Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C41
Nav1.5 deficiency triggered TGF-β1-mediated fibrosis as a key mechanism producing sinus node dysfunction associated with Scn5a disruption and aging in mice
X. Hao1, Y. Zhang2, X. Zhang3, M. Nirmalan1, L. Davies1, D. Konstantinou1, F. Yin1, H. Dobrzynski1, X. Wang4, A. Grace2, H. Zhang3, M. Boyett1, C. L. Huang2, M. Lei1
1. Manchester, Univ Manchester, Manchester, United Kingdom. 2. Departments of Biochemistry and Physiology, University of Cambridge, Cambridge, United Kingdom. 3. School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom. 4. Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
Mutations in the cardiac Na+ channel gene (SCN5A) can adversely affect electrical function in the heart but effects can be age-dependent (Lei et al. 2007). We explored for interacting effects of Scn5a-disruption and aging on the pathogenesis of sinus node dysfunction (SND) in a heterozygous Scn5a knockout (Scn5a+/-) mouse model. We compared in vivo and ex vivo electrical functional, histological and molecular features in young (3-4 month) and old (1 year) wild type and Scn5a+/- mice. In vivo senatorial node (SAN) electrophysiological studies in anaesthetized animals with intraperitoneal injection of 2,2,2-Tribromoethanol (250 mg/kg). ECG was recorded using subcutaneous electrodes with connection to Powerlab 26T system using the Chart v6.0 program (AD Instruments). Both Scn5a-disruption and aging were associated with decreased heart rate variability, reduced sinoatrial node (SAN) automaticity and slowed sinoatrial conduction. Thus, both aging and Scn5a-disruption significantly prolonged both intrinsic cycle length (CL) (CL in ms: young WT, 164±8, n=5; young Scn5a+/−, 211±12, n=7; old WT, 231±25, n=8; old Scn5a+/−, 321±30, n=7) and sinoatrial conduction time (SACT) (SACT in ms: young WT, 8.0± 0.5, n=5; young Scn5a+/−, 11.4±0.7, n=7; old WT, 12.0±1.1, n=8; old Scn5a+/−, 21.9±1.9, n=7). Furthermore, these effects interacted to produce the greatest functional changes in the old Scn5a+/− hearts (CL: Scn5a+/− vs. WT, P =0.005; old vs. young, P<0.001. SACT: Scn5a+/− vs. WT, P<0.001; old vs. young, P<0.001. Interaction of the two effects, P = 0.04). They also led to increased collagen and fibroblast levels and up-regulated TGF-β1 and vimentin transcripts providing measures of fibrosis, and reduced Nav1.5 expression. All these effects were most noticeable in old Scn5a+/- mice. Na+ channel inhibition by E3-Nav1.5 antibody directly increased TGF-β1 production in both cultured human cardiac myocytes and fibroblasts. Finally, aging was associated with down-regulation of a wide range of ion channel and related transcripts, again greatest in old Scn5a+/- mice. The quantitative results from these studies permitted computer simulations that successfully replicated the observed SAN phenotypes shown by the different experimental groups. These results implicate a tissue degeneration, triggered by Nav1.5-deficiency, manifesting as a TGF-β1 mediated fibrosis accompanied by electrical remodelling, in the SND associated with Scn5a-disruption or aging. The latter effects interact to produce the most severe phenotype in old Scn5a+/- mice. In demonstrating this, our findings suggest a novel regulatory role for Nav1.5 in cellular biological processes additional to its electrical function.
Where applicable, experiments conform with Society ethical requirements