Regulation of claudins in arterial hypertension due to high salt intake and environmental factors (corticosteroids, epidermal growth factor and ouabain): intracellular signaling patterns and nuclear processes that activate, and the role played by autophagy , the transcription factor STAT3 and the proteasome.
The interstitial concentration of Na + is strongly regulated in mammals, particularly by the renal epithelia. These tissues reabsorb or secrete Na +via transcellular or paracellular pathways. The latter is made up of tight junctions (TJs), a type of intercellular junction composed mainly of claudins (CLDNs), the family of transmembrane proteins that form paracellular ion channels. Epithelia exhibit characteristic paracellular selectivity and permeability, depending on the type of CLDNs they express. Thus, the epithelium of the proximal convoluted tubule is specialized for Na + reabsorption and expresses CLDN2, a protein that forms paracellular Na + channels , while in the distal convoluted tubule it reabsorbs Cl - , it expresses CLDN4, which forms paracellular Cl channels. - and a barrier to Na +. The degree of tight junction sealing, and therefore the expression of the CLDNs, is adjusted to the environmental conditions. For example, rats that consume a lot of NaCl decrease CLDN2 expression in the proximal convoluted tubule and increase CLDN4 in the distal one.
Humans have increased salt intake in recent centuries and, consequently, essential arterial hypertension that affects more than one billion people in the world and 31.5% of the Mexican population and is associated with a high risk of cardiovascular events, metabolic syndrome and renal fibrosis. 45% of patients with essential hypertension have elevated cardiotonic steroids (CS) in plasma and urine, especially ouabain or a very similar substance. Ouabain is the prototypical CS and is now considered a hormone that regulates natriuresis, blood pressure, and cell differentiation. We have already shown that epidermal growth factor (EGF) and ouabain downregulate CLDN2 in canine kidney epithelial MDCK cells through EGF receptor activation. Src and ERK1/2 kinases and the transcription factor STAT3. The transcellular pathway is important for hypertension, but how the paracellular pathway is involved is unknown.
In our laboratory we investigate how claudins are regulated in response to signals from the environment and under pathological conditions.
We studied how CLDN2 is regulated in hypertension due to high salt intake and the role that STAT3 activation plays in the process. We used cultured MDCK cells, in which we overexpressed the wild-type protein or mutants of the phosphorylation or acetylation sites, or we silenced the wild type and observed if they altered the response of MDCK cells to ouabain and/or EGF, measuring the content. of CLDNs by immunofluorescence and immunoblotting, and of their mRNAs by quantitative PCR, the degree of tight junction sealing as estimated by measurement of transepithelial electrical resistance, paracellular permeability by fluorescent paracellular tracer flux, and the degree of cell polarity by immunofluorescence and confocal microscopy of polarity markers.
We investigated the transcriptional regulation of CLDN2 and CLDN4 in MDCK cells. We wonder if the promoter contains any element sensitive to ouabain and/or EGF related to STAT3 and if this mechanism operates in the proximal convoluted tubule of genetically hypertensive rats or due to high salt intake.We investigated whether EGF or ouabain induce epigenetic control of CLDN2 and CLDN4, autophagy of CLDNs, and whether the proteasome is involved in the CLDN2 degradation process.
We investigated whether ouabain induces distinct spatiotemporal activation patterns depending on concentration and whether these influence claudin expression and tight junction function.
We investigated whether corticosteroids (dexamethasone) control CLDN4 transcription or synthesis and what role STAT3 plays in the process.To carry out these investigations, we also use ion measurements by atomic absorption, gene mutation, transfection of wild type and mutated genes, messenger silencing, measurement of transcriptional activity with reporter genes, and we induce hypertension in rats by offering them a high salt intake. .
