A calcium-dependent protease as a potential therapeutic target for Wolfram syndrome.

Wolfram syndrome is a genetic disorder characterized by diabetes and neurodegeneration and considered as an endoplasmic reticulum (ER) disease. Despite the underlying importance of ER dysfunction in Wolfram syndrome and the identification of two causative genes, Wolfram syndrome 1 (WFS1) and Wolfram syndrome 2 (WFS2), a molecular mechanism linking the ER to death of neurons and ß cells has not been elucidated. Here we implicate calpain 2 in the mechanism of cell death in Wolfram syndrome. Calpain 2 is negatively regulated by WFS2, and elevated activation of calpain 2 by WFS2-knockdown correlates with cell death. Calpain activation is also induced by high cytosolic calcium mediated by the loss of function of WFS1. Calpain hyperactivation is observed in the WFS1 knockout mouse as well as in neural progenitor cells derived from induced pluripotent stem (iPS) cells of Wolfram syndrome patients. A small-scale small-molecule screen targeting ER calcium homeostasis reveals that dantrolene can prevent cell death in neural progenitor cells derived from Wolfram syndrome iPS cells. Our results demonstrate that calpain and the pathway leading its activation provides potential therapeutic targets for Wolfram syndrome and other ER diseases.

Thioredoxin-interacting protein mediates ER stress-induced ß cell death through initiation of the inflammasome.

Recent clinical and experimental evidence suggests that endoplasmic reticulum (ER) stress contributes to the life-and-death decisions of ß cells during the progression of type 1 and type 2 diabetes. Although crosstalk between inflammation and ER stress has been suggested to play a significant role in ß cell dysfunction and death, a key molecule connecting ER stress to inflammation has not been identified. Here we report that thioredoxin-interacting protein (TXNIP) is a critical signaling node that links ER stress and inflammation. TXNIP is induced by ER stress through the PERK and IRE1 pathways, induces IL-1ß mRNA transcription, activates IL-1ß production by the NLRP3 inflammasome, and mediates ER stress-mediated ß cell death. Collectively, our results suggest that TXNIP is a potential therapeutic target for diabetes and ER stress-related human diseases such as Wolfram syndrome.

Protein arginine methyltransferase 5 (Prmt5) promotes gene expression of peroxisome proliferator-activated receptor γ2 (PPARγ2) and its target genes during adipogenesis.

Regulation of adipose tissue formation by adipogenic-regulatory proteins has long been a topic of interest given the ever-increasing health concerns of obesity and type 2 diabetes in the general population. Differentiation of precursor cells into adipocytes involves a complex network of cofactors that facilitate the functions of transcriptional regulators from the CCATT/enhancer binding protein, and the peroxisome proliferator-activated receptor (PPAR) families. Many of these cofactors are enzymes that modulate the structure of chromatin by altering histone-DNA contacts in an ATP-dependent manner or by posttranslationally modifying the histone proteins. Here we report that inhibition of protein arginine methyltransferase 5 (Prmt5) expression in multiple cell culture models for adipogenesis prevented the activation of adipogenic genes. In contrast, overexpression of Prmt5 enhanced adipogenic gene expression and differentiation. Chromatin immunoprecipitation experiments indicated that Prmt5 binds to and dimethylates histones at adipogenic promoters. Furthermore, the presence of Prmt5 promoted the binding of ATP-dependent chromatin-remodeling enzymes and was required for the binding of PPARγ2 at PPARγ2-regulated promoters. The data indicate that Prmt5 acts as a coactivator for the activation of adipogenic gene expression and promotes adipogenic differentiation.

Measuring ER stress and the unfolded protein response using mammalian tissue culture system.

The endoplasmic reticulum (ER) functions to properly fold and process secreted and transmembrane proteins. Environmental and genetic factors that disrupt ER function cause an accumulation of misfolded and unfolded proteins in the ER lumen, a condition termed ER stress. ER stress activates a signaling network called the Unfolded Protein Response (UPR) to alleviate this stress and restore ER homeostasis, promoting cell survival and adaptation. However, under unresolvable ER stress conditions, the UPR promotes apoptosis. Here, we discuss the current methods to measure ER stress levels, UPR activation, and subsequent pathways in mammalian cells. These methods will assist us in understanding the UPR and its contribution to ER stress-related disorders such as diabetes and neurodegeneration.

The binary switch that controls the life and death decisions of ER stressed ß cells.

Diabetes mellitus is a group of common metabolic disorders defined by hyperglycemia. One of the most important factors contributing to hyperglycemia is dysfunction and death of ß cells. Increasing experimental, clinical, and genetic evidence indicates that endoplasmic reticulum (ER) stress plays an important role in ß cell dysfunction and death during the progression of type 1 and type 2 diabetes as well as genetic forms of diabetes such as Wolfram syndrome. The mechanisms of ER stress-mediated ß cell dysfunction and death are complex and not homogenous. Here we review the recent key findings on the role of ER stress and the unfolded protein response (UPR) in ß cells and the mechanisms of ER stress-mediated ß cell dysfunction and death. Complete understanding of these mechanisms will lead to novel therapeutic modalities for diabetes.

The binary switch between life and death of endoplasmic reticulum-stressed beta cells.

PURPOSE OF REVIEW: beta-Cell death is an important pathogenic component of both type 1 and type 2 diabetes. However, the specific molecular pathways and interactions involved in this process are not completely understood. Increasing evidence indicates that a type of cell stress called endoplasmic reticulum stress (ER stress) plays an important role in beta-cell death. In the present article, we discuss a potential paradigm of ER stress-mediated beta-cell death. RECENT FINDINGS: Upon ER stress conditions, a signaling network termed the unfolded protein response (UPR) is activated. The UPR regulates adaptive effectors to attenuate ER stress and restore ER homeostasis promoting cell survival. Paradoxically the UPR also regulates apoptotic effectors. When adaptive effectors fail to attenuate ER stress, these apoptotic effectors take into effect leading to cell death. The nature of this switch between life and death is currently under study. SUMMARY: Depending on the nature of the stress condition, the UPR either protects beta cells or promotes their death. The mechanisms of this switch are not well understood but involve the balance between adaptive and apoptotic factors regulated by the UPR. In the present article, we review examples of this UPR balancing act between life and death and the potential mechanisms involved.

Wolfram syndrome 1 gene negatively regulates ER stress signaling in rodent and human cells.

Wolfram syndrome is an autosomal-recessive disorder characterized by insulin-dependent diabetes mellitus, caused by nonautoimmune loss of beta cells, and neurological dysfunctions. We have previously shown that mutations in the Wolfram syndrome 1 (WFS1) gene cause Wolfram syndrome and that WFS1 has a protective function against ER stress. However, it remained to be determined how WFS1 mitigates ER stress. Here we have shown in rodent and human cell lines that WFS1 negatively regulates a key transcription factor involved in ER stress signaling, activating transcription factor 6alpha (ATF6alpha), through the ubiquitin-proteasome pathway. WFS1 suppressed expression of ATF6alpha target genes and repressed ATF6alpha-mediated activation of the ER stress response element (ERSE) promoter. Moreover, WFS1 stabilized the E3 ubiquitin ligase HRD1, brought ATF6alpha to the proteasome, and enhanced its ubiquitination and proteasome-mediated degradation, leading to suppression of ER stress signaling. Consistent with these data, beta cells from WFS1-deficient mice and lymphocytes from patients with Wolfram syndrome exhibited dysregulated ER stress signaling through upregulation of ATF6alpha and downregulation of HRD1. These results reveal a role for WFS1 in the negative regulation of ER stress signaling and in the pathogenesis of diseases involving chronic, unresolvable ER stress, such as pancreatic beta cell death in diabetes.

Valproate, a mood stabilizer, induces WFS1 expression and modulates its interaction with ER stress protein GRP94.

BACKGROUND: Valproate is a standard treatment for bipolar disorder and a first-line mood stabilizer. The molecular mechanisms underlying its actions in bipolar disorder are unclear. It has been suggested that the action of valproate is linked to changes in gene expression and induction of endoplasmic reticulum (ER) stress-response proteins. PRINCIPAL FINDINGS: Here we show that valproate modulates the ER stress response through the regulation of WFS1, an important component for mitigating ER stress. Therapeutic concentrations of valproate induce expression of WFS1 mRNA and activate the WFS1 promoter. In addition, WFS1 forms a complex with GRP94, an ER stress-response protein, in which valproate dose-dependently enhances its dissociation from GRP94. CONCLUSIONS: These results suggest that the therapeutic effects of valproate in bipolar disorder may be mediated by WFS1 expression and its dissociation from GRP94.