TAZ couples Hippo/Wnt signalling and insulin sensitivity through Irs1 expression

Crosstalk among canonical Wnt and Hippo pathway members in skeletal muscle and at the neuromuscular junction

Skeletal muscles are essential for locomotion, posture, and metabolic regulation. To understand physiological processes, exercise adaptation, and muscle-related disorders, it is critical to understand the molecular pathways that underlie skeletal muscle function. The process of muscle contraction, orchestrated by a complex interplay of molecular events, is at the core of skeletal muscle function. Muscle contraction is initiated by an action potential and neuromuscular transmission requiring a neuromuscular junction. Within muscle fibers, calcium ions play a critical role in mediating the interaction between actin and myosin filaments that generate force. Regulation of calcium release from the sarcoplasmic reticulum plays a key role in excitation-contraction coupling. The development and growth of skeletal muscle are regulated by a network of molecular pathways collectively known as myogenesis. Myogenic regulators coordinate the differentiation of myoblasts into mature muscle fibers. Signaling pathways regulate muscle protein synthesis and hypertrophy in response to mechanical stimuli and nutrient availability. Several muscle-related diseases, including congenital myasthenic disorders, sarcopenia, muscular dystrophies, and metabolic myopathies, are underpinned by dysregulated molecular pathways in skeletal muscle. Therapeutic interventions aimed at preserving muscle mass and function, enhancing regeneration, and improving metabolic health hold promise by targeting specific molecular pathways. Other molecular signaling pathways in skeletal muscle include the canonical Wnt signaling pathway, a critical regulator of myogenesis, muscle regeneration, and metabolic function, and the Hippo signaling pathway. In recent years, more details have been uncovered about the role of these two pathways during myogenesis and in developing and adult skeletal muscle fibers, and at the neuromuscular junction. In fact, research in the last few years now suggests that these two signaling pathways are interconnected and that they jointly control physiological and pathophysiological processes in muscle fibers. In this review, we will summarize and discuss the data on these two pathways, focusing on their concerted action next to their contribution to skeletal muscle biology. However, an in-depth discussion of the non-canonical Wnt pathway, the fibro/adipogenic precursors, or the mechanosensory aspects of these pathways is not the focus of this review.

Inhibition of CILP2 Improves Glucose Metabolism and Mitochondrial Dysfunction in Sarcopenia via the Wnt Signalling Pathway

BACKGROUND

Skeletal muscle is the primary organ involved in insulin-mediated glucose metabolism. Elevated levels of CILP2 are a significant indicator of impaired glucose tolerance and are predominantly expressed in skeletal muscle. It remains unclear whether CILP2 contributes to age-related muscle atrophy through regulating the glucose homeostasis and insulin sensitivity.

METHODS

Initially, the expression levels of CILP2 were assessed in elderly mice and patients with sarcopenia. Lentiviral vectors were used to induce either silencing or overexpression of CILP2 in C2C12 myoblast cells. The effects of CILP2 on proliferation, myogenic differentiation, insulin sensitivity and glucose uptake were evaluated using immunofluorescence, western blotting, real-time quantitative polymerase chain reaction, RNA sequencing, glucose uptake experiments, dual-luciferase reporter assays and co-immunoprecipitation (CO-IP). An adeno-associated virus-9 containing a muscle-specific promoter was injected into SAMP8 senile mice to observe the efficacy of CILP2 knockout.

RESULTS

We found that there was more CLIP2 expressed in the skeletal muscle of ageing mice (+1.1-fold, p < 0.01) and in patients with sarcopenia (+2.5-fold, p < 0.01) compared to the control group. Following the overexpression of CILP2, Ki67 (-65%, p < 0.01), PCNA (-32%, p < 0.05), MyoD1 (-89%, p < 0.001), MyoG (-31%, p < 0.05) and MyHC (-85%, p < 0.001), which indicate proliferation and differentiation potential, were significantly reduced. In contrast, MuRF-1 (+59%, p < 0.05), atrogin-1 (+43%, p < 0.05) and myostatin (+31%, p < 0.05), the markers of muscular atrophy, were significantly increased. Overexpression of CILP2 decreased insulin sensitivity, glucose uptake (-18%, p < 0.001), GLUT4 translocation to the membrane and the maximum respiratory capacity of mitochondria. Canonical Wnt signalling was identified through RNA sequencing as a potential pathway for CILP2 regulation in C2C12, and Wnt3a was confirmed as an interacting protein of CILP2 in the CO-IP assay. The addition of recombinant Wnt3a protein reversed the inhibitory effects on myogenesis and glucose metabolism caused by CILP2 overexpression. Conversely, CILP2 knockdown promoted myogenesis and glucose metabolism. CILP2 knockdown improved muscle atrophy in mice, characterized by significant increases in time to exhaustion (+42%, p < 0.001), grip strength (+19%, p < 0.01), muscle mass (+15%, p < 0.001) and mean muscle cross-sectional area (+37%, p < 0.01). CILP2 knockdown enhanced glycogen synthesis (+83%, p < 0.001) and the regeneration of oxidative and glycolytic muscle fibres in SAMP8 ageing mice via the Wnt/β-catenin signalling pathway.

CONCLUSIONS

Our results indicate that CILP2 interacts with Wnt3a to suppress the Wnt/β-catenin signalling pathway and its downstream cascade, leading to impaired insulin sensitivity and glucose metabolism in skeletal muscle. Targeting CILP2 inhibition could offer potential therapeutic benefits for sarcopenia.

Danggui Shaoyao San Alleviates Early Cognitive Impairment in Alzheimer's Disease Mice Through IRS1/GSK3β/Wnt3a-β-Catenin Pathway

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disease characterized by Amyloid plaques and neurofibrillary tangles. We explored the potential mechanism by which Danggui Shaoyao San (DSS) modulates central glucose metabolism via the insulin receptor substrate 1 (IRS1)/glycogen synthase kinase-3β (GSK3β)/Wnt3a-β-catenin pathway, thereby exerting protective effects on cognitive functions.

METHODS

In vitro, HT22 cells were induced with streptozotocin (STZ) to investigate the impact of GSK3β on pathway transduction. The active components in the DSS stock solution were validated using mass spectrometry. Subsequently, an AD model in C57BL/6J mice was established through STZ injection into both ventricles. The success of the model was validated behaviorally and pathologically. The Morris Water Maze (MWM) test, immunohistochemistry, Western blotting, quantitative reverse transcription-PCR, and 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) were employed to evaluate the influence of DSS on memory and pathological changes in AD.

RESULTS

The DSS stock solution, rich in active components, ameliorated the memory deficits in AD mice in the MWM. In vitro, GSK3β exhibited regulatory control over Wnt and β-catenin, with GSK3β inhibition mitigating β-amyloid and tau redundancies at protein and gene levels, facilitating signal transduction. In vivo, DSS impacted key targets in the IRS1/GSK3β/Wnt3a-β-catenin pathway, mitigated senile plaques resulting from amyloid β (Aβ) deposition and neurofiber tangles induced by tau hyperphosphorylation, and alleviated the decline in central glucose metabolism observed in FDG-PET.

CONCLUSIONS

Our findings suggest that DSS potentially confers cognitive protection by alleviating central hypoglycemia through the IRS1/GSK3β/Wnt3a-β-catenin pathway. This may serve as a promising therapeutic avenue for AD.

TAZ deficiency exacerbates psoriatic pathogenesis by increasing the histamine-releasing factor

BACKGROUND

Transcriptional coactivator with PDZ-biding motif (TAZ) is widely expressed in most tissues and interacts with several transcription factors to regulate cell proliferation, differentiation, and death, thereby influencing organ development and size control. However, very little is known about the function of TAZ in the immune system and its association with inflammatory skin diseases, so we investigated the role of TAZ in the pathogenesis of psoriasis.

RESULTS

Interestingly, TAZ was expressed in mast cells associated, particularly in lysosomes, and co-localized with histamine-releasing factor (HRF). TAZ deficiency promoted mast cell maturation and increased HRF expression and secretion by mast cells. The upregulation of HRF in TAZ deficiency was not due to increased transcription but to protein stabilization, and TAZ restoration into TAZ-deficient cells reduced HRF protein. Interestingly, imiquimod (IMQ)-induced psoriasis, in which HRF serves as a major pro-inflammatory factor, was more severe in TAZ KO mice than in WT control. HRF expression and secretion were increased by IMQ treatment and were more pronounced in TAZ KO mice treated with IMQ.

CONCLUSIONS

Thus, as HRF expression was stabilized in TAZ KO mice, psoriatic pathogenesis progressed more rapidly, indicating that TAZ plays an important role in preventing psoriasis by regulating HRF protein stability.

TAZ deficiency impairs the autophagy-lysosomal pathway through NRF2 dysregulation and lysosomal dysfunction

Transcriptional coactivator with a PDZ-binding motif (TAZ) plays a key role in normal tissue homeostasis and tumorigenesis through interaction with several transcription factors. In particular, TAZ deficiency causes abnormal alveolarization and emphysema, and persistent TAZ overexpression contributes to lung cancer and pulmonary fibrosis, suggesting the possibility of a complex mechanism of TAZ function. Recent studies suggest that nuclear factor erythroid 2-related factor 2 (NRF2), an antioxidant defense system, induces TAZ expression during tumorigenesis and that TAZ also activates the NRF2-mediated antioxidant pathway. We thus thought to elucidate the cross-regulation of TAZ and NRF2 and the underlying molecular mechanisms and functions. TAZ directly interacted with NRF2 through the N-terminal domain and suppressed the transcriptional activity of NRF2 by preventing NRF2 from binding to DNA. In addition, the return of NRF2 to basal levels after signaling was inhibited in TAZ deficiency, resulting in sustained nuclear NRF2 levels and aberrantly increased expression of NRF2 targets. TAZ deficiency failed to modulate optimal NRF2 signaling and concomitantly impaired lysosomal acidification and lysosomal enzyme function, accumulating the abnormal autophagy vesicles and reactive oxygen species and causing protein oxidation and cellular damage in the lungs. TAZ restoration to TAZ deficiency normalized dysregulated NRF2 signaling and aberrant lysosomal function and triggered the normal autophagy-lysosomal pathway. Therefore, TAZ is indispensable for the optimal regulation of NRF2-mediated autophagy-lysosomal pathways and for preventing pulmonary damage caused by oxidative stress and oxidized proteins.

LINC MIR503HG Controls SC-β Cell Differentiation and Insulin Production by Targeting CDH1 and HES1

Stem cell-derived pancreatic progenitors (SC-PPs), as an unlimited source of SC-derived β (SC-β) cells, offers a robust tool for diabetes treatment in stem cell-based transplantation, disease modeling, and drug screening. Whereas, PDX1+/NKX6.1+ PPs enhances the subsequent endocrine lineage specification and gives rise to glucose-responsive SC-β cells in vivo and in vitro. To identify the regulators that promote induction efficiency and cellular function maturation, single-cell RNA-sequencing is performed to decipher the transcriptional landscape during PPs differentiation. The comprehensive evaluation of functionality demonstrated that manipulating LINC MIR503HG using CRISPR in PP cell fate decision can improve insulin synthesis and secretion in mature SC-β cells, without effects on liver lineage specification. Importantly, transplantation of MIR503HG-/- SC-β cells in recipients significantly restored blood glucose homeostasis, accompanied by serum C-peptide release and an increase in body weight. Mechanistically, by releasing CtBP1 occupying the CDH1 and HES1 promoters, the decrease in MIR503HG expression levels provided an excellent extracellular niche and appropriate Notch signaling activation for PPs following differentiation. Furthermore, this exhibited higher crucial transcription factors and mature epithelial markers in CDH1High expressed clusters. Altogether, these findings highlighted MIR503HG as an essential and exclusive PP cell fate specification regulator with promising therapeutic potential for patients with diabetes.

Microvesicles facilitate the differentiation of mesenchymal stem cells into pancreatic beta-like cells via miR-181a-5p/150-5p

Transplantation of pancreatic islet cells is a promising strategy for the long-term treatment of type 1 diabetes (T1D). The stem cell-derived beta cells showed great potential as substitute sources of transplanted pancreatic islet cells. However, the current efficiency of stem cell differentiation still cannot match the requirements for clinical transplantation. Here, we report that microvesicles (MVs) from insulin-producing INS-1 cells could induce mesenchymal stem cell (MSC) differentiation into pancreatic beta-like cells. The combination of MVs with small molecules, nicotinamide and insulin-transferrin-selenium (ITS), dramatically improved the efficiency of MSC differentiation. Notably, the function of MVs in MSC differentiation requires their entry into MSCs through giant pinocytosis. The MVs-treated or MVs combined with small molecules-treated MSCs show pancreatic beta-like cell morphology and response to glucose stimulation in insulin secretion. Using high throughput small RNA-sequencing, we found that MVs induced MSC differentiation into the beta-like cells through miR-181a-5p/150-5p. Together, our findings reveal the role of MVs or the MV-enriched miR-181a-5p/150-5p as a class of biocompatible reagents to differentiate MSCs into functional beta-like cells and demonstrate that the combined usage of MVs or miR-181a-5p/150-5p with small molecules can potentially be used in making pancreatic islet cells for future clinical purposes.

Hippo pathway in intestinal diseases: focusing on ferroptosis

The incidence of intestinal diseases, such as inflammatory bowel disease, gastric cancer, and colorectal cancer, has steadily increased over the past decades. The Hippo pathway is involved in cell proliferation, tissue and organ damage, energy metabolism, tumor formation, and other physiologic processes. Ferroptosis is a form of programmed cell death characterized by the accumulation of iron and lipid peroxides. The Hippo pathway and ferroptosis are associated with various intestinal diseases; however, the crosstalk between them is unclear. This review elaborates on the current research on the Hippo pathway and ferroptosis in the context of intestinal diseases. We summarized the connection between the Hippo pathway and ferroptosis to elucidate the underlying mechanism by which these pathways influence intestinal diseases. We speculate that a mutual regulatory mechanism exists between the Hippo pathway and ferroptosis and these two pathways interact in several ways to regulate intestinal diseases.

Crosstalk between the mTOR and Hippo pathways

Cell behavior changes in response to multiple stimuli, such as growth factors, nutrients, and cell density. The mechanistic target of the rapamycin (mTOR) pathway is activated by growth factors and nutrient stimuli to regulate cell growth and autophagy, whereas the Hippo pathway has negative effects on cell proliferation and tissue growth in response to cell density, DNA damage, and hormonal signals. These two signaling pathways must be precisely regulated and integrated for proper cell behavior. This integrative mechanism is not completely understood; nevertheless, recent studies have suggested that components of the mTOR and Hippo pathways interact with each other. Herein, as per contemporary knowledge, we review the molecular mechanisms of the interaction between the mTOR and Hippo pathways in mammals and Drosophila. Moreover, we discuss the advantage of this interaction in terms of tissue growth and nutrient consumption.

DNA methylation and gene expression analysis in adipose tissue to identify new loci associated with T2D development in obesity

BACKGROUND

Obesity is accompanied by excess adipose fat storage, which may lead to adipose dysfunction, insulin resistance, and type 2 diabetes (T2D). Currently, the tendency to develop T2D in obesity cannot be explained by genetic variation alone-epigenetic mechanisms, such as DNA methylation, might be involved. Here, we aimed to identify changes in DNA methylation and gene expression in visceral adipose tissue (VAT) that might underlie T2D susceptibility in patients with obesity.

METHODS

We investigated DNA methylation and gene expression in VAT biopsies from 19 women with obesity, without (OND = 9) or with T2D (OD = 10). Differences in genome-scale methylation (differentially methylated CpGs [DMCs], false discovery rate < 0.05; and differentially methylated regions [DMRs], p value < 0.05) and gene expression (DEGs, p value <0.05) between groups were assessed. We searched for overlap between altered methylation and expression and the impact of altered DNA methylation on gene expression, using bootstrap Pearson correlation. The relationship of altered DNA methylation to T2D-related traits was also tested.

RESULTS

We identified 11 120 DMCs and 96 DMRs distributed across all chromosomes, with the greatest density of epigenomic alterations at the MHC locus. These alterations were found in newly and previously T2D-related genes. Several of these findings were supported by validation and extended multi-ethnic analyses. Of 252 DEGs in the OD group, 68 genes contained DMCs (n = 88), of which 24 demonstrated a significant relationship between gene expression and methylation (p values <0.05). Of these, 16, including ATP11A, LPL and EHD2 also showed a significant correlation with fasting glucose and HbA1c levels.

CONCLUSIONS

Our results revealed novel candidate genes related to T2D pathogenesis in obesity. These genes show perturbations in DNA methylation and expression profiles in patients with obesity and diabetes. Methylation profiles were able to discriminate OND from OD individuals; DNA methylation is thus a potential biomarker.

Geranylgeranyl pyrophosphate depletion by statins compromises skeletal muscle insulin sensitivity

BACKGROUND

Statins are widely prescribed cholesterol-lowering drugs but have been shown to increase the risk of type 2 diabetes mellitus. However, the molecular mechanisms underlying the diabetogenic effect of statins are still not fully understood.

METHODS

The effects of geranylgeranyl transferase I and II (GGTase I and II) inhibition on insulin-stimulated glucose uptake and GLUT4 translocation, and the dependence of these effects on insulin signalling were investigated in skeletal muscle cells. The protective effects of geranylgeranyl pyrophosphate (GGPP) and its precursor geranylgeraniol (GGOH) on simvastatin-induced insulin resistance were evaluated in vitro and in vivo. The effect of GGTase II inhibition in skeletal muscle on insulin sensitivity in vivo was confirmed by adeno-associated virus serotype 9 (AAV9)-mediated knockdown of the specific subunit of GGTase II, RABGGTA. The regulatory mechanisms of GGTase I on insulin signalling and GGTase II on insulin-stimulated GLUT4 translocation were investigated by knockdown of RhoA, TAZ, IRS1, geranylgeranylation site mutation of RhoA, RAB8A, and RAB13.

RESULTS

Both inhibition of GGTase I and II mimicked simvastatin-induced insulin resistance in skeletal muscle cells. GGPP and GGOH were able to prevent simvastatin-induced skeletal muscle insulin resistance in vitro and in vivo. GGTase I inhibition suppressed the phosphorylation of AKT (Ser473) (-51.3%, P < 0.01), while GGTase II inhibition had no effect on it. AAV9-mediated knockdown of RABGGTA in skeletal muscle impaired glucose disposal without disrupting insulin signalling in vivo (-46.2% for gastrocnemius glucose uptake, P < 0.001; -52.5% for tibialis anterior glucose uptake, P < 0.001; -17.8% for soleus glucose uptake, P < 0.05; -31.4% for extensor digitorum longus glucose uptake, P < 0.01). Inhibition of RhoA, TAZ, IRS1, or geranylgeranylation deficiency of RhoA attenuated the beneficial effect of GGPP on insulin signalling in skeletal muscle cells. Geranylgeranylation deficiency of RAB8A inhibited insulin-stimulated GLUT4 translocation and concomitant glucose uptake in skeletal muscle cells (-42.8% for GLUT4 translocation, P < 0.01; -50.6% for glucose uptake, P < 0.001).

CONCLUSIONS

Geranylgeranyl pyrophosphate regulates glucose uptake via GGTase I-mediated insulin signalling-dependent way and GGTase II-mediated insulin signalling-independent way in skeletal muscle. Supplementation of GGPP/GGOH could be a potential therapeutic strategy for statin-induced insulin resistance.

CD133-Src-TAZ signaling stimulates ductal fibrosis following DDC diet-induced liver injury

Chronic liver injury follows inflammation and liver fibrosis; however, the molecular mechanism underlying fibrosis has not been fully elucidated. In this study, the role of ductal WW domain-containing transcription regulator 1 (WWTR1)/transcriptional coactivator with PDZ-binding motif (TAZ) was investigated after liver injury. Ductal TAZ-knockout (DKO) mice showed decreased liver fibrosis following a Diethyl 1,4-dihydro-2,4,6-trimethyl-3,5-pyridinedicarboxylate (DDC) diet compared to wild-type (WT) mice, as evidenced by decreased expression levels of fibrosis inducers, including connective tissue growth factor (Ctgf)/cellular communication network factor 2 (CCN2), cysteine-rich angiogenic inducer 61 (Cyr61/CCN1), and transforming growth factor beta 1 (Tgfb1), in DKO mice. Similarly, TAZ-knockout (KO) cholangiocyte organoids showed decreased expression of fibrosis inducers. Additionally, the culture supernatant of TAZ-KO cholangiocyte organoids decreased the fibrogenic gene expression in liver stellate cells. Further studies revealed that prominin 1 (PROM1/CD133) stimulated TAZ for fibrosis. After the administration of DDC diet, fibrosis was decreased in CD133-KO (CD133-KO) mice compared to that in WT mice. Similarly, CD133-KO cholangiocyte organoids showed decreased Ctgf, Cyr61, and Tgfb1 expression levels compared to WT cholangiocyte organoids. Mechanistically, CD133 stabilized TAZ via Src activation. Inhibition of Src decreased TAZ levels. Similarly, CD133-knockdown HCT116 cells showed decreased TAZ levels, but reintroduction of active Src recovered the TAZ levels. Taken together, our results suggest that TAZ facilitates liver fibrosis after a DDC diet via the CD133-Src-TAZ axis.

Discovering the Secret of Diseases by Incorporated Tear Exosomes Analysis via Rapid-Isolation System: iTEARS

Nanoscale small extracellular vesicles (sEVs, exosomes) in tears allow us to investigate the multisignatures of diseases. However, the translations of tear sEVs for biomarker discovery and clinical diagnostics are practically limited by low recovery, long processing time, and small sample volume. Here, we report an incorporated tear-exosomes analysis via rapid-isolation system (iTEARS) via nanotechnology to discover the secrets of ocular disorders and systemic diseases. We isolate exosomes rapidly with high yield and purity from a few teardrops (∼10 μL) within 5 min via nanoporous membrane-based resonators for the quantitative detection and biomarker discovery through proteomic and transcriptomic analysis. We have identified 904 proteins, among which 228 proteins are discovered, 426 proteins are detected from exosomes of dry eye disease, and demonstrate CALML5, KRT6A, and S100P for the classification of dry eye disease. We have also investigated 484 miRNAs in tear exosomes and show miR-145-5p, miR-214-3p, miR-218-5p, and miR-9-5p are dysregulated during diabetic retinopathy development. We believe iTEARS can be used for improving molecular diagnostics via tears to identify ocular disorders, systemic diseases, and numerous other neurodegenerative diseases and cancer.

Hepatocyte Rap1a contributes to obesity- and statin-associated hyperglycemia

Excessive hepatic glucose production contributes to the development of hyperglycemia and is a key feature of type 2 diabetes. Here, we report that activation of hepatocyte Rap1a suppresses gluconeogenic gene expression and glucose production, whereas Rap1a silencing stimulates them. Rap1a activation is suppressed in obese mouse liver, and restoring its activity improves glucose intolerance. As Rap1a′s membrane localization and activation depends on its geranylgeranylation, which is inhibited by statins, we show that statin-treated hepatocytes and the human liver have lower active-Rap1a levels. Similar to Rap1a inhibition, statins stimulate hepatic gluconeogenesis and increase fasting blood glucose in obese mice. Geranylgeraniol treatment, which acts as the precursor for geranylgeranyl isoprenoids, restores Rap1a activity and improves statin-mediated glucose intolerance. Mechanistically, Rap1a activation induces actin polymerization, which suppresses gluconeogenesis by Akt-mediated FoxO1 inhibition. Thus, Rap1a regulates hepatic glucose homeostasis, and blocking its activity, via lowering geranylgeranyl isoprenoids, contributes to statin-induced glucose intolerance.

Wang et al. show that activation of hepatic Rap1a suppresses gluconeogenic gene expression and improves glucose intolerance via Akt-mediated FoxO1 inhibition. Statins lower intracellular isoprenoid levels and inhibit Rap1a activation, which contributes to their hyperglycemic effect. These findings identify a role of hepatic Rap1a in obesity- and statin-associated glucose homeostasis.

CTGF-D4 Amplifies LRP6 Signaling to Promote Grafts of Adult Epicardial-derived Cells That Improve Cardiac Function After Myocardial Infarction

Transplantation of stem/progenitor cells holds promise for cardiac regeneration in patients with myocardial infarction (MI). Currently, however, low cell survival and engraftment after transplantation present a major barrier to many forms of cell therapy. One issue is that ligands, receptors, and signaling pathways that promote graft success remain poorly understood. Here, we prospectively isolate uncommitted epicardial cells from the adult heart surface by CD104 (β-4 integrin) and demonstrate that C-terminal peptide from connective tissue growth factor (CTGF-D4), when combined with insulin, effectively primes epicardial-derived cells (EPDC) for cardiac engraftment after MI. Similar to native epicardial derivatives that arise from epicardial EMT at the heart surface, the grafted cells migrated into injured myocardial tissue in a rat model of MI with reperfusion. By echocardiography, at 1 month after MI, we observed significant improvement in cardiac function for animals that received epicardial cells primed with CTGF-D4/insulin compared with those that received vehicle-primed (control) cells. In the presence of insulin, CTGF-D4 treatment significantly increased the phosphorylation of Wnt co-receptor LRP6 on EPDC. Competitive engraftment assays and neutralizing/blocking studies showed that LRP6 was required for EPDC engraftment after transplantation. Our results identify LRP6 as a key target for increasing EPDC engraftment after MI and suggest amplification of LRP6 signaling with CTGF-D4/insulin, or by other means, may provide an effective approach for achieving successful cellular grafts in regenerative medicine.

TAZ promotes PDX1-mediated insulinogenesis

Transcriptional co-activator with PDZ-binding motif (TAZ) is a key mediator of the Hippo signaling pathway and regulates structural and functional homeostasis in various tissues. TAZ activation is associated with the development of pancreatic cancer in humans, but it is unclear whether TAZ directly affects the structure and function of the pancreas. So we sought to identify the TAZ function in the normal pancreas. TAZ defect caused structural changes in the pancreas, particularly islet cell shrinkage and decreased insulin production and β-cell markers expression, leading to hyperglycemia. Interestingly, TAZ physically interacted with the pancreatic and duodenal homeobox 1 (PDX1), a key insulin transcription factor, through the N-terminal domain of TAZ and the homeodomain of PDX1. TAZ deficiency decreased the DNA-binding and transcriptional activity of PDX1, whereas TAZ overexpression promoted PDX1 activity and increased insulin production even in a low glucose environment. Indeed, high glucose increased insulin production by turning off the Hippo pathway and inducing TAZ activation in pancreatic β-cells. Ectopic TAZ overexpression along with PDX1 activation was sufficient to produce insulin in non-β-cells. TAZ deficiency impaired the mesenchymal stem cell differentiation into insulin-producing cells (IPCs), whereas TAZ recovery restored normal IPCs differentiation. Compared to WT control, body weight increased in TAZ-deficient mice with age and even more with a high-fat diet (HFD). TAZ deficiency significantly exacerbated HFD-induced glucose intolerance and insulin resistance. Therefore, TAZ deficiency impaired pancreatic insulin production, causing hyperglycemia and exacerbating HFD-induced insulin resistance, indicating that TAZ may have a beneficial effect in treating insulin deficiency in diabetes.

Mevalonate pathway orchestrates insulin signaling via RAB14 geranylgeranylation-mediated phosphorylation of AKT to regulate hepatic glucose metabolism

Statin use accompanies with increased risk of new onset of type 2 diabetes, however, the underlying mechanisms remain not be fully understood and effective prevention strategies are still lacking. Herein, we find that both pharmacological and genetic inhibition of GGTase II mimic the disruption of simvastatin on hepatic insulin signaling and glucose metabolism in vitro. AAV8-mediated knockdown of liver RABGGTA, the specific subunit of GGTase II, triggers systemic glucose metabolism disorders in vivo. By adopting a small-scale siRNA screening, we identify RAB14 as a regulator of hepatic insulin signaling and glucose metabolism. Geranylgeranylation deficiency of RAB14 inhibits the phosphorylation of AKT (Ser473) and disrupts hepatic insulin signaling and glucose metabolism possibly via impeding mTORC2 complex assembly. Finally, geranylgeranyl pyrophosphate (GGPP) supplementation is sufficient to prevent simvastatin-caused disruption of hepatic insulin signaling and glucose metabolism in vitro. Geranylgeraniol (GGOH), a precursor of GGPP, is able to ameliorate simvastatin-induced systemic glucose metabolism disorders in vivo. In conclusion, our data indicate that statins-targeted mevalonate pathway regulates hepatic insulin signaling and glucose metabolism via geranylgeranylation of RAB14. GGPP/GGOH supplementation might be an effective strategy for the prevention of the diabetic effects of statins.

Profiling the Skeletal Muscle Proteome in Patients on Atypical Antipsychotics and Mood Stabilizers

Atypical antipsychotics (AAP) are used in the treatment of severe mental illness. They are associated with several metabolic side effects including insulin resistance. The skeletal muscle is the primary tissue responsible for insulin-stimulated glucose uptake. Dysfunction of protein regulation within the skeletal muscle following treatment with AAPs may play a role in the associated metabolic side effects. The objective of this study was to measure protein abundance in the skeletal muscle of patients on long-term AAP or mood stabilizer treatment. Cross-sectional muscle biopsies were obtained from patients with bipolar disorder and global protein abundance was measured using stable isotope labeling by amino acid (SILAC) combined with high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Sixteen patients completed muscle biopsies and were included in the proteomic analyses. A total of 40 proteins were significantly different between the AAP group and the mood stabilizer group. In-silico pathway analysis identified significant enrichment in several pathways including glucose metabolism, cell cycle, apoptosis, and folate metabolism. Proteome abundance changes also differed based on protein biological processes and function. In summary, significant differences in proteomic profiles were identified in the skeletal muscle between patients on AAPs and mood stabilizers. Future work is needed to validate these findings in prospectively sampled populations.

TAZ links exercise to mitochondrial biogenesis via mitochondrial transcription factor A

Mitochondria are energy-generating organelles and mitochondrial biogenesis is stimulated to meet energy requirements in response to extracellular stimuli, including exercise. However, the mechanisms underlying mitochondrial biogenesis remain unknown. Here, we demonstrate that transcriptional coactivator with PDZ-binding motif (TAZ) stimulates mitochondrial biogenesis in skeletal muscle. In muscle-specific TAZ-knockout (mKO) mice, mitochondrial biogenesis, respiratory metabolism, and exercise ability were decreased compared to wild-type mice. Mechanistically, TAZ stimulates the translation of mitochondrial transcription factor A via Ras homolog enriched in brain (Rheb)/Rheb like 1 (Rhebl1)-mTOR axis. TAZ stimulates Rhebl1 expression via TEA domain family transcription factor. Rhebl1 introduction by adeno-associated virus or mTOR activation recovered mitochondrial biogenesis in mKO muscle. Physiologically, mKO mice did not stimulate exercise-induced mitochondrial biogenesis. Collectively, our results suggested that TAZ is a novel stimulator for mitochondrial biogenesis and exercise-induced muscle adaptation.

Lovastatin Inhibits RhoA to Suppress Canonical Wnt/β-Catenin Signaling and Alternative Wnt-YAP/TAZ Signaling in Colon Cancer

Statins are first-line drugs used to control patient lipid levels, but there is recent evidence that statin treatment can lower colorectal cancer (CRC) incidence by 50% and prolong CRC patient survival through mechanisms that are poorly understood. In this study, we found that the treatment of APCmin mice by the mevalonate pathway inhibitor lovastatin significantly reduced the number of colonic masses and improved hypersplenism and peripheral anemia. Furthermore, reverse transcription polymerase chain reaction (RT-PCR) analysis of colonic mass tissues showed a potent inhibitory effect in both Wnt/β-catenin signaling and YAP/TAZ signaling in the lovastatin treatment group. The results of our transcriptomic analyses in RKO indicated that lovastatin regulated several proliferation-related signaling pathways. Moreover, lovastatin suppressed important genes and proteins related to the canonical Wnt/β-catenin and alternative Wnt-YAP/TAZ signaling pathways in RKO and SW480 cells, and these effects were rescued by mevalonic acid (MVA), as confirmed through a series of Western blotting, RT-PCR, and reporter assays. Given that statins suppress oncogenic processes primarily through the inhibition of Rho GTPase in the mevalonate pathway, we speculate that lovastatin can inhibit certain Rho GTPases to suppress both canonical Wnt/β-catenin signaling and alternative Wnt-YAP/TAZ signaling. In RKO cells, lovastatin showed similar inhibitory properties as the RhoA inhibitor CCG1423, being able to inhibit β-catenin, TAZ, and p-LATS1 protein activity. Our results revealed that lovastatin inhibited RhoA activity, thereby suppressing the downstream canonical Wnt/β-catenin and alternative Wnt-YAP/TAZ pathways in colon cancer cells. These inhibitory properties suggest the promise of statins as a treatment for CRC. Altogether, the present findings support the potential clinical use of statins in non-cardiovascular contexts and highlight novel targets for anticancer treatments.

dTBP2 attenuates severe airway inflammation by blocking inflammatory cellular network mediated by dTCTP

Dimeric translationally controlled tumor protein (dTCTP), also known as histamine-releasing factor, amplifies allergic responses and its production has been shown to increase in inflammatory diseases such as allergic asthma. Despite the critical role of dTCTP in allergic inflammation, little is known about its production pathways, associated cellular networks, and underlying molecular mechanisms. In this study, we explored the dTCTP-mediated inflammatory networks and molecular mechanisms of dTCTP associated with lipopolysaccharides (LPS)-induced severe asthma. LPS stimulation increased dTCTP production by mast cells and dTCTP secretion during degranulation, and extracellular dTCTP subsequently increased the production of pro-inflammatory molecules, including IL-8, by airway epithelial cells without affecting mast cell activation. Furthermore, dimeric TCTP-binding peptide 2 (dTBP2), a dTCTP inhibitor peptide, selectively blocked the dTCTP-mediated signaling network from mast cells to epithelial cells and decreased IL-8 production through IkB induction and nuclear p65 export in airway epithelial cells. More importantly, dTBP2 efficiently attenuated LPS-induced severe airway inflammation in vivo, resulting in decreased immune cell infiltration and IL-17 production and attenuated dTCTP secretion. These results suggest that dTCTP produced by mast cells exacerbates airway inflammation through activation of airway epithelial cells in a paracrine signaling manner, and that dTBP2 is beneficial in the treatment of severe airway inflammation by blocking the dTCTP-mediated inflammatory cellular network.

TAZ inhibits glucocorticoid receptor and coordinates hepatic glucose homeostasis in normal physiological states

The elucidation of the mechanisms whereby the liver maintains glucose homeostasis is crucial for the understanding of physiological and pathological states. Here, we show a novel role of hepatic transcriptional co-activator with PDZ-binding motif (TAZ) in the inhibition of glucocorticoid receptor (GR). TAZ is abundantly expressed in pericentral hepatocytes and its expression is markedly reduced by fasting. TAZ interacts via its WW domain with the ligand-binding domain of GR to limit the binding of GR to the GR response element in gluconeogenic gene promoters. Therefore, liver-specific TAZ knockout mice show increases in glucose production and blood glucose concentration. Conversely, the overexpression of TAZ in mouse liver reduces the binding of GR to gluconeogenic gene promoters and glucose production. Thus, our findings demonstrate that hepatic TAZ inhibits GR transactivation of gluconeogenic genes and coordinates gluconeogenesis in response to physiological fasting and feeding.

Insulin action at a molecular level - 100 years of progress

The discovery of insulin 100 years ago and its application to the treatment of human disease in the years since have marked a major turning point in the history of medicine. The availability of purified insulin allowed for the establishment of its physiological role in the regulation of blood glucose and ketones, the determination of its amino acid sequence, and the solving of its structure. Over the last 50 years, the function of insulin has been applied into the discovery of the insulin receptor and its signaling cascade to reveal the role of impaired insulin signaling-or resistance-in the progression of type 2 diabetes. It has also become clear that insulin signaling can impact not only classical insulin-sensitive tissues, but all tissues of the body, and that in many of these tissues the insulin signaling cascade regulates unexpected physiological functions. Despite these remarkable advances, much remains to be learned about both insulin signaling and how to use this molecular knowledge to advance the treatment of type 2 diabetes and other insulin-resistant states.

MicroRNA-191 blocking the translocation of GLUT4 is involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway

Environmental exposure to arsenic can cause a variety of health problems. Epidemiological and experimental studies have established a diabetogenic role for arsenic, but the mechanisms responsible for arsenic-induced impairment of insulin action are unclear. MicroRNAs (miRNAs) are involved in various metabolic disorders, particularly in the development of insulin resistance. The present study investigated whether arsenite, an active form of arsenic, induces hepatic insulin resistance and the mechanisms underlying it. After male C57BL/6J mice were exposed to arsenite (0 or 20 ppm) in drinking water for 12 months, intraperitoneal glucose tolerance tests (IPGTTs) and insulin tolerance tests (ITTs) revealed an arsenite-induced glucose metabolism disorder. Hepatic glycogen levels were lower in arsenite-exposed mice. Further, for livers of mice exposed to arsenite, miR-191 levels were higher, and protein levels of insulin receptor substrate 1 (IRS1), p-IRS1, and phospho-protein kinase B (p-AKT) were lower. Further, glucose transporter 4 (GLUT4) had lower levels on the plasma membrane. For insulin-treated L-02 cells, arsenite decreased glucose consumption and glycogen levels, increased miR-191 levels, and inhibited the IRS1/AKT pathway and the translocation of GLUT4 from the cytoplasm to the plasma membrane. For insulin-treated L-02 cells, the decreases of glucose consumption, glycogen levels, GLUT4 on the plasma membrane, and p-AKT levels induced by arsenite were reversed by SC79 (agonist of AKT) and an miR-191 inhibitor; these effects caused by miR-191 inhibitor were restored by IRS1 siRNA. In insulin-treated L-02 cells, miR-191, via IRS1, was involved in the arsenite-induced decreases of glucose consumption and glycogen levels and in inhibition of the translocation of GLUT4. Thus, miR-191 blocking the translocation of GLUT4 was involved in arsenite-induced hepatic insulin resistance through inhibiting the IRS1/AKT pathway. Our study reveals a mechanism for arsenite-induced hepatic insulin resistance, which provides clues for discovering biomarkers for the development of type 2 diabetes and for prevention and treatment of arsenic poisoning.

KIBRA connects Hippo signaling and cancer

The Hippo signaling pathway is a tumor suppressor pathway that plays an important role in tissue homeostasis and organ size control. KIBRA is one of the many upstream regulators of the Hippo pathway. It functions as a tumor suppressor by positively regulating the core Hippo kinase cascade. However, there are accumulating shreds of evidence showing that KIBRA has an oncogenic function, which we speculate may arise from its functions away from the Hippo pathway. In this review, we have attempted to provide an overview of the Hippo signaling with a special emphasis on evidence showing the paradoxical role of KIBRA in cancer.

Integration of Hippo-YAP Signaling with Metabolism

The Hippo-Yes-associated protein (YAP) signaling network plays a central role as an integrator of signals that control cellular proliferation and differentiation. The past several years have provided an increasing appreciation and understanding of the diverse mechanisms through which metabolites and metabolic signals influence Hippo-YAP signaling, and how Hippo-YAP signaling, in turn, controls genes that direct cellular and organismal metabolism. These connections enable Hippo-YAP signaling to coordinate organ growth and homeostasis with nutrition and metabolism. In this review, we discuss the current understanding of some of the many interconnections between Hippo-YAP signaling and metabolism and how they are affected in disease conditions.

Activation of Wnt/β-catenin signaling restores insulin sensitivity in insulin resistant neurons through transcriptional regulation of IRS-1

Aberrant expression and phosphorylation of insulin receptor substrate 1 (IRS-1) contribute to brain insulin resistance. However, the underlying mechanism remains elusive. The insulin signaling and Wnt/β-catenin signaling are two critical pathways for normal cellular function, which interact in both peripheral tissues and the brain and may contribute to insulin resistance. In this study, we aimed to investigate the regulation of IRS-1 and its downstream insulin signaling by Wnt/β-catenin signaling in primary neurons. We found that the Wnt agonist Wnt3a enhances the insulin signaling in neurons at the basal state via up-regulation of IRS-1. Moreover, Wnt3a up-regulates IRS-1 expression and effectively ameliorates insulin resistance in rat primary neurons induced by chronic high insulin exposure. The insulin-mediated glucose uptake is also stimulated by Wnt3a at both basal and insulin resistant states. We observed that Wnt activation up-regulates IRS-1 gene transcription and the subsequent protein expression in SH-SY5Y cells and rat primary neurons via different means of Wnt/β-catenin signaling activation, including S33Y β-catenin over-expression, CHIR99021 and Wnt3a treatment. We further clarified the molecular mechanism of IRS-1 transcriptional activation by Wnt/β-catenin signaling. The Wnt transcription factor TCF4 binds to the -529 bp to -516 bp of the human IRS-1 promoter fragment and activates IRS-1 transcription. Overall, these data suggested that Wnt/β-catenin signaling positively regulates IRS-1 and insulin signaling and protects against insulin resistance in neurons.

Network-regulated organ allometry: The developmental regulation of morphological scaling

Morphological scaling relationships, or allometries, describe how traits grow coordinately and covary among individuals in a population. The developmental regulation of scaling is essential to generate correctly proportioned adults across a range of body sizes, while the mis-regulation of scaling may result in congenital birth defects. Research over several decades has identified the developmental mechanisms that regulate the size of individual traits. Nevertheless, we still have poor understanding of how these mechanisms work together to generate correlated size variation among traits in response to environmental and genetic variation. Conceptually, morphological scaling can be generated by size-regulatory factors that act directly on multiple growing traits (trait-autonomous scaling), or indirectly via hormones produced by central endocrine organs (systemically regulated scaling), and there are a number of well-established examples of such mechanisms. There is much less evidence, however, that genetic and environmental variation actually acts on these mechanisms to generate morphological scaling in natural populations. More recent studies indicate that growing organs can themselves regulate the growth of other organs in the body. This suggests that covariation in trait size can be generated by network-regulated scaling mechanisms that respond to changes in the growth of individual traits. Testing this hypothesis, and one of the main challenges of understanding morphological scaling, requires connecting mechanisms elucidated in the laboratory with patterns of scaling observed in the natural world. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Comparative Development and Evolution > Organ System Comparisons Between Species.

Downregulation of the Ca2+-activated K+ channel KCa3.1 in mouse preosteoblast cells treated with vitamin D receptor agonist

The maturity of osteoblasts by proliferation and differentiation in preosteoblasts is essential for maintaining bone homeostasis. The beneficial effects of vitamin D on bone homeostasis in mammals have been demonstrated experimentally and clinically. However, the direct actions of vitamin D on preosteoblasts remain to be fully elucidated. In this study, we found that the functional activity of intermediate-conductance Ca²⁺-activated K⁺ channels (K_Ca3.1) positively regulated cell proliferation in MC3T3-E1 cells derived from mouse preosteoblasts by enhancing intracellular Ca²⁺ signaling. We examined the effects of treatment with vitamin D receptor (VDR) agonist on the expression and activity of K_Ca3.1 by real-time PCR examination, Western blotting, Ca²⁺ imaging, and patch clamp analyses in mouse MC3T3-E1 cells. Following the downregulation of K_Ca3.1 transcriptional modulators such as Fra-1 and HDAC2, K_Ca3.1 activity was suppressed in MC3T3-E1 cells treated with VDR agonists. Furthermore, application of the K_Ca3.1 activator DCEBIO attenuated the VDR agonist-evoked suppression of cell proliferation rate. These findings suggest that a decrease in K_Ca3.1 activity is involved in the suppression of cell proliferation rate in VDR agonist-treated preosteoblasts. Therefore, K_Ca3.1 plays an important role in bone formation by promoting osteoblastic proliferation under physiological conditions.

Transcriptional coactivator with PDZ-binding motif suppresses the expression of steroidogenic enzymes by nuclear receptor 4 A1 in Leydig cells

Transcriptional coactivator with PDZ-binding motif (TAZ) plays crucial role in maintaining testicular structure and function via regulation of senescence of spermatogenic cells. However, it remains unclear whether TAZ is involved in testosterone biosynthesis in testicular Leydig cells. We found that TAZ deficiency caused aberrant Leydig cell expansion and increased lipid droplet formation, which was significantly associated with increased lipogenic enzyme expression. Additionally, the expression of key steroidogenic enzymes, including steroidogenic acute regulatory protein, cytochrome P450 (CYP) 11A1, CYP17A1, and 3β-hydroxysteroid dehydrogenase, was greatly increased in TAZ-deficient testes and primary Leydig cells. Interestingly, the transcriptional activity of nuclear receptor 4 A1 (NR4A1) was dramatically suppressed by TAZ; however, the protein expression and the subcellular localization of NR4A1 were not affected by TAZ. TAZ directly associated with the N-terminal region of NR4A1 and substantially suppressed its DNA-binding and transcriptional activities. Stable expression of TAZ in the mouse Leydig TM3 cell line decreased the expression of key steroidogenic enzymes, whereas knockdown of endogenous TAZ in TM3 cells increased transcripts of steroidogenic genes induced by NR4A1. Consistently, testosterone production was enhanced within TAZ-deficient Leydig cells. However, TAZ deficiency resulted in decreased testosterone secretion caused by dysfunctional mitochondria and lysosomes. Therefore, TAZ plays essential role in NR4A1-induced steroidogenic enzyme expression and testosterone production in Leydig cells.

Transcriptional coactivator with PDZ-binding motif stimulates epidermal regeneration via induction of amphiregulin expression after ultraviolet damage

Ultraviolet (UV) irradiation induces the proliferation and differentiation of keratinocytes in the basal layer of the epidermis, which increases epidermal thickness in skin regeneration. However, the mechanism underlying this phenomenon is not yet known in detail. In this study, we aimed to demonstrate that the transcriptional coactivator with PDZ-binding motif (TAZ) stimulates epidermal regeneration by increasing keratinocyte proliferation. During epidermal regeneration, TAZ is localized in the nucleus of keratinocytes of the basal layer and stimulates epidermal growth factor receptor (EGFR) signaling. TAZ depletion in keratinocytes decreased EGFR signaling activation, which delays epidermal regeneration. Interestingly, TAZ stimulated the transcription of amphiregulin (AREG), a ligand of EGFR, through TEAD-mediated transcriptional activation. Together, these results show that TAZ stimulates EGFR signaling through AREG induction, suggesting that it plays an important role in epidermal regeneration.

Dysfunctional Mechanotransduction through the YAP/TAZ/Hippo Pathway as a Feature of Chronic Disease

In order to ascertain their external environment, cells and tissues have the capability to sense and process a variety of stresses, including stretching and compression forces. These mechanical forces, as experienced by cells and tissues, are then converted into biochemical signals within the cell, leading to a number of cellular mechanisms being activated, including proliferation, differentiation and migration. If the conversion of mechanical cues into biochemical signals is perturbed in any way, then this can be potentially implicated in chronic disease development and processes such as neurological disorders, cancer and obesity. This review will focus on how the interplay between mechanotransduction, cellular structure, metabolism and signalling cascades led by the Hippo-YAP/TAZ axis can lead to a number of chronic diseases and suggest how we can target various pathways in order to design therapeutic targets for these debilitating diseases and conditions.

The role of Wnt signaling pathway in tumor metabolic reprogramming

The occurrence and development of tumors is a complex process involving long-term multi-factor participation. In this process, tumor cells from a set of abnormal metabolic patterns that are different from normal cells. This abnormal metabolic change is called metabolic reprogramming of tumors. Wnt signaling pathway is one of the critical signaling pathways regulating cell proliferation and differentiation. In recent years, it has been found that Wnt signaling participates in the occurrence and development of malignant tumors by affecting metabolic reprogramming. This paper reviews the role of Wnt signaling in tumor metabolic reprogramming to provide crucial theoretical guidance for targeted therapy and drug response of tumors.

Exploring the Role of Insulin Signaling in Relative Growth: A Case Study on Wing-Body Scaling in Lepidoptera

Adult forms emerge from the relative growth of the body and its parts. Each appendage and organ has a unique pattern of growth that influences the size and shape it attains. This produces adult size relationships referred to as static allometries, which have received a great amount of attention in evolutionary and developmental biology. However, many questions remain unanswered, for example: What sorts of developmental processes coordinate growth? And how do these processes change given variation in body size? It has become increasingly clear that nutrition is one of the strongest influences on size relationships. In insects, nutrition acts via insulin/TOR signaling to facilitate inter- and intra-specific variation in body size and appendage size. Yet, the mechanism by which insulin signaling influences the scaling of growth remains unclear. Here we will discuss the potential roles of insulin signaling in wing-body scaling in Lepidoptera. We analyzed the growth of wings in animals reared on different diet qualities that induce a range of body sizes not normally present in our laboratory populations. By growing wings in tissue culture, we survey how perturbation and stimulation of insulin/TOR signaling influences wing growth. To conclude, we will discuss the implications of our findings for the development and evolution of organismal form.