Aldehyde Dehydrogenase-2 Is a Host Factor Required for Effective Bone Marrow Mesenchymal Stem Cell Therapy

Therapeutic silencing miR-146b-5p improves cardiac remodeling in a porcine model of myocardial infarction by modulating the wound reparative phenotype

Fibrotic remodeling is an adverse consequence of immune response-driven phenotypic modulation of cardiac cells following myocardial infarction (MI). MicroRNA-146b (miR-146b) is an active regulator of immunomodulation, but its function in the cardiac inflammatory cascade and its clinical implication in fibrotic remodeling following MI remain largely unknown. Herein, miR-146b-5p was found to be upregulated in the infarcted myocardium of mice and the serum of myocardial ischemia patients. Gain- and loss-of-function experiments demonstrated that miR-146b-5p was a hypoxia-induced regulator that governed the pro-fibrotic phenotype transition of cardiac cells. Overexpression of miR-146b-5p activated fibroblast proliferation, migration, and fibroblast-to-myofibroblast transition, impaired endothelial cell function and stress survival, and disturbed macrophage paracrine signaling. Interestingly, the opposite effects were observed when miR-146b-5p expression was inhibited. Luciferase assays and rescue studies demonstrated that the miR-146b-5p target genes mediating the above phenotypic modulations included interleukin 1 receptor associated kinase 1 (IRAK1) and carcinoembryonic antigen related cell adhesion molecule 1 (CEACAM1). Local delivery of a miR-146b-5p antagomir significantly reduced fibrosis and cell death, and upregulated capillary and reparative macrophages in the infarcted myocardium to restore cardiac remodeling and function in both mouse and porcine MI models. Local inhibition of miR-146b-5p may represent a novel therapeutic approach to treat cardiac fibrotic remodeling and dysfunction following MI.

Acetaldehyde dehydrogenase 2 deficiency exacerbates cardiac fibrosis by promoting mobilization and homing of bone marrow fibroblast progenitor cells

Cardiac fibrosis is a common feature of various cardiovascular diseases. Previous studies showed that acetaldehyde dehydrogenase 2 (ALDH2) deficiency exacerbated pressure overload-induced heart failure. However, the role and mechanisms of cardiac fibrosis in this process remain largely unknown. This study aimed to investigate the effect of ALDH2 deficiency on cardiac fibrosis in transverse aortic constriction (TAC) induced pressure overload model in mice. Echocardiography and histological analysis revealed cardiac dysfunction and enhanced cardiac fibrosis in TAC-operated animals; ALDH2 deficiency further aggravated these changes. ALDH2 chimeric mice were generated by bone marrow (BM) transplantation of WT mice into the lethally irradiated ALDH2KO mice. The proportion of circulating fibroblast progenitor cells (FPCs) and ROS level in BM after TAC were significantly higher in ALDH2KO mice than in ALDH2 chimeric mice. Furthermore, FPCs were isolated and cultured for in vitro mechanistic studies. The results showed that the stem cell-derived factor 1 (SDF-1)/C-X-C chemokine receptor 4 (CXCR4) axis played a major role in the recruitment of FPCs. In conclusion, our research reveals that increased bone marrow FPCs mobilization and myocardial homing contribute to the enhanced cardiac fibrosis and dysfunction induced by TAC in ALDH2 KO mice via exacerbating accumulation of ROS in BM and myocardial SDF-1 expression.

Aldehyde Dehydrogenase 2 and Heart Failure

Heart failure (HF) is a structural or functional cardiac abnormal syndrome characterized with series of symptoms and signs such as breathlessness, fatigue, pulmonary crackles, and peripheral edema. Being a terminal phase of most myocardial lesions, HF has become a leading cause of mobility and mortality worldwide, associated with heavy clinical burden and economic costs affecting over 23 million people [14]. There is an increase to 5.5% with systolic dysfunction and an increase to 36.0% with diastolic dysfunction in people 60 years or older [85]. The costs accompanied with heart failure stand 2-3% of the total healthcare system expenditure in high-income countries and are expected to increase >2-fold in the next 2 decades [34].

The Bidirectional Effect of Defective ALDH2 Polymorphism and Disease Prevention

Despite the role of aldehyde dehydrogenase 2 (ALDH2) in the detoxification of endogenous aldehydes, the defective polymorphism (rs671), which is highly prevalent among East Asians, does not show a serious phenotype, such as congenital abnormality. However, unfavorable and favorable impacts of the variant allele, ALDH2*2, on various disease risks have been reported. The underlying mechanisms are often complicated due to the compensatory aldehyde detoxification systems. As the phenotypes emerge due to overlapping environmental factors (e.g., alcohol intake and tobacco smoke) or individual vulnerabilities (e.g., aging and apolipoprotein E ε4 allele), polymorphism is therefore considered to be important in the field of preventative medicine. For example, it is important to recognize that ALDH2*2 carriers are at a high risk of alcohol drinking-related cancers; however, their drinking habit has less adverse effects on physiological indices, such as blood pressure, body mass index, levels of lipids, and hepatic deviation enzymes in the blood, than in non-ALDH2*2 carriers. Therefore, opportunities to reconsider their excessive drinking habit before adverse events occur can be missed. To perform effective disease prevention, the effects of ALDH2*2 on various diseases and the biological mechanisms should be clarified.

Mitochondrial aldehyde dehydrogenase-2 deficiency compromises therapeutic effect of ALDH bright cell on peripheral ischemia

The autologous ALDH bright (ALDH^br) cell therapy for ischemic injury is clinically safe and effective, while the underlying mechanism remains elusive. Here, we demonstrated that the glycolysis dominant metabolism of ALDH^br cells is permissive to restore blood flow in an ischemic hind limb model compared with bone marrow mononuclear cells (BMNCs). PCR array analysis showed overtly elevated Aldh2 expression of ALDH^br cells following hypoxic challenge. Notably, ALDH^br cells therapy induced blood flow recovery in this model was reduced in case of ALDH2 deficiency. Moreover, significantly reduced glycolysis flux and increased reactive oxygen species (ROS) levels were detected in ALDH^br cell from Aldh2-/- mice. Compromised effect on blood flow recovery was also noticed post transplanting the human ALDH^br cell from ALDH2 deficient patients (GA or AA genotypes) in this ischemic hindlimb mice model. Taken together, our findings illustrate the indispensable role of ALDH2 in maintaining glycolysis dominant metabolism of ALDH^br cell and advocate that patient's Aldh2 genotype is a prerequisite for the efficacy of ALDH^br cell therapy for peripheral ischemia.

Chloroquine exacerbates serum withdrawal-induced G1 phase arrest via an autophagy-independent mechanism

Chloroquine exacerbates serum withdrawal-induced G₁ phase arrest via an autophagy-independent, but an oxidative stress-dependent mechanism in endothelial cells.

Mitochondrial Aldehyde Dehydrogenase 2 Regulates Revascularization in Chronic Ischemia: Potential Impact on the Development of Coronary Collateral Circulation

OBJECTIVE

Revascularization is an essential process to compensate for cardiac underperfusion and, therefore, preserves cardiac function in the face of chronic ischemic injury. Recent evidence suggested a vital role of aldehyde dehydrogenase 2 (ALDH2) in cardiac protection after ischemia. This study was designed to determine whether ALDH2 regulates chronic ischemia-induced angiogenesis and to explore the underlying mechanism involved. Moreover, the clinical impact of the ALDH2 mutant allele on the development of coronary collateral circulation (CCC) was evaluated.

APPROACH AND RESULTS

Mice limb ischemia was performed. Compared with wild-type, ALDH2 deletion significantly reduced perfusion recovery, small artery and capillary density, and increased muscle atrophy in this ischemic model. In vitro, ALDH2-knockdown reduced proliferation, migration and hypoxia triggered endothelial tube formation of endothelial cells, the effects of which were restored by ALDH2 transfection. Further examination revealed that ALDH2 regulated angiogenesis possibly through hypoxia-inducible factor-1α/vascular endothelial growth factor pathways. To further discern the role of ALDH2 deficiency in the function of bone marrow stem/progenitor cells, cross bone marrow transplantation was performed between wild-type and ALDH2-knockout mice. However, there was no significant improvement for wild-type bone marrow transplantation into knockout mice. ALDH2 genotyping was screened in 139 patients with chronic total occlusion recruited to Zhongshan Hospital (2011.10-2014.4). Patients with poor CCC (Rentrop 0-1; n=51) exhibited a higher frequency of the AA genotype than those with enriched CCC (Rentrop 2-3; n=88; 11.76% versus 1.14%; P=0 0.01). However, the AA group displayed less enriched CCC frequency in Logistic regression model when compared with the GG group (odds ratio=0.08; 95% confidence interval, 0.009-0.701; P=0 0.026). Furthermore, serum vascular endothelial growth factor level tended to be lower in patients with ALDH2 mutation.

CONCLUSIONS

This study demonstrated that ALDH2 possesses an intrinsic capacity to regulate angiogenesis via hypoxia-inducible factor-1α and vascular endothelial growth factor. Patients with ALDH2-deficient genotype displayed a higher risk of developing poor CCC. Therapeutic individualization based on ALDH2 allele distribution may thus improve the therapeutic benefit, especially in the East Asian decedents.

Stem/Progenitor cells in vascular regeneration

A series of studies has been presented in the search for proof of circulating and resident vascular progenitor cells, which can differentiate into endothelial and smooth muscle cells and pericytes in animal and human studies. In terms of pluripotent stem cells, including embryonic stem cells, iPS, and partial-iPS cells, they display a great potential for vascular lineage differentiation. Development of stem cell therapy for treatment of vascular and ischemic diseases remains a major challenging research field. At the present, there is a clear expansion of research into mechanisms of stem cell differentiation into vascular lineages that are tested in animal models. Although there are several clinical trials ongoing that primarily focus on determining the benefits of stem cell transplantation in ischemic heart or peripheral ischemic tissues, intensive investigation for translational aspects of stem cell therapy would be needed. It is a hope that stem cell therapy for vascular diseases could be developed for clinic application in the future.