The role of JNK proteins in metabolism

Adipose c-Jun NH2-terminal kinase promotes angiotensin II-induced and deoxycorticosterone acetate salt-induced hypertension and vascular dysfunction by inhibition of adiponectin production and activation of SGK1 in mice

BACKGROUND

Adipose c-Jun NH2-terminal kinase 1/2 (JNK1/2) is a central mediator involved in the development of obesity and its complications. However, the roles of adipose JNK1/2 in hypertension remain elusive. Here we explored the role of adipose JNK1/2 in hypertension.

METHODS AND RESULTS

The roles of adipose JNK1/2 in hypertension were investigated by evaluating the impact of adipose JNK1/2 inactivation in both angiotensin II (Ang II)-induced and deoxycorticosterone acetate (DOCA) salt-induced hypertensive mice. Specific inactivation of JNK1/2 in adipocytes significantly alleviates Ang II-induced and DOCA salt-induced hypertension and target organ damage in mice. Interestingly, such beneficial effects are also observed in hypertensive mice after oral administration of JNK1/2 inhibitor SP600125. Mechanistically, adipose JNK1/2 acts on adipocytes to reduce the production of adiponectin (APN), then leads to promote serum and glucocorticoid-regulated kinase 1 (SGK1) phosphorylation and increases epithelial Na + channel α-subunit (ENaCα) expression in both renal cells and adipocytes, respectively, finally exacerbates Na + retention. In addition, chronic treatment of recombinant mouse APN significantly augments the beneficial effects of adipose JNK1/2 inactivation in DOCA salt-induced hypertension. By contrast, the blood pressure-lowering effects of adipose JNK1/2 inactivation are abrogated by adenovirus-mediated SGK1 overexpression in Ang II -treated adipose JNK1/2 inactivation mice.

CONCLUSION

Adipose JNK1/2 promotes hypertension and targets organ impairment via fine-tuning the multiorgan crosstalk among adipose tissue, kidney, and blood vessels.

The Role of the Dysregulated JNK Signaling Pathway in the Pathogenesis of Human Diseases and Its Potential Therapeutic Strategies: A Comprehensive Review

JNK is named after c-Jun N-terminal kinase, as it is responsible for phosphorylating c-Jun. As a member of the mitogen-activated protein kinase (MAPK) family, JNK is also known as stress-activated kinase (SAPK) because it can be activated by extracellular stresses including growth factor, UV irradiation, and virus infection. Functionally, JNK regulates various cell behaviors such as cell differentiation, proliferation, survival, and metabolic reprogramming. Dysregulated JNK signaling contributes to several types of human diseases. Although the role of the JNK pathway in a single disease has been summarized in several previous publications, a comprehensive review of its role in multiple kinds of human diseases is missing. In this review, we begin by introducing the landmark discoveries, structures, tissue expression, and activation mechanisms of the JNK pathway. Next, we come to the focus of this work: a comprehensive summary of the role of the deregulated JNK pathway in multiple kinds of diseases. Beyond that, we also discuss the current strategies for targeting the JNK pathway for therapeutic intervention and summarize the application of JNK inhibitors as well as several challenges now faced. We expect that this review can provide a more comprehensive insight into the critical role of the JNK pathway in the pathogenesis of human diseases and hope that it also provides important clues for ameliorating disease conditions.

Canagliflozin Delays Aging of HUVECs Induced by Palmitic Acid via the ROS/p38/JNK Pathway

Vascular aging is an important factor contributing to cardiovascular diseases, such as hypertension and atherosclerosis. Hyperlipidemia or fatty accumulation may play an important role in vascular aging and cardiovascular diseases. Canagliflozin (CAN), a sodium-glucose cotransporter inhibitor, can exert a cardiovascular protection effect that is likely independent of its hypoglycemic activities; however, the exact mechanisms remain undetermined. We hypothesized that CAN might have protective effects on blood vessels by regulating vascular aging induced by hyperlipidemia or fatty accumulation in blood vessel walls. In this study, which was undertaken on the basis of aging and inflammation, we investigated the protective effects and mechanisms of CAN in human umbilical vein endothelial cells induced by palmitic acid. We found that CAN could delay vascular aging, reduce the secretion of the senescence-associated secretory phenotype (SASP) and protect DNA from damage, as well as exerting an effect on the cell cycle of senescent cells. These actions likely occur through the attenuation of the excess reactive oxygen species (ROS) produced in vascular endothelial cells and/or down-regulation of the p38/JNK signaling pathway. In summary, our study revealed a new role for CAN as one of the sodium-dependent glucose transporter 2 inhibitors in delaying lipotoxicity-induced vascular aging by targeting the ROS/p38/JNK pathway, giving new medicinal value to CAN and providing novel therapeutic ideas for delaying vascular aging in patients with dyslipidemia.

Characterization of Maternal Circulating MicroRNAs in Obese Pregnancies and Gestational Diabetes Mellitus

Maternal obesity (MO) is expanding worldwide, contributing to the onset of Gestational Diabetes Mellitus (GDM). MO and GDM are associated with adverse maternal and foetal outcomes, with short- and long-term complications. Growing evidence suggests that MO and GDM are characterized by epigenetic alterations contributing to the pathogenesis of metabolic diseases. In this pilot study, plasma microRNAs (miRNAs) of obese pregnant women with/without GDM were profiled at delivery. Nineteen women with spontaneous singleton pregnancies delivering by elective Caesarean section were enrolled: seven normal-weight (NW), six obese without comorbidities (OB/GDM(-)), and six obese with GDM (OB/GDM(+)). miRNA profiling with miRCURY LNA PCR Panel allowed the analysis of the 179 most expressed circulating miRNAs in humans. Data acquisition and statistics (GeneGlobe and SPSS software) and Pathway Enrichment Analysis (PEA) were performed. Data analysis highlighted patterns of significantly differentially expressed miRNAs between groups: OB/GDM(-) vs. NW: n = 4 miRNAs, OB/GDM(+) vs. NW: n = 1, and OB/GDM(+) vs. OB/GDM(-): n = 14. For each comparison, PEA revealed pathways associated with oxidative stress and inflammation, as well as with nutrients and hormones metabolism. Indeed, miRNAs analysis may help to shed light on the complex epigenetic network regulating metabolic pathways in both the mother and the foeto-placental unit. Future investigations are needed to deepen the pregnancy epigenetic landscape in MO and GDM.

The COVID-19-diabetes mellitus molecular tetrahedron

Accumulating molecular evidence suggests that insulin resistance, rather than SARS-CoV-2- provoked beta-cell impairment, plays a major role in the observed rapid metabolic deterioration in diabetes, or new-onset hyperglycemia, during the COVID-19 clinical course. In order to clarify the underlying complexity of COVID-19 and diabetes mellitus interactions, we propose the imaginary diabetes-COVID-19 molecular tetrahedron with four lateral faces consisting of SARS-CoV-2 entry via ACE2 (lateral face 1), the viral hijacking and replication (lateral face 2), acute inflammatory responses (lateral face 3), and the resulting insulin resistance (lateral face 4). The entrance of SARS-CoV-2 using ACE2 receptor triggers an array of multiple molecular signaling beyond that of the angiotensin II/ACE2-Ang-(1-7) axis, such as down-regulation of PGC-1 α/irisin, increased SREBP-1c activity, upregulation of CD36 and Sirt1 inhibition leading to insulin resistance. In another arm of the molecular cascade, the SARS-CoV-2 hijacking and replication induces a series of molecular events in the host cell metabolic machinery, including upregulation of SREBP-2, decrement in Sirt1 expression, dysregulation in PPAR-ɣ, and LPI resulting in insulin resistance. The COVID-19-diabetes molecular tetrahedron may suggest novel targets for therapeutic interventions to overcome insulin resistance that underlies the pathophysiology of worsening metabolic control in patients with diabetes mellitus or the new-onset of hyperglycemia in COVID-19.

Gastric Bypass Regulates Early Inflammatory Responses in High-Fat Diet-Induced Obese Mice

INTRODUCTION

Obesity and diabetes are characterized by chronic inflammatory responses. Roux-en-Y gastric bypass (RYGB) is increasingly regarded as an effective approach for the improvement of glucose homeostasis. In this study, we examined the effects of RYGB on the regulation of early inflammatory responses in the liver and adipose tissue in high-fat diet (HFD)-induced obese (DIO) mice.

MATERIALS AND METHODS

RYGB was performed in DIO mice followed by analyses of adiposity, insulin sensitivity, plasma and tissue cytokines and adipokines, tissue NF-κB and JNK/c-Jun activation, and tissue macrophage and T-cell subsets.

RESULTS

We found that RYGB resulted in sustained improvement of adiposity and insulin sensitivity. Plasma insulin and leptin levels were increased in untreated DIO mice and reduced in RYGB mice. RYGB maintained plasma adiponectin levels and inhibited monocyte chemoattractant protein-1 and interleukin 6 in white adipose tissue (WAT) and liver. RYGB inhibited NF-κB activation in WAT and muscle, but not in the liver. However, RYGB attenuated the JNK/c-Jun signaling pathway in the liver and WAT at 1 wk after surgery, suggesting that RYGB regulates the tissue-specific inflammatory pathway. RYGB reduced M1-like (F4/80+/CD11c+) differentiation and enhanced M2-like population (F4/80+/CD206c+). RYGB also regulated CD4+ and CD8+ T-cell infiltration and increased Treg cells in the liver and WAT at the same time point.

CONCLUSIONS

Our findings demonstrate that RYGB improves obesity and insulin resistance, which are associated with the regulation of early inflammatory reactions in the liver and WAT.

In Vivo Metabolic Roles of G Proteins of the Gi Family Studied With Novel Mouse Models

G protein-coupled receptors (GPCRs) are the target of ~30% to 35% of all US Food and Drug Administration-approved drugs. The individual members of the GPCR superfamily couple to 1 or more functional classes of heterotrimeric G proteins. The physiological outcome of activating a particular GPCR in vivo depends on the pattern of receptor distribution and the type of G proteins activated by the receptor. Based on the structural and functional properties of their α-subunits, heterotrimeric G proteins are subclassified into 4 major families: Gs, Gi/o, Gq/11, and G12/13. Recent studies with genetically engineered mice have yielded important novel insights into the metabolic roles of Gi/o-type G proteins. For example, recent data indicate that Gi signaling in pancreatic α-cells plays a key role in regulating glucagon release and whole body glucose homeostasis. Receptor-mediated activation of hepatic Gi signaling stimulates hepatic glucose production, suggesting that inhibition of hepatic Gi signaling could prove clinically useful to reduce pathologically elevated blood glucose levels. Activation of adipocyte Gi signaling reduces plasma free fatty acid levels, thus leading to improved insulin sensitivity in obese, glucose-intolerant mice. These new data suggest that Gi-coupled receptors that are enriched in metabolically important cell types represent potential targets for the development of novel drugs useful for the treatment of type 2 diabetes and related metabolic disorders.

Hepatic Mitochondrial SAB Deletion or Knockdown Alleviates Diet-Induced Metabolic Syndrome, Steatohepatitis, and Hepatic Fibrosis

BACKGROUND AND AIMS

The hepatic mitogen-activated protein kinase (MAPK) cascade leading to c-Jun N-terminal kinase (JNK) activation has been implicated in the pathogenesis of nonalcoholic fatty liver (NAFL)/NASH. In acute hepatotoxicity, we previously identified a pivotal role for mitochondrial SH3BP5 (SAB; SH3 homology associated BTK binding protein) as a target of JNK, which sustains its activation through promotion of reactive oxygen species production. Therefore, we assessed the role of hepatic SAB in experimental NASH and metabolic syndrome.

APPROACH AND RESULTS

In mice fed high-fat, high-calorie, high-fructose (HFHC) diet, SAB expression progressively increased through a sustained JNK/activating transcription factor 2 (ATF2) activation loop. Inducible deletion of hepatic SAB markedly decreased sustained JNK activation and improved systemic energy expenditure at 8 weeks followed by decreased body fat at 16 weeks of HFHC diet. After 30 weeks, mice treated with control-antisense oligonucleotide (control-ASO) developed steatohepatitis and fibrosis, which was prevented by Sab-ASO treatment. Phosphorylated JNK (p-JNK) and phosphorylated ATF2 (p-ATF2) were markedly attenuated by Sab-ASO treatment. After 52 weeks of HFHC feeding, control N-acetylgalactosamine antisense oligonucleotide (GalNAc-Ctl-ASO) treated mice fed the HFHC diet exhibited progression of steatohepatitis and fibrosis, but GalNAc-Sab-ASO treatment from weeks 40 to 52 reversed these findings while decreasing hepatic SAB, p-ATF2, and p-JNK to chow-fed levels.

CONCLUSIONS

Hepatic SAB expression increases in HFHC diet-fed mice. Deletion or knockdown of SAB inhibited sustained JNK activation and steatohepatitis, fibrosis, and systemic metabolic effects, suggesting that induction of hepatocyte Sab is an important driver of the interplay between the liver and the systemic metabolic consequences of overfeeding. In established NASH, hepatocyte-targeted GalNAc-Sab-ASO treatment reversed steatohepatitis and fibrosis.

ANGPTL8 in metabolic homeostasis: more friend than foe?

ANGPTL8 is an important cytokine, which is significantly increased in type 2 diabetes mellitus (T2DM), obesity and metabolic syndrome. Many studies have shown that ANGPTL8 can be used as a bio-marker of these metabolic disorders related diseases, and the baseline ANGPTL8 level has also been found to be positively correlated with retinopathy and all-cause mortality in patients with T2DM. This may be related to the inhibition of lipoprotein lipase activity and the reduction of circulating triglyceride (TG) clearance by ANGPTL8. Consistently, inhibition of ANGPTL8 seems to prevent or improve atherosclerosis. However, it is puzzling that ANGPTL8 seems to have a directing function for TG uptake in peripheral tissues; that is, ANGPTL8 specifically enhances the reserve and buffering function of white adipose tissue, which may alleviate the ectopic lipid accumulation to a certain extent. Furthermore, ANGPTL8 can improve insulin sensitivity and inhibit hepatic glucose production. These contradictory results lead to different opinions on the role of ANGPTL8 in metabolic disorders. In this paper, the correlation between ANGPTL8 and metabolic diseases, the regulation of ANGPTL8 and the physiological role of ANGPTL8 in the process of glucose and lipid metabolism were summarized, and the physiological/pathological significance of ANGPTL8 in the process of metabolic disorder was discussed.

Mechanistic insight into high-fat diet-induced metabolic inflammation in the arcuate nucleus of the hypothalamus

A high-fat diet (HFD) is linked with cytokines production by non-neuronal cells within the hypothalamus, which mediates metabolic inflammation. These cytokines then activate different inflammatory mediators in the arcuate nucleus of the hypothalamus (ARC), a primary hypothalamic area accommodating proopiomelanocortin (POMC) and agouti-related peptide (AGRP) neurons, first-order neurons that sense and integrate peripheral metabolic signals and then respond accordingly. These mediators, such as inhibitor of κB kinase-β (IKKβ), suppression of cytokine signaling 3 (SOCS3), c-Jun N-terminal kinases (JNKs), protein kinase C (PKC), etc., cause insulin and leptin resistance in POMC and AGRP neurons and support obesity and related metabolic complications. On the other hand, inhibition of these mediators has been shown to counteract the impaired metabolism. Therefore, it is important to discuss the contribution of neuronal and non-neuronal cells in HFD-induced hypothalamic inflammation. Furthermore, understanding few other questions, such as the diets causing hypothalamic inflammation, the gender disparity in response to HFD feeding, and how hypothalamic inflammation affects ARC neurons to cause impaired metabolism, will be helpful for the development of therapeutic approaches to prevent or treat HFD-induced obesity.

Role of the DNAJ/HSP40 family in the pathogenesis of insulin resistance and type 2 diabetes

Insulin resistance (IR) underpins a wide range of metabolic disorders including type 2 diabetes (T2D), metabolic syndrome and cardiovascular diseases. IR is characterized by a marked reduction in the magnitude and/or delayed onset of insulin to stimulate glucose disposal. This condition is due to defects in one or several intracellular intermediates of the insulin signaling cascade, ranging from insulin receptor substrate (IRS) inactivation to reduced glucose phosphorylation and oxidation. Genetic predisposition, as well as other precipitating factors such as aging, obesity, and sedentary lifestyles are among the risk factors underlying the pathogenesis of IR and its subsequent progression to T2D. One of the cardinal hallmarks of T2D is the impairment of the heat shock response (HSR). Human and animal studies provided compelling evidence of reduced expression of several components of the HSR (i.e. Heat shock proteins or HSPs) in diabetic samples in a manner that correlates with the degree of IR. Interventions that induce the HSR, irrespective of the means to achieve it, proved their effectiveness in enhancing insulin sensitivity and improving glycemic index. However, most of these studies have been focused on HSP70 family. In this review, we will focus on the novel role of DNAJ/HSP40 cochaperone family in metabolic diseases associated with IR.

JNK signaling pathway in metabolic disorders: An emerging therapeutic target

Metabolic Syndrome is a multifactorial disease associated with increased risk of cardiovascular disorders, type 2 diabetes mellitus, fatty liver disease, etc. Various stress stimuli such as reactive oxygen species, endoplasmic reticulum stress, mitochondrial dysfunction, increased cytokines, or free fatty acids are known to aggravate progressive development of hyperglycemia and hyperlipidemia. Although the exact mechanism contributing to altered metabolism is unclear. Evidence suggests stress kinase role to be a crucial one in metabolic syndrome. Stress kinase, c-jun N-terminal kinase activation (JNK) is involved in various metabolic manifestations including obesity, insulin resistance, fatty liver disease as well as cardiometabolic disorders. It emerged as a foremost mediator in regulating metabolism in the liver, skeletal muscle, adipose tissue as well as pancreatic β cells. It has three isoforms each having a unique and tissue-specific role in altered metabolism. Current findings based on genetic manipulation or chemical inhibition studies identified JNK isoforms to play a central role in the regulation of whole-body metabolism, suggesting it to be a novel therapeutic target. Hence, it is imperative to elucidate its role in metabolic syndrome onset and progression. The purpose of this review is to elucidate in vitro and in vivo implications of JNK signaling along with the therapeutic strategy to inhibit specific isoform. Since metabolic syndrome is an array of diseases and complex pathway, carefully examining each tissue will be important for specific treatment strategies.

URM1 Promoted Tumor Growth and Suppressed Apoptosis via the JNK Signaling Pathway in Hepatocellular Carcinoma

Objective

Ubiquitin-related modifier 1 (URM1) is a member of the ubiquitin-like regulator family, which acts as a post-translational protein modifier in the oxidative emergency response mechanism. Previous studies have shown that URM1 may be involved in the process of apoptosis and may play a role in JNK signaling pathway. In this study, we aimed to investigate the role and possible mechanism of URM1 in HCC progression.

Patients and Methods

Expression of URM1 was determined in 90 pairs of matched liver cancer and adjacent non-cancerous tissues by immunohistochemistry. The impacts of URM1 on HCC cell proliferation, apoptosis, migration and invasion capacities were verified by CCK-8, colony formation, TUNEL staining, wound healing assay and transwell, respectively. Then, the effect of URM1 on subcutaneous tumor formation in vitro was explored by nude mouse xenograft model of liver cancer. Finally, the expression of apoptosis-related proteins was analyzed in URM1 knockdown samples by Western blotting.

Results

In this study, compared with paired adjacent non-cancerous tissues, the expression of URM1 was higher in liver cancer tissues (P <0.01). Kaplan-Meier survival analysis showed that high URM1 expression was significantly associated with poor prognosis (P <0.05). Moreover, URM1 knockdown inhibited liver cancer cell proliferation and migration. Furthermore, URM1 knockdown promoted apoptosis of liver cancer cells. At the same time, URM1 knockdown inhibited tumor growth in nude mouse xenograft model of liver cancer. In addition, URM1 knockdown downregulated the expression of the apoptosis-related factors JNK1/2 and TP53 and upregulated the phosphorylation of JNK1/2 and P53.

Conclusion

In summary, our results suggested that URM1 expression is increased in liver cancer tissues, and URM1 knockdown inhibits the proliferation and migration of liver cancer cells and accelerates apoptosis. High URM1 expression is associated with poor prognosis in patients with HCC.

JNK signaling contributes to skeletal muscle wasting and protein turnover in pancreatic cancer cachexia

Cancer cachexia patients experience significant muscle wasting, which impairs the quality of life and treatment efficacy for patients. Skeletal muscle protein turnover is imparted by increased expression of ubiquitin-proteasome pathway components. Mitogen-activated protein kinases p38 and ERK have been shown to augment E3 ubiquitin ligase expression. Utilizing reverse-phase protein arrays, we identified pancreatic cancer cell-conditioned media-induced activation of JNK signaling in myotubes differentiated from C2C12 myoblasts. Inhibition of JNK signaling with SP600125 reduced cancer cell-conditioned media-induced myotube atrophy, myosin heavy chain protein turnover, and mRNA expression of cachexia-specific ubiquitin ligases Trim63 and Fbxo32. Furthermore, utilizing an orthotopic pancreatic cancer cachexia mouse model, we demonstrated that treatment of tumor-bearing mice with SP600125 improved longitudinal measurements of forelimb grip strength. Post-necropsy measurements demonstrated that SP600125 treatment rescued body weight, carcass weight, and gastrocnemius muscle weight loss without impacting tumor growth. JNK inhibitor treatment also rescued myofiber degeneration and reduced the muscle expression of Trim63 and Fbxo32. These data demonstrate that JNK signaling contributes to muscle wasting in cancer cachexia, and its inhibition has the potential to be utilized as an anti-cachectic therapy.

c-Jun NH2-terminal kinase suppression significantly inhibits the growth of transplanted breast tumors in mice

Objective

The current study investigated the effect of c-Jun NH2-terminal kinase (JNK) expression on the growth of transplanted breast cancer tumors in mice.

Methods

A breast cancer transplantation model was established in BALB/c mice, which were then treated with SP600125 (30 mg/kg) for 24 days. After sacrificing the mice, the inhibitory effects of SP600125 on breast cancer growth were calculated by weighing tumors. Moreover, vascular endothelial growth factor (VEGF) expression and the tumor microvascular density (MVD) were evaluated via immunohistochemistry. Cell apoptosis was also examined using a TUNEL kit.

Results

Compared with the findings in the control group, SP600125 treatment (30 mg/kg) obviously suppressed tumor growth during the 15-day observation period. SP600125 treatment markedly inhibited JNK mRNA expression. Furthermore, VEGF protein expression (50% vs. 100%) and MVD (18.27 ± 1.70 vs. 23.17 ± 4.02) were also significantly decreased by SP600125 treatment, whereas the apoptosis index was significantly higher in the treatment group (10.23 ± 1.97% vs. 4.53 ± 1.40%).

Conclusion

Inhibition of JNK signaling can significantly suppress the growth of transplanted breast tumors in mice.

MiRNAs and mRNAs Analysis during Abdominal Preadipocyte Differentiation in Chickens

Simple Summary

We sequenced the miRNAs and mRNAs of preabdominal fat cells and differentiated adipocytes, and target genes of miRNA combined with mRNA transcriptome data jointly. We found that the MAPK signal pathway, insulin signal pathway, fatty acid metabolism, ECM( extracellular matrix)–receptor interaction, and other signal pathways were involved in the differentiation of preabdominal fat cells. In addition, we found that some miRNAs–mRNAs combinations were strongly related to the differentiation of fat cells (miR-214−ACSBG2, NFKB2, CAMK2A, ACLY, CCND3, PLK3, ITGB2; miR-148a-5p−ROCK2; miR-10a-5p−ELOVL5; miR-146b-5p−LAMA4; miR-6615-5p−FLNB; miR-1774−COL6A1). Our findings provide important resources for the study of adipocyte differentiation.

Abstract

The excessive deposition of abdominal fat has become an important factor in restricting the production efficiency of chickens, so reducing abdominal fat deposition is important for improving growth rate. It has been proven that miRNAs play an important role in regulating many physiological processes of organisms. In this study, we constructed a model of adipogenesis by isolating preadipocytes (Ab-Pre) derived from abdominal adipose tissue and differentiated adipocytes (Ab-Ad) in vitro. Deep sequencing of miRNAs and mRNAs expressed in Ab-Pre and Ab-Ad groups was conducted to explore the effect of miRNAs and mRNAs on fat deposition. We identified 80 differentially expressed miRNAs (DEMs) candidates, 58 of which were up-regulated and 22 down-regulated. Furthermore, six miRNAs and six mRNAs were verified by qRT-PCR, and the results showed that the expression of the DEMs and differentially expressed genes (DEGs) in the two groups was consistent with our sequencing results. When target genes of miRNA were combined with mRNA transcriptome data, a total of 891 intersection genes were obtained, we predicted the signal pathways of cross genes enrichment to the MAPK signal pathway, insulin signal pathway, fatty acid metabolism, and ECM–receptor interaction. Meanwhile, we constructed miRNA and negatively correlated mRNA target networks, including 12 miRNA–mRNAs pairs, which showed a strong association with the abdominal adipocyte differentiation (miR-214−ACSBG2, NFKB2, CAMK2A, ACLY, CCND3, PLK3, ITGB2; miR-148a-5p−ROCK2; miR-10a-5p−ELOVL5; miR-146b-5p−LAMA4; miR-6615-5p−FLNB; miR-1774−COL6A1). Overall, these findings provide a background for further research on lipid metabolism. Thus, we can better understand the molecular genetic mechanism of chicken abdominal fat deposition.

trans-Fatty acids facilitate DNA damage-induced apoptosis through the mitochondrial JNK-Sab-ROS positive feedback loop

trans-Fatty acids (TFAs) are unsaturated fatty acids that contain one or more carbon-carbon double bonds in trans configuration. Epidemiological evidence has linked TFA consumption with various disorders, including cardiovascular diseases. However, the underlying pathological mechanisms are largely unknown. Here, we show a novel toxic mechanism of TFAs triggered by DNA damage. We found that elaidic acid (EA) and linoelaidic acid, major TFAs produced during industrial food manufacturing (so-called as industrial TFAs), but not their corresponding cis isomers, facilitated apoptosis induced by doxorubicin. Consistently, EA enhanced UV-induced embryonic lethality in C. elegans worms. The pro-apoptotic action of EA was blocked by knocking down Sab, a c-Jun N-terminal kinase (JNK)-interacting protein localizing at mitochondrial outer membrane, which mediates mutual amplification of mitochondrial reactive oxygen species (ROS) generation and JNK activation. EA enhanced doxorubicin-induced mitochondrial ROS generation and JNK activation, both of which were suppressed by Sab knockdown and pharmacological inhibition of either mitochondrial ROS generation, JNK, or Src-homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1) as a Sab-associated protein. These results demonstrate that in response to DNA damage, TFAs drive the mitochondrial JNK-Sab-ROS positive feedback loop and ultimately apoptosis, which may provide insight into the common pathogenetic mechanisms of diverse TFA-related disorders.

ASK1 inhibition reduces cell death and hepatic fibrosis in an Nlrp3 mutant liver injury model

Hepatic inflammasome activation is considered a major contributor to liver fibrosis in NASH. Apoptosis signal-regulating kinase 1 (ASK1) is an apical mitogen-activated protein kinase that activates hepatic JNK and p38 to promote apoptosis, inflammation, and fibrosis. The aim of the current study was to investigate whether pharmacologic inhibition of ASK1 could attenuate hepatic fibrosis driven by inflammasome activation using gain-of-function NOD-like receptor protein 3 (Nlrp3) mutant mice. Tamoxifen-inducible Nlrp3 knock-in (Nlrp3A350V/+CreT-KI) mice and WT mice were administered either control chow diet or diet containing the selective ASK1 inhibitor GS-444217 for 6 weeks. Livers of Nlrp3-KI mice had increased inflammation, cell death, and fibrosis and increased phosphorylation of ASK1, p38, and c-Jun. GS-444217 reduced ASK1 pathway activation, liver cell death, and liver fibrosis. ASK1 inhibition resulted in a significant downregulation of genes involved in collagen production and extracellular matrix deposition, as well as in a reduced hepatic TNF-α expression. ASK1 inhibition also directly reduced LPS-induced gene expression of Collagen 1A1 (Col1a1) in hepatic stellate cells isolated from Nlrp3-KI mice. In conclusion, ASK1 inhibition reduced liver cell death and fibrosis downstream of inflammatory signaling induced by NLRP3. These data provide mechanistic insight into the antifibrotic mechanisms of ASK1 inhibition.

Transcriptome Modifications in the Porcine Intramuscular Adipocytes during Differentiation and Exogenous Stimulation with TNF-α and Serotonin

Adipocytes are dynamic cells that have critical functions to maintain body energy homeostasis. Adipocyte physiology is affected by the adipogenic differentiation, cell program, as well as by the exogenous stimulation of biochemical factors, such as serotonin and TNF-α. In this work, we investigated the global transcriptome modifications when porcine intramuscular preadipocyte (PIP) was differentiated into porcine mature adipocyte (pMA). Moreover, we studied transcriptome changes in pMA after stimulation with serotonin or TNF-α by using a microarray approach. Transcriptome analysis revealed that the expression of 270, 261, and 249 genes were modified after differentiation, or after serotonin and TNF-α stimulation, respectively. Expression changes in APP, HNF4A, ESR1, EGR1, SRC, HNF1A, FN1, ALB, STAT3, CBL, CEBPB, AR, FOS, CFTR, PAN2, PTPN6, VDR, PPARG, STAT5A and NCOA3 genes which are enriched in the ‘PPAR signaling’ and ‘insulin resistance’ pathways were found in adipocytes during the differentiation process. Dose-dependent serotonin stimulation resulted in a decreased fat accumulation in pMAs. Serotonin-induced differentially expressed genes in pMAs were found to be involved in the significant enrichment of ′GPCR ligand-binding′, ‘cell chemotaxis’, ‘blood coagulation and complement’, ‘metabolism of lipid and lipoproteins’, ‘regulation of lipid metabolism by PPARA’, and ‘lipid digestion, mobilization and transport’ pathways. TNF-α stimulation also resulted in transcriptome modifications linked with proinflammatory responses in the pMA of intramuscular origin. Our results provide a landscape of transcriptome modifications and their linked-biological pathways in response to adipogenesis, and exogenous stimulation of serotonin- and TNF-α to the pMA of intramuscular origin.

New Insights into Bioactive Compounds of Traditional Chinese Medicines for Insulin Resistance Based on Signaling Pathways

Type 2 diabetes is a serious metabolic disease as a long-term threat to human health. Insulin resistance is not only the basis and major feature of type 2 diabetes, but also the main etiology of diseases such as hypertension, hyperlipidemia and coronary heart disease. It has been shown that Traditional Chinese Medicines (TCMs) play an important role in the treatment of type 2 diabetes, through attenuating insulin resistance, whereas the mechanism involved is not yet well understood. Therefore, it is important to elucidate the pharmacological mechanism of these bioactive compounds so that one can pave the way for the modernization of TCMs. In this review, we focus on the recent progresses of some bioactive ingredients from TCMs with different functional groups, which exhibit therapeutic potential for the treatment of diabetic insulin resistance. It is expected that this review can provide new references for developing TCM-derived drugs against diabetes and insulin resistance in the future.

α-Ketoglutarate-Activated NF-κB Signaling Promotes Compensatory Glucose Uptake and Brain Tumor Development

The rapid proliferation of cancer cells and dysregulated vasculature within the tumor leads to limited nutrient accessibility. Cancer cells often rewire their metabolic pathways for adaption to nutrient stress, and the underlying mechanism remains largely unknown. Glutamate dehydrogenase 1 (GDH1) is a key enzyme in glutaminolysis that converts glutamate to α-ketoglutarate (α-KG). Here, we show that, under low glucose, GDH1 is phosphorylated at serine (S) 384 and interacts with RelA and IKKβ. GDH1-produced α-KG directly binds to and activates IKKβ and nuclear factor κB (NF-κB) signaling, which promotes glucose uptake and tumor cell survival by upregulating GLUT1, thereby accelerating gliomagenesis. In addition, GDH1 S384 phosphorylation correlates with the malignancy and prognosis of human glioblastoma. Our finding reveals a unique role of α-KG to directly regulate signal pathway, uncovers a distinct mechanism of metabolite-mediated NF-κB activation, and also establishes the critical role of α-KG-activated NF-κB in brain tumor development.

RNAs and RNA-Binding Proteins in Immuno-Metabolic Homeostasis and Diseases

The increasing prevalence of worldwide obesity has emerged as a major risk factor for type 2 diabetes (T2D), hepatosteatosis, and cardiovascular disease. Accumulating evidence indicates that obesity has strong inflammatory underpinnings tightly linked to the development of metabolic diseases. However, the molecular mechanisms by which obesity induces aberrant inflammation associated with metabolic diseases are not yet clearly defined. Recently, RNAs have emerged as important regulators of stress responses and metabolism. RNAs are subject to changes in modification status, higher-order structure, and cellular localization; all of which could affect the affinity for RNA-binding proteins (RBPs) and thereby modify the RNA-RBP networks. Proper regulation and management of RNA characteristics are fundamental to cellular and organismal homeostasis, as well as paramount to health. Identification of multiple single nucleotide polymorphisms (SNPs) within loci of fat mass- and obesity-associated protein (FTO) gene, an RNA demethylase, through genome-wide association studies (GWAS) of T2D, and functional assessments of FTO in mice, support the concept that disruption in RNA modifications leads to the development of human diseases including obesity and metabolic disorder. In obesity, dynamic alterations in modification and localization of RNAs appear to modulate the RNA-RBP networks and activate proinflammatory RBPs, such as double-stranded RNA (dsRNA)-dependent protein kinase (PKR), Toll-like receptor (TLR) 3 and TLR7, and RNA silencing machinery. These changes induce aberrant inflammation and the development of metabolic diseases. This review will describe the current understanding of the underlying causes of these common and altered characteristics of RNA-RBP networks which will pave the way for developing novel approaches to tackle the pandemic issue of obesity.

Therapeutic Mechanisms of Herbal Medicines Against Insulin Resistance: A Review

Insulin resistance is a condition in which insulin sensitivity is reduced and the insulin signaling pathway is impaired. Although often expressed as an increase in insulin concentration, the disease is characterized by a decrease in insulin action. This increased workload of the pancreas and the consequent decompensation are not only the main mechanisms for the development of type 2 diabetes (T2D), but also exacerbate the damage of metabolic diseases, including obesity, nonalcoholic fatty liver disease, polycystic ovary syndrome, metabolic syndrome, and others. Many clinical trials have suggested the potential role of herbs in the treatment of insulin resistance, although most of the clinical trials included in this review have certain flaws and bias risks in their methodological design, including the generation of randomization, the concealment of allocation, blinding, and inadequate reporting of sample size estimates. These studies involve not only the single-flavored herbs, but also herbal formulas, extracts, and active ingredients. Numerous of in vitro and in vivo studies have pointed out that the role of herbal medicine in improving insulin resistance is related to interventions in various aspects of the insulin signaling pathway. The targets involved in these studies include insulin receptor substrate, phosphatidylinositol 3-kinase, glucose transporter, AMP-activated protein kinase, glycogen synthase kinase 3, mitogen-activated protein kinases, c-Jun-N-terminal kinase, nuclear factor-kappaB, protein tyrosine phosphatase 1B, nuclear factor-E2-related factor 2, and peroxisome proliferator-activated receptors. Improved insulin sensitivity upon treatment with herbal medicine provides considerable prospects for treating insulin resistance. This article reviews studies of the target mechanisms of herbal treatments for insulin resistance.

Influenza Virus Infections and Cellular Kinases

Influenza A viruses (IAVs) are a major cause of respiratory illness and are responsible for yearly epidemics associated with more than 500,000 annual deaths globally. Novel IAVs may cause pandemic outbreaks and zoonotic infections with, for example, highly pathogenic avian influenza virus (HPAIV) of the H5N1 and H7N9 subtypes, which pose a threat to public health. Treatment options are limited and emergence of strains resistant to antiviral drugs jeopardize this even further. Like all viruses, IAVs depend on host factors for every step of the virus replication cycle. Host kinases link multiple signaling pathways in respond to a myriad of stimuli, including viral infections. Their regulation of multiple response networks has justified actively targeting cellular kinases for anti-cancer therapies and immune modulators for decades. There is a growing volume of research highlighting the significant role of cellular kinases in regulating IAV infections. Their functional role is illustrated by the required phosphorylation of several IAV proteins necessary for replication and/or evasion/suppression of the innate immune response. Identified in the majority of host factor screens, functional studies further support the important role of kinases and their potential as host restriction factors. PKC, ERK, PI3K and FAK, to name a few, are kinases that regulate viral entry and replication. Additionally, kinases such as IKK, JNK and p38 MAPK are essential in mediating viral sensor signaling cascades that regulate expression of antiviral chemokines and cytokines. The feasibility of targeting kinases is steadily moving from bench to clinic and already-approved cancer drugs could potentially be repurposed for treatments of severe IAV infections. In this review, we will focus on the contribution of cellular kinases to IAV infections and their value as potential therapeutic targets.

Tumor Progression Locus 2 in Hepatocytes Potentiates Both Liver and Systemic Metabolic Disorders in Mice

Tumor progression locus 2 (TPL2), a serine/threonine kinase, has been regarded as a potentially interesting target for the treatment of various diseases with an inflammatory component. However, the function of TPL2 in regulating hepatocyte metabolism and liver inflammation during the progression of nonalcoholic fatty liver disease (NAFLD) is poorly understood. Here, we report that TPL2 protein expression was significantly increased in fatty liver from diverse species, including humans, monkeys, and mice. Further investigations revealed that compared to wild-type (WT) littermates, hepatocyte-specific TPL2 knockout (HKO) mice exhibited improved lipid and glucose imbalance, reserved insulin sensitivity, and alleviated inflammation in response to high-fat diet (HFD) feeding. Overexpression of TPL2 in hepatocytes led to the opposite phenotype. Regarding the mechanism, we found that mitogen-activated protein kinase kinase 7 (MKK7) was the specific substrate of TPL2 for c-Jun N-terminal kinase (JNK) activation. TPL2-MKK7-JNK signaling in hepatocytes represents a promising drugable target for treating NAFLD and associated metabolic disorders. Conclusion: In hepatocytes, TPL2 acts as a key mediator that promotes both liver and systemic metabolic disturbances by specifically increasing MKK7-JNK activation.

Current trials and novel therapeutic targets for alcoholic hepatitis

Alcoholic hepatitis is a clinical syndrome in which patients present with acute-on-chronic liver failure and a high risk of short-term mortality. The current treatment of alcoholic hepatitis is suboptimal. Results recently published from the STOPAH study have improved our understanding of how best to design clinical trials for this condition. Although emerging data on liver transplantation for patients with alcoholic hepatitis are encouraging, less than 2% of these patients qualify. Clearly, there is an unmet need for novel treatments to improve the survival of these patients. Changes in the gut microbiota, inflammatory and cytokine signalling, oxidative stress and mitochondrial dysfunction, and abnormalities in the hepatic regenerative capacity alone or in combination contribute to the pathology of alcoholic hepatitis. In this chapter, we will describe the novel therapeutic agents targeting various pathways in the pathophysiology of alcoholic hepatitis. Specifically, we will describe the ongoing clinical trials in which some of these agents are being studied.

Gα12 ablation exacerbates liver steatosis and obesity by suppressing USP22/SIRT1-regulated mitochondrial respiration

Nonalcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge with activated GPCRs to modulate cell-signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of G protein α12 (Gα12) on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα12 levels in mouse liver. Gα12 ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12-KO liver revealed that the Gα12-signaling pathway regulated sirtuin 1 (SIRT1) and PPARα, which are responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12-KO mice, which was reversed by lentivirus-mediated Gα12 overexpression in hepatocytes. Mechanistically, Gα12 stabilized SIRT1 protein through transcriptional induction of ubiquitin-specific peptidase 22 (USP22) via HIF-1α increase. Gα12 levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12-KO mice fed a high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα12 regulates SIRT1-dependent mitochondrial respiration through HIF-1α-dependent USP22 induction, identifying Gα12 as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.

Omega-3 Fatty Acids and Insulin Resistance: Focus on the Regulation of Mitochondria and Endoplasmic Reticulum Stress

Mitochondrial dysfunction and endoplasmic reticulum (ER) stress have been suggested to play a key role in insulin resistance development. Reactive oxygen species (ROS) production and lipid accumulation due to mitochondrial dysfunction seemed to be important mechanisms leading to cellular insulin resistance. Moreover, mitochondria are functionally and structurally linked to ER, which undergoes stress in conditions of chronic overnutrition, activating the unfolded protein response, which in turn activates the principal inflammatory pathways that impair insulin action. Among the nutrients, dietary fats are believed to play key roles in insulin resistance onset. However, not all dietary fats exert the same effects on cellular energy metabolism. Dietary omega 3 polyunsaturated fatty acids (PUFA) have been suggested to counteract insulin resistance development by modulating mitochondrial bioenergetics and ER stress. In the current review, we summarized current knowledge on the role played by mitochondrial and ER stress in inflammation and insulin resistance onset, focusing on the modulation role of omega 3 PUFA on these stress pathways. Understanding the mechanisms by which omega 3 PUFA modulates cellular metabolism and insulin resistance in peripheral tissues may provide additional details on the potential impact of omega 3 PUFA on metabolic function and the management of insulin resistance in humans.

Hepatic Gi signaling regulates whole-body glucose homeostasis

An increase in hepatic glucose production (HGP) is a key feature of type 2 diabetes. Excessive signaling through hepatic Gs-linked glucagon receptors critically contributes to pathologically elevated HGP. Here, we tested the hypothesis that this metabolic impairment can be counteracted by enhancing hepatic Gi signaling. Specifically, we used a chemogenetic approach to selectively activate Gi-type G proteins in mouse hepatocytes in vivo. Unexpectedly, activation of hepatic Gi signaling triggered a pronounced increase in HGP and severely impaired glucose homeostasis. Moreover, increased Gi signaling stimulated glucose release in human hepatocytes. A lack of functional Gi-type G proteins in hepatocytes reduced blood glucose levels and protected mice against the metabolic deficits caused by the consumption of a high-fat diet. Additionally, we delineated a signaling cascade that links hepatic Gi signaling to ROS production, JNK activation, and a subsequent increase in HGP. Taken together, our data support the concept that drugs able to block hepatic Gi-coupled GPCRs may prove beneficial as antidiabetic drugs.

Co-culture with neonatal cardiomyocytes enhances the proliferation of iPSC-derived cardiomyocytes via FAK/JNK signaling

Background

We previously reported that the pluripotent stem cells can differentiate into cardiomyocytes (CMs) by co-culture with neonatal CMs (NCMs) in vitro. However, the involving mechanism is not clear.

Methods

Mouse induced pluripotent stem cells (iPSCs) were cultured in hanging drops to form embryoid bodies (EBs) and to induce myocardial differentiation. Co-culture of EBs and NCMs was established in a transwell insert system, while EBs grown alone in the wells were used as controls.

Results

Co-culture with NCMs markedly increased the generation of functional CMs from iPSCs. The focal adhesion kinase (FAK) phosphorylation, and c-Jun N-terminal kinase (JNK) phosphorylation in co-culture were higher than that in EBs grown alone. Treating FAK small interfering RNA (FAK siRNA) or specific inhibitor for JNK (SP600125) to iPSCs significantly reduced the phosphorylation of JNK and the expressions of Mef2c and Bcl-2. The expressions of cTnT and MLC-2V were also decreased. Our results revealed that co-culture with NCMs significantly enhance the differentiation ability of iPSCs by increasing Mef2c and Bcl-2 expressions concomitantly with a marked augment on cell proliferation through JNK signaling pathways.

Conclusions

These findings indicated that co-culture of EBs with NCMs induces genes expressed in a mature pattern and stimulates the proliferation of iPSC-derived CMs (iPS-CMs) by activating FAK/JNK signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-016-0112-2) contains supplementary material, which is available to authorized users.

Jnk1 Deficiency in Hematopoietic Cells Suppresses Macrophage Apoptosis and Increases Atherosclerosis in Low-Density Lipoprotein Receptor Null Mice

OBJECTIVE

The c-Jun NH2-terminal kinases (JNK) are regulated by a wide variety of cellular stresses and have been implicated in apoptotic signaling. Macrophages express 2 JNK isoforms, JNK1 and JNK2, which may have different effects on cell survival and atherosclerosis.

APPROACH AND RESULTS

To dissect the effect of macrophage JNK1 and JNK2 on early atherosclerosis, Ldlr(-/-) mice were reconstituted with wild-type, Jnk1(-/-), and Jnk2(-/-) hematopoietic cells and fed a high cholesterol diet. Jnk1(-/-)→Ldlr(-/-) mice have larger atherosclerotic lesions with more macrophages and fewer apoptotic cells than mice transplanted with wild-type or Jnk2(-/-) cells. Moreover, genetic ablation of JNK to a single allele (Jnk1(+/-)/Jnk2(-/-) or Jnk1(-/-)/Jnk2(+/-)) in marrow of Ldlr(-/-) recipients further increased atherosclerosis compared with Jnk1(-/-)→Ldlr(-/-) and wild-type→Ldlr(-/-) mice. In mouse macrophages, anisomycin-mediated JNK signaling antagonized Akt activity, and loss of Jnk1 gene obliterated this effect. Similarly, pharmacological inhibition of JNK1, but not JNK2, markedly reduced the antagonizing effect of JNK on Akt activity. Prolonged JNK signaling in the setting of endoplasmic reticulum stress gradually extinguished Akt and Bad activity in wild-type cells with markedly less effects in Jnk1(-/-) macrophages, which were also more resistant to apoptosis. Consequently, anisomycin increased and JNK1 inhibitors suppressed endoplasmic reticulum stress-mediated apoptosis in macrophages. We also found that genetic and pharmacological inhibition of phosphatase and tensin homolog abolished the JNK-mediated effects on Akt activity, indicating that phosphatase and tensin homolog mediates crosstalk between these pathways.

CONCLUSIONS

Loss of Jnk1, but not Jnk2, in macrophages protects them from apoptosis, increasing cell survival, and this accelerates early atherosclerosis.

Endothelial Dysfunction in Human Diabetes Is Mediated by Wnt5a-JNK Signaling

OBJECTIVE

Endothelial dysfunction is linked to insulin resistance, inflammatory activation, and increased cardiovascular risk in diabetes mellitus; however, the mechanisms remain incompletely understood. Recent studies have identified proinflammatory signaling of wingless-type family member (Wnt) 5a through c-jun N-terminal kinase (JNK) as a regulator of metabolic dysfunction with potential relevance to vascular function. We sought to gain evidence that increased activation of Wnt5a-JNK signaling contributes to impaired endothelial function in patients with diabetes mellitus.

APPROACH AND RESULTS

We measured flow-mediated dilation of the brachial artery and characterized freshly isolated endothelial cells by protein expression, eNOS activation, and nitric oxide production in 85 subjects with type 2 diabetes mellitus (n=42) and age- and sex-matched nondiabetic controls (n=43) and in human aortic endothelial cells treated with Wnt5a. Endothelial cells from patients with diabetes mellitus displayed 1.3-fold higher Wnt5a levels (P=0.01) along with 1.4-fold higher JNK activation (P<0.01) without a difference in total JNK levels. Higher JNK activation was associated with lower flow-mediated dilation, consistent with endothelial dysfunction (r=0.53, P=0.02). Inhibition of Wnt5a and JNK signaling restored insulin and A23187-mediated eNOS activation and improved nitric oxide production in endothelial cells from patients with diabetes mellitus. In endothelial cells from nondiabetic controls, rWnt5a treatment inhibited eNOS activation replicating the diabetic endothelial phenotype. In human aortic endothelial cells, Wnt5a-induced impairment of eNOS activation and nitric oxide production was reversed by Wnt5a and JNK inhibition.

CONCLUSIONS

Our findings demonstrate that noncanonical Wnt5a signaling and JNK activity contribute to vascular insulin resistance and endothelial dysfunction and may represent a novel therapeutic opportunity to protect the vasculature in patients with diabetes mellitus.

Inflammation-induced ROS generation causes pancreatic cell death through modulation of Nrf2/NF-κB and SAPK/JNK pathway

Chronic pancreatitis is characterized by progressive loss of exocrine and endocrine functions of the pancreas and is considered to be the single most important cause for development of pancreatic cancer. Recent evidence suggests that inflammation and oxidative stress play pivotal roles in the development of clinical conditions like pancreatitis, type 2 diabetes mellitus, and metabolic syndrome. Nonetheless, molecular signaling pathways linking inflammation, oxidative stress, and pancreatic cell death are not yet well defined. In this study, bacterial lipopolysaccharide (LPS) was used (injected twice a week for three weeks) to emulate a chronic systemic inflammatory state in experimental Swiss albino mice. Using this model, we traced the genesis of inflammation-induced pancreatic dysfunction and mapped the signaling events which contribute to the induction of this state. Histopathological studies revealed the appearance of cell injuries and increased collagen content in LPS-exposed group, indicative of fibrosis. Assays for intraperitoneal glucose tolerance, insulin levels, and insulin receptor mRNA expression signified inflammation-induced insulin insensitivity. For the first time we present evidence that cellular inflammation and subsequent oxidative stress modulate the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)/NF-E2-related factor 2 or Nuclear factor (erythroid-derived 2)-like 2 pathway and initiates pancreatic cell death by activation of stress-responsive Rho/stress-activated protein kinase or SAPK/Jun-N-terminal kinase (JNK) pathway. Scavenging of intracellular reactive oxygen species (ROS) by a standard antioxidant N-acetyl cysteine led to pancreatic cell survival. The data obtained strongly indicates that the LPS/toll-like receptor-4 or TLR-4/ROS/NF-κB pathway is critically involved in the initiation of inflammation, oxidative stress, and pancreatic cell death and might prove to be an excellent choice as a target for novel therapeutic strategies in the management of metabolic disorders.

Calcium Homeostasis and Organelle Function in the Pathogenesis of Obesity and Diabetes

A number of chronic metabolic pathologies, including obesity, diabetes, cardiovascular disease, asthma, and cancer, cluster together to present the greatest threat to human health. As research in this field has advanced, it has become clear that unresolved metabolic inflammation, organelle dysfunction, and other cellular and metabolic stresses underlie the development of these chronic metabolic diseases. However, the relationship between these systems and pathological mechanisms is poorly understood. Here we discuss the role of cellular Ca(2+) homeostasis as a critical mechanism integrating the myriad of cellular and subcellular dysfunctional networks found in metabolic tissues such as liver and adipose tissue in the context of metabolic disease, particularly in obesity and diabetes.

Fyn Activation of mTORC1 Stimulates the IRE1α-JNK Pathway, Leading to Cell Death

We previously reported that the skeletal muscle-specific overexpression of Fyn in mice resulted in a severe muscle wasting phenotype despite the activation of mTORC1 signaling. To investigate the bases for the loss of muscle fiber mass, we examined the relationship between Fyn activation of mTORC1, JNK, and endoplasmic reticulum stress. Overexpression of Fyn in skeletal muscle in vivo and in HEK293T cells in culture resulted in the activation of IRE1α and JNK, leading to increased cell death. Fyn synergized with the general endoplasmic reticulum stress inducer thapsigargin, resulting in the activation of IRE1α and further accelerated cell death. Moreover, inhibition of mTORC1 with rapamycin suppressed IRE1α activation and JNK phosphorylation, resulting in protecting cells against Fyn- and thapsigargin-induced cell death. Moreover, rapamycin treatment in vivo reduced the skeletal muscle IRE1α activation in the Fyn-overexpressing transgenic mice. Together, these data demonstrate the presence of a Fyn-induced endoplasmic reticulum stress that occurred, at least in part, through the activation of mTORC1, as well as subsequent activation of the IRE1α-JNK pathway driving cell death.

Invited review: Inflammation during the transition to lactation: New adventures with an old flame

For dairy cattle, the first several weeks of lactation represent the highest-risk period in their lives after their own neonatal period. Although more than 50% of cows during this period are estimated to suffer from at least one subclinical disorder, the complicated admixture of normal adaptations to lactation, infectious challenges, and metabolic disorders has made it difficult to determine which physiological processes are adaptive and which are pathological during this time. Subacute inflammation, a condition that has been well documented in obesity, has been a subject of great interest among dairy cattle physiologists in the past decade. Many studies have now clearly shown that essentially all cows experience some degree of systemic inflammation in the several days after parturition. The magnitude and likely persistence of the inflammatory state varies widely among cows, and several studies have linked the degree of postpartum inflammation to increased disease risk and decreased whole-lactation milk production. In addition to these associations, enhancing postpartum inflammation with repeated subacute administration of cytokines has impaired productivity and markers of health, whereas targeted use of nonsteroidal anti-inflammatory drugs during this window of time has enhanced whole-lactation productivity in several studies. Despite these findings, many questions remain about postpartum inflammation, including which organs are key initiators of this state and what signaling molecules are responsible for systemic and tissue-specific inflammatory states. Continued in vivo work should help clarify the degree to which mild postpartum inflammation is adaptive and whether the targeted use of anti-inflammatory drugs or nutrients can improve the health and productivity of dairy cows.

Acute rhabdomyolysis and inflammation

Rhabdomyolysis results from the rapid breakdown of skeletal muscle fibers, which leads to leakage of potentially toxic cellular content into the systemic circulation. Acquired causes by direct injury to the sarcolemma are most frequent. The inherited causes are: i) metabolic with failure of energy production, including mitochondrial fatty acid ß-oxidation defects, LPIN1 mutations, inborn errors of glycogenolysis and glycolysis, more rarely mitochondrial respiratory chain deficiency, purine defects and peroxysomal α-methyl-acyl-CoA-racemase defect (AMACR), ii) structural causes with muscle dystrophies and myopathies, iii) calcium pump disorder with RYR1 gene mutations, iv) inflammatory causes with myositis. Irrespective of the cause of rhabdomyolysis, the pathology follows a common pathway, either by the direct injury to sarcolemma by increased intracellular calcium concentration (acquired causes) or by the failure of energy production (inherited causes), which leads to fiber necrosis. Rhabdomyolysis are frequently precipitated by febrile illness or exercise. These conditions are associated with two events, elevated temperature and high circulating levels of pro-inflammatory mediators such as cytokines and chemokines. To illustrate these points in the context of energy metabolism, protein thermolability and the potential benefits of arginine therapy, we focus on a rare cause of rhabdomyolysis, aldolase A deficiency. In addition, our studies on lipin-1 (LPIN1) deficiency raise the possibility that several diseases involved in rhabdomyolysis implicate pro-inflammatory cytokines and may even represent primarily pro-inflammatory diseases. Thus, not only thermolability of mutant proteins critical for muscle function, but also pro-inflammatory cytokines per se, may lead to metabolic decompensation and rhabdomyolysis.

Brain metabolic stress and neuroinflammation at the basis of cognitive impairment in Alzheimer's disease

Brain metabolic dysfunction is known to influence brain activity in several neurological disorders, including Alzheimer’s disease (AD). In fact, deregulation of neuronal metabolism has been postulated to play a key role leading to the clinical outcomes observed in AD. Besides deficits in glucose utilization in AD patients, recent evidence has implicated neuroinflammation and endoplasmic reticulum (ER) stress as components of a novel form of brain metabolic stress that develop in AD and other neurological disorders. Here we review findings supporting this novel paradigm and further discuss how these mechanisms seem to participate in synapse and cognitive impairments that are germane to AD. These deleterious processes resemble pathways that act in peripheral tissues leading to insulin resistance and glucose intolerance, in an intriguing molecular connection linking AD to diabetes. The discovery of detailed mechanisms leading to neuronal metabolic stress may be a key step that will allow the understanding how cognitive impairment develops in AD, thereby offering new avenues for effective disease prevention and therapeutic targeting.

A critical role for PKR complexes with TRBP in Immunometabolic regulation and eIF2α phosphorylation in obesity

Aberrant stress and inflammatory responses are key factors in the pathogenesis of obesity and metabolic dysfunction, and the double-stranded RNA-dependent kinase (PKR) has been proposed to play an important role in integrating these pathways. Here, we report the formation of a complex between PKR and TAR RNA-binding protein (TRBP) during metabolic and obesity-induced stress, which is critical for the regulation of eukaryotic translation initiation factor 2 alpha (eIF2α) phosphorylation and c-Jun N-terminal kinase (JNK) activation. We show that TRBP phosphorylation is induced in the setting of metabolic stress, leading to PKR activation. Suppression of hepatic TRBP reduced inflammation, JNK activity, and eIF2α phosphorylation and improved systemic insulin resistance and glucose metabolism, while TRBP overexpression exacerbated the impairment in glucose homeostasis in obese mice. These data indicate that the association between PKR and TRBP integrates metabolism with translational control and inflammatory signaling and plays important roles in metabolic homeostasis and disease.

The effects of an ActRIIb receptor Fc fusion protein ligand trap in juvenile simian immunodeficiency virus-infected rhesus macaques

There are no approved therapies for muscle wasting in children infected with human immunodeficiency virus (HIV), which portends poor disease outcomes. To determine whether a soluble ActRIIb receptor Fc fusion protein (ActRIIB.Fc), a ligand trap for TGF-β/activin family members including myostatin, can prevent or restore loss of lean body mass and body weight in simian immunodeficiency virus (SIV)-infected juvenile rhesus macaques (Macaca mulatta). Fourteen pair-housed, juvenile male rhesus macaques were inoculated with SIVmac239 and, 4 wk postinoculation (WPI) treated with intramuscular injections of 10 mg ⋅ kg(-1) ⋅ wk(-1) ActRIIB.Fc or saline placebo. Body weight, lean body mass, SIV titers, and somatometric measurements were assessed monthly for 16 wk. Age-matched SIV-infected rhesus macaques were injected with saline. Intervention groups did not differ at baseline. Gains in lean mass were significantly greater in the ActRIIB.Fc group than in the placebo group (P < 0.001). Administration of ActRIIB.Fc was associated with greater gains in body weight (P = 0.01) and upper arm circumference than placebo. Serum CD4(+) T-lymphocyte counts and SIV copy numbers did not differ between groups. Administration of ActRIIB.Fc was associated with higher muscle expression of myostatin than placebo. ActRIIB.Fc effectively blocked and reversed loss of body weight, lean mass, and fat mass in juvenile SIV-infected rhesus macaques.