1,25-(OH)2D3 protects pancreatic beta cells against H2O2-induced apoptosis through inhibiting the PERK-ATF4-CHOP pathway

1,25-dihydroxyvitamin D3 affects thapsigargin-induced endoplasmic reticulum stress in 3T3-L1 adipocytes

BACKGROUND/OBJECTIVES

Endoplasmic reticulum (ER) stress in adipose tissue causes an inflammatory response and leads to metabolic diseases. However, the association between vitamin D and adipose ER stress remains poorly understood. In this study, we investigated whether 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) alleviates ER stress in adipocytes.

MATERIALS/METHODS

3T3-L1 cells were treated with different concentrations (i.e., 10-100 nM) of 1,25(OH)2D3 after or during differentiation (i.e., on day 0-7, 3-7, or 7). They were then incubated with thapsigargin (TG, 500 nM) for an additional 24 h to induce ER stress. Next, we measured the mRNA and protein levels of genes involved in unfold protein response (UPR) and adipogenesis using real-time polymerase chain reaction and western blotting and quantified the secreted protein levels of pro-inflammatory cytokines. Finally, the mRNA levels of UPR pathway genes were measured in adipocytes transfected with siRNA-targeting Vdr.

RESULTS

Treatment with 1,25(OH)2D3 during various stages of adipocyte differentiation significantly inhibited ER stress induced by TG. In fully differentiated 3T3-L1 adipocytes, 1,25(OH)2D3 treatment suppressed mRNA levels of Ddit3, sXbp1, and Atf4 and decreased the secretion of monocyte chemoattractant protein-1, interleukin-6, and tumor necrosis factor-α. However, downregulation of the mRNA levels of Ddit3, sXbp1, and Atf4 following 1,25(OH)2D3 administration was not observed in Vdr-knockdown adipocytes. In addition, exposure of 3T3-L1 preadipocytes to 1,25(OH)2D3 inhibited transcription of Ddit3, sXbp1, Atf4, Bip, and Atf6 and reduced the p-alpha subunit of translation initiation factor 2 (eIF2α)/eIF2α and p-protein kinase RNA-like ER kinase (PERK)/PERK protein ratios. Furthermore, 1,25(OH)2D3 treatment before adipocyte differentiation reduced adipogenesis and the mRNA levels of adipogenic genes.

CONCLUSIONS

Our data suggest that 1,25(OH)2D3 prevents TG-induced ER stress and inflammatory responses in mature adipocytes by downregulating UPR signaling via binding with Vdr. In addition, the inhibition of adipogenesis by vitamin D may contribute to the reduction of ER stress in adipocytes.

Investigation of the applicability of the zebrafish model for the evaluation of aristolochic acid-related nephrotoxicity

BACKGROUND

The risk of compounds/drugs, including aristolochic acid-induced nephrotoxicity remains high and is a significant public health concern. Therefore, it is particularly important to select reasonable animal models for rapid screening and evaluation of different samples with complex chemical systems. The zebrafish (Danio rerio) has been used to study chemical-induced renal toxicity. However, most of the published literature was performed on individual components or drugs, and the key evidence confirming the applicability of zebrafish larvae for the evaluation of aristolochic acid-related nephrotoxicity in complex chemical systems, such as in traditional Chinese medicine (TCM), was insufficient.

METHODS

High-performance liquid chromatography (HPLC) was used to determine the content of aristolochic acid (AA) in herbs and Chinese patent medicines. The zebrafish larvae at 4 days post-fertilization (dpf) were used to evaluate the nephrotoxicity of various samples, respectively, based on the phenotype of the kidney and histological, and biochemical. Transcriptome technology was used to investigate the related signaling pathways and potential mechanisms after treatment with AA, which was verified by RT-PCR technology.

RESULTS

The results showed that the total amounts of AAI, AAII, and ALI ranged from 0.0004 to 0.1858 g·g-1( %) from different samples, including Aristolochia debilis, Fibraurea recisa, Asarum, Wantongjingu tablets, Jiuweiqianghuo granules, and Xiaoqinglong granules in descending order. Moreover, compared with the negative/blank control, substantial changes in phenotype, histomorphology and biochemical parameters of renal function were observed in the groups challenged with the sublethal concentration of drugs. The transcriptomics results showed the upregulation of most genes in PERK/ATF4/CHOP, ATM/Chk2/p53, Caspase/Bax/Bcl-2a, TGF/Smad/ERK, PI3K/Akt, induced by aristolochic acid analogues, which were essentially consistent with those of the q-RT-PCR experiments, highlighting the similar toxicity response to the previously published article with the other traditional evaluation model.

CONCLUSION

The stability, accuracy and feasibility of the zebrafish larval model in screening and evaluating the nephrotoxicity of TCM were validated for the first time on the AAs-related drugs in a unified manner, confirming and promoting the applicability of zebrafish in assessing nephrotoxicity of samples with complex chemical character.

Vitamin D Receptor Activation Attenuates Olanzapine-Induced Dyslipidemia in Mice Through Alleviating Hepatic Endoplasmic Reticulum Stress

The involvement of vitamin D (VD) signaling in atypical antipsychotics (AAPs)-induced metabolic disturbances has been previously established. This study aims to elucidate the role of VD in maintaining endoplasmic reticulum (ER) homeostasis and its impact on AAPs-induced metabolic adverse effects. Female C57BL/6 mice receive either calcitriol or vehicle one week prior to co-treatment with olanzapine (OLZ) for an additional four weeks. Metabolic parameters, hepatic ER homeostasis, and the SREBPs pathway are assessed through biochemical assays and protein expression profiling. HepG2 cells are transfected with vitamin D receptor (VDR) siRNA for VDR knockdown. OLZ-treated HepG2 cells are exposed to calcitriol to examine its effects on SREBPs and the unfolded protein response (UPR) pathways. VDR activation by calcitriol reduces OLZ-induced hepatic ER stress, leading to decreased SREBPs activity and lipid accumulation. Conversely, the knockdown of VDR in HepG2 cells diminishes the protective effects of calcitriol against OLZ-induced ER stress and SREBPs activation. This resulted in sustained UPR activation, elevated cleaved SREBPs levels, and increased lipid accumulation. These findings highlight an essential role of VDR signaling in the beneficial effects of VD on OLZ-induced metabolic side effects. Targeting VDR to resolve ER stress is likely an applicable therapeutic strategy for AAPs-induced metabolic disturbances.

1,25D/VDR inhibits pancreatic β cell ferroptosis by downregulating FOXO1 expression in diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a global health problem that seriously threatens human health. Vitamin D (VD) has antidiabetic effects. However, the protective mechanism of 1,25-dihydroxyvitamin D3 (1,25D) on T2DM is still unclear.

METHODS

A rat model of T2DM was constructed using a high-fat diet combined with intraperitoneal injection of streptozotocin (STZ). Glucose tolerance was assessed by an oral glucose tolerance test (OGTT). Insulin secretion in blood and cell supernatant was determined by ELISA. Cell viability was analysed by CCK-8 assay. The level of ROS was detected by the DCFH-DA fluorescent probe method. The iron level in pancreatic tissues and cells was detected by an iron assay kit. Immunofluorescence staining was used to detect the expression of the pancreatic β cell marker CD49a. Furthermore, the protein expression levels of ferroptosis pathway-related proteins and vitamin D receptor (VDR) were detected by western blot. Downstream VDR targets were screened by proteomic sequencing.

RESULTS

The DM group had increased glucose levels and decreased insulin secretion, while 1,25D treatment decreased glucose levels and increased insulin secretion. 1,25D also suppressed DM-induced ferroptosis in pancreatic tissues in vivo. In addition, 1,25D significantly enhanced the viability of pancreatic β cells and reduced the levels of ROS and iron. 1,25D significantly upregulated the expression of VDR and the ferroptosis-related pathway protein GPX4 and downregulated the expression of ACSL4. Furthermore, knockdown of VDR reversed the effects of 1,25D on cell viability, ROS and iron levels, and ferroptosis-related protein expression in pancreatic β cells. Proteomic sequencing revealed that FOXO1 was the downstream target gene of VDR. Knockdown of FOXO1 reduced pancreatic β cell death, decreased ROS, iron and ACSL4 levels, and increased GPX4 levels.

CONCLUSION

1,25D/VDR inhibited pancreatic β cell ferroptosis in T2DM by downregulating the expression of FOXO1. This study provides a new theoretical basis for basic research on T2DM and is expected to establish a new idea for the treatment of T2DM.

Vitamin D and Beta Cells in Type 1 Diabetes: A Systematic Review

The prevalence of type 1 diabetes (T1D) is rising steadily. A potential contributor to the rise is vitamin D. In this systematic review, we examined the literature around vitamin D and T1D. We identified 22 papers examining the role of vitamin D in cultured β-cell lines, islets, or perfused pancreas, and 28 papers examining vitamin D in humans or human islets. The literature reports strong associations between T1D and low circulating vitamin D. There is also high-level (systematic reviews, meta-analyses) evidence that adequate vitamin D status in early life reduces T1D risk. Several animal studies, particularly in NOD mice, show harm from D-deficiency and benefit in most studies from vitamin D treatment/supplementation. Short-term streptozotocin studies show a β-cell survival effect with supplementation. Human studies report associations between VDR polymorphisms and T1D risk and β-cell function, as assessed by C-peptide. In view of those outcomes, the variable results in human trials are generally disappointing. Most studies using 1,25D, the active form of vitamin D were ineffective. Similarly, studies using other forms of vitamin D were predominantly ineffective. However, it is interesting to note that all but one of the studies testing 25D reported benefit. Together, this suggests that maintenance of optimal circulating 25D levels may reduce the risk of T1D and that it may have potential for benefits in delaying the development of absolute or near-absolute C-peptide deficiency. Given the near-complete loss of β-cells by the time of clinical diagnosis, vitamin D is much less likely to be useful after disease-onset. However, given the very low toxicity of 25D, and the known benefits of preservation of C-peptide positivity for long-term complications risk, we recommend considering daily cholecalciferol supplementation in people with T1D and people at high risk of T1D, especially if they have vitamin D insufficiency.

Curcumin ameliorates HO-induced injury through SIRT1-PERK-CHOP pathway in pancreatic beta cells

Oxidative stress and endoplasmic reticulum (ER) stress play crucial roles in pancreatic β cell destruction, leading to the development and progression of type 1 diabetes mellitus (T1DM). Curcumin, extracted from plant turmeric, possesses multiple bioactivities such as antioxidant, anti-inflammatory and anti-apoptosis properties and . However, it remains unknown whether curcumin improves ER stress to prevent β cells from apoptosis. In this study, we aim to investigate the role and mechanism of curcumin in ameliorating HO-induced injury in MIN6 (a mouse insulinoma cell line) cells. Cell viability is examined by CCK8 assay. Hoechst 33258 staining, TUNEL and flow cytometric assay are performed to detect cell apoptosis. The relative amounts of reactive oxygen species (ROS) are measured by DCFH-DA. WST-8 is used to determine the total superoxide dismutase (SOD) activity. Protein expressions are determined by western blot analysis and immunofluorescence staining. Pretreatment with curcumin prevents MIN6 cells from HO-induced cell apoptosis. Curcumin decreases ROS generation and inhibits protein kinase like ER kinase (PERK)-C/EBP homologous protein (CHOP) signaling axis, one of the critical branches of ER stress pathway. Moreover, incubation with curcumin activates silent information regulator 1 (SIRT1) expression and subsequently decreases the expression of CHOP. Additionally, EX527, a specific inhibitor of SIRT1, blocks the protective effect of curcumin on MIN6 cells exposed to HO. In sum, curcumin inhibits the PERK-CHOP pathway of ER stress mediated by SIRT1 and thus ameliorates HO-induced MIN6 cell apoptosis, suggesting that curcumin and SIRT1 may provide a potential therapeutic approach for T1DM.

Non-coding RNAs in diabetes mellitus and diabetic cardiovascular disease

More than 10% of the world's population already suffers from varying degrees of diabetes mellitus (DM), but there is still no cure for the disease. Cardiovascular disease (CVD) is one of the most common and dangerous of the many health complications that can be brought on by DM, and has become the leading cause of death in people with diabetes. While research on DM and associated CVD is advancing, the specific mechanisms of their development are still unclear. Given the threat of DM and CVD to humans, the search for new predictive markers and therapeutic ideas is imminent. Non-coding RNAs (ncRNAs) have been a popular subject of research in recent years. Although they do not encode proteins, they play an important role in living organisms, and they can cause disease when their expression is abnormal. Numerous studies have observed aberrant ncRNAs in patients with DM complications, suggesting that they may play an important role in the development of DM and CVD and could potentially act as biomarkers for diagnosis. There is additional evidence that treatment with existing drugs for DM, such as metformin, alters ncRNA expression levels, suggesting that regulation of ncRNA expression may be a key mechanism in future DM treatment. In this review, we assess the role of ncRNAs in the development of DM and CVD, as well as the evidence for ncRNAs as potential therapeutic targets, and make use of bioinformatics to analyze differential ncRNAs with potential functions in DM.