PGC-1α functions as a co-suppressor of XBP1s to regulate glucose metabolism

Differential susceptibility of BRL cells with/without insulin resistance and the role of endoplasmic reticulum stress signaling pathway in response to acrylamide-exposure toxicity effects in vitro

Acrylamide (ACR) is an endogenous food contaminant, high levels of ACR have been detected in a large number of foods, causing widespread concern. Since different organism states respond differently to the toxic effects of pollutants, this study establishes an insulin-resistant BRL cell model to explore the differential susceptibility of BRL cells with/without insulin resistance in response to acrylamide-exposure (0.0002, 0.02, or 1 mM) toxicity effects and its mechanism. The results showed that ACR exposure decreased glucose uptake and increased intracellular lipid levels by promoting the expression of fatty acid synthesis, transport, and gluconeogenesis genes and inhibiting the expression of fatty acid metabolism genes, thereby further exacerbating disorders of gluconeogenesis and lipid metabolism in insulin-resistant BRL cells. Simultaneously, its exposure also exacerbated BRL cells with/without insulin-resistant damage. Meanwhile, insulin resistance significantly raised susceptibility to BRL cell response to ACR-induced toxicity. Furthermore, ACR exposure further activated the endoplasmic reticulum stress (ERS) signaling pathway (promoting phosphorylation of PERK, eIF-2α, and IRE-1α) and the apoptosis signaling pathway (activating Caspase-3 and increasing the Bax/Bcl-2 ratio) in BRL cells with insulin-resistant, which were also attenuated after ROS scavenging or ERS signaling pathway blockade. Overall results suggested that ACR evokes a severer toxicity effect on BRL cells with insulin resistance through the overactivation of the ERS signaling pathway.

Constitutive expression of spliced X-box binding protein 1 inhibits dentin formation in mice

Upon endoplasmic reticulum (ER) stress, inositol-requiring enzyme 1 (IRE1) is activated, which subsequently converts an unspliced X-box binding protein 1 (XBP1U) mRNA to a spliced mRNA that encodes a potent XBP1S transcription factor. XBP1S is essential for relieving ER stress and secretory cell differentiation. We previously established Twist2-Cre;Xbp1 CS/+ mice that constitutively expressed XBP1S in the Twist2-expressing cells as well as in the cells derived from the Twist2-expressing cells. In this study, we analyzed the dental phenotype of Twist2-Cre;Xbp1 CS/+ mice. We first generated a mutant Xbp1s minigene that corresponds to the recombinant Xbp1 Δ26 allele (the Xbp1 CS allele that has undergone Cre-mediated recombination) and confirmed that the Xbp1s minigene expressed XBP1S that does not require IRE1α activation in vitro. Consistently, immunohistochemistry showed that XBP1S was constitutively expressed in the odontoblasts and other dental pulp cells in Twist2-Cre;Xbp1 CS/+ mice. Plain X-ray radiography and µCT analysis revealed that constitutive expression of XBP1S altered the dental pulp chamber roof- and floor-dentin formation, resulting in a significant reduction in dentin/cementum formation in Twist2-Cre;Xbp1 CS/+ mice, compared to age-matched Xbp1 CS/+ control mice. However, there is no significant difference in the density of dentin/cementum between these two groups of mice. Histologically, persistent expression of XBP1S caused a morphological change in odontoblasts in Twist2-Cre;Xbp1 CS/+ mice. Nevertheless, in situ hybridization and immunohistochemistry analyses showed that continuous expression of XBP1S had no apparent effects on the expression of the Dspp and Dmp1 genes. In conclusion, these results support that sustained production of XBP1S adversely affected odontoblast function and dentin formation.

PGC1α deficiency reverses cholestasis-induced liver injury via attenuating hepatic inflammation and promoting bile duct remodeling

OBJECTIVES

Cholestatic liver diseases are characterized by hepatocellular damage, cholangiocyte proliferation, and progressive fibrosis. Bile duct ligation (BDL) is widely used to resemble liver injuries induced by cholestasis. Peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC1α) was reported to play a critical role in multiple biological responses. Nevertheless, whether PGC1α is involved in bile acid metabolism and biliary disorders remains unclear. This study aimed to investigate the effect of PGC1α on hepatic responses after cholestatic injury.

MATERIALS AND METHODS

Wild-type mice were subjected to BDL or sham surgery for 14 days and human liver specimens from patients with primary biliary cholangitis (PBC) were collected to detect the expression of PGC1α. Hepatic-specific PGC1α knockout mice (HKO) were constructed and subjected to BDL, in which the effects of PGC1α on cholestatic liver injury were demonstrated by biochemical and histopathological assessments, immunoblotting, and metabolomics.

RESULTS

The expression of PGC1α was upregulated in the liver of PBC patients and murine models. Both in vivo and in vitro experiments supported the protective effects of PGC1α on cholestasis-induced hepatocyte injury. Infiltrated inflammatory cells after BDL were decreased in HKO mice. Inhibited Wnt/β-Catenin pathway and enhanced Notch signaling promoted transdifferentiation of hepatic progenitor cells (HPC)/ hepatocytes into cholangiocytes, leading to the greater ductular reaction observed in the HKO mice. But bile acids metabolism and mitochondrial function were not affected due to hepatic PGC1α deficiency in cholestasis.

CONCLUSIONS

Hepatic-specific deletion of PGC1α regulated liver regeneration by promoting ductular reactions, thereby exerting protective effects against BDL-induced liver injury, which could be a new potential therapeutic target.

Taxifolin-3-O-glucoside from Osbeckia nepalensis Hook. mediates antihyperglycemic activity in CC1 hepatocytes and in diabetic Wistar rats via regulating AMPK/G6Pase/PEPCK signaling axis

ETHNOPHARMACOLOGICAL RELEVANCE

Osbeckia nepalensis Hook. f. is an ICMR documented plant well known for its antidiabetic uses among the folk people of Northeast Region of India. In-depth study with scientific substantiation of the plant may uphold the therapeutic potential against the treatment of type 2 diabetes mellitus (T2DM).

AIM OF THE STUDY

The present study evaluates the traditionally claimed prophylactic potential of O. nepalensis and its extracts along with the isolated compound taxifolin-3-O-glucoside (TG) against the downregulation of T2DM related hepatic gluconeogenesis through in vitro, in vivo and in silico conditions as a means of ameliorating hyperglycemia.

MATERIALS AND METHODS

Antidiabetic potential of O. nepalensis was carried out in both CC1 hepatocytes (in vitro) and STZ-induced diabetic male Wistar rats (in vivo). Enriched bioactive fraction and bioactive molecules were isolated through bioactivity-guided fractionation, yielding two major molecules, taxifolin-3-O-glucoside and quercitin-3-O-rhamnoside. The bioactivity of taxifolin-3-O-glucoside was validated through immunoblotting techniques aided by in silico molecular docking and simulations.

RESULTS

Methanolic extract of O. nepalensis and taxifolin-3-O-glucoside (TG) isolated thereof enhanced the uptake of glucose in CC1 hepatocytes and downregulates the gluconeogenic enzymes (G6Pase and PEPCK) and its related transcription factors (FOXO1, HNF4α and PGC1α) through the stimulation of AMPK phosphorylation in in vitro condition. Moreover, in in vivo experiments, the in vitro most active fraction BuSFr1 (consisting of the two active major compounds taxifolin-3-O-glucoside and quercitin-3-O-rhamnoside) exhibited a substantial decrease in elevated blood glucose level and increase the glucose tolerance as well as plasma insulin level. In silico molecular docking and simulations for TG with the protein G6Pase inferred the docking sites and stability and showed taxifolin-3-O-glucoside as more potent and non-toxic as compared to quercitin-3-O-rhamnoside.

CONCLUSION

The traditionally claimed antidiabetic effect of O. nepalensis has been proved to be effective in lowering the blood glucose level through in vitro, in vivo and in silico analysis which will pave a way for the development of antidiabetic phytopharmaceutical drugs which can be validated through further clinical studies.

Astragalus polysaccharide mitigates transport stress-induced hepatic metabolic stress via improving hepatic glucolipid metabolism in chicks

In the modern poultry industry, newly hatched chicks are unavoidably transported from the hatching to the rearing foster. Stress caused by multiple physical and psychological stressors during transportation is particularly harmful to the liver. Astragalus polysaccharide (APS) possesses multiple benefits against hepatic metabolic disorders. Given that transport stress could disturb hepatic glucolipid metabolism and the role of APS in metabolic regulation, we speculated that APS could antagonize transport stress-induced disorder of hepatic glucolipid metabolism. Firstly, newly hatched chicks were transported for 0, 2, 4, 8 h, respectively. Subsequently, to further investigated the effects of APS on transport stress-induced hepatic glucolipid metabolism disturbance, chicks were pretreated with water or APS and then subjected to transport treatment. Our study suggested that APS could relieve transport stress induced lipid deposition in liver. Meanwhile, transport stress also induced disturbances in glucose metabolism, reflected by augmented mRNA expression of key molecules in gluconeogenesis and glycogenolysis. Surprisingly, APS could simultaneously alleviate these alterations via PGC1α/SIRT1/AMPK pathway. Moreover, APS treatment regulated the level of PPARα and PPARγ, thereby alleviating transport stress-induced alterations of VLDL synthesis, cholesterol metabolism, lipid oxidation, synthesis and transport-related molecules. These findings indicated that APS could prevent the potential against transport stress-induced hepatic glucolipid metabolism disorders via PGC1α/ SIRT1/ AMPK/ PPARα/ PPARγ signaling system.

X-box Binding Protein 1: An Adaptor in the Pathogenesis of Atherosclerosis

Atherosclerosis (AS), the formation of fibrofatty lesions in the vessel wall, is the primary cause of heart disease and stroke and is closely associated with aging. Disrupted metabolic homeostasis is a primary feature of AS and leads to endoplasmic reticulum (ER) stress, which is an abnormal accumulation of unfolded proteins. By orchestrating signaling cascades of the unfolded protein response (UPR), ER stress functions as a double-edged sword in AS, where adaptive UPR triggers synthetic metabolic processes to restore homeostasis, whereas the maladaptive response programs the cell to the apoptotic pathway. However, little is known regarding their precise coordination. Herein, an advanced understanding of the role of UPR in the pathological process of AS is reviewed. In particular, we focused on a critical mediator of the UPR, X-box binding protein 1 (XBP1), and its important role in balancing adaptive and maladaptive responses. The XBP1 mRNA is processed from the unspliced isoform (XBP1u) to the spliced isoform of XBP1 (XBP1s). Compared with XBP1u, XBP1s predominantly functions downstream of inositol-requiring enzyme-1α (IRE1α) and transcript genes involved in protein quality control, inflammation, lipid metabolism, carbohydrate metabolism, and calcification, which are critical for the pathogenesis of AS. Thus, the IRE1α/XBP1 axis is a promising pharmaceutical candidate against AS.

Riligustilide alleviates hepatic insulin resistance and gluconeogenesis in T2DM mice through multitarget actions

Riligustilide (RG), one of the dimeric phthalides of Angelica sinensis and Ligusticum chuanxiong, was confirmed effective against many diseases. However, its effects on type 2 diabetes mellitus (T2DM) and the underlying molecular mechanisms have not been clearly elucidated yet. The current study was designed to investigate the hypoglycemic potential by which RG affects the pathogenesis of T2DM. Comprehensive insights into the effects and underlying molecular mechanisms of RG on attenuating aberrant metabolism of glucose were determined in high-fat diet-induced T2DM mice and insulin-resistant (IR) HepG2 cells. In high-fat diet-induced C57BL/6J mice, RG administration significantly reduced hyperglycemia, decreased hyperinsulinemia, and ameliorated glucose intolerance. Mechanistically, RG activated PPARγ and insulin signaling pathway to improve insulin sensitivity, and increase glucose uptake as well as glycogenesis. In addition, RG also upregulated AMPK-TORC2-FoxO1 axis to attenuate gluconeogenesis in vivo and in vitro. According to the findings, RG may be a promising candidate for the treatment of T2DM.

RIG-I Deficiency Promotes Obesity-Induced Insulin Resistance

Inflammation and immunity are linked to the onset and development of obesity and metabolic disorders. Pattern recognition receptors (PRRs) are key regulators of inflammation and immunity in response to infection and stress, and they have critical roles in metainflammation. In this study, we investigated whether RIG-I (retinoic acid-inducible gene I)-like receptors were involved in the regulation of obesity-induced metabolic stress in RIG-I knockout (KO) mice fed a high-fat diet (HFD). RIG-I KO mice fed an HFD for 12 weeks showed greater body weight gain, higher fat composition, lower lean body mass, and higher epididymal white adipose tissue (eWAT) weight than WT mice fed HFD. In contrast, body weight gain, fat, and lean mass compositions, and eWAT weight of MDA5 (melanoma differentiation-associated protein 5) KO mice fed HFD were similar to those of WT mice fed a normal diet. RIG-I KO mice fed HFD exhibited more severely impaired glucose tolerance and higher HOMA-IR values than WT mice fed HFD. IFN-β expression induced by ER stress inducers, tunicamycin and thapsigargin, was abolished in RIG-I-deficient hepatocytes and macrophages, showing that RIG-I is required for ER stress-induced IFN-β expression. Our results show that RIG-I deficiency promotes obesity and insulin resistance induced by a high-fat diet, presenting a novel role of RIG-I in the development of obesity and metabolic disorders.

Hirsutine ameliorates hepatic and cardiac insulin resistance in high-fat diet-induced diabetic mice and in vitro models

Closely associated with type 2 diabetes mellitus (T2DM), hepatic steatosis and cardiac hypertrophy resulting from chronic excess intake can exacerbate insulin resistance (IR). The current study aims to investigate the pharmacological effects of hirsutine, one indole alkaloid isolated from Uncaria rhynchophylla, on improving hepatic and cardiac IR, and elucidate the underlying mechanism. T2DM and IR in vivo were established by high-fat diet (HFD) feeding for 3 months in C57BL/6J mice. In vitro IR models were induced by high-glucose and high-insulin (HGHI) incubation in HepG2 and H9c2 cells. Hirsutine administration for 8 weeks improved HFD-induced peripheral hyperglycemia, glucose tolerance and IR by OGTT and ITT assays, and simultaneously attenuated hepatic steatosis and cardiac hypertrophy by pathological observation. The impaired p-Akt expression was activated by hirsutine in liver and heart tissues of HFD mice, and also in the models in vitro. Hirsutine exhibited the effects on enhancing glucose consumption and uptake in IR cell models via activating phosphatidylinositol 3-kinase (PI3K)/Akt pathway, which was blocked by PI3K inhibitor LY294002. Moreover, the effect of hirsutine on promoting glucose uptake and GLUT4 expression in HGHI H9c2 cells was also prevented by Compound C, an inhibitor of AMP-activated protein kinase (AMPK). Enhancement of glycolysis might be another factor of hirsutine showing its effects on glycemic control. Collectively, it was uncovered that hirsutine might exert beneficial effects on regulating glucose homeostasis, thus improving hepatic and cardiac IR, and could be a promising compound for treating diet-induced T2DM.

Roles of XBP1s in Transcriptional Regulation of Target Genes

The spliced form of X-box binding protein 1 (XBP1s) is an active transcription factor that plays a vital role in the unfolded protein response (UPR). Under endoplasmic reticulum (ER) stress, unspliced Xbp1 mRNA is cleaved by the activated stress sensor IRE1α and converted to the mature form encoding spliced XBP1 (XBP1s). Translated XBP1s migrates to the nucleus and regulates the transcriptional programs of UPR target genes encoding ER molecular chaperones, folding enzymes, and ER-associated protein degradation (ERAD) components to decrease ER stress. Moreover, studies have shown that XBP1s regulates the transcription of diverse genes that are involved in lipid and glucose metabolism and immune responses. Therefore, XBP1s has been considered an important therapeutic target in studying various diseases, including cancer, diabetes, and autoimmune and inflammatory diseases. XBP1s is involved in several unique mechanisms to regulate the transcription of different target genes by interacting with other proteins to modulate their activity. Although recent studies discovered numerous target genes of XBP1s via genome-wide analyses, how XBP1s regulates their transcription remains unclear. This review discusses the roles of XBP1s in target genes transcriptional regulation. More in-depth knowledge of XBP1s target genes and transcriptional regulatory mechanisms in the future will help develop new therapeutic targets for each disease.

PGC1s and Beyond: Disentangling the Complex Regulation of Mitochondrial and Cellular Metabolism

Metabolism is the central engine of living organisms as it provides energy and building blocks for many essential components of each cell, which are required for specific functions in different tissues. Mitochondria are the main site for energy production in living organisms and they also provide intermediate metabolites required for the synthesis of other biologically relevant molecules. Such cellular processes are finely tuned at different levels, including allosteric regulation, posttranslational modifications, and transcription of genes encoding key proteins in metabolic pathways. Peroxisome proliferator activated receptor γ coactivator 1 (PGC1) proteins are transcriptional coactivators involved in the regulation of many cellular processes, mostly ascribable to metabolic pathways. Here, we will discuss some aspects of the cellular processes regulated by PGC1s, bringing up some examples of their role in mitochondrial and cellular metabolism, and how metabolic regulation in mitochondria by members of the PGC1 family affects the immune system. We will analyze how PGC1 proteins are regulated at the transcriptional and posttranslational level and will also examine other regulators of mitochondrial metabolism and the related cellular functions, considering approaches to identify novel mitochondrial regulators and their role in physiology and disease. Finally, we will analyze possible therapeutical perspectives currently under assessment that are applicable to different disease states.

Constitutive expression of spliced XBP1 causes perinatal lethality in mice

Upon endoplasmic reticulum (ER) stress, inositol-requiring enzyme 1 (IRE1) is activated and catalyzes nonconventional splicing of an unspliced X-box binding protein 1 (XBP1U) mRNA to yield a spliced XBP1 (XBP1S) mRNA that encodes a potent XBP1S transcription factor. XBP1S is a key mediator of the IRE1 branch that is essential for alleviating ER stress. We generated a novel mouse strain (referred to as "Xbp1^CS/+ " mice) that constitutively expressed XBP1S after Cre recombinase-mediated recombination. Further breeding of these mice with Twist2 Cre recombinase (Twist2-Cre) knock-in mice generated Twist2-Cre;Xbp1^CS/+ mice. Most Twist2-Cre;Xbp1^CS/+ mice died shortly after birth. Reverse-transcription polymerase chain reaction (RT-PCR) showed that constitutive expression of XBP1S occurred in various mouse tissues examined, but not in the brain. Immunohistochemistry confirmed that although the immunostaining signals for total XBP1 (XBP1U and XBP1S) were found in the calvarial bones in both Twist2-Cre;Xbp1^CS/+ and control mice, the signals for XBP1S were only detected in the Twist2-Cre;Xbp1^CS/+ mice, but not in the control mice. These results suggest that a precise control of XBP1S production is essential for normal mouse development.

The Impact of Sugar-Sweetened Beverage Consumption on the Liver: A Proteomics-based Analysis

Cardiometabolic complications such as the metabolic syndrome and Type 2 Diabetes Mellitus (T2DM) are major causes of global morbidity and mortality. As sugar-sweetened beverages (SSBs) are implicated in this process, this study aimed to obtain greater mechanistic insights. Male Wistar rats (~200 g) were gavaged with a local SSB every day for a period of six months while the control group was gavaged with an iso-volumetric amount of water. Experimental dosages were calculated according to the surface area-to-volume ratio and were equivalent to 125 mL/day (in human terms). A proteomic analysis was performed on isolated liver samples and thereafter, markers of endoplasmic reticulum (ER) stress, antioxidant/oxidant capacity, calcium regulation, and mitochondrial functionality were assessed. These data show that SSB consumption resulted in (a) the induction of mild hepatic ER stress; (b) altered hepatic mitochondrial dynamics; and (c) perturbed calcium handling across mitochondria-associated ER membranes. Despite significant changes in markers of ER stress, the antioxidant response and calcium handling (proteomics data), the liver is able to initiate adaptive responses to counteract such stressors. However, the mitochondrial data showed increased fission and decreased fusion that may put the organism at risk for developing insulin resistance and T2DM in the longer term.

Transcriptional Coactivator PGC-1α Binding to Newly Synthesized RNA via CBP80: A Nexus for Co- and Posttranscriptional Gene Regulation

Mammalian cells have many quality-control mechanisms that regulate protein-coding gene expression to ensure proper transcript synthesis, processing, and translation. Should a step in transcript metabolism fail to fulfill requisite spatial, temporal, or structural criteria, including the proper acquisition of RNA-binding proteins, then that step will halt, fail to proceed to the next step, and ultimately result in transcript degradation. Quality-control mechanisms constitute a continuum of processes that initiate in the nucleus and extend to the cytoplasm. Here, we present published and unpublished data for protein-coding genes whose expression is activated by the transcriptional coactivator PGC-1α. We show that PGC-1α movement from chromatin, to which it is recruited by DNA-binding proteins, to CBP80 at the 5' cap of nascent transcripts begins a series of co- and posttranscriptional quality- and quantity-control steps that, in total, ensure proper gene expression.

Inhibition of XBP1s ubiquitination enhances its protein stability and improves glucose homeostasis

BACKGROUND

Hepatic ER stress is a risk factor of insulin resistance and type 2 diabetes. X-box binding protein 1 spliced (XBP1s), a transcription factor, plays a key role in ameliorating insulin resistance and maintaining glucose homeostasis. Unfortunately, the short half-life of the protein dampens its clinical application, and the specific site of lysine residue that could be ubiquitinated and involved in the degradation of XBP1s remains elusive.

METHODS AND RESULTS

Here, we identified K60 and K77 on XBP1s as two pivotal ubiquitin sites required for its proteasome-dependent degradation. We also constructed a double mutant form of XBP1s (K60/77R) and found that it showed higher capacity in resisting against ubiquitin-mediated protein degradation, increasing nuclear translocation, enhancing transcriptional activity, suppressing ER stress and promoting Foxo1 degradation, compared to that of wild type XBP1s (WT). Consistently, overexpression of the K60/77R XBP1s mutant in DIO mice increased the ability to reduce ER stress and decrease Foxo1 levels, thus contributed to maintaining glucose homeostasis.

CONCLUSION

Our results suggest that delaying the degradation of XBP1s by preventing ubiquitination might provide a strategic approach for reducing ER stress as an anti-diabetes therapy.

A systematic review on the mechanisms of vitamin K effects on the complications of diabetes and pre-diabetes

Diabetes mellitus and pre-diabetes are prevalent endocrine disorders associated with substantial morbidity and premature mortality. Vitamin K is known to have several beneficial effects on complications of diabetes and pre-diabetes. However, systematic consolidation of evidence is required to quantify these effects in order to inform clinical practice and research. A systematic search in PubMed, Scopus, Embase, ProQuest, and Google Scholar databases was undertaken from database inception up to October 2018 to evaluate functional roles of different forms of vitamin K on diabetes and pre-diabetes. From 3,734 identified records, nine articles met the inclusion criteria and were evaluated. Vitamin K supplementation was found to be associated with significant reductions in blood glucose (six studies), increased fasting serum insulin (four studies), reduced hemoglobin A1c (three studies), reduced homeostatic model assessment-insulin resistance index (HOMA-IR) (two studies), and increased ß-cell function (two studies) in diabetic animal studies. Following 2-hour oral glucose tolerance test, vitamin K supplementation was observed to be effective in reducing blood glucose and insulin levels in the pre-diabetic population. However, no evidence of effect was observed for fasting blood sugar, insulin, HOMA-IR, and homeostatic model assessment-β-cell function index (two studies). A statistically significant effect was also noted with vitamin K in improving dyslipidemia (three studies) as well as oxidative stress and inflammatory markers (five studies) in diabetic animals. In conclusion, clinical trials and animal studies confirm that vitamin K supplementation may improve both clinical features and complications of diabetes and pre-diabetes. However, quantification of clinical efficacy in the pre-diabetic population and among individuals with comorbidities requires further investigation.

FOXO1 inhibition prevents renal ischemia-reperfusion injury via cAMP-response element binding protein/PPAR-γ coactivator-1α-mediated mitochondrial biogenesis

BACKGROUND AND PURPOSE

Growing evidence indicates targeting mitochondrial dynamics and biogenesis could accelerate recovery from renal ischemia-reperfusion (I/R) injury, but the underlying mechanisms remain elusive. Transcription factor forkhead box O1 (FOXO1) is a key regulator of mitochondrial homeostasis and plays a pathological role in the progression of renal disease.

EXPERIMENTAL APPROACH

A mouse model of renal I/R injury and a hypoxia/reoxygenation (H/R) injury model for human renal tubular epithelial cells were used.

KEY RESULTS

I/R injury up-regulated renal expression of FOXO1 and treatment with FOXO1-selective inhibitor AS1842856 prior to I/R injury decreased serum urea nitrogen, serum creatinine and the tubular damage score after injury. Post-I/R injury AS1842856 treatment could also ameliorate renal function and improve the survival rate of mice following injury. AS1842856 administration reduced mitochondrial-mediated apoptosis, suppressed the overproduction of mitochondrial ROS and accelerated recovery of ATP both in vivo and in vitro. Additionally, FOXO1 inhibition improved mitochondrial biogenesis and suppressed mitophagy. Expression of PPAR-γ coactivator 1α (PGC-1α), a master regulator of mitochondrial biogenesis, was down-regulated in both I/R and H/R injury, which could be abrogated by FOXO1 inhibition. Experiments using integrated bioinformatics analysis and coimmunoprecipitation established that FOXO1 inhibited PGC-1α transcription by competing with cAMP-response element binding protein (CREB) for its binding to transcriptional coactivators CREBBP/EP300 (CBP/P300).

CONCLUSION AND IMPLICATIONS

These findings suggested that FOXO1 was critical to maintain mitochondrial function in renal tubular epithelial cells and FOXO1 may serve as a therapeutic target for pharmacological intervention in renal I/R injury.

Cellular Stress-Modulating Drugs Can Potentially Be Identified by in Silico Screening with Connectivity Map (CMap)

Accompanied by increased life span, aging-associated diseases, such as metabolic diseases and cancers, have become serious health threats. Recent studies have documented that aging-associated diseases are caused by prolonged cellular stresses such as endoplasmic reticulum (ER) stress, mitochondrial stress, and oxidative stress. Thus, ameliorating cellular stresses could be an effective approach to treat aging-associated diseases and, more importantly, to prevent such diseases from happening. However, cellular stresses and their molecular responses within the cell are typically mediated by a variety of factors encompassing different signaling pathways. Therefore, a target-based drug discovery method currently being used widely (reverse pharmacology) may not be adequate to uncover novel drugs targeting cellular stresses and related diseases. The connectivity map (CMap) is an online pharmacogenomic database cataloging gene expression data from cultured cells treated individually with various chemicals, including a variety of phytochemicals. Moreover, by querying through CMap, researchers may screen registered chemicals in silico and obtain the likelihood of drugs showing a similar gene expression profile with desired and chemopreventive conditions. Thus, CMap is an effective genome-based tool to discover novel chemopreventive drugs.

The orphan nuclear receptor SHP regulates ER stress response by inhibiting XBP1s degradation

In this study, Sun et al. investigated the role of the orphan nuclear receptor SHP, a well-known transcriptional corepressor of bile acid and lipid metabolism in the liver, in other tissues. They report that SHP functions as a regulator of ER stress in the exocrine pancreas, specifically via the regulation of XBP1s stability.

The orphan nuclear receptor SHP (small heterodimer partner) is a well-known transcriptional corepressor of bile acid and lipid metabolism in the liver; however, its function in other tissues is poorly understood. Here, we report an unexpected role for SHP in the exocrine pancreas as a modulator of the endoplasmic reticulum (ER) stress response. SHP expression is induced in acinar cells in response to ER stress and regulates the protein stability of the spliced form of X-box-binding protein 1 (XBP1s), a key mediator of ER stress response. Loss of SHP reduces XBP1s protein level and transcriptional activity, which in turn attenuates the ER stress response during the fasting–feeding cycle. Consequently, SHP-deficient mice also are more susceptible to cerulein-induced pancreatitis. Mechanistically, we show that SHP physically interacts with the transactivation domain of XBP1s, thereby inhibiting the polyubiquitination and degradation of XBP1s by the Cullin3–SPOP (speckle-type POZ protein) E3 ligase complex. Together, our data implicate SHP in governing ER homeostasis and identify a novel posttranslational regulatory mechanism for the key ER stress response effector XBP1.

PGC-1α activation: a therapeutic target for type 2 diabetes?

Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) has gained popularity as a very attractive target for diabetic therapies due to its role in lipid and glucose metabolism. Pharmacological activation of PGC-1α is thought to elicit health benefits. However, this notion has been questioned by increasing evidence, which suggests that insulin resistant is exacerbated when PGC-1α expression is far beyond normal physiological limits and is prevented under the condition of PGC-1α deficiency. This narrative review suggests that PGC-1α, as a master metabolic regulator, exerts roles in insulin sensitivity in a tissue-specific manner and in a physical activity/age-dependent fashion. When using PGC-1α as a target for therapeutic strategies against insulin resistance and T2DM, we should take these factors into consideration.Level of evidence: Level V, narrative review.

The role of YAP/TAZ activity in cancer metabolic reprogramming

In contrast to normal cells, which use the aerobic oxidation of glucose as their main energy production method, cancer cells prefer to use anaerobic glycolysis to maintain their growth and survival, even under normoxic conditions. Such tumor cell metabolic reprogramming is regulated by factors such as hypoxia and the tumor microenvironment. In addition, dysregulation of certain signaling pathways also contributes to cancer metabolic reprogramming. Among them, the Hippo signaling pathway is a highly conserved tumor suppressor pathway. The core oncosuppressive kinase cascade of Hippo pathway inhibits the nuclear transcriptional co-activators YAP and TAZ, which are the downstream effectors of Hippo pathway and oncogenic factors in many solid cancers. YAP/TAZ function as key nodes of multiple signaling pathways and play multiple regulatory roles in cancer cells. However, their roles in cancer metabolic reprograming are less clear. In the present review, we examine progress in research into the regulatory mechanisms of YAP/TAZ on glucose metabolism, fatty acid metabolism, mevalonate metabolism, and glutamine metabolism in cancer cells. Determining the roles of YAP/TAZ in tumor energy metabolism, particularly in relation to the tumor microenvironment, will provide new strategies and targets for the selective therapy of metabolism-related cancers.

Endoplasmic Reticulum Stress in Metabolic Disorders

Metabolic disorders have become among the most serious threats to human health, leading to severe chronic diseases such as obesity, type 2 diabetes, and non-alcoholic fatty liver disease, as well as cardiovascular diseases. Interestingly, despite the fact that each of these diseases has different physiological and clinical symptoms, they appear to share certain pathological traits such as intracellular stress and inflammation induced by metabolic disturbance stemmed from over nutrition frequently aggravated by a modern, sedentary life style. These modern ways of living inundate cells and organs with saturating levels of sugar and fat, leading to glycotoxicity and lipotoxicity that induce intracellular stress signaling ranging from oxidative to ER stress response to cope with the metabolic insults (Mukherjee, et al., 2015). In this review, we discuss the roles played by cellular stress and its responses in shaping metabolic disorders. We have summarized here current mechanistic insights explaining the pathogenesis of these disorders. These are followed by a discussion of the latest therapies targeting the stress response pathways.