Melatonin, an endogenously produced neurohormone secreted by the pineal gland, has a variety of physiological functions and neuroprotective effects. It can modulate the functions of neural stem cells (NSCs) including proliferation and differentiation in embryonic brain tissue but its effect and mechanism on the stem cells in hypoxia remains to be explored. Here, we show that melatonin stimulates proliferation of NSCs during hypoxia. Additionally, it also promoted the differentiation of NSCs into neurons. However, it did not appear to exert an obvious effect on the differentiation of astrocytes. The present results have further shown that the promotional effect of NSCs proliferation by melatonin involved the MT1 receptor and increased phosphorylation of ERK1/2. The effect of melatonin on differentiation of NSCs is linked to altered expression of differentiation-related genes. In the light of these findings, it is suggested that melatonin may be beneficial as a supplement for treatment of neonatal hypoxic-ischemic brain injury for promoting the proliferation and differentiation of NSCs.

Mitophagy, a selective form of autophagy, is excessively activated in myocardial ischemia/reperfusion (I/R). The study investigated whether aldehyde dehydrogenase 2 (ALDH2) exerted its cardioprotective effect by regulating mitophagy. Myocardial infarct size and apoptosis after I/R in rats were ameliorated by Alda-1, an ALDH2 activator, and aggravated by ALDH2 inhibition. Both in I/R rats and hypoxia/reoxygenation H9C2 cells, ALDH2 activation suppressed phosphatase and tensin homolog-induced putative kinase 1 (PINK1)/Parkin expression, regulating mitophagy, by preventing 4-hydroxynonenal, reactive oxygen species and mitochondrial superoxide accumulation. Furthermore, the effect was enhanced by ALDH2 inhibition. Thus, ALDH2 may protect hearts against I/R injury by suppressing PINK1/Parkin–dependent mitophagy.

The POU family transcription factor OCT4 is required for maintaining the pluripotency of embryonic stem cells and for generating induced pluripotent stem cells. Although OCT4 is clearly shown to be expressed in some pluripotent germ cell tumours, its expression in human somatic tumours remains controversial. Some studies have shown that OCT4 is expressed in adult stem cells, somatic cancers and, further, cancer stem cells, while other studies failed to make such an observation. It is thus important to ascertain whether OCT4 is expressed in human somatic tumours. By using RT-PCR and sequencing analysis, three OCT4 pseudogenes, viz. OCT4-pg1, OCT4-pg3 and OCT4-pg4 but excluding the OCT4 gene, were found to be expressed in two types of human solid tumours, glioma and breast carcinoma, from which cancer stem cells had earlier been isolated. The protein expression of these pseudogenes was further demonstrated by immunochemistry and western blotting. Along with this, it was shown that OCT4 pseudogenes lacked OCT4-like activities. The expression of OCT4 splicing variant and various pseudogenes at both the mRNA and protein levels in human somatic tumours might call into question the reliability of the results regarding OCT4 expression and function in tumourigenesis. Hence, in investigations of OCT4 expression in cancers and stem cells, different approaches with appropriate controls would be desirable to exclude possibility of false-positive results.

Objective: Hypoxia-induced pulmonary hypertension (HPH) increases lipid peroxidation with generation of toxic aldehydes that are metabolized by detoxifying enzymes, including ALDH2 (aldehyde dehydrogenase 2). However, the role of lipid peroxidation and ALDH2 in HPH pathogenesis remain undefined. Approach and Results: To determine the role of lipid peroxidation and ALDH2 in HPH, C57BL/6 mice, ALDH2 transgenic mice, and ALDH2 knockout (ALDH2 −/− ) mice were exposed to chronic hypoxia, and recombinant tissue-specific ALDH2 overexpression adeno-associated viruses were introduced into pulmonary arteries via tail vein injection for ALDH2 overexpression. Human pulmonary artery smooth muscle cells were used to elucidate underlying mechanisms in vitro. Chronic hypoxia promoted lipid peroxidation due to the excessive production of reactive oxygen species and increased expression of lipoxygenases in lung tissues. 4-hydroxynonenal but not malondialdehyde level was increased in hypoxic lung tissues which might reflect differences in detoxifying enzymes. ALDH2 overexpression attenuated the development of HPH, whereas ALDH2 knockout aggravated it. Specific overexpression of ALDH2 using AAV1 (adeno-associated virus)-ICAM (intercellular adhesion molecule) 2p-ALDH2 and AAV2-SM22αp (smooth muscle 22 alpha)-ALDH2 viral vectors in pulmonary artery smooth muscle cells, but not endothelial cells, prevented the development of HPH. Hypoxia or 4-hydroxynonenal increased stabilization of HIF (hypoxia-inducible factor)-1α, phosphorylation of Drp1 (dynamin-related protein 1) at serine 616, mitochondrial fission, and pulmonary artery smooth muscle cells proliferation, whereas ALDH2 activation suppressed the latter 3. Conclusions: Increased 4-hydroxynonenal level plays a critical role in the development of HPH. ALDH2 attenuates the development of HPH by regulating mitochondrial fission and smooth muscle cell proliferation suggesting ALDH2 as a potential new therapeutic target for pulmonary hypertension.