Angiotensin II (Ang II), an effective component of renin-angiotensin system, plays a pivotal role in cardiac fibrosis, which may further contribute to heart failure. Single-stranded DNA-binding protein 1 (SSBP1), a DNA damage response protein, regulates both mitochondrial function and extracellular matrix remodeling. In this study, we aim to investigate the role of SSBP1 in cardiac fibrosis that is induced by Ang II. We infused C57BL/ 6J mice with vehicle or Ang II and valsartan using implanted osmotic mini-pumps. Moreover, heart function was examined by echocardiography and cardiac fibrosis was analyzed via picrosirus red staining. The expression of COL1A1, COL3A1, SSBP1, p53, Nox1, and Nox4 was analyzed via qRT-PCR and/or immunoblots. The SSBP1 expression was manipulated via SSBP1 shRNA and pcDNA3.1/SSBP1 plasmids, while the p53 expression was enhanced via AdCMV-p53 infection. The exposure to Ang II increased the mouse heart weight, systolic blood pressure, interventricular septal thickness diastolic (IVSTD) and left ventricular end posterior wall dimension diastolic (LVPWD), which were counteracted by valsartan. While cardiac fibrosis was induced with Ang II treatment, it was relieved using valsartan. Furthermore, Ang II treatment caused mitochondrial dysfunction, oxidative stress, and down-regulated SSBP1 expression. The knockdown of SSBP1 increased cardiac fibroblast proliferation, collagen expression, and decreased p53 expression, which was impeded via SSBP1 overexpression. Moreover, the forced expression of p53 abated the fibroblast proliferation and collagen expression that was induced by Ang II. To summarize, SSBP1 was down-regulated by Ang II and implicated in cardiac fibroblast proliferation and collagen expression partly via the p53 protein.

Chromosomal maintenance 1 (CRM1) inhibitors display antihypertrophic effects and control protein trafficking between the nucleus and the cytoplasm. PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1alpha) is a type of transcriptional coactivator that predominantly resides in the nucleus and is downregulated during heart failure. NT-PGC-1α is an alternative splicing variant of PGC-1α that is primarily distributed in the cytoplasm. We hypothesized that the use of a CRM1 inhibitor could shuttle NT-PGC-1α into the nucleus and activate PGC-1α target genes to potentially improve cardiac function in a mouse model of myocardial infarction (MI). We showed that PGC-1α and NT-PGC-1α were decreased in MI-induced heart failure mice. Phenylephrine and angiotensin II were applied to induce hypertrophy in neonatal rat ventricular myocytes (NRVMs). The antihypertrophic effects of the CRM1-inhibitor Selinexor was verified through profiling the expression of β-MHC and through visualizing the cell cross-sectional area. NRVMs were transfected with adenovirus-NT-PGC-1α or adenovirus-NLS (nucleus localization sequence)-NT-PGC-1α and then exposed to Selinexor. Confocal microscopy was then used to observe the shuttling of NT-PGC-1α. After NT-PGC-1α was shuttled into the nucleus, there was increased expression of its related genes, including PPAR-α, Tfam, ERR-γ, CPT1b, PDK4, and Nrf2. The effects of Selinexor on post-MI C57BL/6j mice were determined by echocardiography and qPCR. We found that Selinexor showed antihypertrophic effects but did not influence the ejection fraction of MI-mice. Interestingly, the antihypertrophic effects of Selinexor might be independent of NT-PGC-1α transportation.