Purinergic-Mediated Calcium Signaling in Quiescent and Activated Hepatic Stellate Cells: Evidence That P2Y1 Receptor Delays Activation

Hepatic stellate cells (HSC) play a crucial role in the fibrotic response of the liver when they transdifferentiate from quiescent cells (qHSC) to myofibroblast (MFB). Ca²⁺ responses mediated by purinergic P2Y receptors are not fully characterized in qHSC and MFB. The objective of this study was to compare the expression of purinergic receptors with the capacity to mobilize intracellular Ca²⁺ in both phenotypes, as well as to explore the potential role of these signals in HSCs activation. Isolated mouse HSC were quiescent on day 2 and became MFB on day 7 when cultured in high stiffness substrate. Both phenotypes expressed the transcripts of <i>P2ry1</i>, <i>P2ry2</i>, <i>P2ry6</i> and <i>P2x7</i>, and exhibited a similar Ca²⁺ response to UDP, UTP and Bz-ATP, indicating comparable activity in P2Y6, P2Y2 and P2X7 receptors. In contrast, <i>P2y12</i> transcript was detected only in MFB. Remarkably, P2Y1 receptor was identified in qHSC, an observation that had not yet been reported. Evidence of P2Y1 receptor functionality was obtained from stimulation with ADP. ADP-elicited Ca²⁺ mobilization was more potent in qHSC in comparison to MFB. Interestingly, ADP stimulation worsens the transdifferentiation of qHSC to MFB after 4 or 7 days in culture, strongly suggesting the role of this purinergic receptor in HSC activation.