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Background/Aims: Aberrant vascular smooth muscle cell (VSMC) proliferation plays an important role in the development of pulmonary artery hypertension (PAH). Dysregulated microRNAs (miRNAs, miRs) have been implicated in the progression of PAH. miR-222 has a pro-proliferation effect on VSMCs while it has an anti-proliferation effect on vascular endothelial cells (ECs). As the biological function of a single miRNA could be cell-type specific, the role of miR-222 in pulmonary artery smooth muscle cell (PASMC) proliferation is not clear and deserves to be explored. Methods: PASMCs were transfected with miR-222 mimic or inhibitor and PASMC proliferation was determined by Western blot for PCNA, Ki-67 and EdU staining and cell number counting. The target genes of miR-222 including P27 and TIMP3 were determined by luciferase assay and Western blot. In addition, the functional rescue experiments were performed based on miR-222 inhibitor and siRNAs to target genes. Results: miR-222 mimic promoted PASMC proliferation while miR-222 inhibitor decreased that. TIMP3 was identified to be a direct target gene of miR-222 based on luciferase assay. Meanwhile, P27 and TIMP3 were up-regulated by miR-222 inhibitor and down-regulated by miR-222 mimic. Moreover, P27 siRNA and TIMP3 siRNA could both attenuate the anti-proliferation effect of miR-222 inhibitor in PASMCs, supporting that P27 and TIMP3 are at least partially responsible for the regulatory effect of miR-222 in PASMCs. Conclusion: miR-222 promotes PASMC proliferation at least partially through targeting P27 and TIMP3. [ABSTRACT FROM AUTHOR]

Background: MicroRNAs play a crucial role in the regulation of pathological cardiac remodeling and heart failure. Previously, we found that overexpression of miR-221 induces heart failure in mice. The miR-222 and miR-221 share the same gene cluster, however, the role of miR-222 in the regulation of cardiac function remained ill-defined. Methods and Results: Transgenic mice with cardiac-specific expression of miR-222 (Tg-miR-222) mice were generated. The Tg-miR-222 mice developed significantly enlarged hearts at 4 weeks of age. Transthoracic echocardiograph data indicated that the hearts of Tg-miR-222 mice exhibited an increased left ventricular end-diastolic internal diameter and decreased fractional shortening. We observed that the LC3-II in Tg-miR-222 mice was decreased accompanied with the upregulation of p62, indicating the autophagy inhibition in the hearts of Tg-miR-222 mice. The mTOR pathway, a negative regulator of autophagy, was activated in the hearts of Tg-miR-222 mice. The expression of p27 was downregulated by miR-222 overexpression. Conclusion: Our data indicate that miR-222 overexpression induces heart failure in mice. The downregulation of p27 and the activation of mTOR pathway may be involved in miR-222-induced heart failure and autophagy inhibition. Thus, targeting miR-222 expression may be a therapeutic strategy against pathological cardiac remodeling. [ABSTRACT FROM AUTHOR]