Blockade of TLR4 Within the Paraventricular Nucleus Attenuates Blood Pressure by Regulating ROS and Inflammatory Cytokines in Prehypertensive Rats

Abstract

Toll-like receptor 4 (TLR4) has been implicated in the progression of cardiovascular disease, including hypertension. However, the role of TLR4 in the development of prehypertension is uncertain. METHODS Prehypertensive rats were treated with 8% salt for 12 weeks to induce prehypertension. These rats were then given either TAK- 242 selective TLR4 blocker, or vehicle by bilateral micro-injection to the paraventricular nucleus (PVN). Blood pressure (BP) and renal sympathetic nerve activity were recorded. PVN expression of TLR4, myeloid differentiation factor 88 (Myd88), nuclear factor-kappa B (NF-κB) p65, proinflammation cytokines (PICs), interleukin (IL)-1β, IL-6, tumor necrosis factor-alpha (TNF-α), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2), NADPH oxidase 4 (NOX4), Cu/Zn superoxide dismutase (SOD) level, tyrosine hydroxylase, and 67 kDa isoform of glutamate decarboxylase (GAD67) were tested to determine the influence of TLR4 blockade. RESULTS TLR4 expression increased significantly in the PVN of high-salt groups with a corresponding increase in reactive oxygen species (ROS) and PICs. TLR4 blockade significantly reduced the signaling molecules downstream TLR4 and the expression of TNF-α, IL-6, IL-1β, decreased ROS, NOX2, NOX4 level, increased Cu/Zn-SOD, re-balanced neurotransmitters, and regulated sympathetic nerve activity in the PVN of prehypertensive rats. CONCLUSIONS Salt-induced prehypertension is partly due to the upregulation of TLR4 in PVN. Blockade of TLR4 in the brain reduced salt-induced prehypertension response, possibly through downregulation of ROS and PICs expression, and the restorage of neurotransmitter balance in the PVN. Keywords: blood pressure; hypertension; hypothalamic paraventricular nucleus; inflammatory cytokines; neurotransmitters; prehypertension; ROS; TLR4. doi:10.1093/ajh/hpy074