Diverse roles of microRNA-145 in regulating smooth muscle (dys)function in health and disease

N6-methyladenosine-driven miR-143/145-KLF4 circuit orchestrates the phenotypic switch of pulmonary artery smooth muscle cells

Pulmonary hypertension (PH) is characterized by vascular remodeling predominantly driven by a phenotypic switching in pulmonary artery smooth muscle cells (PASMCs). However, the underlying mechanisms for this phenotypic alteration remain incompletely understood. Here, we identified that RNA methyltransferase METTL3 is significantly elevated in the lungs of hypoxic PH (HPH) mice and rats, as well as in the pulmonary arteries (PAs) of HPH rats. Targeted deletion of Mettl3 in smooth muscle cells exacerbated hemodynamic consequences of hypoxia-induced PH and accelerated pulmonary vascular remodeling in vivo. Additionally, the absence of METTL3 markedly induced phenotypic switching in PASMCs in vitro. Mechanistically, METTL3 depletion attenuated m6A modification and hindered the processing of pri-miR-143/145, leading to a downregulation of miR-143-3p and miR-145-5p. Inhibition of hnRNPA2B1, an m6A mediator involved in miRNA maturation, similarly resulted in a significant reduction of miR-143-3p and miR-145-5p. We demonstrated that miR-145-5p targets Krüppel-like factor 4 (KLF4) and miR-143-3p targets fascin actin-bundling protein 1 (FSCN1) in PASMCs. The decrease of miR-145-5p subsequently induced an upregulation of KLF4, which in turn suppressed miR-143/145 transcription, establishing a positive feedback circuit between KLF4 and miR-143/145. This regulatory circuit facilitates the persistent suppression of contractile marker genes, thereby sustaining PASMC phenotypic switch. Collectively, hypoxia-induced upregulation of METTL3, along with m6A mediated regulation of miR-143/145, might serve as a protective mechanism against phenotypic switch of PASMCs. Our results highlight a potential therapeutic strategy targeting m6A modified miR-143/145-KLF4 loop in the treatment of PH.

Smooth muscle cells-specific loss of OCT4 accelerates neointima formation after acute vascular injury

Introduction

There is growing evidence that smooth muscle cell (SMC) phenotypic transitions play critical roles during normal developmental and tissue recovery processes and in pathological conditions such as atherosclerosis. However, the molecular mechanisms responsible for these transitions are not well understood. Recently, we found that the embryonic stem cell/induced pluripotent stem cell (iPSC) factor OCT4, which was believed to be silenced in somatic cells, plays an atheroprotective role in SMC, and regulates angiogenesis after corneal alkali burn and hindlimb ischemia by mediating microvascular SMC and pericyte migration. However, the kinetics of OCT4 activation in arterial SMC and its role in acute pathological conditions are still unknown.

Methods and Results

Here, using an Oct4-IRES-GFP reporter mouse model, we found that OCT4 is reactivated in the carotid artery 18 hours post-acute ligation-induced injury, a common in vivo model of the SMC phenotypic transitions. Next, using a tamoxifen-inducible Myh11-CreERT2 Oct4 knockout mouse model, we found that the loss of OCT4, specifically in SMC, led to accelerated neointima formation and increased tunica media following carotid artery ligation, at least in part by increasing SMC proliferation within the media. Bulk RNA sequencing analysis on the cultured SMC revealed significant down-regulation of the SMC contractile markers and dysregulation of the genes belonging to the regulation of cell proliferation and, positive and negative regulation for cell migration ontological groups following genetic inactivation of Oct4. We also found that loss of Oct4 resulted in suppression of contractile SMC markers after the injury and in cultured aortic SMC. Further mechanistic studies revealed that OCT4 regulates SMC contractile genes, ACTA2 and TAGLN, at least in part by direct binding to the promoters of these genes.

Conclusion

These results demonstrate that the pluripotency factor OCT4 is quickly activated in SMC after the acute vascular injury and inhibits SMC hyperproliferation, which may be protective in preventing excessive neointima formation.

Vascular smooth muscle cells specific deletion of angiopoietin-like protein 8 prevents angiotensin II-promoted hypertension and cardiovascular hypertrophy

AIMS

Angiopoietin-like protein 8 (ANGPTL8) plays important roles in lipid metabolism, glucose metabolism, inflammation, and cell proliferation and migration. Clinical studies have indicated that circulating ANGPTL8 concentrations are increased in patients with hypertension and positively associated with blood pressure. ANGPTL8 deficiency ameliorates blood pressure in mice treated with chronic intermittent hypoxia. Currently, little is known regarding the pathophysiological role of the vascular smooth muscle cell (VSMC)-derived ANGPTL8 in hypertension and hypertensive cardiovascular remodelling.

METHODS AND RESULTS

Circulating ANGPTL8 concentrations, as determined by enzyme-linked immunosorbent assay, were significantly higher in hypertensive patients than in controls (524.51 ± 26.97 vs. 962.92 ± 15.91 pg/mL; P < 0.001). In hypertensive mice [angiotensin II (AngII) treatment for 14 days] and spontaneously hypertensive rats, ANGPTL8 expression was increased and predominantly located in VSMCs. In AngII-treated mice, systolic and diastolic blood pressure in Tagln-Cre-ANGPTL8fl/fl mice were approximately 15-25 mmHg lower than that in ANGPTL8fl/fl mice. AngII-induced vascular remodelling, vascular constriction, and increased expression of cell markers of proliferation (PCNA and Ki67) and migration (MMP-2 and MMP-9) were strikingly attenuated in Tagln-Cre-ANGPTL8fl/fl mice compared with ANGPTL8fl/fl mice. Furthermore, the AngII-induced increase in the heart size, heart weight, heart/body weight ratio, cardiomyocyte cross-sectional area, and collagen deposition was ameliorated in Tagln-Cre-ANGPTL8fl/fl mice compared with ANGPTL8fl/fl mice. In rat artery smooth muscle cells, ANGPTL8-short hairpin RNA decreased intracellular calcium levels and prevented AngII-induced proliferation and migration through the PI3K-Akt pathway, as shown using LY294002 (inhibitor of PI3K) and Akt inhibitor VIII.

CONCLUSION

This study suggests that ANGPTL8 in VSMCs plays an important role in AngII-induced hypertension and associated cardiovascular remodelling. ANGPTL8 may be a novel therapeutic target against pathological hypertension and hypertensive cardiovascular hypertrophy.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

Enhanced Local Delivery of microRNA-145a-5P into Mouse Aorta via Ultrasound-Targeted Microbubble Destruction Inhibits Atherosclerotic Plaque Formation

Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) play a key role in the formation and rupture of atherosclerotic plaques. Previous studies have confirmed that microRNA-145 (miR-145) is involved in the phenotypic regulation of VSMCs and reduction of atherosclerosis. At present, seeking safe and effective gene delivery remains a key problem restricting the development of gene therapy. In recent years, ultrasound-targeted microbubble destruction (UTMD) has become a safe and effective transfection method that is widely used in the basic research of gene therapy for heart and tumor diseases. Here, we synthesized cationic microbubbles to encapsulate miR-145 and targeted their release into VSMCs in vitro and in vivo using ultrasound. The feasibility of this gene therapy was verified by fluorescence microscopy and an in vivo imaging system. The results showed that treatment with miR-145 delivered via UTMD considerably improved the gene transfection efficiency and promoted the contraction phenotype of VSMCs in vitro. In vivo, this treatment reduced the atherosclerotic plaque area by 48.04% compared with treatment with free miR-145. Therefore, UTMD-mediated miRNA therapy may provide a new targeted therapeutic approach for atherosclerotic plaques.

Role of MicroRNA-145 in DNA Damage Signalling and Senescence in Vascular Smooth Muscle Cells of Type 2 Diabetic Patients

Increased cardiovascular morbidity and mortality in individuals with type 2 diabetes (T2DM) is a significant clinical problem. Despite advancements in achieving good glycaemic control, this patient population remains susceptible to macrovascular complications. We previously discovered that vascular smooth muscle cells (SMC) cultured from T2DM patients exhibit persistent phenotypic aberrancies distinct from those of individuals without a diagnosis of T2DM. Notably, persistently elevated expression levels of microRNA-145 co-exist with characteristics consistent with aging, DNA damage and senescence. We hypothesised that increased expression of microRNA-145 plays a functional role in DNA damage signalling and subsequent cellular senescence specifically in SMC cultured from the vasculature of T2DM patients. In this study, markers of DNA damage and senescence were unambiguously and permanently elevated in native T2DM versus non-diabetic (ND)-SMC. Exposure of ND cells to the DNA-damaging agent etoposide inflicted a senescent phenotype, increased expression of apical kinases of the DNA damage pathway and elevated expression levels of microRNA-145. Overexpression of microRNA-145 in ND-SMC revealed evidence of functional links between them; notably increased secretion of senescence-associated cytokines and chronic activation of stress-activated intracellular signalling pathways, particularly the mitogen-activated protein kinase, p38α. Exposure to conditioned media from microRNA-145 overexpressing cells resulted in chronic p38α signalling in naïve cells, evidencing a paracrine induction and reinforcement of cell senescence. We conclude that targeting of microRNA-145 may provide a route to novel interventions to eliminate DNA-damaged and senescent cells in the vasculature and to this end further detailed studies are warranted.