PAC1 Receptor Internalization and Endosomal MEK/ERK Activation Is Essential for PACAP-Mediated Neuronal Excitability

Abstract

Pituitary adenylate cyclase activating polypeptide (PACAP, Adcyap1) activation of PAC1 receptors (Adcyap1r1) can significantly increase the excitability of diverse neurons through differential mechanisms. For guinea pig cardiac neurons, the modulation of excitability can be mediated in part by PAC1 receptor plasma membrane G protein-dependent activation of adenylyl cyclase and downstream signaling cascades. By contrast, PAC1 receptor-mediated excitability of hippocampal dentate gyrus granule cells appears independent of membrane delimited AC/cAMP/PKA and PLC/PKC signaling. For both neuronal types, there is mechanistic convergence demonstrating that endosomal PAC1 receptor signaling has prominent roles. In these models, neuronal exposure to Pitstop2 to inhibit β-arrestin/clathrin-mediated PAC1 receptor internalization eliminates PACAP modulation of excitability. β-arrestin is a scaffold for a number of effectors especially MEK/ERK and notably, paradigms that inhibit PAC1 receptor endosome formation and ERK signaling also blunt the PACAP-induced increase in excitability. Detailed PAC1 receptor internalization and endosomal ERK signaling mechanisms have been confirmed in HEK PAC1R-EGFP cells and shown to be long lasting which appear to recapitulate the sustained electrophysiological responses. Thus, PAC1 receptor internalization/endosomal recruitment efficiently and efficaciously activates MEK/ERK signaling and appears to represent a singular and critical common denominator in regulating neuronal excitability by PACAP.

First‐in‐human development of a pharmacodynamic biomarker for PAC1 receptor antagonists using intradermal injections of maxadilan

“… 3 , 19 Second, the PAC 1 receptor can be subject to internalization and endosomal activation of extracellular signal‐regulated kinase (ERK). 26 The latter activates glial cells, which in turn stimulate the production of inflammatory mediators and neuronal activity, thereby enhancing and maintaining nociception. However, the exact inflammatory mediators involved still need to be uncovered and the PAC 1 ‐ERK pathway has thus far most profoundly been studied in the CNS.…”

Viral-Mediated Knockdown of Nucleus Accumbens Shell PAC1 Receptor Promotes Excessive Alcohol Drinking in Alcohol-Preferring Rats

“…The PACAP/PAC1R has been shown to affect glutamatergic and GABAergic signaling in other brain areas, through pre- or post-synaptic mechanisms ( Macdonald et al, 2005 ; Costa et al, 2009 ; Varodayan et al, 2020 ). PACAP is also capable of exerting effects on neuronal excitability in the absence of glutamatergic or GABAergic input ( May et al, 2021 ). This highlights the need for follow-up electrophysiological studies to further understand the specific actions of PAC1R activation in the NAcc Shell.…”

Presence of Systemic Amyloidosis in Mice with Partial Deficiency in Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Aging

“…In contrast to the severe symptoms observed in mice partially lacking PACAP, no sign of amyloidosis or other marked histological alteration in any organ could be observed in the PAC1 receptor knockout mice. The involvement of the PAC1 receptor has been proven in several physiological processes [11,35,46,47]. Accordingly, the lack of the receptor is expected to lead to severe alterations in these processes.…”