Calcitriol inhibits apoptosis via activation of autophagy in hyperosmotic stress stimulated corneal epithelial cells in vivo and in vitro

Calcitriol ameliorates the progression of hepatic fibrosis through autophagy-related gene 16-like 1-mediated autophagy

BACKGROUND

Calcitriol has the potential to counteract fibrotic diseases beyond its classical action of maintaining calcium and bone metabolism; however, its functional mechanism remains unknown. Autophagy-related gene 16-like 1 (Atg16l1) is one of the genes related to autophagy and is involved in protecting against fibrotic diseases. The present study aimed to explore the contribution of autophagy to the inhibition of calcitriol-induced hepatic fibrosis, as well as its potential molecular mechanism.

METHODS

Carbon tetrachloride (Ccl4)-treated mice were established as hepatic fibrosis models and received calcitriol treatment for 6 weeks. Quantification of Sirius red staining and measurement of key fibrotic markers (collagen-1 and α-SMA) was performed to detect hepatic fibrosis. Chloroquine (CQ) treatment was used to observe autophagic flux, and 3-methyladenine (3-MA) was used to inhibit autophagy. Furthermore, the effects of calcitriol on transforming growth factor β1 (TGFβ1)-stimulated primary hepatic stellate cells (HSCs) were detected. Downregulation of Atg16l1 or vitamin D receptor (VDR) in LX-2 cells was used to explore the mechanism of action of calcitriol in fibrosis and autophagy. Additionally, the electrophoretic mobility shift assay (EMSA) was used to investigate the interactions between VDR and ATG16L1.

RESULTS

Calcitriol increased the expression of VDR and ATG16L1, enhanced autophagy and attenuated hepatic fibrosis. 3-MA treatment and VDR silencing abolished the protective effects of calcitriol against fibrosis. Calcitriol-induced anti-fibrosis effects were blocked by ATG16L1 suppression. Furthermore, VDR bound to the ATG16L1 promoter and downregulation of VDR decreased the expression of ATG16L1 in LX-2 cells.

CONCLUSION

Calcitriol mitigates hepatic fibrosis partly through ATG16L1-mediated autophagy.

Puerarin alleviates hyperosmotic stress-induced oxidative stress, inflammation, apoptosis and barrier damage of human corneal epithelial cells by targeting SIRT1/NLRP3 signaling

The increase of tear osmolarity caused by excessive evaporation of tear phase is the main pathological mechanism of dry eye disease (DED). Puerarin, the major bioactive ingredient isolated from the root of the Pueraria lobata (Willd.) Ohwi, has been reported to improve ophthalmic diseases in clinic. However, the effect and the potential regulatory mechanism related to silent information regulator sirtuin 1 (SIRT1)/NOD-like receptor family pyrin domain containing 3 (NLRP3) signaling of puerarin in DED has not been evaluated. In this study, we aimed to explore the effect and mechanism of hyperosmotic stress (Hyp)-induced human corneal epithelial cell line (HCE-2). The viability of HCE-2 cells induced by Hyp with or without puerarin treatment was assessed by a CCK-8 assay. Results indicated that puerarin treatment enhanced cell viability, reduced reactive oxygen species (ROS) content, increased CAT and SOD activities, and elevated the ratio of GSH/GSSG in HCE-2 cells exposed to Hyp. Besides, TNF-α, IL-1β and IL-6 contents were decreased by puerarin. Additionally, puerarin inhibited Hyp-induced apoptosis and barrier disruption of HCE-2 cells. Moreover, molecular docking method suggested that puerarin bound to SIRT1, and upregulated SIRT1 and downregulated NLRP3 inflammasome proteins after puerarin treatment was observed. Furthermore, SIRT1 silencing alleviated the protective effects of puerarin on Hyp-induced HCE-2 cell damage. Collectively, puerarin attenuates Hyp-induced injury of HCE-2 cells by targeting regulating SIRT1/NLRP3 signaling.

Effect of Calcitriol and Vitamin D Receptor Modulator 2 on Recovery of Injured Skeletal Muscle in Wistar Rats

Muscle injuries often result in functional limitations due to insufficient healing. This study assessed the influence of calcitriol and vitamin D Receptor Modulator 2 (VDRM2) on muscle regeneration in male Wistar rats following open blunt muscle injury. The injured left soleus muscle of the rats was treated for the first four days after trauma with local injections of either calcitriol, VDRM2, or a 10% ethanol solution (control). Although muscle strength significantly decreased post-injury, all groups showed gradual improvement but did not achieve full recovery. By the 14th day, calcitriol-treated rats significantly outperformed the control group in the incomplete tetanic force, with VDRM2-treated rats showing muscle strength values that fell between the control and calcitriol groups. Similar trends were observed in complete tetanic contractions and were confirmed histologically via muscle cell width quantification. Additionally, histological analysis showed increased cellular turnover on the fourth postoperative day in the calcitriol group, as indicated by elevated cell proliferation rates and fewer apoptotic cells. VDRM2-treated animals showed only an increased proliferative activity on day 4 after injury. No noticeable differences between the groups for CAE-positive cells or visible muscle tissue area were found. In conclusion, predominantly calcitriol positively influenced post-trauma muscle recovery, where VDRM2 had substantially lower biological activity.

Long Noncoding RNA MIATNB Regulates Hyperosmotic Stress-induced Corneal Epithelial Cell Injury by Inhibiting Autophagy in Dry Eye Disease

PURPOSE

Dry eye disease (DED) has a complex etiology and the roles of long noncoding RNAs (lncRNAs) in its pathophysiology are not completely understood. Autophagy is a self-eating process important for cell survival and homeostasis. The present study explored the role of myocardial infarction-associated transcript neighbor (MIATNB) long non-coding RNA in hyperosmolarity-induced autophagy and apoptosis in human corneal epithelial cell (HCEC)-based model of dry eye disease.

METHODS

In vitro assays were performed with a human SV40 immortalized corneal epithelial cell line. Different concentrations of NaCl were used to create hyperosmolarity. HCECs were cultured in presence of 70-120 mM NaCl for 24 h to create an in vitro model of dry eye. RT-qPCR was performed to assess the expression of dry eye related LC3B, ATG16L, BECN1, ATG1, ATG7, ATG13, ATG5, ATG10, and ATG101 mRNAs and western blot analysis of LC3B and P62 and RFP -GFP-tagged LC3. Flow cytometry and western blot analysis of caspase 3, BCL2 and BAX were performed to detect apoptosis. Chloroquine (CQ) was used to inhibit autophagy pharmacologically.

RESULTS

Autophagy flux was activated in HCECs subjected to hyperosmotic stress. Hyperosmolarity activated apoptosis and inhibited HCEC migration and autophagy. Hyperosmolarity upregulated MIATNB expression, while MIATNB knockdown inhibited autophagosome degradation and promoted HCEC apoptosis. Under hyperosmolar conditions, MIATNB knockdown also inhibited the degradation of autophagolysosomes and stimulated HCEC apoptosis.

CONCLUSION

MIATNB plays a vital role in dry eye pathogenesis and serves as a bridge between autophagy and apoptosis. Targeting MIATNB for DED treatment should be further evaluated.

Salidroside alleviates oxidative stress in dry eye disease by activating autophagy through AMPK-Sirt1 pathway

Dry eye disease (DED) is a multifactorial disease, and oxidative stress plays a crucial role in its pathogenesis. Recently, multiple studies have shown that upregulation of autophagy can protect the cornea from oxidative stress damage. The present study investigated the therapeutic effects of salidroside, the main component of Rhodiola crenulata, in both in vivo and in vitro dry eye models. The results showed that topical eye drop treatment with salidroside restored corneal epithelium damage, increased tear secretion, and reduced cornea inflammation in the DED mice. Salidroside activated autophagy through AMP-activated protein kinase (AMPK)-sirtuin-1 (Sirt1) signaling pathway, which promoted the nuclear translocation of nuclear factor erythroid-2-related factor 2 (Nrf2) and increased the expression of downstream antioxidant factors heme oxygenase-1 (HO-1) and NAD(P)H quinone dehydrogenase 1 (NQO1). This process restored antioxidant enzyme activity, reduced reactive oxygen species (ROS) accumulation, and alleviated oxidative stress. The application of autophagy inhibitor chloroquine and AMPK inhibitor Compound C reversed the therapeutic efficacy of salidroside, validating the above findings. In conclusion, our data suggest that salidroside is a promising candidate for DED treatment.

Autophagy in the normal and diseased cornea

The cornea and covering tear film are together the 'objective lens' of the eye through which 80% of light is refracted. Despite exposure to a physically harsh and at times infectious or toxic environment, transparency essential for sight is in most cases maintained. Such resiliency makes the avascular cornea a superb model for the exploration of autophagy in the regulation of homeostasis with relevancy to all organs. Nonetheless, missense mutations and inflammation respectively clog or apparently overwhelm autophagic flux to create dystrophies much like in neurodegenerative diseases or further exacerbate inflammation. Here there is opportunity to generate novel topical therapies towards the restoration of homeostasis with potential broad application.

Temporal Change in Pro-Inflammatory Cytokine Expression from Immortalized Human Corneal Epithelial Cells Exposed to Hyperosmotic Stress

PURPOSE

To determine the metabolic activity, and cytokine expression over time from immortalized human corneal epithelial cells (HCECs) exposed to hyperosmotic stress.

METHODS

HCECs were cultured and expanded in DMEM/F-12 with 10% FBS. The cells were exposed to either normal media (295 mmol/kg) or hyperosmolar media (500 mmol/kg) for 0.25, 3, 6, and 12 hours. After each exposure duration, metabolic activity was quantified using alamarBlue, and a panel of pro-inflammatory cytokines (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, TNF-α, IFN-γ, and IL-17A) was quantified using multiplexed electrochemiluminescence (Meso Scale Diagnostics, Rockville, MD).

RESULTS

Metabolic activity of the HCEC exposed to hyperosmolar conditions was significantly reduced at the 3-, 6-, and 12-hour mark compared to the control (all p < 0.01). There was no significant difference in cytokine expression between the hyperosmolar media and control at the 0.25- and 3-hour mark for all cytokines (all p ≥ 0.28). The difference in cytokine expression between the hyperosmolar media and the control was significant for IL-1β, IL-4, IL-6, IL-8, IL-12p70, IL-13, and TNF-α at the 6-hour mark (all p ≤ 0.02). No significant change in cytokine expression between the hyperosmolar media and control was noted for IL-2, IL-10, IL-17A, and IFN-γ (all p ≥ 0.74) at the 6-hour mark.

CONCLUSION

Hyperosmolar stress reduced cell metabolic activity and increased expression of IL-1β, IL-4, IL6, IL8, IL-12p70, IL-13, and TNF-α over a 6-hour period in an immortalized HCEC line.

Vitamin D, the Vitamin D Receptor, Calcitriol Analogues and Their Link with Ocular Diseases

The global prevalence of eye diseases continues to grow, bringing with it a reduction in the activity levels and quality of life of patients, and partial or complete blindness if left untreated. As such, there is considerable interest in identifying more effective therapeutic options and preventive agents. One such agent is vitamin D, known to have a range of anti-cancer, anti-angiogenic, anti-inflammatory and anti-oxidative properties, and whose deficiency is linked to the pathogenesis of a range of cardiovascular, cancer, and inflammatory diseases. This review presents the current stage of knowledge concerning the link between vitamin D and its receptor and the occurrence of eye disease, as well as the influence of analogues of calcitriol, an active metabolite of vitamin D. Generally, patients affected by various ocular disorders have vitamin D deficiency. In addition, previous findings suggest that vitamin D modulates the course of eye diseases and may serve as a marker, and that its supplementation could mitigate some disorders. However, as these studies have some limitations, we recommend further randomized trials to clarify the link between vitamin D and its activity with eye disease.

Exosomes and autophagy in ocular surface and retinal diseases: new insights into pathophysiology and treatment

BACKGROUND

Ocular surface and retinal diseases are widespread problems that cannot be ignored in today's society. However, existing prevention and treatment still have many shortcomings and limitations, and fail to effectively hinder the occurrence and development of them.

MAIN BODY

The purpose of this review is to give a detailed description of the potential mechanism of exosomes and autophagy. The eukaryotic endomembrane system refers to a range of membrane-bound organelles in the cytoplasm that are interconnected structurally and functionally, which regionalize and functionalize the cytoplasm to meet the needs of cells under different conditions. Exosomal biogenesis and autophagy are two important components of this system and are connected by lysosomal pathways. Exosomes are extracellular vesicles that contain multiple signaling molecules produced by multivesicular bodies derived from endosomes. Autophagy includes lysosome-dependent degradation and recycling pathways of cells or organelles. Recent studies have revealed that there is a common molecular mechanism between exosomes and autophagy, which have been, respectively, confirmed to involve in ocular surface and retinal diseases.

CONCLUSION

The relationship between exosomes and autophagy and is mostly focused on fundus diseases, while a deeper understanding of them will provide new directions for the pathological mechanism, diagnosis, and treatment of ocular surface and retinal diseases.

Exosomes From Human Umbilical Cord Mesenchymal Stem Cells Treat Corneal Injury via Autophagy Activation

Corneal injury (CI) affects corneal integrity and transparency, deteriorating the patient's quality of life. This study aimed to explore the molecular mechanisms by which exosomes secreted from human umbilical cord mesenchymal stem cells (hucMSC-Exos) affect autophagy in human corneal epithelial cells (HCECs) and CI models. We isolated and identified hucMSC-Exos using nanoparticle tracking analysis, transmission electron microscopy, and western blotting. The effects of hucMSC-Exos combined with autophagy regulators on HCECs and CI mice were assessed using cell viability assays, scratch assay, cell cycle assay, apoptosis assay, corneal fluorescein staining, haze grades, pathological examinations, western blotting, and quantitative polymerase chain reaction (qPCR). In vitro results indicated that hucMSC-Exos combined with the autophagy activator had positive effects in promoting the cell proliferation, migration capacity, and the cell cycle by upregulating the proportions of cells in the S phase and the expression of PCNA, Cyclin A, Cyclin E, and CDK2. Meanwhile, the combination treatment reduced the apoptotic rate of HCECs. In vivo results indicated that hucMSC-Exos especially combined them with the autophagy activator significantly alleviated corneal epithelial defects and stromal opacity, reduced the levels of the apoptotic markers Bax and cleaved Caspase-3, reduced the inflammatory response products TNF-α, IL-1β, IL-6, and CXCL-2, and increased the Bcl-2. This was achieved by upregulating pAMPK/AMPK and pULK1/ULK1 ratios, and Beclin-1 and LC3B II/I, and by downregulating the pmTOR/mTOR ratio and p62. In contrast, clinical indications, apoptosis, and inflammation were aggravated after the application of the autophagy inhibitor. HucMSC-Exos combined with an autophagy activator significantly enhanced HCECs functions and alleviated corneal defects, apoptosis, and inflammation by activating the autophagy signaling pathway, AMPK-mTOR-ULK1, providing a new biological therapy for corneal wound healing and ocular surface regeneration.

Calcitriol Alleviates MPP+- and MPTP-Induced Parthanatos Through the VDR/PARP1 Pathway in the Model of Parkinson's Disease

The pathogenesis of Parkinson’s disease (PD) is currently unclear. Recent studies have suggested a correlation between vitamin D and PD. Vitamin D and its analogs have protective effects in animal models of PD, but these studies have not clarified the mechanism. Parthanatos is a distinct type of cell death caused by excessive activation of poly (ADP-ribose) polymerase-1 (PARP1), and the activation of PARP1 in PD models suggests that parthanatos may exist in PD pathophysiology. 1,25-Dihydroxyvitamin D3 (calcitriol) is a potential inhibitor of PARP1 in macrophages. This study aimed to investigate whether calcitriol treatment improves PD models and its effects on the parthanatos pathway. A 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell model and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) subacute animal model were selected as the in vitro and in vivo PD models, and calcitriol was applied in these models. Results showed that parthanatos existed in the MPP⁺-induced cell model and pretreatment with calcitriol improved cell viability, reduced the excessive activation of PARP1, and relieved parthanatos. The application of calcitriol in the MPTP subacute animal model also improved behavioral tests, restored the damage to dopamine neurons, and reduced the activation of PARP1-related signaling pathways. To verify whether calcitriol interacts with PARP1 through its vitamin D receptor (VDR), siRNA, and overexpression plasmids were used to downregulate or overexpress VDR. Following the downregulation of VDR, the expression and activation of PARP1 increased and PARP1 was inhibited when VDR was overexpressed. Coimmunoprecipitation verified the combination of VDR and PARP1. In short, calcitriol can substantially improve parthanatos in the MPP⁺-induced cell model and MPTP model, and the protective effect might be partly through the VDR/PARP1 pathway, which provides a new possibility for the treatment of PD.

Calcitriol Alleviates Hyperosmotic Stress-Induced Corneal Epithelial Cell Damage via Inhibiting the NLRP3-ASC-Caspase-1-GSDMD Pyroptosis Pathway in Dry Eye Disease

Purpose

Inflammasome activation in response to elevated tear osmolarity behaves as an initial signal in dry eye-related corneal inflammation. Pyroptosis is another prominent consequence of inflammasome activation, which is featured by gasdermin D (GSDMD)-driven cell lysis. This study aims to explore the role of pyroptosis in dry eye, and also to verify if calcitriol, a potential therapeutic agent for dry eye, has certain effects against hyperosmotic stress (HS)-induced pyroptosis in human corneal epithelial cells (iHCECs) and the underlying mechanism.

Methods

The expression of pyroptosis executor GSDMD in tears from dry eye patients was examined using western blotting. iHCECs were grown in hyperosmotic medium (450 mOsM) to mimic the feature of elevated tear osmolality of dry eye in vitro. Exogenous calcitriol or pyroptosis inhibitor disulfiram was used. The extent of pyroptosis of iHCECs under various treatments was examined by scanning electron microscopy, caspase-1 and propidium iodide (PI) double staining by flow cytometry, immunofluorescent staining for ASC speck formation, and western blotting. Cell viability was measured by a CCK-8 assay and an LDH release assay.

Results

We found that pyroptosis was presented in dry eye patients, shown as the elevation of its effector GSDMD N-terminal domain (N-GSDMD) in patients' tears. Further in vitro results showed that HS promoted pyroptosis in human corneal epithelial cells, while exogeneous supplementation of disulfiram could reduce the number of iHCECs with pyroptotic markers. More importantly, we demonstrated that, in line with the effect of disulfiram, calcitriol could also alleviate HS-induced pyroptosis, through inhibiting the NLRP3-ASC-caspase-1-GSDMD pyroptosis pathway.

Conclusion

The current study provided direct evidence showing increased pyroptosis in dry eye patients. We demonstrated that calcitriol was able to effectively alleviate HS-induced corneal epithelial cell damage through inhibiting the NLRP3-ASC-caspase-1-GSDMD pyroptosis pathway. This study underlined calcitriol as a promising therapeutic agent for dry eye given its multiple therapeutic targets.