Hypertensive Female Mice Are Protected from Impaired Parenchymal Arteriolar TRPV4‐Mediated Dilation and Reactive Astrogliosis

Abstract

Hypertension is a leading risk factor for cerebral small vessel disease. Our lab has previously demonstrated that cerebral parenchymal arterioles (PAs) are dependent on transient receptor potential vanilloid 4 (TRPV4) function for endothelium‐dependent dilation, and that this dilation is impaired in angiotensin II (AngII)‐hypertensive male mice. This PA dilation impairment is associated with cognitive deficits and increased inflammation. However, sex differences in hypertension‐associated dementia development are not well understood. To better understand the effect of female sex hormones during hypertension, we tested the hypothesis that young, cycling hypertensive female mice will be protected from impaired TRPV4‐mediated PA dilation and reactive astrogliosis observed in male mice. AngII‐filled osmotic minipumps (800ng/kg/min, 4 weeks) were implanted in 16‐18‐week‐old male C56BL/6 mice. Age‐matched female mice received either an AngII dose that matches the dose used in male mice (800ng/kg/min) or a higher dose (1200ng/kg/day) that produces an elevation in blood pressure similar to male mice. Sham mice served as control. Blood pressure was measured by tail‐cuff plethysmography. Pressure myography was used to assess TRPV4‐mediated dilation in PAs. An anti‐glial fibrillary acidic protein (GFAP) antibody was used in paraformaldehyde‐fixed 40μm coronal brain sections to assess the quantity and morphology of astrocytes. Data are presented as means ± SEM (n=5‐10). Male data were compared by Student’s t‐test and female data were compared by one‐way ANOVA unless otherwise stated. Systolic blood pressure was elevated in AngII‐treated male mice (sham: 133 ± 10, AngII: 181 ± 11mmHg; p=0.005) and in 1200ng AngII‐treated female mice (sham: 146 ± 8, 800ng AngII: 161 ± 13, 1200ng AngII: 179 ± 7mmHg; p=0.0482) vs sham. PA dilation in response to the TRPV4 agonist GSK1016790A (10‐9‐10‐5M) was not impaired in AngII‐treated female mice (sham: 85 ± 5, 800ng AngII: 73 ± 7, 1200ng AngII: 77 ± 8% maximum dilation; p=0.4381), contrasting with what we have previously reported in male mice. There was an increase in astrocytes in the corpus callosum of hypertensive male mice (sham: 65 ± 2; AngII: 77 ± 5; p=0.039). Interestingly, sham female mice had more astrocytes than sham male mice, and AngII infusion reduced the quantity (sham: 81 ± 3, 800ng AngII: 71 ± 3, 1200ng AngII: 69 ± 3; p=0.011). Sholl analysis was used to assess astrocyte morphology. Astrocytes from hypertensive male mice had more arborization further from the soma compared to sham (p=0.0348 at 14‐15μm from the soma, by two‐way ANOVA and Bonferroni correction). Female mice receiving the 1200ng dose AngII, however, had fewer arborizations away from the soma compared to sham (p=0.0263 at 13‐15μm from the soma, by two‐way ANOVA and Bonferroni correction). Female mice are resistant to AngII‐induced hypertension and protected from the associated deleterious cerebrovascular effects, supporting our hypothesis.