Epithelial -mesenchymal transition (EMT) is an important mechanism of cardiac fibrosis after myocardial infarction (MI). However, it remains unclear whether Snail1, an important regulator of EMT, is involved in cardiac fibrosis. In this study, we explored the expression patterns of Snail1 and a cardiac fibrosis markerperiostin-after MI in mice and then investigated the coexpression between Snail1 and periostin after MI in mice. Our results showed that the mRNA and protein levels of Snail1 and periostin were significantly increased in the infarct area. The Snail1 expression pattern appeared to be parabolic within 14 days after MI. In addition, after MI, all Snail1-positive cells were able to express periostin. These results indicate that Snail1 is mainly activated in the infarct area and is involved in de novo cardiac fibrosis after MI in mice. Thus, it is a potential molecular target in the development of drug interventions for ventricular remodeling after MI.

The activity of pacemaker cells in the sinoatrial node (SAN) is an indicator of normal sinus rhythm. Clinical studies have revealed that the dysfunction of the SAN progressively increases with aging. In this study, we determined the changes in hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) expression and the relationship between aging and canine SAN dysfunction. The results of cardiac electrophysiological determination revealed that the intrinsic heart rate decreased from 168 ± 11 beats min −1 in young canines to 120 ± 9 beats min −1 in adults and to 88 ± 9 beats min −1 in aged canines. The sinus node recovery time (SNRT) increased from 412 ± 32 ms in young canines to 620 ± 56 ms in adults and to 838 ± 120 ms in aged canines. Corrected SNRT (CSNRT) increased from 55 ± 12 ms in young canines to 117 ± 27 ms in adults and to 171 ± 37 ms in aged canines. These results indicated that SAN function deteriorated with aging in the canine heart. However, histological staining illustrated that fibrosis was not significantly increased with aging in canine SAN. Real-time polymerase chain reaction indicated that the expression of HCN4 mRNA was downregulated in the elderly canine SAN. Similarly, we also verified that HCN4 protein expression within the SAN declined with aging via immunofluorescence staining and western blot analysis. Taken together, our data show that electrical remodeling, related to the down-regulation of HCN4, is responsible for the gradually increased incidence of SAN dysfunction with aging. Our results provide further evidence for explaining the mechanisms of age-related deterioration in the SAN.

Whole-mount in situ hybridization (WISH) is a useful method for detecting specific gene expression patterns at their site of action during embryonic development. Traditional WISH methods are costly and suitable only for mouse embryos younger than 11.5 days. We present here an economical and practical in situ hybridization method using DIG-labeled RNA probes. We changed the conditions in several steps to make the WISH method suitable for whole mouse embryos from embryonic days 9.5 to 12.5 and for older stage mouse embryonic organs. We performed all steps in one microcentrifuge tube up to the staining steps to avoid losing or damaging the mouse embryos. We re-used the solutions and materials to make the method more economical and suitable for less sophisticated laboratories. We also performed β-galactosidase staining on Tb × 18 Cre/Rosa26/LacZ mouse embryos; the results agreed with the in situ hybridization results. Finally, we sectioned the specimens after hybridization and β-galactosidase staining; the results agreed with the literature.

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