High glucose suppresses autophagy through the AMPK pathway while it induces autophagy via oxidative stress in chondrocytes

HDAC1 Promotes Mitochondrial Pathway Apoptosis and Inhibits the Endoplasmic Reticulum Stress Response in High Glucose-Treated Schwann Cells via Decreased U4 Spliceosomal RNA

Dysfunction of Schwann cells, including cell apoptosis, autophagy inhibition, dedifferentiation, and pyroptosis, is a pivotal pathogenic factor in induced diabetic peripheral neuropathy (DPN). Histone deacetylases (HDACs) are an important family of proteins that epigenetically regulate gene transcription by affecting chromatin dynamics. Here, we explored the effect of HDAC1 on high glucose-cultured Schwann cells. HDAC1 expression was increased in diabetic mice and high glucose-cultured RSC96 cells, accompanied by cell apoptosis. High glucose also increased the mitochondrial pathway apoptosis-related Bax/Bcl-2 and cleaved caspase-9/caspase-9 ratios and decreased endoplasmic reticulum response-related GRP78, CHOP, and ATF4 expression in RSC96 cells (P < 0.05). Furthermore, overexpression of HDAC1 increased the ratios of Bax/Bcl-2, cleaved caspase-9/caspase-9, and cleaved caspase-3 and reduced the levels of GRP78, CHOP, and ATF4 in RSC96 cells (P < 0.05). In contrast, knockdown of HDAC1 inhibited high glucose-promoted mitochondrial pathway apoptosis and suppressed the endoplasmic reticulum response. Moreover, RNA sequencing revealed that U4 spliceosomal RNA was significantly reduced in HDAC1-overexpressing RSC96 cells. Silencing of U4 spliceosomal RNA led to an increase in Bax/Bcl-2 and cleaved caspase-9 and a decrease in CHOP and ATF4. Conversely, overexpression of U4 spliceosomal RNA blocked HDAC1-promoted mitochondrial pathway apoptosis and inhibited the endoplasmic reticulum response. In addition, alternative splicing analysis of HDAC1-overexpressing RSC96 cells showed that significantly differential intron retention (IR) of Rpl21, Cdc34, and Mtmr11 might be dominant downstream targets that mediate U4 deficiency-induced Schwann cell dysfunction. Taken together, these findings indicate that HDAC1 promotes mitochondrial pathway-mediated apoptosis and inhibits the endoplasmic reticulum stress response in high glucose-cultured Schwann cells by decreasing the U4 spliceosomal RNA/IR of Rpl21, Cdc34, and Mtmr11.

SIRT3 alleviates high glucose-induced chondrocyte injury through the promotion of autophagy and suppression of apoptosis in osteoarthritis progression

A growing amount of epidemiological evidence proposes diabetes mellitus (DM) to be an independent risk factor for osteoarthritis (OA). Sirtuin 3 (SIRT3), which is mainly located in mitochondria, belongs to the family of nicotinamide adenine dinucleotide (NAD+)-dependent protein deacetylases and is involved in the physiological and pathological processes of cell regulation. The aim of this study was to investigate the effects of SIRT3 on diabetic OA and underlying mechanisms in the prevention of type 2 DM (T2DM)-induced articular cartilage damage. High-fat and high-sugar diets combined with streptozotocin (STZ) injection were used for establishing an experimental T2DM rat model. The destabilization of medial meniscus (DMM) surgery was applied to induce the rat OA model. Primary rat chondrocytes were cultivated with a concentration of gradient glucose. Treatment with intra-articular injection of SIRT3 overexpression lentivirus was achieved in vivo, and intervention with SIRT3 knockdown was performed using siRNA transfection in vitro. High glucose content was found to activate inflammatory response, facilitate apoptosis, downregulate autophagy, and exacerbate mitochondrial dysfunction in a dose-dependent manner in rat chondrocytes, which can be deteriorated by SIRT3 knockdown. In addition, articular cartilage damage was found to be more severe in T2DM-OA rats than in DMM-induced OA rats, which can be mitigated by the intra-articular injection of SIRT3 overexpression lentivirus. Targeting SIRT3 is a potential therapeutic strategy for the alleviation of diabetic OA.

Downregulation of VEGFA accelerates AGEs-mediated nucleus pulposus degeneration through inhibiting protective mitophagy in high glucose environments

Intervertebral disc degeneration (IVDD) contributes largely to low back pain. Recent studies have highlighted the exacerbating role of diabetes mellitus (DM) in IVDD, mainly due to the influence of hyperglycemia (HG) or the accumulation of advanced glycation end products (AGEs). Vascular endothelial growth factor A (VEGFA) newly assumed a distinct impact in nonvascular tissues through mitophagy regulation. However, the combined actions of HG and AGEs on IVDD and the involved role of VEGFA remain unclear. We confirmed the potential relation between VEGFA and DM through bioinformatics and biological specimen detection. Then we observed that AGEs induced nucleus pulposus (NP) cell degeneration by upregulating cellular reactive oxygen species (ROS), and HG further aggravated ROS level through breaking AGEs-induced protective mitophagy. Furthermore, this adverse effect could be strengthened by VEGFA knockdown. Importantly, we identified that the regulation of VEGFA and mitophagy were vital mechanisms in AGEs-HG-induced NP cell degeneration through Parkin/Akt/mTOR and AMPK/mTOR pathway. Additionally, VEGFA overexpression through local injection with lentivirus carrying VEGFA plasmids significantly alleviated NP degeneration and IVDD in STZ-induced diabetes and puncture rat models. In conclusion, the findings first confirmed that VEGFA protects against AGEs-HG-induced IVDD, which may represent a therapeutic strategy for DM-related IVDD.

Near infrared in and out: Deep imaging for scrap leather induced autophagy in vivo by an ultrasensitive two-photon polarity probe

As one of the important means for eukaryotic cells to maintain homeostasis, autophagy allows for transporting deformed biomacromolecules and damaged organelles to lysosome for digestion and degradation. The process of autophagy entails the merging of autophagosomes and lysosomes, culminating in the breakdown of biomacromolecules. This, in turn, leads to a change in lysosomal polarity. Therefore, fully understanding the changes of lysosomal polarity during autophagy is of significance to the study of membrane fluidity and enzymatic reaction. However, the shorter emission wavelength has greatly damaged the imaging depth, thus seriously limiting its biological application. Therefore, in this work, a near infrared in and out lysosome-targeted polarity-sensitive probe NCIC-Pola was developed. The fluorescence intensity of NCIC-Pola showed an approximate 1160-fold increase when the polarity decreased under two-photon excitation (TPE). In addition, the excellent fluorescence emission wavelength (692 nm) enabled the deep imaging analysis of scrap leather induced autophagy in vivo.

Cell culture-derived extracellular vesicles: Considerations for reporting cell culturing parameters

Cell culture-conditioned medium (CCM) is a valuable source of extracellular vesicles (EVs) for basic scientific, therapeutic and diagnostic applications. Cell culturing parameters affect the biochemical composition, release and possibly the function of CCM-derived EVs (CCM-EV). The CCM-EV task force of the Rigor and Standardization Subcommittee of the International Society for Extracellular Vesicles aims to identify relevant cell culturing parameters, describe their effects based on current knowledge, recommend reporting parameters and identify outstanding questions. While some recommendations are valid for all cell types, cell-specific recommendations may need to be established for non-mammalian sources, such as bacteria, yeast and plant cells. Current progress towards these goals is summarized in this perspective paper, along with a checklist to facilitate transparent reporting of cell culturing parameters to improve the reproducibility of CCM-EV research.

The Beneficial and Adverse Effects of Autophagic Response to Caloric Restriction and Fasting

Each cell is equipped with a conserved housekeeping mechanism, known as autophagy, to recycle exhausted materials and dispose of injured organelles via lysosomal degradation. Autophagy is an early-stage cellular response to stress stimuli in both physiological and pathological situations. It is thought that the promotion of autophagy flux prevents host cells from subsequent injuries by removing damaged organelles and misfolded proteins. As a correlate, the modulation of autophagy is suggested as a therapeutic approach in diverse pathological conditions. Accumulated evidence suggests that intermittent fasting or calorie restriction can lead to the induction of adaptive autophagy and increase longevity of eukaryotic cells. However, prolonged calorie restriction with excessive autophagy response is harmful and can stimulate a type II autophagic cell death. Despite the existence of a close relationship between calorie deprivation and autophagic response in different cell types, the precise molecular mechanisms associated with this phenomenon remain unclear. Here, we aimed to highlight the possible effects of prolonged and short-term calorie restriction on autophagic response and cell homeostasis.

Pyruvate Dehydrogenase Kinase 1 inhibition mediated oxidative phosphorylation enhancement in cartilage promotes osteoarthritis progression

Osteoarthritis (OA) is a common disease characterized by cartilage degradation. Growing evidence showed that glucose metabolism impacts joint homeostasis and an imbalance between glycolysis and oxidative phosphorylation (OXPHOS) may exacerbate OA progression, however, a definitive link is yet to be established. Here, we report that pyruvate metabolism and oxidative phosphorylation pathway is enriched in OA cartilage through gene set enrichment analysis (GSEA) and expression of Pyruvate Dehydrogenase Kinase 1 (PDK1), an enzyme that can phosphorylate Pyruvate Dehydrogenase (PDH), and inhibit pyruvate fluxes into the tricarboxylic acid (TCA) cycle and to OXPHOS, in articular cartilage is notably reduced through destabilization of medial meniscus (DMM). Moreover, by inhibiting PDK1, cartilage loss is markedly accelerated in DMM-induced OA through extracellular matrix (ECM) degradation and apoptosis of chondrocytes. These results indicate that PDK1 is involved in the progression of OA through accelerating cartilage matrix degradation and synovium inflammation to ameliorate cartilage degeneration.

Transcriptomic profiling and differential analysis reveal the renal toxicity mechanisms of mice under cantharidin exposure

Cantharidin (CTD), extracted from the traditional Chinese medicine mylabris, has shown significant curative effects against a variety of tumors, but its clinical application is limited by its high toxicity. Studies have revealed that CTD can cause toxicity in the kidneys; however, the underlying molecular mechanisms remain unclear. In this study, we investigated the toxic effects in mouse kidneys following CTD treatment by pathological and ultrastructure observations, biochemical index detection, and transcriptomics, and explored the underlying molecular mechanisms by RNA sequencing (RNA-seq). The results showed that after CTD exposure, the kidneys had different degrees of pathological damage, altered uric acid and creatinine levels in serum, and the antioxidant indexes in tissues were significantly increased. These changes were more pronounced at medium and high doses of CTD. RNA-seq analysis revealed 674 differentially expressed genes compared with the control group, of which 131 were upregulated and 543 were downregulated. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed that many differentially expressed genes were closely related to the stress response, the CIDE protein family, and the transporter superfamily, as well as the MAPK, AMPK, and HIF-1 pathways. The reliability of the RNA-seq results was verified by qRT-PCR of the six target genes. These findings offer insight into the molecular mechanisms of renal toxicity caused by CTD and provide an important theoretical basis for the clinical treatment of CTD-induced nephrotoxicity.

Hyperglycemia Aggravates Periodontitis via Autophagy Impairment and ROS-Inflammasome-Mediated Macrophage Pyroptosis

Macrophage pyroptosis drives the secretion of IL-1β, which has been recently reported to be a featured salivary biomarker for discriminating periodontitis in the presence of diabetes. This study aimed to explore whether macrophage pyroptosis plays a role in the development of diabetes mellitus–periodontitis, as well as potential therapeutic strategies. By establishing a model of experimental diabetes mellitus–periodontitis in rats, we found that IL-1β and gasdermin D were highly expressed, leading to aggravated destruction of periodontal tissue. MCC950, a potent and selective molecule inhibitor of the NLRP3 inflammasome, effectively inhibited macrophage pyroptosis and attenuated alveolar bone losses in diabetes mellitus–periodontitis. Consistently, in vitro, high glucose could induce macrophage pyroptosis and thus promoted IL-1β production in macrophages stimulated by lipopolysaccharide. In addition, autophagy blockade by high glucose via the mTOR-ULK1 pathway led to severe oxidative stress response in macrophages stimulated by lipopolysaccharide. Activation of autophagy by rapamycin, clearance of mitochondrial ROS by mitoTEMPO, and inhibition of inflammasome by MCC950 could significantly reduce macrophage pyroptosis and IL-1β secretion. Our study demonstrates that hyperglycemia promotes IL-1β production and pyroptosis in macrophages suffered by periodontal microbial stimuli. Modulation of autophagy activity and specific targeting of the ROS-inflammasome pathway may offer promising therapeutic strategies to alleviate diabetes mellitus–periodontitis.

Induction of Cardiac Pathology: Endogenous versus Exogenous Nrf2 Upregulation

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master regulator of the endogenous antioxidant response to reactive oxygen species as well as a controller of Phase II detoxification in response to xenobiotics. This amenity to specific external manipulation exploits the binding affinity of Nrf2 for its constitutive repressor and degradation facilitator Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1 (Keap1). Derived from both natural and synthesized origins, these compounds have been extensively tested without definitive beneficial results. Unfortunately, multiple terminated trials have shown a negative side to Nrf2 with regard to cardiac pathologies while animal-based studies have demonstrated cardiomyocyte hypertrophy and heart failure after chronic Nrf2 upregulation. Putatively based on autophagic control of Nrf2 activity-modulating upstream factors, new evidence of miRNA involvement has added complexity to this mechanism. What follows is an extensive survey of Nrf2-regulating exogenous compounds that may promote cardiomyopathy, clinical trial evidence, and a comparison to exercise-induced factors that also upregulate Nrf2 while preventing cardiac pathologies.

Role of AMPK in autophagy

Adenosine monophosphate-activated protein kinase (AMPK) is a significant energy sensor in the maintenance of cellular energy homeostasis. Autophagy is a highly conserved catabolic process that involves an intracellular degradation system in which cytoplasmic components, such as protein aggregates, organelles, and other macromolecules, are directed to the lysosome through the self-degradative process to maintain cellular homeostasis. Given the triggered autophagy process in various situations including the nutrient deficit, AMPK is potentially linked with different stages of autophagy. Above all, AMPK increases ULK1 activity by directly phosphorylating Ser467, Ser555, Thr574, and Ser637 at least four sites, which increases the recruitment of autophagy-relevant proteins (ATG proteins) to the membrane domains which affects autophagy at the initiation stage. Secondly, AMPK inhibits VPS34 complexes that do not contain pro-autophagic factors and are thus involved in isolation membrane forming processes, by direct phosphorylation of VPS34 on Thr163 and Ser165. After phosphorylation, AMPK can govern autophagosome formation through recruiting downstream autophagy-related proteins to the autophagosome formation site. Finally, the AMPK-SIRT1 signaling pathway can be activated by upregulating the transcription of autophagy-related genes, thereby enhancing autophagosome-lysosome fusion. This review provides an introduction to the role of AMPK in different stages of autophagy.

Metformin as a potential disease-modifying drug in osteoarthritis: a systematic review of pre-clinical and human studies

OBJECTIVE

Osteoarthritis causes significant pain and disability with no approved disease-modifying drugs. We systematically reviewed the evidence from both pre-clinical and human studies for the potential disease-modifying effect of metformin in osteoarthritis.

METHODS

Ovid Medline, Embase and CINAHL were searched between inception and June 2021 using MeSH terms and key words to identify studies examining the association between metformin use and outcome measures related to osteoarthritis. Two reviewers performed the risk of bias assessment and 3 reviewers extracted data independently. Qualitative evidence synthesis was performed. This systematic review is registered on PROSPERO (CRD42021261052 and CRD42021261060).

RESULTS

Fifteen (10 pre-clinical and 5 human) studies were included. Most studies (10 pre-clinical and 3 human) assessed the effect of metformin using knee osteoarthritis models. In pre-clinical studies, metformin was assessed for the effect on structural outcomes (n = 10); immunomodulation (n = 5); pain (n = 4); and molecular pathways of its effect in osteoarthritis (n = 7). For human studies, metformin was evaluated for the effect on structural progression (n = 3); pain (n = 1); and immunomodulation (n = 1). Overall, pre-clinical studies consistently showed metformin having a chondroprotective, immunomodulatory and analgesic effect in osteoarthritis, predominantly mediated by adenosine monophosphate-activated protein kinase activation. Evidence from human studies, although limited, was consistent with findings in pre-clinical studies.

CONCLUSION

We found consistent evidence across pre-clinical and human studies to support a favourable effect of metformin on chondroprotection, immunomodulation and pain reduction in knee osteoarthritis. Further high-quality clinical trials are needed to confirm these findings as metformin could be a novel therapeutic drug for the treatment of osteoarthritis.

AT2 Receptor Stimulation Inhibits Vascular Smooth Muscle Cell Senescence Induced by Angiotensin II and Hyperglycemia

BACKGROUND

Hyperglycemia has been widely reported to induce vascular senescence. We have previously demonstrated that angiotensin II (Ang II) could promote brain vascular smooth muscle cell (VSMC) senescence, and its type 2 (AT2) receptor deletion could enhance VSMC senescence. Therefore, we examined the possible cross-talk between Ang II and hyperglycemia on VSMC senescence, and the roles of AT2 receptor agonist, compound 21 (C21) on it.

METHODS

Aortic VSMCs were prepared from adult male mice and stimulated with Ang II and/or high glucose (Glu) and/or C21 and/or an autophagy inhibitor, 3-methyladenine (3-MA), and/or an autophagy agonist, rapamycin (RAP) for the indicated times. Cellular senescence, oxidative stress, and protein expressions were evaluated.

RESULTS

Combination treatment with Ang II and Glu synergistically increased the proportion of VSMC senescent area compared with control group and each treatment alone, which was almost completely attenuated by C21 treatment. Moreover, combination treatment induced significant changes in the levels of superoxide anion, the expressions of p21 and pRb, and the ratio of LC3B II/I expression, which were also significantly attenuated by C21 treatment. The proportion of VSMC senescent area and the levels of superoxide anion by combination treatment were increased after 3-MA treatment, and the proportion of senescent area and the expressions of p21 and pRb were decreased after RAP treatment, both of which were further attenuated by C21 treatment.

CONCLUSIONS

Ang II and hyperglycemia synergistically promoted VSMC senescence, at least partly through the participation by autophagy, oxidative stress, and p21-pRb pathway, which could be inhibited by C21.

HIF-1α upregulation exerts the antagonistic effect against angiogenesis inhibition in manganese deficiency-induced tibial dyschondroplasia of broiler chicks

Manganese (Mn) is an essential microelement for broiler breeding and its deficiency causes tibial dyschondroplasia (TD). Tibial growth plate (TGP) development and metaphyseal vascularization are crucial for tibia growth in fast-growing broiler chickens, but their roles in Mn deficiency-induced TD in chicks remain unclear. This study was designed to clarify this issue. A total of 36 one-day-old broilers were divided into the control group and Mn-deficiency (Mn-D) group, which were fed with a standard diet (60 mg Mn/kg) and Mn deficiency diet (22 mg Mn/kg) for 42 days, respectively. TGP and proximal tibial metaphysis were collected to perform the related assays. This study found that Mn deficiency decreased the tibia length and TGP thickness in the TD model. Also, Mn deficiency increased the irregular and white tibial dyschondroplasia lesions (TDL) region under the TGP, and reduced the expression levels of vascular endothelial growth factor (VEGF) and macrophage migration inhibitory factor (MIF). Combined with histological assessment, it was suggested that Manganese deficiency inhibited angiogenesis in the proximal tibial metaphysis. Meanwhile, Mn deficiency enhanced the expression levels of hypoxia-inducible factor-1 α (HIF-1α), autophagy-related protein 5 (ATG5), and microtubule-associated protein 1 light chain 3 β (LC3-II) in TGP, but decreased the expression level of SQSTM1 (P62), which suggested that autophagy was activated during this process. Collectively, these data indicate that HIF-1α up-regulation and concurrent autophagy activation exert a protective effect against Mn deficiency-induced angiogenesis inhibition, which may provide useful guidance to prevent TD in broilers.

Epigenetic regulation of autophagy in coronavirus disease 2019 (COVID-19)

The coronavirus disease 2019 (COVID-19) pandemic has become the most serious global public health issue in the past two years, requiring effective therapeutic strategies. This viral infection is a contagious disease caused by new coronaviruses (nCoVs), also called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Autophagy, as a highly conserved catabolic recycling process, plays a significant role in the growth and replication of coronaviruses (CoVs). Therefore, there is great interest in understanding the mechanisms that underlie autophagy modulation. The modulation of autophagy is a very complex and multifactorial process, which includes different epigenetic alterations, such as histone modifications and DNA methylation. These mechanisms are also known to be involved in SARS-CoV-2 replication. Thus, molecular understanding of the epigenetic pathways linked with autophagy and COVID-19, could provide novel therapeutic targets for COVID-19 eradication. In this context, the current review highlights the role of epigenetic regulation of autophagy in controlling COVID-19, focusing on the potential therapeutic implications.

New uses of Melatonin as a Drug, a Review

Melatonin is a simple compound with a proper chemical name N-acetyl-5-methoxy tryptamine and known as a hormone controlling circadian rhythm. Humans produce melatonin at night which is the reason for sleeping in the night and awakening over the day. Melatonin interacts with melatonin receptors MT1 and MT2 but it was also revealed that melatonin is a strong antioxidant and it also has a role in regulation of cell cycle. Currently, melatonin is used as a drug for some types of sleep disorder but the recent research points to the fact that melatonin can also serve for the other purposes including prophylaxis or therapy of lifestyle diseases, cancer, neurodegenerative disorders and exposure to chemicals. This review summarizes basic facts and direction of the current research on melatonin. The actual literature was scrutinized for the purpose of this review.

Effects of quercetin on apoptosis and extracellular matrix degradation of chondrocytes induced by oxidative stress-mediated pyroptosis

Quercetin has been preliminarily proven to serve as a potential agent for the treatment of osteoarthritis (OA). However, its effects and potential mechanisms on the pathological process of OA are not very clear. This study aimed to study the protective effect of quercetin on OA. Lipopolysaccharide (LPS)-treated chondrocytes (C28/I2 cell) and anterior cruciate ligament transection with partial medial meniscectomy-treated Wistar rats were used as models of OA in vitro and in vivo. Cell counting kit-8 (CCK-8 kit), flow cytometry, enzyme-linked immunosorbent assay (ELISA) kit, western blot, dichlorodihydrofluorescein diacetate (DCFH-DA) kit, thiobarbituric acid (TBA) test, toluidine blue staining, Hematoxylin eosin (HE) staining and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining were used to evaluate cell viability, cell apoptosis, inflammatory cytokines level, protein expression, reactive oxygen species (ROS) level, malondialdehyde (MDA) content, morphological changes, and chondrocyte apoptosis of cartilage, respectively. Results showed that quercetin could reduce LPS-induced C28/I2 cell apoptosis, extracellular matrix (ECM) degradation, and cell pyroptosis, and overexpression of nucleotide-binding domain and leucine-rich-repeat-containing (NLR) family, pyrin domain-containing 3 (NLRP3) revealed that quercetin reduced chondrocyte apoptosis and ECM degradation by inhibiting NLRP3-mediated pyroptosis. Furthermore, quercetin could reduce chondrocyte apoptosis and ECM degradation, and inhibit NLRP3-mediated pyroptosis through blocking oxidative stress. It was further confirmed in the rat OA model that quercetin alleviated OA by blocking oxidative stress, reduces chondrocyte pyroptosis, apoptosis, and ECM degradation. In conclusion, quercetin inhibited OA via blocking oxidative stress-induced chondrocyte pyroptosis in models of OA in vitro and in vivo.