PACAP and Maxadilan (PAC1 Agonist) Influence Plaque Progression, Migratory Ability, and Mitochondrial Morphology and Dynamics in Vascular Smooth Muscle Cells

Background: Pituitary adenylate cyclase-activating polypeptide (PACAP) functions as an anti-atherogenic neuropeptide. Maxadilan, a PAC1 receptor agonist, offers atheroprotection by acting downstream of vascular inflammation caused by hypercholesterolemia. This study aims to explore how PACAP and Maxadilan influence migration and apoptosis in human coronary artery smooth muscle cells (HCASMCs). Methods: To investigate the role of PACAP deficiency in the pathogenesis of atherosclerosis under standard chow (SC) in vivo, PACAP−/−-mice were crossed with ApoE−/−-mice to generate PACAP−/−/ApoE−/−-mice. The whole aorta was isolated and stained with OilRedO (ORO). Atherosclerotic lesions and lumen stenosis in the brachiocephalic trunk were quantified using ImageJ 1.54p (Fiji). To further investigate the role of PACAP and Maxadilan in the pathogenesis of atherosclerosis with special respect to HCASMC under a lipid-enriched environment, HCASMCs were treated with oxLDL, with or without PACAP or Maxadilan. Uptake and accumulation of oxLDL were analyzed using BodipyTM493/503, and cell viability was assessed with PrestoBlue®. Cell migration was evaluated using the scratch assay and the MRI wound-healing tool in ImageJ (Fiji). Mitochondrial morphology was examined with MitoTracker Green and the MiNA tool in ImageJ (Fiji). Apoptotic processes were analyzed by Western blot, immunocytofluorescence staining, and ELISA. Results: In vivo, PACAP−/−/ApoE−/−-mice showed increased lumen stenosis and decreased plaque burden compared with ApoE−/−-mice. In vitro, PACAP enhanced the viability of oxLDL-treated HCASMCs, while neither PACAP nor Maxadilan influenced lipid content in HCASMCs, regardless of oxLDL presence. Both oxLDL and PACAP slowed cell migration, but Maxadilan increased migration in oxLDL-treated HCASMCs. The protein level of the proliferation marker Ki67 was reduced in cells treated with oxLDL and Maxadilan. Additionally, BAX, which promotes intrinsic apoptosis, was elevated in HCASMCs stimulated with Maxadilan and oxLDL. Investigations of mitochondrial morphology indicated that oxLDL and PACAP increased the individual and network structures, with a decrease in branches per network. Conclusion: Our data highlight the complex role of the PACAP/PAC1 system in vascular pathology and suggest that selective modulation—such as targeted PAC1 activation or PACAP supplementation—could lead to new strategies for stabilizing atherosclerotic plaques. In the long term, this could improve the balance between plaque formation and vascular function.