Pharmacological Targeting of Endoplasmic Reticulum Stress in Pancreatic Beta Cells

Potential Role of Endoplasmic Reticulum Stress in Modulating Protein Homeostasis in Oligodendrocytes to Improve White Matter Injury in Preterm Infants

Preterm white matter injury (WMI) is a demyelinating disease with high incidence and mortality in premature infants. Oligodendrocyte cells (OLs) are a specialized glial cell that produces myelin proteins and adheres to the axons providing energy and metabolic support which susceptible to endoplasmic reticulum protein quality control. Disruption of cellular protein homeostasis led to OLs dysfunction and cell death, immediately, the unfolded protein response (UPR) activated to attempt to restore the protein homeostasis via IRE1/XBP1s, PERK/eIF2α and ATF6 pathway that reduced protein translation, strengthen protein-folding capacity, and degraded unfolding/misfolded protein. Moreover, recent works have revealed the conspicuousness function of ER signaling pathways in regulating influenced factors such as calcium homeostasis, mitochondrial reactive oxygen generation, and autophagy activation to regulate protein hemostasis and improve the myelination function of OLs. Each of the regulation modes and their corresponding molecular mechanisms provides unique opportunities and distinct perspectives to obtain a deep understanding of different actions of ER stress in maintaining OLs' health and function. Therefore, our review focuses on summarizing the current understanding of ER stress on OLs' protein homeostasis micro-environment in myelination during white matter development, as well as the pathophysiology of WMI, and discussing the further potential experimental therapeutics targeting these factors that restore the function of the UPR in OLs myelination function.

Long non-coding RNA-mediated modulation of endoplasmic reticulum stress under pathological conditions

Endoplasmic reticulum (ER) stress, which ensues from an overwhelming protein folding capacity, activates the unfolded protein response (UPR) in an effort to restore cellular homeostasis. As ER stress is associated with numerous diseases, it is highly important to delineate the molecular mechanisms governing the ER stress to gain insight into the disease pathology. Long non-coding RNAs, transcripts with a length of over 200 nucleotides that do not code for proteins, interact with proteins and nucleic acids, fine-tuning the UPR to restore ER homeostasis via various modes of actions. Dysregulation of specific lncRNAs is implicated in the progression of ER stress-related diseases, presenting these molecules as promising therapeutic targets. The comprehensive analysis underscores the importance of understanding the nuanced interplay between lncRNAs and ER stress for insights into disease mechanisms. Overall, this review consolidates current knowledge, identifies research gaps and offers a roadmap for future investigations into the multifaceted roles of lncRNAs in ER stress and associated diseases to shed light on their pivotal roles in the pathogenesis of related diseases.

Endoplasmic reticulum stress in pancreatic β-cell dysfunction: The potential therapeutic role of dietary flavonoids

Diabetes mellitus (DM) is a global health burden that is characterized by the loss or dysfunction of pancreatic β-cells. In pancreatic β-cells, endoplasmic reticulum (ER) stress is a fact of life that contributes to β-cell loss or dysfunction. Despite recent advances in research, the existing treatment approaches such as lifestyle modification and use of conventional therapeutics could not prevent the loss or dysfunction of pancreatic β-cells to abrogate the disease progression. Therefore, targeting ER stress and the consequent unfolded protein response (UPR) in pancreatic β-cells may be a potential therapeutic strategy for diabetes treatment. Dietary phytochemicals have therapeutic applications in human health owing to their broad spectrum of biochemical and pharmacological activities. Flavonoids, which are commonly obtained from fruits and vegetables worldwide, have shown promising prospects in alleviating ER stress. Dietary flavonoids including quercetin, kaempferol, myricetin, isorhamnetin, fisetin, icariin, apigenin, apigetrin, vitexin, baicalein, baicalin, nobiletin hesperidin, naringenin, epigallocatechin 3-O-gallate hesperidin (EGCG), tectorigenin, liquiritigenin, and acacetin have shown inhibitory effects on ER stress in pancreatic β-cells. Dietary flavonoids modulate ER stress signaling components, chaperone proteins, transcription factors, oxidative stress, autophagy, apoptosis, and inflammatory responses to exert their pharmacological effects on pancreatic β-cells ER stress. This review focuses on the role of dietary flavonoids as potential therapeutic adjuvants in preserving pancreatic β-cells from ER stress. Highlights of the underlying mechanisms of action are also presented as well as possible strategies for clinical translation in the management of DM.

Punicalagin relieves lipotoxic injuries on pancreatic β-cells via regulating the oxidative stress and endoplasmic reticulum stress-mediated apoptosis

Cellular toxicity of hyperlipidemia has been long considered a major cause of various intractable disease such as diabetes. Discovering lipotoxicity antagonist with high efficiency and low side effects is of importance to develop therapeutics for relevant diseases. In the current study, we evaluate the anti-lipotoxic potential of punicalagin (PU) on pancreatic cells and investigate its underpinning mechanism involved. The administration of PU effectively improved cell viability, quenched intracellular reactive oxygen species, alleviated lipid peroxidation, and enhanced cellular antioxidative capacity in RINm5F cells stimulated by sodium palmitate. Besides that, PU treatment significantly inhibited the overload of mitochondrial calcium ions; alleviated the activation of endoplasmic reticulum (ER) stress mediators including glucose-regulated protein 78, protein kinase RNA-like ER kinase, eukaryotic initiation factor 2α, activating transcription factor 6, caspase 12, and C/EBP homologous protein (CHOP); and attenuated the expression of cleaved caspase 3 and poly ADP-ribose polymerase in test cells. Further RNA interference experiment results and miR211-5p expression analysis revealed that PU may directly mitigate CHOP expression and upregulate the expression of miR211-5p to reduce ER stress-induced pancreatic cell death. The efficacy of PU in maintaining redox equilibrium and diminishing ER stress on pancreatic cells stressed by hyperlipidemia suggests that PU can be used as a promising dietary natural product to safeguard the pancreatic health against lipotoxicity.

Redox-Responsive Dendrimer Nanogels Enable Ultrasound-Enhanced Chemoimmunotherapy of Pancreatic Cancer via Endoplasmic Reticulum Stress Amplification and Macrophage Polarization

Developing a multifunctional nanoplatform to achieve efficient theranostics of tumors through multi-pronged strategies remains to be challenging. Here, the design of the intelligent redox-responsive generation 3 (G3) poly(amidoamine) dendrimer nanogels (NGs) loaded with gold nanoparticles (Au NPs) and chemotherapeutic drug toyocamycin (Au/Toy@G3 NGs) for ultrasound-enhanced cancer theranostics is showcased. The constructed hybrid NGs with a size of 193 nm possess good colloidal stability under physiological conditions, and can be dissociated to release Au NPs and Toy in the reductive glutathione-rich tumor microenvironment (TME). The released Toy can promote the apoptosis of cancer cells through endoplasmic reticulum stress amplification and cause immunogenic cell death to maturate dendritic cells. The loaded Au NPs can induce the conversion of tumor-associated macrophages from M2-type to antitumor M1-type to remodulate the immunosuppressive TME. Combined with antibody-mediated immune checkpoint blockade, effective chemoimmunotherapy of a pancreatic tumor mouse model can be realized, and the chemoimmunotherapy effect can be further ultrasound enhanced due to the sonoporation-improved tumor permeability of NGs. The developed Au/Toy@G3 NGs also enable Au-mediated computed tomography imaging of tumors. The constructed responsive dendrimeric NGs tackle tumors through a multi-pronged chemoimmunotherapy strategy targeting both cancer cells and immune cells, which hold a promising potential for clinical translations.

Role of Protein Tyrosine Phosphatase 1B Inhibitor in Early Brain Injury of Subarachnoid Hemorrhage in Mice

Clinically, early brain injury (EBI), which refers to the acute injuries to the whole brain in the phase of the first 72 h following subarachnoid hemorrhage (SAH), is intensely investigated to improve neurological and psychological function. Additionally, it will be meaningful to explore new therapeutic approaches for EBI treatment to improve the prognosis of patients with SAH. To investigate the underlying neuroprotection mechanism in vitro, the Protein tyrosine phosphatase 1B inhibitor (PTP1B-IN-1) was put in primary neurons induced by OxyHb to observe neuroapoptosis, neuroinflammation, and ER stress. Then, one hundred forty male mice were subjected to Experiment two and Experiment three. The mice in the SAH24h + PTP1B-IN-1 group were given an intraperitoneal injection of 5 mg/kg PTP1B-IN-1 30 min before anesthesia. SAH grade, neurological score, brain water content, Western blot, PCR, and Transmission Electron Microscopy (TEM) were performed to observe the underlying neuroprotection mechanism in vivo. Overall, this study suggests that PTP1B-IN-1 could ameliorate neuroapoptosis, neuroinflammation, and ER stress in vitro and in vivo by regulating the IRS-2/AKT signaling pathway, suggesting that PTP1B-IN-1 may be a candidate drug for the treatment of early brain injury after SAH.

Pharmacological inhibitors of β-cell dysfunction and death as therapeutics for diabetes

More than 500 million adults suffer from diabetes worldwide, and this number is constantly increasing. Diabetes causes 5 million deaths per year and huge healthcare costs per year. β-cell death is the major cause of type 1 diabetes. β-cell secretory dysfunction plays a key role in the development of type 2 diabetes. A loss of β-cell mass due to apoptotic death has also been proposed as critical for the pathogenesis of type 2 diabetes. Death of β-cells is caused by multiple factors including pro-inflammatory cytokines, chronic hyperglycemia (glucotoxicity), certain fatty acids at high concentrations (lipotoxicity), reactive oxygen species, endoplasmic reticulum stress, and islet amyloid deposits. Unfortunately, none of the currently available antidiabetic drugs favor the maintenance of endogenous β-cell functional mass, indicating an unmet medical need. Here, we comprehensively review over the last ten years the investigation and identification of molecules of pharmacological interest for protecting β-cells against dysfunction and apoptotic death which could pave the way for the development of innovative therapies for diabetes.

Manganese-induced neuronal apoptosis: new insights into the role of endoplasmic reticulum stress in regulating autophagy-related proteins

Manganese (Mn) is an essential trace element that participates in various physiological and pathological processes. However, epidemiological observations indicate that overexposure to Mn is strongly associated with neurodegenerative disorders and has been recognized as a potential risk factor of neuronal apoptosis. Many mechanisms are involved in the pathogenesis of Mn-induced neuronal apoptosis, such as reactive oxygen species generation, neuroinflammation reactions, protein accumulation, endoplasmic reticulum stress (ER stress), and autophagy, all of which collectively accelerate the process of nerve cell damage. As sophisticated cellular processes for maintaining intracellular homeostasis, ER-mediated unfolded protein response and autophagy both play bilateral roles including cell protection and cell injury under pathophysiological conditions, which might interact with each other. Although emerging evidence suggests that ER stress is involved in regulating the compensatory activation of autophagy to promote cell survival, the inherent relationship between ER stress and autophagy on Mn-induced neurotoxicity remains obscure. Here, our review focuses on discussing the existing mechanisms and connections between ER stress, autophagy, and apoptosis, which provide a new perspective on Mn-induced neuronal apoptosis, and the pathogenesis of neurodegenerative diseases.

Chemical Chaperones to Inhibit Endoplasmic Reticulum Stress: Implications in Diseases

The endoplasmic reticulum (ER) is responsible for structural transformation or folding of de novo proteins for transport to the Golgi. When the folding capacity of the ER is exceeded or excessive accumulation of misfolded proteins occurs, the ER enters a stressed condition (ER stress) and unfolded protein responses (UPR) are triggered in order to rescue cells from the stress. Recovery of ER proceeds toward either survival or cell apoptosis. ER stress is implicated in many pathologies, such as diabetes, cardiovascular diseases, inflammatory diseases, neurodegeneration, and lysosomal storage diseases. As a survival or adaptation mechanism, chaperone molecules are upregulated to manage ER stress. Chemical versions of chaperone have been developed in search of drug candidates for ER stress-related diseases. In this review, synthetic or semi-synthetic chemical chaperones are categorized according to potential therapeutic area and listed along with their chemical structure and activity. Although only a few chemical chaperones have been approved as pharmaceutical drugs, a dramatic increase in literatures over the recent decades indicates enormous amount of efforts paid by many researchers. The efforts warrant clearer understanding of ER stress and the related diseases and consequently will offer a promising drug discovery platform with chaperone activity.

A transcriptional cross species map of pancreatic islet cells

OBJECTIVE

Pancreatic islets of Langerhans secrete hormones to regulate systemic glucose levels. Emerging evidence suggests that islet cells are functionally heterogeneous to allow a fine-tuned and efficient endocrine response to physiological changes. A precise description of the molecular basis of this heterogeneity, in particular linking animal models to human islets, is an important step towards identifying the factors critical for endocrine cell function in physiological and pathophysiological conditions.

METHODS

In this study, we used single-cell RNA sequencing to profile more than 50'000 endocrine cells isolated from healthy human, pig and mouse pancreatic islets and characterize transcriptional heterogeneity and evolutionary conservation of those cells across the three species. We systematically delineated endocrine cell types and α- and β-cell heterogeneity through prior knowledge- and data-driven gene sets shared across species, which altogether capture common and differential cellular properties, transcriptional dynamics and putative driving factors of state transitions.

RESULTS

We showed that global endocrine expression profiles correlate, and that critical identity and functional markers are shared between species, while only approximately 20% of cell type enriched expression is conserved. We resolved distinct human α- and β-cell states that form continuous transcriptional landscapes. These states differentially activate maturation and hormone secretion programs, which are related to regulatory hormone receptor expression, signaling pathways and different types of cellular stress responses. Finally, we mapped mouse and pig cells to the human reference and observed that the spectrum of human α- and β-cell heterogeneity and aspects of such functional gene expression are better recapitulated in the pig than mouse data.

CONCLUSIONS

Here, we provide a high-resolution transcriptional map of healthy human islet cells and their murine and porcine counterparts, which is easily queryable via an online interface. This comprehensive resource informs future efforts that focus on pancreatic endocrine function, failure and regeneration, and enables to assess molecular conservation in islet biology across species for translational purposes.

Targeting pancreatic β cells for diabetes treatment

Insulin is a life-saving drug for patients with type 1 diabetes; however, even today, no pharmacotherapy can prevent the loss or dysfunction of pancreatic insulin-producing β cells to stop or reverse disease progression. Thus, pancreatic β cells have been a main focus for cell-replacement and regenerative therapies as a curative treatment for diabetes. In this Review, we highlight recent advances toward the development of diabetes therapies that target β cells to enhance proliferation, redifferentiation and protection from cell death and/or enable selective killing of senescent β cells. We describe currently available therapies and their mode of action, as well as insufficiencies of glucagon-like peptide 1 (GLP-1) and insulin therapies. We discuss and summarize data collected over the last decades that support the notion that pharmacological targeting of β cell insulin signalling might protect and/or regenerate β cells as an improved treatment of patients with diabetes.

Endoplasmic Reticulum Stress and Dysregulated Autophagy in Human Pancreatic Beta Cells

Pancreatic beta cell homeostasis is crucial for the synthesis and secretion of insulin; disruption of homeostasis causes diabetes, and is a treatment target. Adaptation to endoplasmic reticulum (ER) stress through the unfolded protein response (UPR) and adequate regulation of autophagy, which are closely linked, play essential roles in this homeostasis. In diabetes, the UPR and autophagy are dysregulated, which leads to beta cell failure and death. Various studies have explored methods to preserve pancreatic beta cell function and mass by relieving ER stress and regulating autophagic activity. To promote clinical translation of these research results to potential therapeutics for diabetes, we summarize the current knowledge on ER stress and autophagy in human insulin-secreting cells.

The PERKs of mitochondria protection during stress: insights for PERK modulation in neurodegenerative and metabolic diseases

Protein kinase RNA-like ER kinase (PERK) is an endoplasmic reticulum (ER) stress sensor that responds to the accumulation of misfolded proteins. Once activated, PERK initiates signalling pathways that halt general protein production, increase the efficiency of ER quality control, and maintain redox homeostasis. PERK activation also protects mitochondrial homeostasis during stress. The location of PERK at the contact sites between the ER and the mitochondria creates a PERK-mitochondria axis that allows PERK to detect stress in both organelles, adapt their functions and prevent apoptosis. During ER stress, PERK activation triggers mitochondrial hyperfusion, preventing premature apoptotic fragmentation of the mitochondria. PERK activation also increases the formation of mitochondrial cristae and the assembly of respiratory supercomplexes, enhancing cellular ATP-generating capacity. PERK strengthens mitochondrial quality control during stress by promoting the expression of mitochondrial chaperones and proteases and by increasing mitochondrial biogenesis and mitophagy, resulting in renewal of the mitochondrial network. But how does PERK mediate all these changes in mitochondrial homeostasis? In addition to the classic PERK-eukaryotic translation initiation factor 2α (eIF2α)-activating transcription factor 4 (ATF4) pathway, PERK can activate other protective pathways - PERK-O-linked N-acetyl-glucosamine transferase (OGT), PERK-transcription factor EB (TFEB), and PERK-nuclear factor erythroid 2-related factor 2 (NRF2) - contributing to broader regulation of mitochondrial dynamics, metabolism, and quality control. The pharmacological activation of PERK is protective in models of neurodegenerative and metabolic diseases, such as Huntington's disease, progressive supranuclear palsy and obesity, while the inhibition of PERK was protective in models of Parkinson's and prion diseases and diabetes. In this review, we address the molecular mechanisms by which PERK regulates mitochondrial dynamics, metabolism and quality control, and discuss the therapeutic potential of targeting PERK in neurodegenerative and metabolic diseases.

Evaluation of potential cardiotoxicity of ammonia: l-selenomethionine inhibits ammonia-induced cardiac autophagy by activating the PI3K/AKT/mTOR signaling pathway

Ammonia is a major harmful gas in the environment of livestock and poultry. Studies have shown that excessive ammonia inhalation has adverse effects in pig heart. However, the mechanism of ammonia-induced cardiac toxicity in pigs has not been reported. L-selenomethionine is a kind of organic selenium (Se) which is easily absorbed by the body. Therefore, in this study, twenty-four 125-day-old pigs were randomly divided into 4 groups: C (control) group, A (ammonia) group, Se group (Se content: 0.5 mg kg-1), and A (ammonia) + Se group. The mechanism of ammonia-induced cardiotoxicity and the alleviating effect of L-selenomethionine were examined. The results in the A group showed as follows: a large number of myocardial fiber edema and cytoplasmic bleakness were observed in the heart; a large number of mitochondrial autophagy were observed; ATP content, ATPase activities and hematological parameters decreased significantly; Endoplasmic reticulum stress (ERS) markers (GRP78, IRE1α, ATF4, ATF6, and CHOP) were significantly induced in the mRNA and protein levels; PI3K/AKT/mTOR signaling pathway was activated; and autophagy key genes and proteins (Beclin-1, LC3, ATG3, and ATG5) were significantly up-regulated. The results of comparison between the A + Se group and the A group were as follows: the degree of edema of cardiac muscle fiber in the A + Se group was somewhat relieved; the level of mitochondrial autophagy decreased; ATP content and ATPase activities increased significantly; the mRNA and protein levels of ERS markers were significantly down-regulated; the expression level of PI3K/AKT/mTOR signaling pathway was decreased; and the mRNA and protein levels of key autophagy genes were decreased. However, the changes of these indexes in the A + Se group were still significantly different from those in the C group. Our results indicated that L-selenomethionine supplementation inhibited ammonia-induced cardiac autophagy by activating the PI3K/AKT/mTOR signaling pathway, which confirmed that L-selenomethionine could alleviate the cardiac injury caused by excessive ammonia inhalation to a certain extent. This study aims to enrich the toxicological mechanism of ammonia and provide valuable reference for future intervention of ammonia toxicity.

Genetic manipulation of stress pathways can protect stem-cell-derived islets from apoptosis in vitro

The in vitro production of stem-cell-derived islets (SC-islets) has brought forth the potential of transplanting these cells to restore glycemic control in people with diabetes. Nonetheless, alloimmune and autoimmune responses remain considerable challenges for a broad clinical implementation of β-cell replacement therapies. β-cell stress has been implicated in the onset of β-cell immunogenicity and death and is likely to contribute to β-cell failure following transplantation. We show that inducing stress and/or administering cytokines causes SC-islet apoptosis, cellular dysfunction, and an increased expression of β-cell stress- and immune-interaction-related genes. We then demonstrate that manipulating some of these genes results in enhanced protection of SC-islets from apoptosis in vitro.

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Stem-cell-derived islets (SC-islets) are vulnerable to stress in vitro

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Genetic manipulation protects SC-islets from stress-mediated apoptosis and dysfunction

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Genetic manipulation protects SC-islets from apoptosis mediated by allorecognition

Vertical sleeve gastrectomy triggers fast β-cell recovery upon overt diabetes

OBJECTIVE

The effectiveness of bariatric surgery in restoring β-cell function has been described in type-2 diabetes (T2D) patients and animal models for years, whereas the mechanistic underpinnings are largely unknown. The possibility of vertical sleeve gastrectomy (VSG) to rescue far-progressed, clinically-relevant T2D and to promote β-cell recovery has not been investigated on a single-cell level. Nevertheless, characterization of the heterogeneity and functional states of β-cells after VSG is a fundamental step to understand mechanisms of glycaemic recovery and to ultimately develop alternative, less-invasive therapies.

METHODS

We performed VSG in late-stage diabetic db/db mice and analyzed the islet transcriptome using single-cell RNA sequencing (scRNA-seq). Immunohistochemical analyses and quantification of β-cell area and proliferation complement our findings from scRNA-seq.

RESULTS

We report that VSG was superior to calorie restriction in late-stage T2D and rapidly restored normoglycaemia in morbidly obese and overt diabetic db/db mice. Single-cell profiling of islets of Langerhans showed that VSG induced distinct, intrinsic changes in the β-cell transcriptome, but not in that of α-, δ-, and PP-cells. VSG triggered fast β-cell redifferentiation and functional improvement within only two weeks of intervention, which is not seen upon calorie restriction. Furthermore, VSG expanded β-cell area by means of redifferentiation and by creating a proliferation competent β-cell state.

CONCLUSION

Collectively, our study reveals the superiority of VSG in the remission of far-progressed T2D and presents paths of β-cell regeneration and molecular pathways underlying the glycaemic benefits of VSG.

ER Stress in Cardiometabolic Diseases: From Molecular Mechanisms to Therapeutics

The endoplasmic reticulum (ER) hosts linear polypeptides and fosters natural folding of proteins through ER-residing chaperones and enzymes. Failure of the ER to align and compose proper protein architecture leads to accumulation of misfolded/unfolded proteins in the ER lumen, which disturbs ER homeostasis to provoke ER stress. Presence of ER stress initiates the cytoprotective unfolded protein response (UPR) to restore ER homeostasis or instigates a rather maladaptive UPR to promote cell death. Although a wide array of cellular processes such as persistent autophagy, dysregulated mitophagy, and secretion of proinflammatory cytokines may contribute to the onset and progression of cardiometabolic diseases, it is well perceived that ER stress also evokes the onset and development of cardiometabolic diseases, particularly cardiovascular diseases (CVDs), diabetes mellitus, obesity, and chronic kidney disease (CKD). Meanwhile, these pathological conditions further aggravate ER stress, creating a rather vicious cycle. Here in this review, we aimed at summarizing and updating the available information on ER stress in CVDs, diabetes mellitus, obesity, and CKD, hoping to offer novel insights for the management of these cardiometabolic comorbidities through regulation of ER stress.

Single-cell analysis of the human pancreas in type 2 diabetes using multi-spectral imaging mass cytometry

Type 2 diabetes mellitus (T2D) is a chronic age-related disorder characterized by hyperglycemia due to the failure of pancreatic beta cells to compensate for increased insulin demand. Despite decades of research, the pathogenic mechanisms underlying T2D remain poorly defined. Here, we use imaging mass cytometry (IMC) with a panel of 34 antibodies to simultaneously quantify markers of pancreatic exocrine, islet, and immune cells and stromal components. We analyze over 2 million cells from 16 pancreata obtained from donors with T2D and 13 pancreata from age-similar non-diabetic controls. In the T2D pancreata, we observe significant alterations in islet architecture, endocrine cell composition, and immune cell constituents. Thus, both HLA-DR-positive CD8 T cells and macrophages are enriched intra-islet in the T2D pancreas. These efforts demonstrate the utility of IMC for investigating complex events at the cellular level in order to provide insights into the pathophysiology of T2D.

The Pancreatic ß-cell Response to Secretory Demands and Adaption to Stress

Pancreatic β cells dedicate much of their protein translation capacity to producing insulin to maintain glucose homeostasis. In response to increased secretory demand, β cells can compensate by increasing insulin production capability even in the face of protracted peripheral insulin resistance. The ability to amplify insulin secretion in response to hyperglycemia is a critical facet of β-cell function, and the exact mechanisms by which this occurs have been studied for decades. To adapt to the constant and fast-changing demands for insulin production, β cells use the unfolded protein response of the endoplasmic reticulum. Failure of these compensatory mechanisms contributes to both type 1 and 2 diabetes. Additionally, studies in which β cells are "rested" by reducing endogenous insulin demand have shown promise as a therapeutic strategy that could be applied more broadly. Here, we review recent findings in β cells pertaining to the metabolic amplifying pathway, the unfolded protein response, and potential advances in therapeutics based on β-cell rest.

Partners in Crime: Beta-Cells and Autoimmune Responses Complicit in Type 1 Diabetes Pathogenesis

Type 1 diabetes (T1D) is an autoimmune disease characterized by autoreactive T cell-mediated destruction of insulin-producing pancreatic beta-cells. Loss of beta-cells leads to insulin insufficiency and hyperglycemia, with patients eventually requiring lifelong insulin therapy to maintain normal glycemic control. Since T1D has been historically defined as a disease of immune system dysregulation, there has been little focus on the state and response of beta-cells and how they may also contribute to their own demise. Major hurdles to identifying a cure for T1D include a limited understanding of disease etiology and how functional and transcriptional beta-cell heterogeneity may be involved in disease progression. Recent studies indicate that the beta-cell response is not simply a passive aspect of T1D pathogenesis, but rather an interplay between the beta-cell and the immune system actively contributing to disease. Here, we comprehensively review the current literature describing beta-cell vulnerability, heterogeneity, and contributions to pathophysiology of T1D, how these responses are influenced by autoimmunity, and describe pathways that can potentially be exploited to delay T1D.

Engineering islets from stem cells for advanced therapies of diabetes

Diabetes mellitus is a metabolic disorder that affects more than 460 million people worldwide. Type 1 diabetes (T1D) is caused by autoimmune destruction of β-cells, whereas type 2 diabetes (T2D) is caused by a hostile metabolic environment that leads to β-cell exhaustion and dysfunction. Currently, first-line medications treat the symptomatic insulin resistance and hyperglycaemia, but do not prevent the progressive decline of β-cell mass and function. Thus, advanced therapies need to be developed that either protect or regenerate endogenous β-cell mass early in disease progression or replace lost β-cells with stem cell-derived β-like cells or engineered islet-like clusters. In this Review, we discuss the state of the art of stem cell differentiation and islet engineering, reflect on current and future challenges in the area and highlight the potential for cell replacement therapies, disease modelling and drug development using these cells. These efforts in stem cell and regenerative medicine will lay the foundations for future biomedical breakthroughs and potentially curative treatments for diabetes.

Protein tyrosine phosphatase 1B inhibition improves endoplasmic reticulum stress‑impaired endothelial cell angiogenic response: A critical role for cell survival

Endoplasmic reticulum (ER) stress contributes to endothelial dysfunction, which is the initial step in atherogenesis. Blockade of protein tyrosine phosphatase (PTP)1B, a negative regulator of insulin receptors that is critically located on the surface of ER membrane, has been found to improve endothelial dysfunction. However, the role of ER stress and its related apoptotic sub‑pathways in PTP1B‑mediated endothelial dysfunction, particularly its angiogenic capacity, have not yet been fully elucidated. Thus, the present study aimed to investigate the impact of PTP1B suppression on ER stress‑mediated impaired angiogenesis and examined the contribution of apoptotic signals in this process. Endothelial cells were exposed to pharmacological ER stressors, including thapsigargin (TG) or 1,4‑dithiothreitol (DTT), in the presence or absence of a PTP1B inhibitor or small interfering (si)RNA duplexes. Then, ER stress, angiogenic capacity, cell cycle, apoptosis and the activation of key apoptotic signals were assessed. It was identified that the inhibition of PTP1B prevented ER stress caused by DTT and TG. Moreover, ER stress induction impaired the activation of endothelial nitric oxide synthase (eNOS) and the angiogenic capacity of endothelial cells, while PTP1B inhibition exerted a protective effect. The results demonstrated that blockade or knockdown of PTP1B prevented ER stress‑induced apoptosis and cell cycle arrest. This effect was associated with reduced expression levels of caspase‑12 and poly (ADP‑Ribose) polymerase 1. PTP1B blockade also suppressed autophagy activated by TG. The current data support the critical role of PTP1B in ER stress‑mediated endothelial dysfunction, characterized by reduced angiogenic capacity, with an underlying mechanism involving reduced eNOS activation and cell survival. These findings provide evidence of the therapeutic potential of targeting PTP1B in cardiovascular ischemic conditions.

Effect of Rosolic acid on endothelial dysfunction under ER stress in pancreatic microenvironment

Endothelial cell (EC) dysfunction is the underlying cause for the development of several pathologies, and the interdependency between the pancreatic β-cells and ECs has been established in the pathophysiology of diabetes. ECs release several factors that govern the expression of genes involved in the proliferation, physiology, and survival of the β-cells. Of the known factors that collapse this intricately balanced system, endothelial dysfunction is the crucial condition that manifests as the causative factor for micro and macrovascular diseases. Our earlier studies demonstrated that activation of nuclear factor erythroid-related factor (Nrf2) renders protection to the ECs experiencing ER stress. In this study, using a co-culture system, the crosstalk between pancreatic cells under ER stress and ECs and the effect of a novel Nrf2 activator Rosolic Acid (RA), on the crosstalk was investigated. ECs pre-treated with different concentrations RA and co-cultured with thapsigargin-induced ER stressed pancreatic β-cells showed increased levels of Nrf2 and its downstream targets such as heme oxygenase-1 (HO-1) and NADPH-quinone oxidoreductase-1 (NQO-1), and reduction of ER stress evinced by the decreased levels of glucose-regulated protein (GRP) 78 and C/ERB homologous protein (CHOP). The sensitization of ECs using RA, offered protection to pancreatic cells against ER stress as displayed by increased intracellular insulin and upregulated expression of cell survival and proliferative genes BCl2 and PDX-1. In addition, RA treatment resulted in elevated levels of various angiogenic factors, while inflammatory (TNF-α and IL-1β) and apoptotic markers (CXCL10 and CCL2) decreased. RA treatment normalized the levels of 115 proteins of the 277, which were differentially regulated as revealed by proteomic studies of ER stressed pancreatic β-cells in co-culture conditions. These findings clearly indicate the role of small molecule activators of Nrf2 not only in restoring the functioning of pancreatic cells but also in increasing the cell mass. Further, the study impinges on the strategies that can be developed to balance the pancreatic microenvironment, leading to the restoration of β-cell mass and their normophysiology in diabetic patients.