cells and are required for basal β -cellular activity and insulin secretion [12,17]. Other diffusible autocrine ligands of GPCRs include NO [18,19], CO [20], Zn 2+ [21], neuropeptide Y [22], glutamate [23] and γ-aminobutyric acid [24].…”

Novel regulators of islet function identified from genetic variation in mouse islet Ca2+ oscillations

“…While this does include a few outbred stocks (e.g. NMRI [ Pohorec et al, 2022 ; Sterk et al, 2021 ; Stožer et al, 2021 ], CD-1 [ Dahlgren et al, 2005 ; Hauke et al, 2022 ; Scarl et al, 2019 ]), direct comparisons of these to traditional inbred lines are rare ( Pohorec et al, 2022 ), and studies of specific genes often use traditional inbred lines, as wild-derived lines do not respond as well to the conventional assistive reproductive technologies required for genome editing and transgenesis ( Hirose et al, 2017 ; Mochida et al, 2014 ).…”

Novel regulators of islet function identified from genetic variation in mouse islet Ca2+oscillations

“…While this does include a few outbred stocks (e.g. NMRI (53-55), CD-1 (9, 56, 57)), direct comparisons of these to the traditional inbred lines are rare (53), and studies of specific genes often use traditional inbred lines as wild-derived lines do not respond as well to the conventional assistive reproductive technologies required for genome editing and transgenesis (58, 59).…”