School of Medicine and Health Sciences Poster Presentations

Title

Hypertensive Actions of Long Chain Fatty Acids are Paralleled by Toll-Like Receptor 4 Upregulation and Nuclear Factor-B (NFB) Activation in the Subfornical Organ

Poster Number

284

Document Type

Poster

Status

Postdoc

Abstract Category

Neuroscience

Keywords

Hypertension, Nuclear Factor kappa B, Toll-like receptor 4, Subfornical Organ

Publication Date

Spring 2018

Abstract

Obesity-induced hypertension is characterized by a low-grade inflammatory state along with elevations in circulating long-chain fatty acids (LCFA). Toll-like receptor 4 (TLR4) is a transmembrane receptor that is activated by LCFA, resulting in downstream inflammatory processes. The central nervous system (CNS) is critical for the control of blood pressure, with the circumventricular subfornical (SFO) organ playing a critical role. The contribution of CNS TLR4 in blood pressure regulation, particularly within the SFO, remains unclear. We hypothesized that an SFO LCFA-TLR4-inflammatory pathway is associated with elevations in blood pressure. Adult male C57B1/6 mice were instrumented with radiotelemeters for the measurement of blood pressure and implanted with an intracerebroventricular (ICV) cannula. Following recovery, a LCFA (oleic acid, 30 nmol), or vehicle control, was administered once a day over 2 days. Whereas mean arterial blood pressure was unchanged in control animals, 2-day ICV infusion of LCFA resulted in a pro-hypertensive response (day 2: 95±2 vs. 110±2 mmHg, vehicle vs. LCFA, p<0.05, n=4). Real-time quantitative PCR analysis revealed SFO TLR4 mRNA upregulation following central LCFA administration when compared to vehicle (1.1±0.3 vs. 2.3±0.4 fold vehicle, vehicle vs. LCFA, p<0.05, n=4). In contrast, TLR4 transcript in the paraventricular nucleus of hypothalamus another cardioregulatory region, was not different between groups (1.1±0.2 vs. 1.4±0.3 fold vehicle, vehicle vs. LCFA, p>0.05, n=4). Based on this, we further evaluated TLR4 protein expression in the SFO using immunohistochemical analyses. TLR4-expressing cells were found predominately within the medial to caudal regions of the SFO. Co-immunolabeling indicated that SFO TLR4-expressing cells were exclusively microglia (Iba1 co-localization: 75±4% TLR4 cells, n=3), whereas no co-expression was found on astrocytes or neurons. Given that TLR4 activation results in the activation of the inflammatory transcription factor NFkB, we subsequently assessed LCFA-TLR4 mediated activation of NFkB in the SFO using an in vivo bioluminescence imaging technique. Male C57B1/6 mice (n=2) underwent SFO-targeted injection of an adenovirus encoding firefly luciferase downstream of the NFκB consensus sequence to allow for in vivo imaging of SFO NFκB activity. Two-day ICV LCFA administration resulted in SFO NF-κB activation that was evident within 24 hrs (1.3±0.2 fold baseline) and maintained at 48 hrs (1.3±0.4 fold baseline). These findings indicate that LCFAs act within the CNS to increase arterial blood pressure. Moreover, the hypertensive actions of LCFA are paralleled by SFO TLR4 upregulation and NFκB activation, suggesting that a LCFA-TLR4-NFκB network in this nucleus may contribute to hypertension development, such as during obesity.

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Hypertensive Actions of Long Chain Fatty Acids are Paralleled by Toll-Like Receptor 4 Upregulation and Nuclear Factor-B (NFB) Activation in the Subfornical Organ

Obesity-induced hypertension is characterized by a low-grade inflammatory state along with elevations in circulating long-chain fatty acids (LCFA). Toll-like receptor 4 (TLR4) is a transmembrane receptor that is activated by LCFA, resulting in downstream inflammatory processes. The central nervous system (CNS) is critical for the control of blood pressure, with the circumventricular subfornical (SFO) organ playing a critical role. The contribution of CNS TLR4 in blood pressure regulation, particularly within the SFO, remains unclear. We hypothesized that an SFO LCFA-TLR4-inflammatory pathway is associated with elevations in blood pressure. Adult male C57B1/6 mice were instrumented with radiotelemeters for the measurement of blood pressure and implanted with an intracerebroventricular (ICV) cannula. Following recovery, a LCFA (oleic acid, 30 nmol), or vehicle control, was administered once a day over 2 days. Whereas mean arterial blood pressure was unchanged in control animals, 2-day ICV infusion of LCFA resulted in a pro-hypertensive response (day 2: 95±2 vs. 110±2 mmHg, vehicle vs. LCFA, p<0.05, n=4). Real-time quantitative PCR analysis revealed SFO TLR4 mRNA upregulation following central LCFA administration when compared to vehicle (1.1±0.3 vs. 2.3±0.4 fold vehicle, vehicle vs. LCFA, p<0.05, n=4). In contrast, TLR4 transcript in the paraventricular nucleus of hypothalamus another cardioregulatory region, was not different between groups (1.1±0.2 vs. 1.4±0.3 fold vehicle, vehicle vs. LCFA, p>0.05, n=4). Based on this, we further evaluated TLR4 protein expression in the SFO using immunohistochemical analyses. TLR4-expressing cells were found predominately within the medial to caudal regions of the SFO. Co-immunolabeling indicated that SFO TLR4-expressing cells were exclusively microglia (Iba1 co-localization: 75±4% TLR4 cells, n=3), whereas no co-expression was found on astrocytes or neurons. Given that TLR4 activation results in the activation of the inflammatory transcription factor NFkB, we subsequently assessed LCFA-TLR4 mediated activation of NFkB in the SFO using an in vivo bioluminescence imaging technique. Male C57B1/6 mice (n=2) underwent SFO-targeted injection of an adenovirus encoding firefly luciferase downstream of the NFκB consensus sequence to allow for in vivo imaging of SFO NFκB activity. Two-day ICV LCFA administration resulted in SFO NF-κB activation that was evident within 24 hrs (1.3±0.2 fold baseline) and maintained at 48 hrs (1.3±0.4 fold baseline). These findings indicate that LCFAs act within the CNS to increase arterial blood pressure. Moreover, the hypertensive actions of LCFA are paralleled by SFO TLR4 upregulation and NFκB activation, suggesting that a LCFA-TLR4-NFκB network in this nucleus may contribute to hypertension development, such as during obesity.