Abstract 1372: Characterization Of The Rejuvenation Of Cardiac Sympathetic Nerves In Cardiac Hypertrophy
Background: Cardiac hypertrophy induces the fetal isoform of genes (rejuvenation), including contractile proteins, ion channels, and natriuretic peptides. Cardiac sympathetic nerve function is known to be altered in cardiac hypertrophy and congestive heart failure. We recently reported that alteration of cardiac sympathetic nerves (CSN) was caused by their rejuvenation (Circ Res, 2007). The present study was designed to examine the precise characterization of the rejuvenation of CSN in cardiac hypertrophy.
Methods and Results:
RV hypertrophy was produced by consistent hypoxia (10% O2) in C57/BL6 mice. RV pressure increased to 47 mmHg, and RV/(body weight) ratio increased by 1.6 fold.
Nerve growth factor protein was augmented in hypertrophic RV, but was unchanged in LV.
Double-transgenic mice, which specifically express eGFP (enhanced green fluorescent protein) in the sympathetic neurons, was generated by crossing dopamine β-hydroxylase (DBH)-Cre mice with Floxed-eGFP mice.
The eGFP-positive CSN were markedly increased in hypertrophic RV, but not in LV. Nerve density, quantitated by immunostained area with eGFP and GAP43 (growth-associated corn marker), increased by 8.1 and 9.3 fold, respectively, in RV, but not in LV. (4) Catecholamine content was attenuated in RV. (5) Western blot revealed that tyrosine hydroxylase was markedly down-regulated in RV. (6) Immunostaining clearly demonstrated that the immature neuron markers, PSA-NCAM (highly polysialylated neural cell adhesion molecule) and Ulip-1 (Unc-33-like phosphoprotein 1), were expressed in CSN in hypertrophic RV and stellate ganglia. Basic helix-loop-helix transcription factor, Mash-1 (mammalian achaete-scute complex homolog 1) was strongly expressed in the stellate ganglia. (7) Immature neuron marker-immunopositive cells in stellate ganglia had a markedly decreased TH expression.
Conclusion: The rejuvenated CSN showed various immature and fetal neuron marker genes at not only the peripheral axons but also the cellular bodies at the stellate ganglia. Rejuvenation of CSN might be critically involved in the alteration of sympathetic neuronal function in cardiac hypertrophy, including depressed norepinephrine synthesis and hyperinnervation.