Injection of Matrix Metalloproteinase-9 Leads to Ventricular Remodeling.

Objective: Previous studies have found that some ventricular remodeling is accompanied by increased matrix metalloproteinase-9 (MMP-9) in vivo, and MMP-9 inhibitors can reduce ventricular remodeling. However, there is still no direct evidence that MMP-9 causes ventricular remodeling. In this study, MMP-9 was injected into rats to observe whether MMP-9 caused ventricular remodeling, thereby providing direct evidence of MMP-9-induced ventricular remodeling. Methods: Forty-eight eight-week-old male Wistar rats were randomly divided, by weight, into control, low-, medium-, and high-dose MMP-9 groups and were administered normal saline or recombinant rat MMP-9 0.7, 1.4, or 2.1 ng/g, respectively, via intraperitoneal injection, twice per week. On the 28th day, six rats were randomly selected from each group (Stage I). The remaining rats continued receiving injections until the 56th day (Stage II). Echocardiography was performed to observe cardiac structure and function, and the left ventricular mass index (LVWI) was calculated. Myocardial pathological changes and the collagen volume fraction (CVF) were observed by HE and VG staining in myocardial tissue. MMP-9 levels in serum were tested using ELISA. Myocardial MMP-9 levels were measured using Western blots, and the myocardial expression levels of MMP-9 mRNA were assessed using RT-PCR. Results: During Stage I, serum MMP-9 and myocardial MMP-9 mRNA levels are increased; hypertrophic cardiomyocytes, disorderly arrangement of fibers, and endochylema dissolution are observed in the medium- and high-dose groups. The left ventricular weight index (LVWI) and myocardial MMP-9 increased, and the collagen volume fraction (CVF) reduced in the high-dose group. In Stage II, the left ventricular end-diastolic volume (LVEDV) and diameter (LVIDd) are higher, and CVF decreased in the medium- and high-dose groups. Myocardial pathological lesions intensified. Serum MMP-9 in the model groups and myocardial MMP-9 in the medium- and high-dose groups are increased. Conclusions: Injection of MMP-9 can lead to ventricular remodeling.

Ox-LDL Aggravates the Oxidative Stress and Inflammatory Responses of THP-1 Macrophages by Reducing the Inhibition Effect of miR-491-5p on MMP-9.

Background: Oxidized low-density lipoprotein (ox-LDL) can induce oxidative stress and inflammatory responses in macrophages to facilitate the genesis and development of atherosclerosis. However, the intermediate links remain unclear. MiR-491-5P can inhibit matrix metalloproteinase 9 (MMP-9); however, it remains unclear whether ox-LDL enhances MMP-9 expression and aggravates the oxidative stress and inflammatory responses under the mediating effect of miR-491-5P. Method: THP-1 macrophages were divided into 10 groups: blank (control), model (ox-LDL), miR-491-5P high-expression (miR-491-5P mimic), miR-491-5P control (mimic-NC), MMP-9 high-expression (MMP-9-plasmid), MMP-9 control (plasmid-NC), miR-491-5P+plasmid-NC, miR-491-5P+ MMP-9-plasmid, MMP-9 gene silencing (MMP-9-siRNA), and gene silencing control (siRNA-NC). The cells were transfected for 48 h and then treated with 50 µg/mL of ox-LDL for 24 h. MMP-9 mRNA and miR-491-5P expression levels in the cells were detected using reverse transcription-quantitative polymerase chain reaction, and the MMP-9 levels were detected with western blotting. The levels of oxidative stress factors (malondialdehyde [MDA]), reactive oxygen species (ROS), and antioxidant factors (superoxide dismutase [SOD]), and the expression levels of inflammatory factors (tumor necrosis factor [TNF-α] and interleukin-1ß and-6 [IL-1ß and IL-6]) in the supernatant were detected with enzyme-linked immunosorbent assay. Results: MDA, ROS, TNF-α, IL-1ß, IL-6, and MMP-9 levels were increased, SOD activity was reduced, and miR-491-5P expression was downregulated in the ox-LDL group compared to the control group. In the miR-491-5P mimic group, the MDA, ROS, TNF-α, IL-1ß, IL-6, MMP-9 mRNA and protein levels were downregulated, and SOD activity was enhanced compared to the ox-LDL group. MMP-9-plasmid elevated the MDA, ROS, TNF-α, IL-1ß, IL-6, MMP-9 mRNA and protein levels, and downregulated SOD activity and miR-491-5P expression. Following transfection with MMP-9-siRNA, the MMP-9-plasmid outcomes were nullified, and the resulting trends were similar to the miR-491-5p simulation group. Oxidative stress and inflammatory responses were higher in the miR-491-5P mimic+MMP-9-plasmid co-transfection group than in the miR-491-5P mimic group. Conclusion: Ox-LDL aggravates the oxidative stress and inflammatory responses of THP-1 macrophages by reducing the inhibition effect of miR-491-5p on MMP-9.