Die Bedeutung von PACAP (Pituitary Adenylate Cyclase-Activating Polypeptide) bzw. seines Rezeptors PAC1 für die Entwicklung und Progression der Atherosklerose in 10 Wochen mit Cholesterin-gefütterten ApoE-defizienten Mäusen

The pituitary adenylate cyclase activating polypeptide (PACAP) acts via the pleiotropically distributed G-protein coupled receptors PAC1, VPAC1 and VPAC2. PAC1 is exclusively activated by PACAP. In contrast, VPAC1 and VPAC2 can also be activated by the related vasoactive intestinal peptide (VIP). PACAP acts, among other organ systems, on blood vessels, immune cells and the neuroendocrine system. The present study investigated the in vivo effect of a PACAP or PAC1 deficiency (PACPAP-/- or PAC1-/-) on the development and course of atherosclerosis in the apolipoprotein E knockout (ApoE-/-) mouse model after 10 weeks standard food (SF) and then 10 weeks on a cholesterol enriched diet (CRF). The genotypes ApoE-/-, PACAP-/- / ApoE-/- and PAC1-/- / ApoE-/- were examined. Mice were weighed, their plasma cholesterol and triglyceride concentrations were measured. The truncus brachiocephalicus (TB) was then removed and immediately shock frozen in liquid nitrogen-cooled isopentane. Frozen sections were prepared from the TB and used to quantify luminal stenosis, morphological, remodeling, and inflammatory parameters. Mean body weights were similar in all genotypes, however, the tibiae in PACAP-/-/ApoE-/-- mice were, on average, significantly 1.1-fold longer than that of ApoE-/-- mice. The plasma cholesterol and triglyceride levels of the three genotypes examined were similar. In PACAP-/- / ApoE-/-- mice, mean luminal stenosis was significantly 1.5-fold less than in ApoE-/-- mice. In addition, we found a significantly 1.5-fold smaller percentage of sm-α-actin-positive plaque area in this genotype. On the other hand, the percentage of Ki-67-positive cell nuclei was significantly 2.6 times greater than in the ApoE-/-- control. In addition, the percentage of interleukin-6 positive plaque area was significantly 1.6-fold higher than in ApoE-/- mice. Lumen stenosis was also significantly 4.3-fold lower in PAC1-/- / ApoE-/-- mice than in ApoE-/-- mice. Furthermore, in PAC1-deficient mice, the percentage of MoMa-2-positive plaque area was significantly 5.8-fold smaller than in ApoE-/- mice. Additionally, the percentage of ATG5-positive plaque area was significantly 2.2-fold smaller than in ApoE-/- mice. Overall, both PACAP-/- and PAC1-/- mice showed anti-atherosclerotic effects compared to controls (ApoE-/-). In addition, a lower proportion of myocytes was observed, which could result in reduced plaque stability. In PACAP-/- / ApoE-/-- mice there was also evidence of enlarged proliferation activity in the form of a larger percentage of Ki-67-positive cell nuclei and increased inflammation in the plaque areas. PAC1 deficiency also resulted in reduced monocyte and macrophage density and a lower proportion of ATG5-positive areas in the plaque. Our results confirm and extend the findings of others, i.e. the existing assumption of an effect of PACAP or PAC1 on the development and progression of atherosclerosis could be additionally strengthened by our study. Interestingly, in addition to previously published data, a reduced lumen stenosis due to PACAP or PAC1 deficiency after CRF was shown. The supposedly protective effect of PACAP could therefore also be mediated via the VPAC1 and VPAC2 receptors. The complex and diverse effects of PACAP and its receptors should be investigated in further studies in order to better understand the underlying molecular mechanisms in the respective organ systems. Based on our results and the data available so far, future studies should show whether the development and progression of atherosclerosis can be positively influenced by the pharmacological use of PACAP receptor modulators, such as synthetic PACAP38 or Maxadilan.