CADASIL : a pure model for studying cerebral small vessel disease

Abstract

Cerebral autosomal dominant arteriopathy with subcortical infarct and leukoencephalopathy (CADASIL) is caused by a mutation on the NOTCH3 gene. The pathological driver behind this disease is the loss of vascular smooth muscle cells (VSMCs) in small blood vessels and subsequent fibrotic thickening of the vessel, causing stenosis. Although a great deal of knowledge has been accumulated through CADASIL research, more information is needed to fully grasp the pathological mechanisms as well as understand disease progression. We have focused on the effects of NOTCH3 mutation on VSMCs and identified several novel actors in disease progression.

In our initial study, we investigated factors playing a role in the VSMC proliferative rate. We found that VSMCs carrying a CADASIL mutation express higher levels of TGFβ. This elevated cytokine secretion by CADASIL VSMCs had an inhibitory proliferative effect on not only these cells, but also cells in their vicinity. This phenotype was rescued by adding neutralizing TGFβ antibody to the growth media, which increased CADASIL VSMC proliferation rate to that of control VSMCs, while having a minimal effect on control VSMC proliferation rate. One of the initial events in CADASIL disease progression is NOTCH3 aggregation and accumulation. In our next study, we focused on degradation of aggregated NOTCH3 via autophagy processes. After confirming that NOTCH3 is aggregated and accumulated in our cell line, we further tested the autophagy process in these cells. We discovered that the autophagy process in CADASIL VSMCs is interrupted and, upon further investigation, found that this could be due to a dysfunction in fusion of the autophagosome and lysosome.

Next, we investigated the nutritional requirements in CADASIL VSMCs compared to control VSMCs. One of the most readily available forms of nutrients in myocytes is glucose. Hence, we examined glucose transporter expression in CADASIL VSMCs compared to control VSMCs. CADASIL VSMC glucose transporters were significantly down regulated and this down regulation had a negative functional effect such that CADASIL VSMCs were unable to take up glucose as avidly as control VSMCs. Adding insulin to the media only moderately increased glucose uptake in CADASIL VSMCs since Glut 4 was the only insulin-dependent glucose transporter that was down regulated (other glucose transporters were also down regulated, but they were insulin-independent). VSMCs in CADASIL are frail and less resistant to stress. Based on this fact, we hypothesized that they may secret inflammatory cytokines and thereby affect their neighboring cells in paracrine fashion. Measuring inflammatory cytokine gene expression, we discovered that most of them were up regulated, which translated to an increased amount of protein synthesis. In this study, we have implicated inflammation as a pathological driver in CADASIL. Dampening of this inflammatory response may slow the rate of VSMC loss and, consequently, disease progression.