Biomedical subjects

Klaus Willecke

Publications and source records attributed to Klaus Willecke.

At least 19 recordsLinked to original sources

PubMed2007

Restoration of connexin26 protein level in the cochlea completely rescues hearing in a mouse model of human connexin30-linked deafness.

Mutations in genes coding for connexin26 (Cx26) and/or Cx30 are linked to approximately half of all cases of human autosomal nonsyndromic prelingual deafness. Cx26 and Cx30 are the two major Cx isoforms found in the cochlea, and they coassemble to form hybrid (heteromeric and heterotypic) gap junctions (GJs). This molecular arrangement implies that homomeric GJs would remain in the cochlea if one of the coassembly partners were mutated resulting in null expression. We generated mice in which extra copies of the Cx26 gene were transgenically expressed from a modified bacterial artificial chromosome in a Cx30-/- background. In the absence of the Cx30 gene, Cx26 expressed from extra alleles completely restored hearing sensitivity and prevented hair cell death in deaf Cx30-/- mice. The results indicated that hybrid GJs consisting of Cx26 and Cx30 were not essential for normal hearing in mice and suggested that up-regulation of Cx26 or slowing down its protein degradation might be a therapeutic strategy to prevent and treat deafness caused by Cx30 mutations.

Animals↗

PubMed2007

Analysis of connexin expression during mouse Schwann cell development identifies connexin29 as a novel marker for the transition of neural crest to precursor cells.

Connexins are transmembrane proteins forming gap junction channels for direct intercellular and, for example in myelinating glia cells, intracellular communication. In mature myelin-forming Schwann cells, expression of multiple connexins, i.e. connexin (Cx) 43, Cx29, Cx32, and Cx46 (after nerve injury) has been detected. However, little is known about connexin protein expression during Schwann cell development. Here we use histochemical methods on wildtype and Cx29lacZ transgenic mice to investigate the developmental expression of connexins in the Schwann cell lineage. Our data demonstrate that in the mouse Cx43, Cx29, and Cx32 protein expression is activated in a developmental sequence that is clearly correlated with major developmental steps in the lineage. Only Cx43 was expressed from neural crest cells onwards. Cx29 protein expression was absent from neural crest cells but appeared as neural crest cells generated precursors (embryonic day 12) both in vivo and in vitro. This identifies Cx29 as a novel marker for cells of the defined Schwann cell lineage. The only exception to this were dorsal roots, where the expression of Cx29 was delayed four days relative to ventral roots and spinal nerves. Expression of Cx32 commenced postnatally, coinciding with the onset of myelination. Thus, the coordinated expression of connexin proteins in cells of the embryonic and postnatal Schwann cell lineage might point to a potential role in peripheral nerve development and maturation.

Animals↗

PubMed2007

Injury of skeletal muscle and specific cytokines induce the expression of gap junction channels in mouse dendritic cells.

Dendritic cells (DCs) in culture express at least connexin43, a protein subunit of gap junctions, and form gap junction channels, which could be important for T-cells activation. Here, we evaluated whether DCs express connexins in vivo and also to identify components of their microenvironment that regulate the functional expression of gap junctions. In vivo studies were performed in lymph nodes of mice under control conditions or after skeletal muscle damage. In double immunolabeling studies, connexin45 was frequently detected in DEC205(+) DCs in lymph nodes of control animals, whereas connexin43 was rarely found in DCs. However, connexin43 was upregulated in DCs after skeletal muscle damage. Upregulation of connexin43 gene expression by tissue damage was also confirmed in mice carrying a beta-galactosidase reporter gene in a connexin43 allele. The effect of several cytokines on the expression of functional gap junctions between cultured DCs was also tested. Under control conditions, cultured DCs did not communicate via gap junctions. However, after treatment with keratinocyte-conditioned medium or cytokine mixtures containing at least TNF-alpha and IL-1beta, they became transiently coupled through a pathway sensitive to octanol, a gap junction blocker. Cellular coupling induced by effective cytokine mixtures was prevented by IL-6. Single cytokines (TNF-alpha, IL-1beta, IFN-gamma, or IL-6) or other mixtures than the described above did not induce coupling via gap junctions. Increased levels of connexin43 and connexin45 protein and mRNA accompanied the appearance of cellular coupling. These studies provide demonstration of connexin expression and regulation by specific danger signals in DCs.

Animals↗

PubMed2006

Gating properties of heterotypic gap junction channels formed of connexins 40, 43, and 45.

Connexins (Cxs) 40, 43, and 45 are expressed in many different tissues, but most abundantly in the heart, blood vessels, and the nervous system. We examined formation and gating properties of heterotypic gap junction (GJ) channels assembled between cells expressing wild-type Cx40, Cx43, or Cx45 and their fusion forms tagged with color variants of green fluorescent protein. We show that these Cxs, with exception of Cxs 40 and 43, are compatible to form functional heterotypic GJ channels. Cx40 and Cx43 hemichannels are unable or effectively impaired in their ability to dock and/or assemble into junctional plaques. When cells expressing Cx45 contacted those expressing Cx40 or Cx43 they readily formed junctional plaques with cell-cell coupling characterized by asymmetric junctional conductance dependence on transjunctional voltage, V(j). Cx40/Cx45 heterotypic GJ channels preferentially exhibit V(j)-dependent gating transitions between open and residual states with a conductance of approximately 42 pS; transitions between fully open and closed states with conductance of approximately 52 pS in magnitude occur at substantially lower ( approximately 10-fold) frequency. Cx40/Cx45 junctions demonstrate electrical signal transfer asymmetry that can be modulated between unidirectional and bidirectional by small changes in the difference between holding potentials of the coupled cells. Furthermore, both fast and slow gating mechanisms of Cx40 exhibit a negative gating polarity.

Connexin 43↗

PubMed2006

Ablation of connexin43 in smooth muscle cells of the mouse intestine: functional insights into physiology and morphology.

Connexin43 (Cx43) gap-junction channels are highly abundant in intestinal smooth muscle but their functional impact has not been studied so far. Here, we have aimed to elucidate the functional role of Cx43 in the tunica muscularis of the mouse intestine in vivo. Transgenic mice with conditional deletion of Cx43 in smooth muscle cells (SMC) were generated. Histological investigations by immunofluorescence analyses and organ-bath recordings to assess the contractility of intestinal tissue strips were carried out. Measurements of gastrointestinal transit and of the visceromotor response by utilizing a standardized colorectal distension model to quantify alterations of visceral sensory function were also performed in SMC-specific Cx43 null mice and control littermates. Histologically, we found thickening of the tunica muscularis and a 13-fold increase of neutrophil infiltration of the gastrointestinal wall of SMC-specific Cx43 null mice. These animals also exhibited a decrease of 29% in gastrointestinal transit time. In contrast, the visceromotor response to a standardized colorectal distension was elevated, as was the contractility in SMC-specific Cx43 null mice, compared with controls. Thus, SMC-specific ablation of Cx43 in mice leads to morphological and functional alterations of the intestinal tunica muscularis, to gastrointestinal motor dysfunction and to altered visceral sensory function.

Animals↗

PubMed2006

Low peak bone mass and attenuated anabolic response to parathyroid hormone in mice with an osteoblast-specific deletion of connexin43.

Connexin43 (Cx43) is involved in bone development, but its role in adult bone homeostasis remains unknown. To overcome the postnatal lethality of Cx43 null mutation, we generated mice with selective osteoblast ablation of Cx43, obtained using a Cx43fl allele and a 2.3-kb fragment of the alpha1(I) collagen promoter to drive Cre in osteoblasts (ColCre). Conditionally osteoblast-deleted ColCre;Cx43-/fl mice show no malformations at birth, but develop low peak bone mass and remain osteopenic with age, exhibiting reduced bone formation and defective osteoblast function. By both radiodensitometry and histology, bone mineral content increased rapidly and progressively in adult Cx43+/fl mice after subcutaneous injection of parathyroid hormone (PTH), an effect significantly attenuated in ColCre;Cx43-/fl mice, with Cx43-/fl exhibiting an intermediate response. Attenuation of PTH anabolic action was associated with failure to increase mineral apposition rate in response to PTH in ColCre;Cx43-/fl, despite an increased osteoblast number, suggesting a functional defect in Cx43-deficient bone-forming cells. In conclusion, lack of Cx43 in osteoblasts leads to suboptimal acquisition of peak bone mass, and hinders the bone anabolic effect of PTH. Cx43 represents a potential target for modulation of bone anabolism.

Animals↗

PubMed2006

Cardiomyocyte-restricted deletion of connexin43 during mouse development.

Although the gap junction protein Connexin43 (Cx43) is expressed in various cell types during embryonic development, mice with a global inactivation of Cx43 survive until birth but die perinatally due to an obstruction of the right ventricular outflow tract of the heart. To analyze the functional role of Cx43 gap junction channels in cardiomyocytes of the developing and early postnatal heart, we used alphaMyHC-Cre mice to ablate Cx43 expression selectively in cardiomyocytes during development. We found efficient ablation of Cx43 in cardiomyocytes during embryonic development starting at embryonic day (ED) 9.5 in the ventricular wall. Analyses of cardiac Cx43 protein at birth indicated complete loss of Cx43 expression in cardiomyocytes. All mice homozygously deficient for Cx43 in cardiomyocytes died until postnatal day (PD) 16. Heterozygous inactivation of Cx43 in cardiomyocytes neither altered atrial nor ventricular activation, but homozygous ablation led to changes in ventricular activation, i.e. significant decrease of the QRS-amplitude and prolonged QRS-duration already at PD 4. Cardiac morphology was similar to controls until PD 1, but subtle morphological changes were found in a subgroup of mutant mice at later stages. Besides narrowing of the ventricular outlet region at PD 6, hypertrophy of ventricular myocardium was found at PD 12. Our data indicate that complete inactivation of cardiac Cx43 during development predisposes hearts to develop postnatal morphological alterations, which differ from outflow tract obstructions described for Cx43 null mice. In addition, complete loss of cardiac Cx43 protein during development correlates with slowed ventricular activation at PD 4, impairs viability during development, and leads to death of all mutant mice until PD 16.

Age Factors↗

PubMed2006

Protein kinase A-mediated phosphorylation of connexin36 in mouse retina results in decreased gap junctional communication between AII amacrine cells.

Gap junctions in AII amacrine cells of mammalian retina participate in the coordination of the rod and cone signaling pathway involved in visual adaptation. Upon stimulation by light, released dopamine binds to D(1) receptors on AII amacrine cells leading to increased intracellular cAMP (cyclic adenosine monophosphate) levels. AII amacrine cells express the gap junctional protein connexin36 (Cx36). Phosphorylation of Cx36 has been hypothesized to regulate gap junctional activity of AII amacrine cells. However, until now in vivo phosphorylation of Cx36 has not been reported. Indeed, it had been concluded that Cx36 in bovine retina is not phosphorylated, but in vitro phosphorylation for Cx35, the bass ortholog of Cx36, had been shown. To clarify this experimental discrepancy, we examined protein kinase A (PKA)-induced phosphorylation of Cx36 in mouse retina as a possible mechanism to modulate the extent of gap junctional coupling. The cytoplasmic domains of Cx36 and the total Cx36 protein were phosphorylated in vitro by PKA. Mass spectroscopy revealed that all four possible PKA consensus motifs were phosphorylated; however, domains point mutated at the sites in question showed a prevalent usage of Ser-110 and Ser-293. Additionally, we demonstrated that Cx36 was phosphorylated in cultured mouse retina. Furthermore, activation of PKA increased the level of phosphorylation of Cx36. cAMP-stimulated, PKA-mediated phosphorylation of Cx36 protein was accompanied by a decrease of tracer coupling between AII amacrine cells. Our results link increased phosphorylation of Cx36 to down-regulation of permeability through gap junction channels mediating light adaptation in the retina.

Amacrine Cells↗

PubMed2006

Cardiac morphogenetic defects and conduction abnormalities in mice homozygously deficient for connexin40 and heterozygously deficient for connexin45.

Connexin40 (Cx40) and connexin45 (Cx45) are involved in both cardiac morphogenesis and propagation of electrical activity. We found that Cx40/Cx45 double deficiency (Cx40(-/-)/Cx45(+/-)) causes a variety of cardiac defects leading to high mortality during embryonic development and at birth. The majority of Cx40(-/-)/Cx45(+/-) embryos and postnatal mice suffered from atrioventricular septal defects. Additional cardiac abnormalities, e.g., ventricular septal defects and abnormal myocardial arrangement, occurred at lower abundance. Electrocardiograms of Cx40(-/-)/Cx45(+/+) and Cx40(-/-)/Cx45(+/-) mice revealed prolongation of P-wave, PQ interval and QRS duration compared to controls. Interestingly, in Cx40(-/-)/Cx45(+/-) mice, PQ interval and QRS duration were significantly prolonged compared to Cx40(-/-)/Cx45(+/+) mice. We conclude that the gap junctional proteins Cx40 and Cx45 have overlapping and partially compensatory functions with regard to heart morphogenesis and cardiac conduction. Cx45 might be one of the genetic modifiers that can cause variations in the phenotype of connexin40-deficient animals. Our findings may be particularly relevant for understanding molecular factors contributing to human congenital cardiac diseases.

Animals↗

PubMed2006

Properties of mouse connexin 30.2 and human connexin 31.9 hemichannels: implications for atrioventricular conduction in the heart.

Four connexins (Cxs), mouse (m)Cx30.2, Cx40, Cx43, and Cx45, determine cell-cell electrical signaling in mouse heart, and Cx43 and Cx45 are known to form unapposed hemichannels. Here we show that mCx30.2, which is most abundantly expressed in sinoatrial and atrioventricular nodal regions of the heart, and its putative human ortholog, human (h)Cx31.9, also form functional hemichannels, which, like mCx30.2 cell-cell channels, are permeable to cationic dyes up to approximately 400 Da in size. DAPI uptake by HeLa cells expressing mCx30.2 was >10-fold faster than that by HeLa parental cells. In Ca(2+)-free medium, uptake of DAPI by HeLaCx30.2-EGFP cells was increased approximately 2-fold, but uptake by parental cells was not affected. Conversely, acidification by application of CO(2) reduced DAPI uptake by HeLaCx30.2-EGFP cells but had little effect on uptake by parental cells. Cells expressing mCx30.2 exhibited higher rates of DAPI uptake than did cells expressing any of the other cardiac Cxs. Cardiomyocytes of 2-day-old rats transfected with hCx31.9-EGFP took up DAPI and ethidium bromide 5-10 times faster than wild-type cardiomyocytes. Mefloquine, a close derivative of quinine and quinidine that exhibits antimalarial and antiarrhythmic properties, reduced conductance of cell-cell junctions and dye uptake through mCx30.2 hemichannels with approximately the same affinity (IC(50) = approximately 10 microM) and increased dependence of junctional conductance on transjunctional voltage. Unitary conductance of mCx30.2 hemichannels was approximately 20 pS, about twice the cell-cell channel conductance. Hemichannels formed of mCx30.2 and hCx31.9 may slow propagation of excitation in the sinoatrial and atrioventricular nodes by shortening the space constant and depolarizing the excitable membrane.

Animals↗

PubMed2006

Ablation of gap junctional communication in hepatocytes of transgenic mice does not lead to disrupted cellular homeostasis or increased spontaneous tumourigenesis.

Gap junctions between murine hepatocytes are composed of two subunit proteins, connexin26 (Cx26) and connexin32 (Cx32). Previously, we found increased formation of chemically induced liver tumours but no increase in spontaneous development of preneoplastic hepatic foci in mice that lacked Cx32 and expressed decreased amounts of Cx26. In order to clarify this tumour-suppressive effect and to overcome embryonic lethality of constitutive Cx26-deficient mice, cell type-specific targeting of the Cx26 gene was performed. Mice with loxP-flanked Cx26 coding DNA were crossed with mice expressing the Cre recombinase exclusively in hepatocytes. Progeny mice lacking Cx26 in the liver were viable and fertile with no obvious signs of phenotypic alterations. To generate mice that totally lack gap junctional intercellular coupling, these mice were crossed with constitutive Cx32-deficient mice. We found no increase in spontaneously induced liver tumour formation in Cx26 and double deficient Cx26/Cx32 mice. Occasionally, double deficient livers exhibited morphological alterations, like amyloidosis, and a slightly increased basal proliferation rate of hepatocytes. Although the absence of gap junction channels led to altered expression of adhesion-related proteins like E-cadherin and actin, microarray analyses of total liver transcripts yielded only few differences between Cx26-deficient and double deficient livers compared to control samples. Our results suggest that total lack of gap junctional communication due to hepatocytic ablation of Cx26 and Cx32 does not drastically alter basal hepatocytic function and does not lead to increased spontaneous liver tumour formation.

Animals↗

PubMed2006

The impact of astrocytic gap junctional coupling on potassium buffering in the hippocampus.

Astrocytic gap junctions have been suggested to contribute to spatial buffering of potassium in the brain. Direct evidence has been difficult to gather because of the lack of astrocyte-specific gap junction blockers. We obtained mice with coupling-deficient astrocytes by crossing conditional connexin43-deficient mice with connexin30(-/-) mice. Similar to wild-type astrocytes, genetically uncoupled hippocampal astrocytes displayed negative resting membrane potentials, time- and voltage-independent whole-cell currents, and typical astrocyte morphologies. Astrocyte densities were also unchanged. Using potassium-selective microelectrodes, we assessed changes in potassium buffering in hippocampal slices of mice with coupling-deficient astrocytes. We demonstrate that astrocytic gap junctions accelerate potassium clearance, limit potassium accumulation during synchronized neuronal firing, and aid in radial potassium relocation in the stratum lacunosum moleculare. Furthermore, slices of mice with coupling-deficient astrocytes displayed a reduced threshold for the generation of epileptiform events. However, it was evident that radial relocation of potassium in the stratum radiatum was not dependent on gap junctional coupling. We suggest that the perpendicular array of individual astrocytes in the stratum radiatum makes these cells ideally suited for spatial buffering of potassium released by pyramidal cells, independent of gap junctions. In general, a surprisingly large capacity for K+ clearance was conserved in mice with coupling-deficient astrocytes, indicating that gap junction-dependent processes only partially account for K+ buffering in the hippocampus.

Animals↗

PubMed2006

Expression pattern and functional characterization of connexin29 in transgenic mice.

Using newly generated transgenic mice in which the coding region of the connexin29 (Cx29) gene was replaced by the lacZ reporter gene, we confirmed previous immunochemical results that Cx29 is expressed in Schwann cells, oligodendrocytes and Bergmann glia cells. In addition, we detected lacZ/Cx29 in Schwann cells of the sciatic nerve and in particular of the spiral ganglion in the inner ear, as well as at low abundance in the stria vascularis. Furthermore, we found lacZ/Cx29 expression in nonmyelinating Schwann cells of the adrenal gland, in chondrocytes of intervertebral discs and the epiphysis of developing bones. Electron microscopic analyses of myelin sheaths in the central and peripheral nervous system of Cx29-deficient mice detected no abnormalities. The nerve conduction in the sciatic nerve of adult Cx29-deficient mice and the auditory brain stem response as well as visually evoked potentials in 4- to 10-week-old Cx29-deficient mice were not different from wild-type littermate controls. Thus, in contrast to connexin32 and connexin47, which are also expressed in myelinating cells, Cx29 does not contribute to the function of myelin in adult mice.

Adrenal Medulla↗

PubMed2006

Ablation of connexin43 in uterine smooth muscle cells of the mouse causes delayed parturition.

Gap junctions are characteristically increased in the myometrium during term and preterm delivery and are thought to be essential for the development of uterine contractions during labour. Expression of connexin43 (Cx43), the major myometrial gap junction protein, is increased during delivery. We have generated a mouse mutant (Cx43fl/fl:SM-CreERT2), in which the coding region of Cx43 can be specifically deleted in smooth muscle cells at any given time point by application of tamoxifen. By this approach, we were able to study long-term effects on myometrial functions that are necessary for parturition as well as gap junction intercellular communication in primary myometrial cell cultures. We found a prolongation of the pregnancy in 82% of tamoxifen-treated Cx43fl/fl:SM-CreERT2 mice as well as decreased dye coupling in cultured primary myocytes of these animals. Other parturition-specific parameters such as the regulation of oxytocin receptor, prostaglandin F receptor or progesterone remained unchanged. Our results indicate the important function of Cx43 during parturition in the living animal and suggest further strategies to investigate the role of connexins in uterine contractility in transgenic mice.

Animals↗

PubMed2006

Connexin30.2 containing gap junction channels decelerate impulse propagation through the atrioventricular node.

In the mammalian heart, gap junction channels between electrically coupled cardiomyocytes are necessary for impulse propagation and coordinated contraction of atria and ventricles. Recently, mouse connexin30.2 (Cx30.2) was shown to be expressed in the cardiac conduction system, predominantly in sinoatrial and atrioventricular (AV) nodes. The corresponding gap junctional channels expressed in HeLa cells exhibit the lowest unitary conductance (9 pS) of all connexin channels. Here we report that Cx30.2 slows down the propagation of excitation through the AV node. Mice expressing a LacZ reporter gene instead of the Cx30.2 coding region (Cx30.2(LacZ/LacZ)) exhibit a PQ interval that is approximately 25% shorter than in WT littermates. By recording atrial, His, and ventricular signals with intracardiac electrodes, we show that this decrease is attributed to significantly accelerated conduction above the His bundle (atrial-His interval: 27.9 +/- 5.1 ms in Cx30.2(LacZ/LacZ) versus 37.1 +/- 4.1 ms in Cx30.2(+/+) mice), whereas HV conduction is unaltered. Atrial stimulation revealed an elevated AV-nodal conduction capacity and faster ventricular response rates during induced episodes of atrial fibrillation in Cx30.2(LacZ/LacZ) mice. Our results show that Cx30.2 contributes to the slowdown of impulse propagation in the AV node and additionally limits the maximum number of beats conducted from atria to ventricles. Thus, it is likely to be involved in coordination of atrial and ventricular contraction and to fulfill a protective role toward pathophysiological states such as atrial tachyarrhythmias (e.g., atrial fibrillation) by preventing rapid conduction to the ventricles potentially associated with hemodynamic deterioration.

Animals↗

PubMed2006

Spatiotemporal distribution of Connexin45 in the olivocerebellar system.

The olivocerebellar system is involved in the transmission of information to maintain sensory motor coordination. Gap junctions have been described in various types of neurons in this system, including the neurons in the inferior olive that provide the climbing fibers to Purkinje cells. While it is well established that Connexin36 is necessary for the formation of these neuronal gap junctions, it is not clear whether these electrical synapses can develop without Connexin45. Here we describe the development and spatiotemporal distribution of Connexin45 in relation to that of Connexin36 in the olivocerebellar system. During development Connexin45 is expressed in virtually all neurons of the inferior olive and cerebellar nuclei. During later postnatal development and adulthood there is a considerable overlap of expression of both connexins in subpopulations of all main olivary nuclei and cerebellar nuclei as well as in the stellate cells in the cerebellar cortex. Despite this prominent expression of Connexin45, ultrastructural analysis of neuronal gap junctions in null-mutants of Connexin45 showed that their formation appears normal in contrast to that in knockouts of Connexin36. These morphological data suggest that Connexin45 may play a modifying role in widely distributed, coupled neurons of the olivocerebellar system, but that it is not essential for the creation of its neuronal gap junctions.

Age Factors↗

PubMed2006

Connexin31 cannot functionally replace connexin43 during cardiac morphogenesis in mice.

In the gastrulating mouse embryo, the gap junction protein connexin43 is expressed exclusively in cells derived from the inner cell mass, whereas connexin31 is expressed in cells of the trophoblast lineage. Since connexin43 and connexin31 do not form heterotypic gap junction channels in exogenous expression systems, such as HeLa cells and Xenopus oocytes, previous studies have suggested that the incompatibility of these two connexins could contribute to the separation of connexin43-expressing and connexin31-expressing compartments between embryo and extraembryonic tissues at gastrulation, respectively. Thus, we have generated connexin43 knock-in connexin31 mice, in which the coding region of the connexin43 gene was replaced by that of connexin31. Interbreeding of heterozygous connexin43 knock-in connexin31 mice resulted in homozygous connexin43 knock-in connexin31 mice, but none of them survived to adulthood. As these mice were born at the expected Mendelian frequency, we conclude that the reported incompatibility of connexin43 and connexin31 to form heterotypic gap junction channels does not interfere with normal embryonic development. Neonatal homozygous connexin43 knock-in connexin31 hearts showed malformation in the subpulmonary outlet of the right ventricle, similar to general connexin43-deficient mice. Electrocardiograms of neonatal hearts in homozygous connexin43 knock-in connexin31 mice revealed significantly low voltage of the QRS complex. This is in contrast to previous results from our laboratory which showed that replacement of connexin43 by connexin40 resulted in morphologically and functionally normal hearts. We conclude that connexin31 cannot functionally replace connexin43 during cardiac morphogenesis.

Animals↗

PubMed2006

Connexin43-dependent mechanism modulates renin secretion and hypertension.

To investigate the function of Cx43 during hypertension, we studied the mouse line Cx43KI32 (KI32), in which the coding region of Cx32 replaces that of Cx43. Within the kidneys of homozygous KI32 mice, Cx32 was expressed in cortical and medullary tubules, as well as in some extra- and intraglomerular vessels, i.e., at sites where Cx32 and Cx43 are found in WT mice. Under such conditions, renin expression was much reduced compared with that observed in the kidneys of WT and heterozygous KI32 littermates. After exposure to a high-salt diet, all mice retained a normal blood pressure. However, whereas the levels of renin were significantly reduced in the kidneys of WT and heterozygous KI32 mice, reaching levels comparable to those observed in homozygous littermates, they were not further affected in the latter animals. Four weeks after the clipping of a renal artery (the 2-kidney, 1-clip [2K1C] model), 2K1C WT and heterozygous mice showed an increase in blood pressure and in the circulating levels of renin, whereas 2K1C homozygous littermates remained normotensive and showed unchanged plasma renin activity. Hypertensive, but not normotensive, mice also developed cardiac hypertrophy. The data indicate that replacement of Cx43 by Cx32 is associated with decreased expression and secretion of renin, thus preventing the renin-dependent hypertension that is normally induced in the 2K1C model.

Animals↗