Activin A regulation under global hypoxia in developing mouse brain

Activin A improves the neurological outcome after ischemic stroke in mice by promoting oligodendroglial ACVR1B-mediated white matter remyelination

Activin A plays important roles in ischemic injury and white matter remyelination, but its mechanisms are unclear. In this study, the adult male C57BL/6 J mice were used to establish the model of 1 h middle cerebral artery occlusion/reperfusion (MCAO/R) 1 d to 28 d-induced ischemic stroke in vivo. We found that the neurological outcome was positively correlated with the levels of myelin associated proteins (include MAG, CNPase, MOG and MBP, n = 6 per group) both in corpus callosum and internal capsule of mice with ischemic stroke. The dynamic changes of Luxol fast blue (LFB) staining intensity, oligodendrocyte (CC1+) and proliferated oligodendrocyte precursor (Ki67+/PDGFRα+) cell numbers indicated demyelination and spontaneous remyelination occurred in the corpus callosum of mice after 1 h MCAO/R 1 d-28 d (n = 6 per group). Activin receptor type I (ACVR1) inhibitor SB431542 aggregated neurological deficits, and reduced MAG, MOG and MBP protein levels of mice with ischemic stroke (n = 6 per group). Meanwhile, recombinant mouse (rm) Activin A enhanced the neurological function recovery, MAG, MOG and MBP protein levels of mice with 1 h MCAO/R 28 d. In addition, the injection of AAV-based ACVR1B shRNA with Olig2 promoter could reverse rmActivin A-induced the increases of CC1+ cell number, LFB intensity, MAG, MOG and MBP protein levels in the corpus callosum (n = 6 per group), and neurological function recovery (n = 10 per group) of mice with 1 h MCAO/R 28 d. These results suggested that Activin A improves the neurological outcome through promoting oligodendroglial ACVR1B-mediated white matter remyelination of mice with ischemic stroke, which may provide a potential therapeutic strategy for ischemic stroke.

Hypoxic naked mole-rat brains use microRNA to coordinate hypometabolic fuels and neuroprotective defenses

Naked mole-rats are among the mammalian champions of hypoxia tolerance. They evolved adaptations centered around reducing metabolic rate to overcome the challenges experienced in their underground burrows. In this study, we used next-generation sequencing to investigate one of the factors likely supporting hypoxia tolerance in naked mole-rat brains, posttranscriptional microRNAs (miRNAs). Of the 212 conserved miRNAs identified using small RNA sequencing, 18 displayed significant differential expression during hypoxia. Bioinformatic enrichment revealed that hypoxia-mediated miRNAs were suppressing energy expensive processes including de novo protein translation and cellular proliferation. This suppression occurred alongside the activation of neuroprotective and neuroinflammatory pathways, and the induction of central signal transduction pathways including HIF-1α and NFκB via miR-335, miR-101, and miR-155. MiRNAs also coordinated anaerobic glycolytic fuel sources, where hypoxia-upregulated miR-365 likely suppressed protein levels of ketohexokinase, the enzyme responsible for catalyzing the first committed step of fructose catabolism. This was further supported by a hypoxia-mediated reduction in glucose transporter 5 proteins that import fructose into the cell. Yet, messenger RNA and protein levels of lactate dehydrogenase, which converts pyruvate to lactate in the absence of oxygen, were elevated during hypoxia. Together, this demonstrated the induction of anaerobic glycolysis despite a lack of reliance on fructose as the primary fuel source, suggesting that hypoxic brains are metabolically different than anoxic naked mole-rat brains that were previously found to shift to fructose-based glycolysis. Our findings contribute to the growing body of oxygen-responsive miRNAs "OxymiRs" that facilitate natural miRNA-mediated mechanisms for successful hypoxic exposures.

Activin A in Mammalian Physiology

Activins are dimeric glycoproteins belonging to the transforming growth factor beta superfamily and resulting from the assembly of two beta subunits, which may also be combined with alpha subunits to form inhibins. Activins were discovered in 1986 following the isolation of inhibins from porcine follicular fluid, and were characterized as ovarian hormones that stimulate follicle stimulating hormone (FSH) release by the pituitary gland. In particular, activin A was shown to be the isoform of greater physiological importance in humans. The current understanding of activin A surpasses the reproductive system and allows its classification as a hormone, a growth factor, and a cytokine. In more than 30 yr of intense research, activin A was localized in female and male reproductive organs but also in other organs and systems as diverse as the brain, liver, lung, bone, and gut. Moreover, its roles include embryonic differentiation, trophoblast invasion of the uterine wall in early pregnancy, and fetal/neonate brain protection in hypoxic conditions. It is now recognized that activin A overexpression may be either cytostatic or mitogenic, depending on the cell type, with important implications for tumor biology. Activin A also regulates bone formation and regeneration, enhances joint inflammation in rheumatoid arthritis, and triggers pathogenic mechanisms in the respiratory system. In this 30-yr review, we analyze the evidence for physiological roles of activin A and the potential use of activin agonists and antagonists as therapeutic agents.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Neuroprotective effects of Activin A on endoplasmic reticulum stress-mediated apoptotic and autophagic PC12 cell death

Activin A, a member of the transforming growth factor-beta superfamily, plays a neuroprotective role in multiple neurological diseases. Endoplasmic reticulum (ER) stress-mediated apoptotic and autophagic cell death is implicated in a wide range of diseases, including cerebral ischemia and neurodegenerative diseases. Thapsigargin was used to induce PC12 cell death, and Activin A was used for intervention. Our results showed that Activin A significantly inhibited morphological changes in thapsigargin-induced apoptotic cells, and the expression of apoptosis-associated proteins [cleaved-caspase-12, C/EBP homologous protein (CHOP) and cleaved-caspase-3] and biomarkers of autophagy (Beclin-1 and light chain 3), and downregulated the expression of thapsigargin-induced ER stress-associated proteins [inositol requiring enzyme-1 (IRE1), tumor necrosis factor receptor-associated factor 2 (TRAF2), apoptosis signal-regulating kinase 1 (ASK1), c-Jun N-terminal kinase (JNK) and p38]. The inhibition of thapsigargin-induced cell death was concentration-dependent. These findings suggest that administration of Activin A protects PC12 cells against ER stress-mediated apoptotic and autophagic cell death by inhibiting the activation of the IRE1-TRAF2-ASK1-JNK/p38 cascade.

Kdm6b and Pmepa1 as Targets of Bioelectrically and Behaviorally Induced Activin A Signaling

The transforming growth factor-β (TGF-β) family member activin A exerts multiple neurotrophic and protective effects in the brain. Activin also modulates cognitive functions and affective behavior and is a presumed target of antidepressant therapy. Despite its important role in the injured and intact brain, the mechanisms underlying activin effects in the CNS are still largely unknown. Our goal was to identify the first target genes of activin signaling in the hippocampus in vivo. Electroconvulsive seizures, a rodent model of electroconvulsive therapy in humans, were applied to C57BL/6J mice to elicit a strong increase in activin A signaling. Chromatin immunoprecipitation experiments with hippocampal lysates subsequently revealed that binding of SMAD2/3, the intracellular effectors of activin signaling, was significantly enriched at the Pmepa1 gene, which encodes a negative feedback regulator of TGF-β signaling in cancer cells, and at the Kdm6b gene, which encodes an epigenetic regulator promoting transcriptional plasticity. Underlining the significance of these findings, activin treatment also induced PMEPA1 and KDM6B expression in human forebrain neurons generated from embryonic stem cells suggesting interspecies conservation of activin effects in mammalian neurons. Importantly, physiological stimuli such as provided by environmental enrichment proved already sufficient to engender a rapid and significant induction of activin signaling concomitant with an upregulation of Pmepa1 and Kdm6b expression. Taken together, our study identified the first target genes of activin signaling in the brain. With the induction of Kdm6b expression, activin is likely to gain impact on a presumed epigenetic regulator of activity-dependent neuronal plasticity.

FG-4497: a new target for acute respiratory distress syndrome?

The morbidity and mortality rates associated with acute respiratory distress syndrome (ARDS) remain high and the development of new therapeutic strategies is urgently required. Some pharmacological treatments, proposed or under evaluation for ARDS, seek to protect the endothelium and consequently mitigate fluid extravasation into the alveolar space. FG-4497 is a new compound which acts as a prolyl hydroxylase domain 2 inhibitor and mimics hypoxia in the activation of hypoxia-inducible factor-2α signaling, decreasing VE-cadherin phosphorylation and thus promoting integrity of adherens junctions. In this special report, we discuss the pharmacological characteristics of FG-4497, its effect on lung parenchyma and other organs and future perspectives in ARDS. In short, FG-4497 may be considered a novel pharmacological option targeting endothelial cell repair in lung diseases such as ARDS. Further experimental and clinical studies are warranted to better understand the mechanisms of action of FG-4497 in different types of lung injury.

Activation of Nrf2 in keratinocytes causes chloracne (MADISH)-like skin disease in mice

The transcription factor Nrf2 is a key regulator of the cellular stress response, and pharmacological Nrf2 activation is a promising strategy for skin protection and cancer prevention. We show here that prolonged Nrf2 activation in keratinocytes causes sebaceous gland enlargement and seborrhea in mice due to upregulation of the growth factor epigen, which we identified as a novel Nrf2 target. This was accompanied by thickening and hyperkeratosis of hair follicle infundibula. These abnormalities caused dilatation of infundibula, hair loss, and cyst development upon aging. Upregulation of epigen, secretory leukocyte peptidase inhibitor (Slpi), and small proline-rich protein 2d (Sprr2d) in hair follicles was identified as the likely cause of infundibular acanthosis, hyperkeratosis, and cyst formation. These alterations were highly reminiscent to the phenotype of chloracne/“metabolizing acquired dioxin-induced skin hamartomas” (MADISH) patients. Indeed, SLPI, SPRR2, and epigen were strongly expressed in cysts of MADISH patients and upregulated by dioxin in human keratinocytes in an NRF2-dependent manner. These results identify novel Nrf2 activities in the pilosebaceous unit and point to a role of NRF2 in MADISH pathogenesis.