A preliminary study of the effect of a high-salt diet on transcriptome dynamics in rat hypothalamic forebrain and brainstem cardiovascular control centers

Abstract

Background High dietary salt intake is strongly correlated with cardiovascular (CV) diseases and it is regarded as a major risk factor associated with the pathogenesis of hypertension. The CV control centres in the brainstem (the nucleus tractus solitarii (NTS) and the rostral ventrolateral medulla (RVLM)) and hypothalamic forebrain (the subfornical organ, SFO; the supraoptic nucleus, SON and the paraventricular nucleus, PVN) have critical roles in regulating CV autonomic motor outflows, and thus maintaining blood pressure (BP). Growing evidence has implicated autonomic regulatory networks in salt-sensitive HPN (SSH), but the genetic basis remains to be delineated. We hypothesized that the development and/ or maintenance of SSH is reliant on the change in the expression of genes in brain regions controlling the CV system. Methodology We used RNA-Sequencing (RNA-Seq) to describe the differential expression of genes in SFO, SON, PVN, NTS and RVLM of rats being chronically fed with high-salt (HS) diet. Subsequently, a selection of putatively regulated genes was validated with quantitative reverse transcription polymerase chain reaction (qRT-PCR) in both Spontaneously Hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats. Results The findings enabled us to identify number of differentially expressed genes in SFO, SON, PVN, NTS and RVLM; that are either up-regulated in both strains of rats (SON- Caprin2, Sctr), down-regulated in both strains of rats (PVN- Orc, Gkap1), up-regulated only in SHRs (SFO- Apopt1, Lin52, AVP, OXT; SON- AVP, OXT; PVN- Caprin2, Sclt; RVLM- A4galt, Slc29a4, Cmc1) or down-regulated only in SHRs (SON- Ndufaf2, Kcnv1; PVN- Pi4k2a; NTS- Snrpd2l, Ankrd29, St6galnac6, Rnf157, Iglon5, Csrnp3, Rprd1a; RVLM- Ttr, Faim). Conclusions These findings demonstrated the adverse effects of HS diet on BP, which may be mediated via modulating the signaling systems in CV centers in the hypothalamic forebrain and brainstem.

Effect of TLR4/MyD88/NF‐kB axis in paraventricular nucleus on ventricular arrhythmias induced by sympathetic hyperexcitation in post‐myocardial infarction rats

“…Studies have shown that many cardiovascular diseases, such as MI, HF and hypertension, are characterized by reduced cardiac function due to peripheral inflammation associated with increased central sympathetic tone, while neuroinflammation of the PVN in turn leads to increased central sympathetic tone 4 . Under hypertensive conditions, the PVN activates and releases NE, 23 an excitatory neurotransmitter, thereby promoting sympathetic output 24,25 . In studying diseases such as memory impairment and neurological damage after cerebral ischaemia‐reperfusion, animal models of cerebral ischaemic stroke reflect that the TLR4/MyD88/NF‐kB axis is involved in neuroinflammation 26,27 .…”

“… 4 Under hypertensive conditions, the PVN activates and releases NE, 23 an excitatory neurotransmitter, thereby promoting sympathetic output. 24 , 25 In studying diseases such as memory impairment and neurological damage after cerebral ischaemia‐reperfusion, animal models of cerebral ischaemic stroke reflect that the TLR4/MyD88/NF‐kB axis is involved in neuroinflammation. 26 , 27 We performed a study on the role of TLR4 in the mechanism of PVN‐mediated sympathetic activation after MI.…”

“…4 Under hypertensive conditions, the PVN activates and releases NE, 23 an excitatory neurotransmitter, thereby promoting sympathetic output. 24,25 In studying diseases such as memory impairment and neurological damage after cerebral ischaemia-reperfusion, animal models of cerebral ischaemic stroke reflect that the TLR4/MyD88/NF-kB axis is involved in neuroinflammation. 26,27 We performed a study on the Activation of TLR4 on the microglial cell membrane of the PVN leads to the activation of IkB kinase (IKK) in a MyD88-dependent manner, thereby allowing IkB-a, which locks NF-kB in the cytoplasm when the cell is at rest, to be phosphorylated and degraded, ultimately leading to the NF-kB complex (p50/p65) being phosphorylated and entering the nucleus.…”

Age-associated downregulation of glutamate and GABA neurotransmission-related gene expression in the rostral ventrolateral medulla of male Fischer 344 rats

“…Second, the approach we used here to anchor micropunched regions to atlas-mapped areas of the brain allows for important linkages between gene expression changes and neural substrates implicated in not only autonomic functions but in the regulation of food intake and body weight. A few studies have reported “bulk” or single-cell transcriptomic surveys for brainstem regions implicated in these functions, including (in addition to the RVLM) the area postrema and/or the nucleus of the solitary tract (see, e.g., in rats: Liberini et al, 2016; Ramachandran et al, 2020; in mice: Dowsett et al, 2021). However, these studies have not linked their microdissected regions to precise locations in an atlas reference space.…”

“…First, Pawar et al (2017 and2018) used a two-fold change in gene expression as the threshold for detecting differences between aged vs. young RVLM and it is possible that there might be gene expression differences that are less than two-fold in magnitude. In fact, several studies have used the combination of less than two-fold difference with statistical significance as a framework to establish changes in gene expression (Peart et al, 2005;Raouf et al, 2008). Second, a potential effect of aging on GABA and glutamate neurotransmission-related gene expression in the RVLM of middle-aged F344 rats was not explored.…”