side-chain-oxidized oxysterols upregulate ACE2 and Mas receptor in rat primary neurons

Disturbances in cholesterol metabolism have been associated with hypertension and Alzheimer's disease (AD). We recently reported increased angiotensin-converting enzyme (ACE) activity and angiotensinogen (AGT) levels in the cerebrospinal fluid (CSF) of patients with mild cognitive impairment and AD. ACE activity positively correlated with plasma and CSF 27-hydroxycholesterol (27-OH) levels, an oxysterol that passes to the brain from the blood. Additionally, we showed that 27-OH and 24(S)-hydroxycholesterol (24S-OH) enhance AGT synthesis and modulate renin and ACE activities in brain cells.

To gain insight into how oxysterols affect the brain renin-angiotensin system (RAS), we analyzed the effects of 24S-OH and 27-OH on two other proteins in this system: ACE2 and Mas receptor (MasR).

RT-PCR and Western blot analysis in rat primary neurons treated with either 24S-OH or 27-OH.

The levels of ACE2 and MasR were increased by a physiological concentration (1 μM) of these oxysterols after 24 h.

24S-OH and 27-OH enhance the brain RAS by acting on different levels, from the precursor to several downstream enzymes. Our results support the idea that disturbances in cholesterol metabolism would contribute to alterations in the brain RAS, which further suggest mechanistic links between two well-known risk factors for AD: hypercholesterolemia and hypertension.