Nitric Oxide Regulates c-fosExpression in Nucleus Tractus Solitarii Induced by Baroreceptor Activation via cGMP-Dependent Protein Kinase and cAMP Response Element-Binding Protein Phosphorylation

Abstract

Activation of the arterial baroreceptors induces expression of the proto-oncogene c-fos in the nucleus tractus solitarii (NTS), the terminal site of baroreceptor afferents in the medulla oblongata. This induced expression is an intracellular event that is crucial to long-term maintenance of stable blood pressure. Using Sprague-Dawley rats maintained under propofol anesthesia, we evaluated the role and delineated the underlying molecular mechanisms of nitric oxide (NO) in this process. Baroreceptor activation induced by 30 min of sustained hypertension significantly and sequentially increased the level of cyclic GMP-dependent protein kinase I (PKG-I), phosphorylated cyclic AMP response element-binding protein (pCREB), c-fos mRNA, and Fos protein in the NTS. All of these upregulated expressions were significantly attenuated in animals that were pretreated immediately before baroreceptor activation with bilateral microinjection into the NTS of a selective neuronal nitric-oxide synthase (nNOS) inhibitor, 7-nitroindazole

A fast carrier chromatin immunoprecipitation method applicable to microdissected tissue samples

“…Comparing PE induced hypertensive animals to saline infused animals, PE induced hypertensive increased the c-fos gene promoter enrichment by approximately 2 fold, indicating an increased pCREB binding on the c-fos gene promoter sequences. Such an increase is in agreement with increased gene expression (Chan et al, 2004) and Fos immunoreactivity (Chan and Sawchenko, 1994;Li et al, 1994) seen in the NTS after PE induced hypertension.…”

“…Of course, the binding of pCREB to the c-fos promoter is not limited to the hypertension-responsive cells as pCREB was seen binding to the c-fos promoters at a basal level in the absence of stimulation. However, the increase in pCREB binding in hypertensive NTS compared to saline-treated NTS tissue is certainly due to hypertensive treatment and the increased enrichment observed presumably is from the hypertension responsive cells with increased c-fos expression (Chan et al, 2004;Chan and Sawchenko, 1994;Li et al, 1994). It is noted that this is in the context of a larger quantity of starting material (0.6 mm 3 ) compared to the initial sensitivity testing with cortex tissue (0.2 mm 3 ).…”

“…The NTS plays an integrative role within the baroreflex function and either activates or inhibits the sympathetic and parasympathetic nervous systems to control heart rate, cardiac output, and peripheral vascular resistance, based upon the visceral and emotional inputs (Li et al, 1994;Chan and Sawchenko, 1998). It has been shown that PE induced acute hypertension leads to the immediate early gene c-fos induction and Fos protein accumulation in the NTS (Chan and Sawchenko, 1994;Li et al, 1994;Chan et al, 2004). Phosphorylation of CREB has been suggested to mediate the induction of the c-fos gene expression (Chan et al, 1999;Chan et al, 2004).…”

“…It has been shown that PE induced acute hypertension leads to the immediate early gene c-fos induction and Fos protein accumulation in the NTS (Chan and Sawchenko, 1994;Li et al, 1994;Chan et al, 2004). Phosphorylation of CREB has been suggested to mediate the induction of the c-fos gene expression (Chan et al, 1999;Chan et al, 2004). This has been difficult to demonstrate directly because only a small percentage of the cells in the region respond to blood pressure change.…”

NMDA induces post-transcriptional regulation of α2-guanylyl-cyclase-subunit expression in cerebellar granule cells

“…Although the mechanism by which cGK regulates AUF1 levels remains unclear, one possibility is that cGK suppresses the expression of AUF1 proteins by phosphorylation of CREB or of another transcription factor. Indeed, the influence of PKG on gene expression has been demonstrated in different cell types, including neurons (Gudi et al, 1999;Fujiwara et al, 2002;L'Etoile et al, 2002;Smolenski et al, 2004;Pilz and Broderick, 2005), and in some cases this activity is clearly mediated by CREB phosphorylation (Ciani et al, 2002;Chen et al, 2003;Chan et al, 2004). Based on the data presented here, we hypothesise that NMDA stimulation decreases the amount of AUF1 in granule cells and, as a consequence, stabilises different mRNAs that are targeted by these proteins.…”