Abstract P430: Primary Neuronal Cilium As A Novel Mediator Of Angiotensin II And Hypertension

Abstract

Cilia are membrane-bound, microtubular projections emanating from the cell surface and present on virtually all cell types including neurons. Cilia abnormalities (ciliopathies) have been linked to a broad range of diseases including hypertension. Moreover, we previously reported that DOCA-salt hypertension is associated with alterations in cilia in select nuclei involved in cardiovascular regulation and fluid homeostasis such as the supraoptic nucleus, but the underlying mechanisms are not known. Given the well-established role of the brain renin-angiotensin system in DOCA-salt hypertension, we hypothesized that Angiotensin II (Ang II) contribute to neuronal cilia abnormalities in hypertension. We began by examining the effect of Ang II on cilia in two different neuronal cell lines, mouse hypothalamic N47 and Cath.a. Ang II treatment (100 nM for 4 hrs) caused a significant increase in cilia length of N47 cells that were transiently transfected with a Flag-tagged AT1a receptor (AT1aR) compared to non-transfected cells (3.83±0.15 μm vs 2.25±0.06 μm, P<0.05). No change in cilia length was observed in AT1aR positive (2.71±0.09 μm) or negative cells (2.55±0.07 μm) treated with vehicle. Moreover, Ang II had no effect on cilia in N47 cells transfected with a Flag-tagged AT2R. Ang II also significantly increased cilia length in Cath.a cells which express the endogenous AT1aR. Truncation of AT1aR at position 318 resulted in loss of Ang II induced cilia elongation in N47 cells, indicating that the C-terminus of the receptor is important for Ang II regulation of cilia. Next, we evaluated the effect of Ang II infusion with minipumps (480ng/kg/min) on neuronal cilia in C57BL/6 mice. Mice infused with Ang II for 5 days which have elevated blood pressure displayed abnormally elongated cilia in the supraoptic nucleus (8.28±0.12 μm vs 6.37± 0.11 μm, P<0.05). Interestingly, Ang II-induced cilia elongation preceded the development of hypertension as it was observed in mice infused with Ang II for 2 days when no change in blood pressure was detected. These findings point to Ang II as an important regulator of neuronal cilia via AT1aR. This represents a novel mechanism for cardiovascular regulation by the renin-angiotensin system.