Ablation of the Chaperone Protein ERdj5 Results in a Sjögren's Syndrome-Like Phenotype in Mice, Consistent With an Upregulated Unfolded Protein Response in Human Patients

DNAJC10 maintains survival and self-renewal of leukemia stem cells through PERK branch of the unfolded protein response

Leukemia stem cells (LSC) require frequent adaptation to maintain their self-renewal ability in the face of longer exposure to cell-intrinsic and cell-extrinsic stresses. However, the mechanisms by which LSC maintain their leukemogenic activities, and how individual LSC respond to stress, remain poorly understood. Here, we found that DNAJC10, a member of HSP40 family, was frequently up-regulated in various types of acute myeloid leukemia (AML) and in LSC-enriched cells. Deficiency of DNAJC10 leads to a dramatic increase in the apoptosis of both human leukemia cell lines and LSC-enriched populations. Although DNAJC10 is not required for normal hematopoiesis, deficiency of Dnajc10 significantly abrogated AML development and suppressed self-renewal of LSC in the MLL-AF9-induced murine leukemia model. Mechanistically, inhibition of DNAJC10 specifically induces endoplasmic reticulum stress and promotes activation of PERK-EIF2α-ATF4 branch of unfolded protein response (UPR). Blocking PERK by GSK2606414 (PERKi) or shRNA rescued the loss of function of DNAJC10 both in vitro and in vivo. Importantly, deficiency of DNAJC10 increased sensitivity of AML cells to daunorubicin (DNR) and cytarabine (Ara-C). These data revealed that DNAJC10 functions as an oncogene in MLL-AF9-induced AML via regulation of the PERK branch of the UPR. DNAJC10 may be an ideal therapeutic target for eliminating LSC, and improving the effectiveness of DNR and Ara-C.

Acute kidney injury: exploring endoplasmic reticulum stress-mediated cell death

Acute kidney injury (AKI) is a global health problem, given its substantial morbidity and mortality rates. A better understanding of the mechanisms and factors contributing to AKI has the potential to guide interventions aimed at mitigating the risk of AKI and its subsequent unfavorable outcomes. Endoplasmic reticulum stress (ERS) is an intrinsic protective mechanism against external stressors. ERS occurs when the endoplasmic reticulum (ER) cannot deal with accumulated misfolded proteins completely. Excess ERS can eventually cause pathological reactions, triggering various programmed cell death (autophagy, ferroptosis, apoptosis, pyroptosis). This article provides an overview of the latest research progress in deciphering the interaction between ERS and different programmed cell death. Additionally, the report consolidates insights into the roles of ERS in AKI and highlights the potential avenues for targeting ERS as a treatment direction toward for AKI.

Endoplasmic reticulum stress in T cell-mediated diseases

T cells synthesize a large number of proteins during their development, activation, and differentiation. The build-up of misfolded and unfolded proteins in the endoplasmic reticulum, however, causes endoplasmic reticulum (ER) stress. Thus, T cells can maintain ER homeostasis via endoplasmic reticulum-associated degradation, unfolded protein response, and autophagy. In T cell-mediated diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjogren's syndrome, type 1 diabetes and vitiligo, ER stress caused by changes in the internal microenvironment can cause disease progression by affecting T cell homeostasis. This review discusses ER stress in T cell formation, activation, differentiation, and T cell-mediated illnesses, and may offer new perspectives on the involvement of T cells in autoimmune disorders and cancer.

Genetic disruption of mammalian endoplasmic reticulum-associated protein degradation: Human phenotypes and animal and cellular disease models

Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway.

ERdj5 protects goblet cells from endoplasmic reticulum stress-mediated apoptosis under inflammatory conditions

Endoplasmic reticulum stress is closely associated with the onset and progression of inflammatory bowel disease. ERdj5 is an endoplasmic reticulum-resident protein disulfide reductase that mediates the cleavage and degradation of misfolded proteins. Although ERdj5 expression is significantly higher in the colonic tissues of patients with inflammatory bowel disease than in healthy controls, its role in inflammatory bowel disease has not yet been reported. In the current study, we used ERdj5-knockout mice to investigate the potential roles of ERdj5 in inflammatory bowel disease. ERdj5 deficiency causes severe inflammation in mouse colitis models and weakens gut barrier function by increasing NF-κB-mediated inflammation. ERdj5 may not be indispensable for goblet cell function under steady-state conditions, but its deficiency induces goblet cell apoptosis under inflammatory conditions. Treatment of ERdj5-knockout mice with the chemical chaperone ursodeoxycholic acid ameliorated severe colitis by reducing endoplasmic reticulum stress. These findings highlight the important role of ERdj5 in preserving goblet cell viability and function by resolving endoplasmic reticulum stress.

Loss of ERdj5 exacerbates oxidative stress in mice with alcoholic liver disease via suppressing Nrf2

Alcoholic liver disease is the major cause of chronic liver diseases. Excessive alcohol intake results in endoplasmic reticulum (ER) stress. ERdj5, a member of DNAJ family, is an ER-resident chaperone protein, whose role in alcoholic liver disease remains to be investigated. In this study, we aim to address the effect of ERdj5 on alcoholic liver disease and the underlying mechanism. Hepatic Dnajc10 (ERdj5) mRNA expression was elevated in both human and mouse alcoholic hepatitis. In mice subjected to chronic and binge ethanol feeding, ERdj5 levels were also markedly increased. Hepatic Dnajc10 correlated with Xbp1s mRNA. Tunicamycin, an ER stress inducer, increased ERdj5 levels. Dnajc10 knockout mice exhibited exacerbated alcohol-induced liver injury and hepatic steatosis. However, the macrophage numbers and chemokine levels were similar to those in wild-type mice. Depletion of Dnajc10 promoted oxidative stress. Ethanol feeding increased hepatic H₂O₂ levels, and these were further increased in Dnajc10 knockout mice. Additionally, Dnajc10-deficient hepatocytes produced large amounts of reactive oxygen species. Notably, Nrf2, a central regulator of oxidative stress, was decreased by depletion of Dnajc10 in the nuclear fraction of ethanol-treated mouse liver. Consistently, liver tissues from ethanol-fed Dnajc10 knockout mice had reduced expression of downstream antioxidant genes. Furthermore, hepatic glutathione content in the liver of knockout mice declined compared to wild-type mice. In conclusion, our results demonstrate that ethanol-induced ERdj5 may regulate the Nrf2 pathway and glutathione contents, and have protective effects on liver damage and alcohol-mediated oxidative stress in mice. These suggest that ERdj5 has the potential to protect against alcoholic liver disease.

Ca2+ imbalance caused by ERdj5 deletion affects mitochondrial fragmentation

The endoplasmic reticulum (ER) is the organelle responsible for the folding of secretory/membrane proteins and acts as a dynamic calcium ion (Ca²⁺) store involved in various cellular signalling pathways. Previously, we reported that the ER-resident disulfide reductase ERdj5 is involved in the ER-associated degradation (ERAD) of misfolded proteins in the ER and the activation of SERCA2b, a Ca²⁺ pump on the ER membrane. These results highlighted the importance of the regulation of redox activity in both Ca²⁺ and protein homeostasis in the ER. Here, we show that the deletion of ERdj5 causes an imbalance in intracellular Ca²⁺ homeostasis, the activation of Drp1, a cytosolic GTPase involved in mitochondrial fission, and finally the aberrant fragmentation of mitochondria, which affects cell viability as well as phenotype with features of cellular senescence. Thus, ERdj5-mediated regulation of intracellular Ca²⁺ is essential for the maintenance of mitochondrial homeostasis involved in cellular senescence.

Deficiency of β-arrestin2 alleviates apoptosis through GRP78-ATF6-CHOP signaling pathway in primary Sjögren's syndrome

The etiology of primary Sjögren's syndrome (pSS) remains unknown, and there is no ideal drug for the specific treatment of pSS. β-arrestin2 is a key protein that mediates desensitization and internalization of G protein-coupled receptors (GPCRs) and it participates in inflammatory and immune responses that have been found to mediate apoptosis in autoimmune disease. In this study, we established an experimental Sjögren's syndrome (ESS) mouse model to elucidate the molecular mechanisms of β-arrestin2 in pSS. First, excessive activation of β-arrestin2 and GRP78-ATF6-CHOP apoptosis signaling were detected in specimens from pSS patients. In vivo, we found that inhibition of GRP78-ATF6-CHOP apoptosis signaling improved ESS symptoms, and the targeted deletion of β-arrestin2 significantly increased saliva flow, alleviated salivary gland indices, and improved tissue integrity in the ESS model by downregulating GRP78-ATF6-CHOP apoptosis signaling. In vitro, we used IFNα to stimulate human salivary gland epithelial cells (HSGECs), and the results showed that IFNα activated GRP78-ATF6-CHOP apoptosis signaling, decreased cell viability, and induced apoptosis, which were negatively regulated by the ERS inhibitor 4-PBA. In addition, β-arrestin2 depletion downregulated GRP78-ATF6-CHOP apoptosis signaling to alleviate cell apoptosis, and the effect depended on the interaction between GRP78 and β-arrestin2. In summary, our results suggest that excessive activation of GRP78-ATF6-CHOP apoptosis signaling is involved in the pathogenesis of pSS and that β-arrestin2 encourages inflammation-induced epithelial apoptosis through GRP78-ATF6-CHOP apoptosis signaling. This research further clarified the underlying role of β-arrestin2 and provided an experimental foundation for β-arrestin2 depletion in the treatment of the human autoimmune disorder pSS.

Deregulation of the Kallikrein Protease Family in the Salivary Glands of the Sjögren's Syndrome ERdj5 Knockout Mouse Model

Introduction

The purpose of this study was to identify differentially expressed proteins in salivary glands of the ERdj5 knockout mouse model for Sjögren's syndrome and to elucidate possible mechanisms for the morbid phenotype development. At the same time, we describe for the first time the sexual dimorphism of the murine submandibular salivary gland at the proteome level.

Methods

We performed Liquid Chromatography/Mass Spectrometry in salivary gland tissues from both sexes of ERdj5 knockout and 129SV wildtype mice. The resulting list of proteins was evaluated with bioinformatic analysis and selected proteins were validated by western blot and immunohistochemistry and further analyzed at the transcription level by qRT-PCR.

Results

We identified 88 deregulated proteins in females, and 55 in males in wildtype vs knockout comparisons. In both sexes, Kallikrein 1b22 was highly upregulated (fold change>25, ANOVA p<0.0001), while all other proteases of this family were either downregulated or not significantly affected by the genotype. Bioinformatic analysis revealed a possible connection with the downregulated NGF that was further validated by independent methods. Concurrently, we identified 416 proteins that were significantly different in the salivary gland proteome of wildtype female vs male mice and highlighted pathways that could be driving the strong female bias of the pathology.

Conclusion

Our research provides a list of novel targets and supports the involvement of an NGF-mediating proteolytic deregulation pathway as a focus point towards the better understanding of the underlying mechanism of Sjögren's syndrome.

Recent Advances in Mouse Models of Sjögren's Syndrome

Sjögren's syndrome (SS) is a complex rheumatoid disease that mainly affects exocrine glands, resulting in xerostomia (dry mouth) and xerophthalmia (dry eye). SS is characterized by autoantibodies, infiltration into exocrine glands, and ectopic expression of MHC II molecules on glandular epithelial cells. In contrast to the well-characterized clinical and immunological features, the etiology and pathogenesis of SS remain largely unknown. Animal models are powerful research tools for elucidating the pathogenesis of human diseases. To date, many mouse models of SS, including induced models, in which disease is induced in mice, and genetic models, in which mice spontaneously develop SS-like disease, have been established. These mouse models have provided new insight into the pathogenesis of SS. In this review, we aim to provide a comprehensive overview of recent advances in the field of experimental SS.

AAV-mediated ERdj5 overexpression protects against P23H rhodopsin toxicity

Rhodopsin misfolding caused by the P23H mutation is a major cause of autosomal dominant retinitis pigmentosa (adRP). To date, there are no effective treatments for adRP. The BiP co-chaperone and reductase ERdj5 (DNAJC10) is part of the endoplasmic reticulum (ER) quality control machinery, and previous studies have shown that overexpression of ERdj5 in vitro enhanced the degradation of P23H rhodopsin, whereas knockdown of ERdj5 increased P23H rhodopsin ER retention and aggregation. Here, we investigated the role of ERdj5 in photoreceptor homeostasis in vivo by using an Erdj5 knockout mouse crossed with the P23H knock-in mouse and by adeno-associated viral (AAV) vector-mediated gene augmentation of ERdj5 in P23H-3 rats. Electroretinogram (ERG) and optical coherence tomography of Erdj5-/- and P23H+/-:Erdj5-/- mice showed no effect of ERdj5 ablation on retinal function or photoreceptor survival. Rhodopsin levels and localization were similar to those of control animals at a range of time points. By contrast, when AAV2/8-ERdj5-HA was subretinally injected into P23H-3 rats, analysis of the full-field ERG suggested that overexpression of ERdj5 reduced visual function loss 10 weeks post-injection (PI). This correlated with a significant preservation of photoreceptor cells at 4 and 10 weeks PI. Assessment of the outer nuclear layer (ONL) morphology showed preserved ONL thickness and reduced rhodopsin retention in the ONL in the injected superior retina. Overall, these data suggest that manipulation of the ER quality control and ER-associated degradation factors to promote mutant protein degradation could be beneficial for the treatment of adRP caused by mutant rhodopsin.

Autoimmune epithelitis (Sjögren's syndrome); the impact of metabolic status of glandular epithelial cells on auto-immunogenicity

It is well established that distinct cell metabolic alterations strongly contribute to the modulation of innate and adaptive immune responses. In the past decade the term immunometabolism has been introduced to describe the intracellular metabolic shifts of immune cells that lead to alterations of their functions. The pathogenesis of Sjögren's syndrome (SS), also referred to as autoimmune epithelitis, is not completely understood, but strong evidence supports the central role of the salivary glandular epithelial cells which are the target cells in the initiation of the autoimmune responses. Moreover, the altered epithelial functional phenotype, observed in the salivary gland lesion, may explain their disturbed secretory as well as immunoregulatory functions. From an immunometabolic perspective we have focused our studies on the endoplasmic reticulum (ER) of the salivary gland epithelial cells (SGEC) and the implication of its altered functions in the immunogenicity of these cells in SS. We showed that ER of SGEC in SS patients in situ is stressed and extensively dilated. Using salivary gland cell cultures, we studied in vitro the effect of ER stress on the metabolic behavior and viability of the cells. ER stress induced by thapsigargin increased spliced X-box binding protein-1 (XBP-1, transcription factor that increases the transcription of UPR target genes) levels in a time-dependent manner followed by autophagy and resulted to cell apoptosis. In apoptotic cells, we observed that the autoantigens Ro52 and La were redistributed in apoptotic blebs. During the induction of ER stress autophagy rescued the cells from apoptosis acting as a protective mechanism. We have also shown that adiponectin, a multifunctional hormone, is upregulated in the SGEC of SS patients acting in an autocrine or paracrine manner in the same cells. Adiponectin through activation of AMPK, the major sensor for cell energy demands, protected SGEC from apoptosis. Our results in combination with the work of others indicate that any effort of cell adaptation to ER stress may up regulate a proinflammatory milieu. This enhances the notion that metabolic alterations of the targeted epithelial cells in SS, independently of the cause, may induce an immunogenic phenotype. Therefore, SGEC have the potential to directly regulate susceptibility to and/or severity of autoimmune responses. Since adiponectin plays a vital role in the viability of SGEC through phosphorylation of AMPK, therapeutic interventions using PPAR agonists that upregulate adiponectin and concomitantly modify the energy metabolism, may be promising candidates for therapeutic intervention in SS.