Phenotypic Switching of Atherosclerotic Smooth Muscle Cells is Regulated by Activated PARP1-Dependent TET1 Expression

C/EBPβ-Lin28a positive feedback loop triggered by C/EBPβ hypomethylation enhances the proliferation and migration of vascular smooth muscle cells in restenosis

BACKGROUND

The main cause of restenosis after percutaneous transluminal angioplasty (PTA) is the excessive proliferation and migration of vascular smooth muscle cells (VSMCs). Lin28a has been reported to play critical regulatory roles in this process. However, whether CCAAT/enhancer-binding proteins β (C/EBPβ) binds to the Lin28a promoter and drives the progression of restenosis has not been clarified. Therefore, in the present study, we aim to clarify the role of C/EBPβ-Lin28a axis in restenosis.

METHODS

Restenosis and atherosclerosis rat models of type 2 diabetes (n  =  20, for each group) were established by subjecting to PTA. Subsequently, the difference in DNA methylation status and expression of C/EBPβ between the two groups were assessed. EdU, Transwell, and rescue assays were performed to assess the effect of C/EBPβ on the proliferation and migration of VSMCs. DNA methylation status was further assessed using Methyltarget sequencing. The interaction between Lin28a and ten-eleven translocation 1 (TET1) was analysed using co-immunoprecipitation (Co-IP) assay. Student's t-test and one-way analysis of variance were used for statistical analysis.

RESULTS

C/EBPβ expression was upregulated and accompanied by hypomethylation of its promoter in restenosis when compared with atherosclerosis. In vitroC/EBPβ overexpression facilitated the proliferation and migration of VSMCs and was associated with increased Lin28a expression. Conversely, C/EBPβ knockdown resulted in the opposite effects. Chromatin immunoprecipitation assays further demonstrated that C/EBPβ could directly bind to Lin28a promoter. Increased C/EBPβ expression and enhanced proliferation and migration of VSMCs were observed after decitabine treatment. Further, mechanical stretch promoted C/EBPβ and Lin28a expression accompanied by C/EBPβ hypomethylation. Additionally, Lin28a overexpression reduced C/EBPβ methylation via recruiting TET1 and enhanced C/EBPβ-mediated proliferation and migration of VSMCs. The opposite was noted in Lin28a knockdown cells.

CONCLUSION

Our findings suggest that the C/EBPβ-Lin28a axis is a driver of restenosis progression, and presents a promising therapeutic target for restenosis.

Effects of endoplasmic reticulum stress on erectile function in rats with cavernous nerve injury

Background

Erectile dysfunction (ED) occurs in an increasing number of patients after radical prostatectomy and cystectomy, and the phenotypic modulation of corpus cavernosum smooth muscle cells is closely related to ED.

Aim

To determine whether endoplasmic reticulum stress (ERS) is implicated in the phenotypic modulation of ED induced by bilateral cavernous nerve injury (BCNI).

Methods

In total, 36 Sprague-Dawley rats were randomly divided into 3 groups: sham, in which rats received sham surgery with bilateral cavernous nerve exposure plus phosphate-buffered saline; control, in which rats received BCNI plus phosphate-buffered saline; and experimental, in which rats received BCNI plus 4-phenylbutyric acid. Analysis of variance and a Bonferroni multiple-comparison test were utilized to evaluate differences among groups.

Outcomes

Erectile function, smooth muscle/collagen ratios, and the expression levels of phenotypic modulation and ERS were measured.

Results

Two ratios-maximum intracavernosal pressure/mean arterial pressure and smooth muscle/collagen-were decreased in the control group as compared with the sham group. In penile tissue, there was increased expression of GRP78 (78-kDa glucose-regulated protein), p-PERK/PERK (phosphorylated protein kinase R-like endoplasmic reticulum kinase/protein kinase R-like endoplasmic reticulum kinase), caspase 3, CHOP (C/EBP homologous protein), and OPN (osteopontin) but decreased expression of nNOS (neuronal nitric oxide synthase) and α-SMA (α-smooth muscle actin). As compared with the control group, erectile function was improved and pathologic changes were partially recovered in the experimental group.

Clinical Translation

The present study demonstrated that ERS is involved in ED caused by cavernous nerve injury, thereby providing a new target and theoretical basis for clinical treatment.

Strengths and Limitations

The present study demonstrated for the first time that ERS is related to ED caused by cavernous nerve injury. Inhibition of ERS reverses phenotypic modulation and improves erectile function in rats with BCNI. Additional in vitro studies should be performed to verify these conclusions and explore the specific mechanism of phenotypic modulation.

Conclusion

The present study demonstrated that inhibiting ERS reverses phenotypic modulation and enhances erectile function in rats with BCNI.

Minocycline Counteracts Ectopic Calcification in a Murine Model of Pseudoxanthoma Elasticum: A Proof-of-Concept Study

Pseudoxanthoma elasticum (PXE) is an intractable Mendelian disease characterized by ectopic calcification in skin, eyes and blood vessels. Recently, increased activation of the DNA damage response (DDR) was shown to be involved in PXE pathogenesis, while the DDR/PARP1 inhibitor minocycline was found to attenuate aberrant mineralization in PXE cells and zebrafish. In this proof-of-concept study, we evaluated the anticalcifying properties of minocycline in Abcc6^−/− mice, an established mammalian PXE model. Abcc6^−/− mice received oral minocycline supplementation (40 mg/kg/day) from 12 to 36 weeks of age and were compared to untreated Abcc6^−/− and Abcc6^+/+ siblings. Ectopic calcification was evaluated using X-ray microtomography with three-dimensional reconstruction of calcium deposits in muzzle skin and Yasue’s calcium staining. Immunohistochemistry for the key DDR marker H2AX was also performed. Following minocycline treatment, ectopic calcification in Abcc6^−/− mice was significantly reduced (−43.4%, p < 0.0001) compared to untreated Abcc6^−/− littermates. H2AX immunostaining revealed activation of the DDR at sites of aberrant mineralization in untreated Abcc6^−/− animals. In conclusion, we validated the anticalcifying effect of minocycline in Abcc6^−/− mice for the first time. Considering its favorable safety profile in humans and low cost as a generic drug, minocycline may be a promising therapeutic compound for PXE patients.

Minocycline attenuates excessive DNA damage response and reduces ectopic calcification in pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a hereditary ectopic calcification disorder affecting the skin, eyes and blood vessels. Recently, the DNA damage response (DDR), in particular poly(ADP-ribose) polymerase 1 (PARP1), was shown to be involved in aberrant mineralization raising the hypothesis that excessive DDR/PARP1 signaling also contributes to PXE pathogenesis. Using PXE patient and control fibroblasts, (lesional) skin tissue and abcc6a^-/- zebrafish, we performed expression analysis of DDR/PARP1 targets with QRT-PCR, western blot, immunohistochemistry and enzyme activity assays; before and after treatment with the PARP1 inhibitor minocycline. PARP1 and the ATM-p21-p53 axis was found to be significantly increased in PXE. Additionally, PARP1 downstream targets IL-6, STAT1/3, TET1 and RUNX2 were upregulated while the RUNX2-antagonist microRNA-204 was decreased. In PXE fibroblasts, DDR/PARP1 signaling increased with advancing ectopic calcification. Minocycline treatment attenuated DDR/PARP1 overexpression and reduced aberrant mineralization in PXE fibroblasts and abcc6a^-/- zebrafish. In summary, we demonstrated the involvement of excessive DDR/PARP1 signaling in PXE pathophysiology, identifying a STAT-driven cascade resulting in increased expression of the epigenetic modifier TET1 and pro-calcifying transcription factor RUNX2. Minocycline attenuated this deleterious molecular mechanism and reduced ectopic calcification both in vitro and in vivo, fueling the exciting prospect of a novel therapeutic compound for PXE.