Disease relevance of Gja5

• Using electrocardiographic analysis, we show that Cx40 null mice have cardiac conduction abnormalities characteristic of first-degree atrioventricular block with associated bundle branch block [1].
• CONCLUSIONS: Our data show that (1) in mice, a continuity exists between the common bundle and the septum, and (2) Cx40 deficiency results in right bundle-branch block and impaired left bundle-branch conduction [2].
• The atria showed only mild fibrosis, with heterogeneously disturbed Cx40 and Cx43 expression [3].
• In Cx40-/- mice resulting from crossing of Cx40+/- mice, the most common cardiac malformations were double-outlet right ventricle (DORV), TOF, and endocardial cushion defects [4].
• CONCLUSION: A homozygous disruption of Cx40 results in prolonged AV conduction parameters due to abnormal electrical coupling in the specialized conduction system, which may also predispose to arrhythmia vulnerability [5].

High impact information on Gja5

• The specific effects of Cx40 deficiency on sinus node function, sinoatrial, and atrioventricular conduction properties as well as on atrial vulnerability have not yet been investigated systematically by electrophysiological analysis [6].
• In atrial myocardium of the mouse, Cx40 deficiency results in increased atrial vulnerability and might contribute to arrhythmogenesis [6].
• Further, we demonstrate that Tbx5 exerts in part its key regulatory role in bone growth and maturation by controlling via Cx40 the expression of Sox9 (a transcription factor essential for chondrogenesis and skeleton growth) [7].
• We demonstrate that mice deficient in connexin 40 (Cx40), a Tbx5-regulated gap junction component, shared axial and appendicular skeletal malformations with Tbx5(+/Delta) mice [7].
• Our study strongly suggests that Cx40 deficiency accounts for many skeletal malformations in HOS and that Tbx5 regulation of Cx40 plays a critical role in the exquisite developmental patterning of the forelimbs and sternum [7].

Biological context of Gja5

• The mutation was mapped to chromosome 3 between the markers D3Mit101 and D3Mit77 near the connexin encoding genes Gja5 and Gja8 [8].
• In order to exclude cross reactions of the corresponding antibodies, retinae from targeted connexin-deficient mice (Cx31 -/-, Cx32 -/- and Cx40 -/-) were used as negative controls for immunoblot and immunofluorescence analyses of wild-type retina [9].
• Moreover, ablating different pairs of cardiac connexins results in distinct heart defects, suggesting both common and unique functions for Cx40, Cx43, and Cx37 during cardiac morphogenesis [10].
• Vasomotion was present in small arterioles of both genotypes, but its intensity was exaggerated in Cx40(-/-) mice [11].
• METHODS: To identify the factors involved in the cardiac expression of Cx40, we used transient transfections in mammalian cells coupled with electrophoretic mobility shift assays (EMSA) and RT-PCR [12].

Anatomical context of Gja5

• Deficiencies in the gap junction protein gene connexin 40 (Cx40), a downstream target of Tbx5, did not account for morphologic conduction system defects in Tbx5(del/+) mice [13].
• In diabetes, connexin 40 was expressed in smooth muscle cells along afferent arterioles, glomerular connexin staining was more extensive and connexin 43 was detected in renin-secreting cells [14].
• Both connexins 37 and 40 were expressed in extraglomerular mesangial cells, connexin 40 was abundantly expressed in intraglomerular mesangial cells, but connexin 37 was limited to mesangial cells at the vascular pole [14].
• The CO(2) sensitivity of transjunctional voltage ( V(j)) gating was studied by dual voltage clamp in oocytes expressing mouse Cx40 or its COOH terminus (CT)-truncated mutant (Cx40-TR) [15].
• Iontophoretic injection of Lucifer Yellow or neurobiotin into aortic endothelium of Cx40-deficient mice showed extensive intercellular transfer of neurobiotin but not of Lucifer Yellow [16].

Associations of Gja5 with chemical compounds

• We conclude that loss of Cx40 is associated with hypertension independent of the action of angiotensin II [17].
• Conversely, the angiotensin AT(1)-receptor antagonist, candesartan, decreased pressure to similar extents in Cx40(-/-) and wild-type mice [17].
• However, spreading was severely attenuated in Cx40(-/-) animals (11+/-4% versus 35+/-7% with ACh and 38+/-5% versus 60+/-7% with Bk in Cx40(-/-) and Cx40(+/+), respectively; P<0.05) [11].
• There was a 27-fold reduction in biocytin transfer in embryonic Cx40-/- aortic endothelium, a much larger change than in aortas of 6-7-week-old Cx40-/- animals, which showed a 3.5-fold reduction [18].
• Replacement of two unique glutamate residues, E9 and E13, from the cytoplasmic amino terminal domain of Cx40 with the corresponding lysine residues from Cx43 eliminated the block by 2 mm spermine, reduced the transjunctional voltage (V(j)) gating sensitivity, and reduced the unitary conductance of this Cx40E9,13K gap junction channel protein [19].

Regulatory relationships of Gja5

• Apparently, Cx40-deficient endothelial cells upregulate and redistribute Cx37 as a molecular adaptation to the lack of Cx40 [16].
• NKX2.6 was inactive at ANF but weakly activated transcription of a Cx40 promoter, whereas the F151L mutant lacked this activity [20].

Other interactions of Gja5

• We conclude that Tbx5 is required for Cx40-independent patterning of the cardiac conduction system, and suggest that the electrophysiologic defects in Holt-Oram syndrome reflect a developmental abnormality of the conduction system [13].
• Sequence analysis revealed no differences in the Gja5 gene, but identified a T-->C mutation at position 191 in the Gja8 gene, which was confirmed by an additional Mva 12691 restriction site in the genomic DNA of homozygous mutants [8].
• The expression of Cx31.1 and Cx40 was examined by confocal immunofluorescence microscopy; whereas both could be detected in compacting embryos, only Cx31.1 could be seen in punctate membrane foci indicative of gap junctions [21].
• Lack of vascular connexin 40 is associated with hypertension and irregular arteriolar vasomotion [17].
• Mutagenesis of the Nkx2-5 core site in the Cx40 promoter led to significantly decreased activity in rat smooth muscle cell line A7r5 [12].

Analytical, diagnostic and therapeutic context of Gja5

• As shown by electron microscopy, gap junctions in Cx40-deficient endothelium were morphologically different from those of wild-type vessels [16].
• Cx40 immunohistochemistry on HF-1b tissue-restricted knockouts revealed a requirement for HF-1b in the cardiomyogenic lineage [22].
• Western blots indicated that LPS treatment also caused a reduction in endothelial connexin40 (Cx40) levels to 33% of control levels [23].
• On ECG, the P wave was significantly prolonged in Cx40(-/-) mice (13.4+/-0.5 versus 11.4+/-0.3 ms in Cx40(+/+)) [24].
• We investigated the distribution patterns of the major vascular gap junction proteins in the murine kidney by immunofluorescence staining of frozen sections, and connexin40 (Cx40) was the most prominent connexin detected [25].

References