FAM134B Attenuates Seizure-Induced Apoptosis and Endoplasmic Reticulum Stress in Hippocampal Neurons by Promoting Autophagy

TRPML1 ameliorates seizures-related neuronal injury by regulating autophagy and lysosomal biogenesis via Ca2+/TFEB signaling pathway

Alterations in autophagy have been observed in epilepsy, although their exact etiopathogenesis remains elusive. Transient Receptor Potential Mucolipin Protein 1 (TRPML1) is an ion channel protein that regulates autophagy and lysosome biogenesis. To explore the role of TRPML1 in seizures-induced neuronal injury and the potential mechanisms involved, an hyperexcitable neuronal model induced by Mg2+-free solution was used for the study. Our results revealed that TRPML1 expression was upregulated after seizures, which was accompanied by intracellular ROS accumulation, mitochondrial damage, and neuronal apoptosis. Activation of TRPML1 by ML-SA1 diminished intracellular ROS, restored mitochondrial function, and subsequently alleviated neuronal apoptosis. Conversely, inhibition of TRPML1 had the opposite effect. Further examination revealed that the accumulation of ROS and damaged mitochondria was associated with interrupted mitophagy flux and enlarged defective lysosomes, which were attenuated by TRPML1 activation. Mechanistically, TRPML1 activation allows more Ca2+ to permeate from the lysosome into the cytoplasm, resulting in the dephosphorylation of TFEB and its nuclear translocation. This process further enhances autophagy initiation and lysosomal biogenesis. Additionally, the expression of TRPML1 is positively regulated by WTAP-mediated m6A modification. Our findings highlighted crucial roles of TRPML1 and autophagy in seizures-induced neuronal injury, which provides a new target for epilepsy treatment.

Biological functions of the m6A reader YTHDF2 and its role in central nervous system disorders

N6-methyladenosine (m6A) is a prevalent mRNA modification in eukaryotic cells, characterized by its reversible nature. YTH structural domain family protein 2 (YTHDF2), a key reader of m6A, plays a crucial role in identifying and binding m6A-containing RNAs, thereby influencing RNA metabolism through various functional mechanisms. The upstream and downstream targets of YTHDF2 are critical in the pathogenesis of various central nervous system (CNS) diseases, affecting disease development by regulating signaling pathways and gene expression. This paper provides an overview of current research on the role of YTHDF2 in CNS diseases and investigates the regulatory mechanisms by which YTHDF2 influences the development of these conditions. This exploration aims to improve understanding of disease pathogenesis and offer novel insights for the targeted prevention and treatment of neurological disorders.

FAM134B deletion exacerbates apoptosis and epithelial-to-mesenchymal transition in rat lungs exposed to hyperoxia

Oxygen therapy is widely used in clinical practice; however, prolonged hyperoxia exposure may result in hyperoxic acute lung injury (HALI). In this study, we investigated the role of FAM134B in hyperoxia-induced apoptosis, cell proliferation, and epithelial-to-mesenchymal transition (EMT) using RLE-6TN cells and rat lungs. We also studied the effect of CeO2-NPs on RLE-6TN cells and lungs following hyperoxia exposure. FAM134B was inhibited in RLE-6TN cells and rat lungs following hyperoxia exposure. Overexpressing FAM134B promoted cell proliferation, and reduced EMT and apoptosis following hyperoxia exposure. FAM134B activation increased ER-phagy, decreased apoptosis, improved lung structure damage, and decreased collagen fiber deposition to limit lung injury. These effects could be reversed by PI3K/AKT pathway inhibitor LY294002. Additionally, CeO2-NPs protected RLE-6TN cells and lung damage following hyperoxia exposure by ameliorating impaired ER-phagy. Therefore, FAM134B restoration is a potential therapeutic target for the HALI. Moreover, CeO2-NPs can be used for the treatment of HALI.

ATF5 Attenuates Low-magnesium-induced Apoptosis by Inhibiting Endoplasmic Reticulum Stress Via the Regulation of Mitochondrial Reactive Oxygen Species

Mitochondrial stress and endoplasmic reticulum stress (ERS) are known to be closely linked. ATF5 is a key regulator of mitochondrial stress and is involved in ERS regulation. Previously, we used a seizure model to demonstrate that ATF5 regulates mitochondrial stress. However, whether ATF5 affects ERS in epilepsy models has yet to be elucidated. In the present study, we investigated the effects of ATF5 on low-magnesium-induced ERS and the potential mechanisms that underlie these effects. We found that lentiviral overexpression of ATF5 significantly improved low-magnesium-induced ERS, as confirmed by the reduced expression levels of GRP78, PERK, ATF4, and CHOP. In addition, ATF5 overexpression reduced reactive oxygen species (ROS) production and elevated superoxide dismutase (SOD) activity, thus demonstrating that ATF5 plays a key role in maintaining redox homeostasis. Furthermore, ATF5 overexpression rescued low-magnesium-induced neuronal apoptosis, as evidenced by the reduced expression levels of Cleaved-caspase-3 and Bax, and the restored levels of Bcl2. However, these effects were significantly eliminated by lentiviral transduction with ATF5 interference. In addition, treatment of neurons with the mitochondrial antioxidant mitoquinone attenuated the onset of oxidative stress caused by ATF5 interference, partially restored the effect on ERS, and rescued cells from apoptosis. Collectively, these data show that ATF5 attenuates low-magnesium-induced neuronal apoptosis by inhibiting ERS through preventing the accumulation of mitochondrial ROS.

Involvement of histone methylation in the regulation of neuronal death

Neuronal death occurs in various physiological and pathological processes, and apoptosis, necrosis, and ferroptosis are three major forms of neuronal death. Neuronal apoptosis, necrosis, and ferroptosis are widely identified to involve the progress of stroke, Parkinson's disease, and Alzheimer's disease. A growing body of evidence has pointed out that neuronal death is tightly associated with expression of related genes and alteration of signaling molecules. In addition, recently, epigenetics has been increasingly focused on as a vital regulatory mechanism for neuronal apoptosis, necrosis, and ferroptosis, providing a new direction for treating nervous system diseases. Moreover, growing researches suggest that histone methylation or demethylation is involved in the processes of neuronal apoptosis, necrosis, and ferroptosis. These researches may imply that studying the potential roles of histone methylation is essential for treating the nervous system diseases. Here, we review potential roles of histone methylation and demethylation in neuronal death, which may give us a new direction in treating the nervous system diseases.

Pharmacological modulation of autophagy for epilepsy therapy: opportunities and obstacles

Epilepsy (EP) is a long-term neurological disorder characterized by neuroinflammatory responses, neuronal apoptosis, imbalance between excitatory and inhibitory neurotransmitters, and oxidative stress in the brain. Autophagy is a process of cellular self-regulation to maintain normal physiological functions. Emerging evidence suggests that dysfunctional autophagy pathways in neurons are a potential mechanism underlying EP pathogenesis. In this review, we discuss current evidence and molecular mechanisms of autophagy dysregulation in EP and the probable function of autophagy in epileptogenesis. Moreover, we review the autophagy modulators reported for the treatment of EP models, and discuss the obstacles to, and opportunities for, the potential therapeutic applications of novel autophagy modulators as EP therapies. Teaser: Defective autophagy affects the onset and progression of epilepsy, and many anti-epileptic drugs have autophagy-modulating effects.

Neuroprotection impact of biochanin A against pentylenetetrazol-kindled mice: Targeting NLRP3 inflammasome/TXNIP pathway and autophagy modulation

Recurrent seizures characterize epilepsy, a complicated and multifaceted neurological disease. Several neurological alterations, such as cell death and the growth of gorse fibers, have been linked to epilepsy. The dentate gyrus of the hippocampus is particularly vulnerable to neuronal loss and abnormal neuroplastic changes in the pentylenetetrazol (PTZ) kindling model. Biochanin A has potent anti-inflammatory and antioxidant properties, according to previous evidence and its possible impact in epilepsy has never previously been claimed. The current work aimed to investigate biochanin A's anti-epileptic potential in PTZ-induced kindling model in mice. Chronic epilepsy was established in mice by giving PTZ (35 mg/kg, i.p) every other day for 21 days. Biochanin A (20 mg/kg) was given daily till the end of the experiment. Biochanin A pretreatment significantly reduced the severity of epileptogenesis by 51.7% and downregulated the histological changes in the CA3 region of the hippocampus by 42% along with displaying antioxidant/anti-inflammatory efficacy through upregulated hemeoxygenase-1 (HO-1) and, erythroid 2-related factor 2 (Nrf2) levels in the brain by 1.9-fold and 2-fold respectively, parallel to reduction of malondialdehyde (MDA), myeloperoxidase (MPO), glial fibrillary acidic protein (GFAP) and L-glutamate/IL-1β/TXNIB/NLRP3 axis. Moreover, biochanin A suppressed neuronal damage by reducing the astrocytes' activation and significantly attenuated the PTZ-induced increase in LC3 levels by 55.5%. Furthermore, molecular docking findings revealed that BIOCHANIN A has a higher affinity for phosphoinositide 3-kinase (PI3k), threonine kinase2 (AKT2), and mammalian target of rapamycin complex 1 (mTORC1) indicating the neuroprotective and anti-epileptic characteristics of biochanin A in the brain tissue of PTZ-kindled mice.

Molecular Mechanism and Regulation of Autophagy and Its Potential Role in Epilepsy

Autophagy is an evolutionally conserved degradation mechanism for maintaining cell homeostasis whereby cytoplasmic components are wrapped in autophagosomes and subsequently delivered to lysosomes for degradation. This process requires the concerted actions of multiple autophagy-related proteins and accessory regulators. In neurons, autophagy is dynamically regulated in different compartments including soma, axons, and dendrites. It determines the turnover of selected materials in a spatiotemporal control manner, which facilitates the formation of specialized neuronal functions. It is not surprising, therefore, that dysfunctional autophagy occurs in epilepsy, mainly caused by an imbalance between excitation and inhibition in the brain. In recent years, much attention has been focused on how autophagy may cause the development of epilepsy. In this article, we overview the historical landmarks and distinct types of autophagy, recent progress in the core machinery and regulation of autophagy, and biological roles of autophagy in homeostatic maintenance of neuronal structures and functions, with a particular focus on synaptic plasticity. We also discuss the relevance of autophagy mechanisms to the pathophysiology of epileptogenesis.

Mechanistic Research into the Effects of the Jianpi Xiaozhi Formula on Liver Injury in Diabetic Rats

Objective

The purpose of this study was to explore the mechanism of Jianpi Xiaozhi Formula (JPXZF) action in attenuating liver injury in a rat model of type 2 diabetes mellitus (T2DM).

Methods

A rat model of T2DM was established. Forty-eight male Sprague–Dawley (SD) rats were randomly allocated to six groups: healthy untreated rats (normal control (NC)), rats with diabetes mellitus (DM), diabetic rats treated with low-dosage JPXZF (DM + JL), diabetic rats treated with an intermediate JPXZF dosage (DM + JM), diabetic rats treated with high-dosage JPXZF (DM + JH), and diabetic rats treated with 4-phenylbutyric acid (PBA) (DM + PBA). The rats in each group were given the indicated drugs for 8 weeks, and pathological changes in the liver tissues of each rat group were observed by haematoxylin-eosin (HE) staining. Reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting (WB) were performed to determine the expression of glucose-regulated protein 78 (GRP78), activating transcription factor 6 (ATF6), family with sequence similarity 134, member B (FAM134B), P62, Beclin-1, and light chain 3II/I (LC3II/I) genes and proteins in the liver tissues of the rats in each group. Immunofluorescence was used to observe changes in FAM134B expression.

Results

After successfully establishing the rat model, RT-PCR assays revealed that, compared with those in the NC group rats, the expression levels of GRP78, ATF6, and P62 mRNA in the livers of the DM group rats were significantly increased, and the relative expression levels of FAM134B and Beclin-1 mRNA were significantly decreased. Compared with that in the DM group, the relative expression of GRP78, ATF6, and P62 mRNA in the liver of the rats in each JPXZF intervention group was decreased in a dosage-dependent manner, and the relative expression of FAM134B and Beclin-1 mRNA was increased significantly (p < 0.05). WB indicated that, compared with that in the NC group rats, the LC3II/I protein expression ratio in the liver of the DM group rats was significantly reduced, and the LC3II/I protein expression ratio in the liver of the rats in each JPXZF intervention group was significantly increased. In addition, the expression of the other measured proteins was consistent with that of the corresponding mRNA measured by RT-PCR (p < 0.05). The immunofluorescence assay results showed that FAM134B changes were consistent with the results obtained by RT-PCR and WB (p < 0.05).

Conclusion

Jianpi Xiaozhi Formula may be effective in treating liver injury in diabetic rats by regulating autophagy induced by endoplasmic reticulum stress (ERS).

4-Phenylbutyric Acid Plus Valproic Acid Exhibits the Therapeutic and Neuroprotective Effects in Acute Seizures Induced by Pentylenetetrazole

Endoplasmic reticulum (ER) stress and apoptosis are implicated in the pathogenesis of epilepsy. Here we examine the effects of valproic acid (VA) plus 4-phenylbutyric acid (4-PBA) on abnormal electrical brain activity, ER stress and apoptosis in acute seizures induced by pentylenetetrazole (PTZ). Forty male rats were randomly divided into five groups, each consisting of 8 rats as follows: Sham, PTZ, VA+PTZ, 4-PBA+PTZ, and VA plus 4-PBA+PTZ. The treated groups received VA, 4-PBA and VA plus 4-PBA by intraperitoneal application for 7 days prior to PTZ-induced seizure. On the 8th day, acute epileptic seizures were induced by PTZ (50 mg/kg, i.p.) injection, except for the sham group. Then, the seizure stage was observed and ECoG activities were recorded during the 30 min. At 24th post seizures, the hippocampus and blood samples were collected for biochemical and histopathological examinations. Administration of VA plus 4-PBA prior to PTZ-induced seizures significantly decreased seizure stage, the duration of generalized tonic-clonic seizure and the total number of spikes as increased the latency to the first myoclonic jerk when compared to the PTZ group. 4-PBA suppressed the increased levels of ER stress markers GRP78 and CHOP in the hippocampus. VA plus 4-PBA treatment before seizures significantly inhibited PTZ-induced elevations of apoptosis-related indicators caspase-3 and caspase-12, and significantly reduced the number of histopathological lesions of the hippocampus region at 24th post seizures. These findings suggest that administration of VA plus 4-PBA prior to PTZ-induced seizures may be involved in the neuroprotective potential of these agents for seizures.

High-fat diet exacerbated decabromodiphenyl ether-induced hepatocyte apoptosis via intensifying the transfer of Ca2+ from endoplasmic reticulum to mitochondria

Polybrominated diphenyl ether (PBDE) as the flame retardant is heavily used in daily necessities, causing adverse health effects on humans. This study aimed to evaluate the hepatotoxicity of decabromodiphenyl ether (BDE-209), the most widely used PBDE, in lean and high-fat diet (HFD)-treated obese mice and elucidate the underlying mechanism. Firstly, the increasing levels of TG and proinflammatory factors in the liver and ALT and AST in serum demonstrated the hepatic damage caused by BDE-209 and further exacerbated by HFD. Tunel image revealed that BDE-209 induced more severe hepatocyte apoptosis with the assistant of HFD. Next, the mechanism analysis showed that the pro-apoptotic action of BDE-209 was in an endoplasmic reticulum (ER)/Ca²⁺ flux/mitochondria-dependent manner, concluded from the impairment of mitochondrial membrane potential, the enhancive protein expression of p-PERK/PERK, p-IRE1/IRE1, ATF6, CHOP, Bax/Bcl-2, cleaved caspase-3/caspase-3, IP3R1 and Sig-1R, and the over-transfer of Ca²⁺ from ER to mitochondria. Such proposed mechanism was further confirmed by the IP3R1 siRNA transfection cell experiment, where apoptotic rate was reduced in parallel with the reduced mitochondrial Ca²⁺ level. Finally, the higher expression of PACS-2 protein and the expanded ER contributed to the enriched ER-mitochondria interaction, reflected by the closer distance between ER and mitochondria visually displayed in the TEM image in HFD groups. This change was conducive to the rapid delivery of apoptosis signals via Ca²⁺, as proven, mechanically explaining the strengthening effect of HFD on BDE-209 hepatotoxicity. These findings detailedly explained the mechanism of BDE-209 hepatotoxicity and clarified the auxiliary effect of HFD, providing a theoretical basis for further studying other analogs.

Reverse relationship between autophagy and apoptosis in an in vitro model of cortical neuronal injury

Autophagy and apoptosis are intertwined, and their relationship involves complex cross-talk. Whether the activation and inhibition of autophagy protect or damage neurons in the central nervous system has been a matter of longstanding controversy. We investigated the effect of autophagy on the apoptosis of cortical neurons after oxygen- and glucose-deprivation/reoxygenation (OGD/R) injury in vitro and found that protective mechanism activation was the predominant response to enhanced autophagy activation and increased autophagic flux. After successful establishment of an OGD/R model with cortical neurons, the autophagy activator rapamycin (Rap) or the late-autophagy inhibitor bafilomycin A1 (BafA1) was added to cell groups according to the experimental design. Cell viability was determined by Cell Counting Kit-8 (CCK-8) and lactate dehydrogenase (LDH) assays, and the apoptosis rate was measured by analysing Annexin V-FITC/PI-stained cells. The protein and mRNA expression levels of the apoptosis factors Caspase8 and Caspase3 and autophagy-associated proteins LC3 and p62 were measured by Western blotting and RT-qPCR. The extent of autophagic flux was determined by measuring the intensity of double immunofluorescence labelled protein after cells were transfected with RFP-GFP-LC3-expressing virus, and the ultrastructures of autophagosomes were observed by transmission electron microscopy (TEM). The results showed that cell viability decreased and that cells underwent autophagy and apoptosis after OGD/R. After the addition of Rap, cell viability was increased, and the apoptosis rate was decreased significantly. In addition, the level of the autophagic flux protein LC3II was increased, and the level of p62 was decreased. The number of autophagosomes and the ratio of autophagosomes to lysosomes were increased significantly. After BafA1 intervention, however, these results were reversed, with decreased cell viability, a significantly increased apoptosis rate, and disrupted autophagic flux. In conclusion, enhanced autophagy activation or autophagic flux exerted a significant protective effect on neurons after OGD/R injury in vitro.

Autophagy triggers endoplasmic reticulum stress and C/EBP homologous protein-mediated apoptosis in OGD/R-treated neurons in a caspase-12-independent manner

We reported that a high level of autophagy was initiated by oxygen-glucose deprivation (OGD) and was maintained in neurons even after oxygen-glucose deprivation followed by reoxygenation (OGD/R), accompanied by neuronal apoptosis. This study focused on autophagy-induced apoptosis and its signaling network, especially the role of endoplasmic reticulum stress (ERS). Analysis of primary cultured cortical neurons from mice showed that the autophagy-induced apoptosis depended on caspase-8 and -9 but not on caspase-12. This finding did not mean that the endoplasmic reticulum did not participate in this process. Increases in the levels of endoplasmic reticulum (ER) biomarkers and binding immunoglobulin protein (BiP) were induced by autophagy in OGD/R-treated neurons. In addition, as an apoptotic transcription factor induced by ER stress, C/EBP homologous protein (CHOP) expression was significantly increased in neurons after OGD/R. This result suggested that the autophagy-BiP-CHOP-caspase (8 and 9)-dependent apoptotic signaling pathway at least partly participated in autophagy-induced apoptosis in primary cortical neurons. It revealed that ER induced apoptosis in neurons suffering from OGD/R injury in an ER stress-CHOP-dependent manner rather than a caspase-12-dependent manner. However, more research on signaling or cross-linking networks and intermediate links is needed. The realization of caspase-12-independent BiP-CHOP neuronal apoptosis pathway has expanded our understanding of the neuronal apoptosis network, which may eventually provide endogenous interventional strategies for OGD/R injury after stroke.NEW & NOTEWORTHY ER stress induced by autophagy mediates caspase-8- and caspase-9-dependent apoptosis pathways by regulating CHOP in neurons exposed to OGD/R. We hypothesized that the autophagy-BiP-CHOP-caspase (8 and 9)-dependent apoptotic signaling pathway at least partly participated in autophagy-induced apoptosis in primary cortical neurons.

FAM134B-Mediated ER-Phagy in Mg2+-Free Solution-Induced Mitochondrial Calcium Homeostasis and Cell Death in Epileptic Hippocampal Neurons

Mitochondrial-associated endoplasmic reticulum (ER) membranes (MAMs) regulate calcium (Ca2+) homeostasis via Ca2+ transport-related proteins such as inositol-1,4,5-triphosphate receptor (IP3R). FAM134B-mediated ER-phagy plays an important role in ER homeostasis. However, it remains unknown whether FAM134B-mediated ER-phagy affects mitochondrial Ca2+ homeostasis and cell death through MAMs. In this study, we demonstrated that colocalization degree of FAM134B with LC3 and the LC3-II/LC3-I ratio were elevated in the hippocampal neuronal culture (HNC) model of acquired epilepsy (AE), which indicate an increased level of autophagy. In this model, FAM134B overexpression enhanced ER-phagy, while FAM134B downregulation had the opposite effect. Additionally, FAM134B overexpression significantly reversed the increases in IP3R expression and mitochondrial Ca2+ concentration and the decrease in the ER Ca2+ concentration in this model. FAM134B overexpression also ameliorated the AE-induced ultrastructural damage in neuronal mitochondria, decrease in mitochondrial membrane potential (mMP), cytochrome c (CytC) release and caspase-3 activation, while FAM134B downregulation induced the opposite effects. Altogether, our data indicate that FAM134B-mediated ER-phagy can attenuate AE-induced neuronal apoptosis, possibly by modulating the IP3R in MAMs to alter Ca2+ exchange between ER and mitochondria and thus inhibit mitochondrial structural damage, a decrease in mMP, release of CytC and mitochondrial apoptosis.

ER-Phagy: A New Regulator of ER Homeostasis

The endoplasmic reticulum (ER) is one of the most important cellular organelles and is essential for cell homeostasis. Upon external stimulation, ER stress induces the unfolded protein response (UPR) and ER-associated degradation (ERAD) to maintain ER homeostasis. However, persistent ER stress can lead to cell damage. ER-phagy is a selective form of autophagy that ensures the timely removal of damaged ER, thereby protecting cells from damage caused by excessive ER stress. As ER-phagy is a newly identified form of autophagy, many receptor-mediated ER-phagy pathways have been discovered in recent years. In this review, we summarize our understanding of the maintenance of ER homeostasis and describe the receptors identified to date. Finally, the relationships between ER-phagy and diseases are also discussed.

Rosiglitazone Prevents Autophagy by Regulating Nrf2-Antioxidant Response Element in a Rat Model of Lithium-pilocarpine-induced Status Epilepticus

Status epilepticus (SE) leads to irreversible neuronal damage and consists of a complex pathogenesis that involves oxidative stress and subsequent autophagy. Rosiglitazone has recently been considered as a potential neuroprotective factor in epilepsy because of its antioxidative function. The aim of this study was to assess the effects of rosiglitazone in SE rat models and investigate whether its mechanisms of action involve autophagy via the antioxidant factor, nuclear factor erythroid 2-related factor 2 (Nrf2). The male Sprague-Dawley rats (200-220 g) were used to establish lithium-pilocarpine-induced SE model. We found that rosiglitazone markedly improved neuronal survival at 24-h post-SE as indicated via Hematoxylin-Eosin and Nissl staining. Furthermore, along with a reduction in reactive oxygen species, rosiglitazone pretreatment enhanced the antioxidative activity of superoxide dismutase and the expression level of Nrf2, as detected via chemical assay kits and Western blotting, respectively. In addition, the microtubule-associated protein light chain 3II (LC3II)/LC3I ratio was increased and peaked at 24 h after SE, whereas p62 mRNA levels were sharply elevated at 72 h after SE, both SE-induced increases of which were reversed via rosiglitazone pretreatment. To further test our hypothesis of the key role of Nrf2 in this process, small-interfering RNA for Nrf2 (siNrf2) was then transfected into SE rats to knockdown Nrf2 expression. We found that siNrf2 partially blocked the above effects of rosiglitazone on autophagy-related proteins in SE rats. Taken together, our findings suggest that rosiglitazone attenuates oxidative-stress-induced autophagy via increasing Nrf2 in SE rats and may be used as a promising therapeutic strategy for SE treatment.

ATF4 promotes renal tubulointerstitial fibrosis by suppressing autophagy in diabetic nephropathy

AIM

Diabetic nephropathy (DN) is the dominant cause of end-stage renal disease which is characterized by extracellular matrix accumulation. The purpose of this study was to investigate the role of activating transcription factor 4 (ATF4) in regulating renal fibrosis and autophagy in DN.

MAIN METHOD

Streptozotocin (STZ) was administered to heterozygous ATF4 knockout (KO) and wild-type (WT) mice via an intraperitoneal injection to induce DN. NRK-52E cells were cultured in high glucose to mimic diabetic pathological. qRT-PCR, western blot, immunofluorescence, histology and electron microscopic analysis were performed. The autophagy flux was observed by tandem mRFP-GFP-LC3 fluorescence microscopy.

KEY FINDINGS

DN mice experienced severe renal injury and fibrosis and showed increased expression of ATF4 and inhibition of autophagy in kidney tissues. We found that STZ-induced ATF4 KO mice showed significant improvement in urinary albumin, serum creatinine and blood urea nitrogen and the pathological changes of renal tubulointerstitial fibrosis compared with STZ-induced WT mice. Furthermore, inhibition of ATF4 could restore autophagy in DN mice. Similar results were shown in vitro. Overexpression of ATF4 in NRK-52E cells cultured in high glucose condition suppressed autophagy and upregulated Collagen type 4 (Col-IV) expression, while inhibition of ATF4 could increase the number of the autophagosomes, improve autophagic flux and decrease Col-IV level.

SIGNIFICANCE

Our study provided the evidence of a crucial role for ATF4 in inhibiting autophagy against diabetic kidney damage. Suppression of ATF4 may be an effective therapy in restraining renal tubulointerstitial fibrosis in DN.