All-trans retinoic acid suppresses apoptosis in PC12 cells injured by oxygen and glucose deprivation via the retinoic acid receptor α signaling pathway

All-Trans Retinoic Acid Attenuates Transmissible Gastroenteritis Virus-Induced Apoptosis in IPEC-J2 Cells via Inhibiting ROS-Mediated P38MAPK Signaling Pathway

Transmissible gastroenteritis virus (TGEV) can cause diarrhea, dehydration, and high mortality in piglets, which is closely related to intestinal epithelial cell apoptosis caused by TGEV infection. All-trans retinoic acid (ATRA) is the active metabolite of vitamin A, which has antioxidant and anti-apoptotic properties. However, it is unknown whether ATRA can attenuate TGEV-induced IPEC-J2 cells apoptosis. Therefore, we investigated the protective effects of ATRA on TGEV-induced apoptosis of IPEC-J2 cells and explored the potential molecular mechanism. Our results indicated that TGEV infection caused IPEC-J2 cells damage and apoptosis. However, ATRA treatment attenuated TGEV-induced IPEC-J2 cells damage by upregulating the mRNA expressions of ZO-1, Occludin, and Mucin-1. ATRA treatment also attenuated TGEV-induced apoptosis in IPEC-J2 cells by downregulating the expression of Caspase-3, which is related to the inhibition of death receptor (Fas and Caspase-8) and mitochondrial (Bax, Bcl-2, and Caspase-9) pathways. Moreover, ATRA treatment prevented TGEV-induced ROS and MDA production and the upregulation of P₃₈MAPK phosphorylation level, which is related to the increase in the activities of antioxidant enzymes (SOD, CAT, and T-AOC) and the mRNA abundance of antioxidant-related genes (GPX1, GPX2, SOD1, CAT, GCLC, and GCLM). In addition, treatment of TGEV-infected IPEC-J2 cells with the ROS inhibitors (NAC) significantly reduced the protein levels of p-P₃₈MAPK, Fas, Bax, and Cleaved-caspase-3 and the percentage of apoptotic cells. Our results indicated that ATRA attenuated TGEV-induced apoptosis in IPEC-J2 cells via improving the antioxidant capacity, thereby inhibiting the cell damage. the mechanism of which is associated with the inhibition of ROS-mediated P₃₈MAPK signaling pathway.

bFGF promotes neurological recovery from neonatal hypoxic-ischemic encephalopathy by IL-1β signaling pathway-mediated axon regeneration

INTRODUCTION

Neonatal hypoxia-ischemic brain damage (HIBD) can lead to serious neuron damage and dysfunction, causing a significant worldwide health problem. bFGF as a protective reagent promotes neuron repair under hypoxia/ischemia (HI). However, how bFGF and downstream molecules were regulated in HI remains elusive.

METHODS

We established an in vitro HI model by culturing primary cortical neurons and treated with oxygen-glucose deprivation (OGD). We suppressed the expression of bFGF by using siRNA (small interfering RNA) interference to detect the neuronal morphological changes by immunofluorescence staining. To determine the potential mechanisms regulated by bFGF, the change of downstream molecular including IL-1β was examined in bFGF knockdown condition. IL-1β knockout (KO) rats were generated using CRISPR/Cas9-mediated technologies. We used an accepted rat model of HI, to assess the effect of IL-1β deletion on disease outcomes and carried out analysis on the behavior, histological, cellular, and molecular level.

RESULTS

We identified that OGD can induce endogenous expression of bFGF. Both OGD and knockdown of bFGF resulted in reduction of neuron numbers, enlarged cell body and shortened axon length. We found molecules closely related to bFGF, such as interleukin-1β (IL-1β). IL-1β was up-regulated after bFGF interference under OGD conditions, suggesting complex signaling between bFGF and OGD-mediated pathways. We found HI resulted in up-regulation of IL-1β mRNA in cortex and hippocampus. IL-1β KO rats markedly attenuated the impairment of long-term learning and memory induced by HI. Meanwhile, IL-1β^-/- (KO, homozygous) group showed better neurite growth and less apoptosis in OGD model. Furthermore, serine/threonine protein kinase (AKT1) mRNA and protein expression was significantly up-regulated in IL-1β KO rats.

CONCLUSIONS

We showed that IL-1β-mediated axon regeneration underlie the mechanism of bFGF for the treatment of HIBD in neonatal rats. Results from this study would provide insights and molecular basis for future therapeutics in treating HIBD.

Retinoic acid receptor α expression exerts an anti-apoptosis effect on PC12 cells following oxygen-glucose deprivation

It has been established that the primary form of neuron death following hypoxic ischemic brain damage is apoptosis. Imbalances in the expression of genes in the B-cell lymphoma 2 (Bcl-2) family located in the mitochondrion, and in the expression of their encoded proteins, are key events in the mitochondrial apoptotic pathway, which lead to damage of cellular structure and function. The present study aimed to explore the regulatory effect of retinoic acid receptor α (RAR-α) on the apoptosis of PC12 cells induced by oxygen-glucose deprivation (OGD) in the retinoic acid signaling pathway. Recombinant adenovirus RAR-α small interfering RNA (Ad-siRAR-α) was used to transduce PC12 cells, and the efficiency of RAR-α expression inhibition was detected by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). An empty adenovirus vector was transfected in PC12 cells, which were used as the control. Flow cytometry with Annexin V-propidium iodide (PI) and fluorescence probe JC-1 staining was used to detect the apoptosis rate and mitochondrial transmembrane potential (MMP), respectively, of PC12 cells after transduction with Ad-siRAR-α. Furthermore, the expression levels of key genes in the RAR-α and mitochondrial apoptotic pathway, Bcl-2 and Bcl-2-associated protein (Bax) were analyzed by RT-quantitative (q)PCR and western blot analysis. RAR-α mRNA expression was observed to be decreased in PC12 cells following OGD-induced injury, and this decrease can be reversed by 4 µmol/l ATRA treatment. After 36 h transfection with Ad-siRAR-α, RAR-α gene expression was significantly inhibited compared with the control (P<0.05). The results of Annexin V-PI, fluorescence probe JC-1 staining and flow cytometry demonstrated that the apoptosis rate significantly increased and MMP significantly decreased in OGD-induced PC12 cells following transduction with Ad-siRAR-α compared with the control (both P<0.05). RT-qPCR and western blot analysis indicated that Bax expression was significantly increased and Bcl-2 expression was significantly decreased in PC12 cells transduced with Ad-siRAR-α after OGD-induced injury at the mRNA and protein level (P<0.05). In conclusion, Ad-siRAR-α transduction could promote apoptosis in OGD-induced PC12 cells. This suggests that the expression of Bax and Bcl-2 in the mitochondrial apoptosis signaling pathway is, at least in part, mediated by RAR-α expression, thereby indicating that RAR-α expression exerts an anti-apoptotic effect on OGD-damaged PC12 cells.

Vitamin A bio-modulates apoptosis via the mitochondrial pathway after hypoxic-ischemic brain damage

Our previous studies demonstrated that vitamin A deficiency (VAD) can impair the postnatal cognitive function of rats by damaging the hippocampus. The present study examined the effects of retinoic acid (RA) on apoptosis induced by hypoxic-ischemic damage in vivo and in vitro, and investigated the possible signaling pathway involved in the neuroprotective anti-apoptotic effects of RA. Flow cytometry, immunofluorescence staining and behavioral tests were used to evaluate the neuroprotective and anti-apoptotic effects of RA. The protein and mRNA levels of RARα, PI3K, Akt, Bad, caspase-3, caspase-8, Bcl-2, Bax, and Bid were measured with western blotting and real-time PCR, respectively. We found impairments in learning and spatial memory in VAD group compared with vitamin A normal (VAN) and vitamin A supplemented (VAS) group. Additionally, we showed that hippocampal apoptosis was weaker in the VAN group than that in VAD group. Relative to the VAD group, the VAN group also had increased mRNA and protein levels of RARα and PI3K, and upregulated phosphorylated Akt/Bad levels in vivo. In vitro, excessively low or high RA signaling promoted apoptosis. Furthermore, the effects on apoptosis involved the mitochondrial membrane potential (MMP). These data support the idea that sustained VAD following hypoxic-ischemic brain damage (HIBD) inhibits RARα, which downregulates the PI3K/Akt/Bad and Bcl-2/Bax pathways and upregulates the caspase-8/Bid pathway to influence the MMP, ultimately producing deficits in learning and spatial memory in adolescence. This suggests that clinical interventions for HIBD should include suitable doses of VA.

Intravenous administration of retinoic acid-loaded polymeric nanoparticles prevents ischemic injury in the immature brain

Perinatal stroke is often difficult to diagnose and an established treatment has not yet been validated, except for symptomatic measures. Herein, we propose to test the neuroprotective potential of the intravenous injection of retinoic acid-loaded nanoparticles (RA-NP) upon ischemic injury to the immature brain. The role of RA-NP on endothelial cells and organotypic slice cultures exposed to oxygen and glucose deprivation was assessed by evaluating markers pertaining to survival, proliferation, oxidative stress (NO, ROS), neuronal damage (enolase), vascular oxidation (p47phox) and microglia activation (CD68). Data showed that RA-NP (3 μg/ml) increased endothelial proliferation and survival, and normalized NO and ROS levels. The intravenous administration of RA-NP (10 μg/g) prevented ischemic injury in the hippocampus of 2-day-old mice by inhibiting cell death and normalizing markers of neurovascular function and inflammation. In sum, systemic administration of RA-NP protected neurovascular integrity and the inflammatory milieu from ischemia in the immature brain, highlighting its therapeutic value for perinatal stroke.

Retinoic acid receptors α and γ are involved in antioxidative protection in renal tubular epithelial cells injury induced by hypoxia/reoxygenation

Renal interstitial fibrosis (RIF) is a common outcome in various chronic kidney diseases. Injury to renal tubular epithelial cell (RTEC) is major link in RIF. Hypoxia is one of the common factors for RTEC damage. Retinoic acid receptors (RARs), RARα, RARβ and RARγ, are evolutionary conserved and pleiotropic proteins that have been involved in various cellular functions, including proliferation, differentiation, apoptosis, and transcription. Recently, we discovered that aberrant expression of RARs was involved in the development of RIF in rats. Here, we investigated the role of RARs in the hypoxia/reoxygenation (HR) damage model in RTEC with virus-based delivery vectors to knockdown or overexpress RARs. Relevant indicators were detected. Our results showed that HR inhibited RARα and RARγ expressions in a time-dependent manner in RTECs; however, the expression of RARβ was not changed obviously. RARα and RARγ overexpression could protect cells from oxidative stress-induced injury by inhibiting HR-induced intracellular superoxide anion (O2-) generation, cell viability and mitochondria membrane potential (MMP) decrease and transforming growth factor β1 (TGF-β1) expression and promoting endogenous antioxidant defense components, superoxide dismutase (SOD) and glutathione (GSH). Meanwhile, inhibition of RARα and RARγ expressions by small interference RNAs (siRNA) resulted in a less resistance of RTEC to HR as shown in increased O2- production and TGF-β1 expression and decreased cell viability, MMP, SOD and GSH levels. These data indicates that RARα and RARγ act as positive regulators to offset oxidative damage and profibrosis cytokine accumulation and therefore has an antioxidative effect.