GLP-2 ameliorates D-galactose induced muscle aging by IGF-1/Pi3k/Akt/FoxO3a signaling pathway in C2C12 cells and mice.

BACKGROUND: The study aimed to investigate the effect of Glucagon-like peptide-2 (GLP-2) on muscle aging in vivo and in vitro. METHODS: Six-week-old C57BL/6J mice were administered with D-galactose (200 mg/kg/day, intraperitoneally) for 8weeks, followed by daily subcutaneous injections of GLP-2 (300 or 600 µg/kg/day) for 4weeks. Skeletal muscle function and mass were evaluated using relative grip strength and muscle weight. The sizes and types of muscle fibers and apoptosis were assessed through histological analysis, immunofluorescence staining, and TUNEL staining, respectively. C2C12 myotubes were treated with D-galactose (40 mg/mL) and GLP-2. Protein expression of differentiation-related myogenic differentiation factor D (MyoD), myogenin (MyoG), and myosin heavy chain (Myhc), degradation-related Muscle RING finger 1 (MuRF-1), and muscle atrophy F-box (MAFbx)/Atrogin-1, and apoptosis-related B-cell leukemia/lymphoma 2 (Bcl-2) and Bax, were assessed using western blots. The Pi3k inhibitor LY294002 was applied to investigate whether GLP-2 regulated myogenesis and myotube aging via IGF-1/Pi3k/Akt/FoxO3a signaling pathway. RESULTS: The results demonstrated that GLP-2 significantly reversed the decline in muscles weight, relative grip strength, diameter, and cross-sectional area of muscle fibers induced by D-galactose in mice. Apart from suppressing the expressions of MuRF-1 and Atrogin-1 in the muscles and C2C12 myotubes, GLP-2 significantly increased the expressions of MyoD, MyoG, and Myhc compared to the D-galactose. GLP-2 significantly suppressed cell apoptosis. Western blot analysis indicated that the regulation of GLP-2 may be attributed to the activation of theIGF-1/Pi3k/Akt/FoxO3a phosphorylation pathway. CONCLUSIONS: This study suggested that GLP-2 ameliorated D-galactose induced muscle aging by IGF-1/Pi3k/Akt/FoxO3a pathway.

Glucagon like peptide 2 has a positive impact on osteoporosis in ovariectomized rats.

AIMS: In this study, we evaluate the effects of glucagon-like peptide 2 (GLP-2) on bone microarchitecture, bone turnover markers (BTMs) and inflammation markers in ovariectomized (OVX) rats. MATERIAL AND METHODS: In total, 31 Sprague-Dawley rats were divided into the following three groups: sham (control sham-operated with vehicle, n = 7), OV (OVX with vehicle, n = 12), and GLP-2 (OVX with GLP-2, n = 12). Intervention began at the 12th week after surgery and lasted for 4 weeks. The dosage of the GLP-2 was 160 µg/kg/d through subcutaneous injections, and normal saline was used as the vehicle agent. After 4 weeks of treatment, serum BTM and inflammation marker levels were measured by ELISA, and femora samples were analyzed by qRT-PCR, micro-CT, histology and histomorphometry. KEY FINDINGS: After 4 weeks of treatment, serum TRAcP-5b and RANKL levels as well as the CTX-1/P1NP ratio in the GLP-2 group decreased, and ALP activity, P1NP level, and OPG/RANKL ratio increased significantly; qRT-PCR analysis showed that mRNA levels of RANKL decreased, and Runx2, ALP, and Col-1 levels as well as the OPG/RANKL ratio increased significantly in the GLP-2 group compared with the OV group. In bone histology analysis, GLP-2 significantly decreased the AV/MV, Oc.N and Oc.S but increased the Ob.N, BFR and MAR. Analysis with µ-CT showed that the BMD, BV/TV, Tb.N and Conn.D increased significantly in the GLP-2 group compared with the OV group. The levels of serum inflammation markers TNF-α, IL-1ß and IL-6 decreased, and TGF-ß levels increased in the GLP-2 group compared with the OV group. SIGNIFICANCE: GLP-2 may have a positive impact on osteoporosis by promoting bone formation, inhibiting bone resorption and decreasing circulatory inflammation in ovariectomized rats.

Transgelin-2 is a novel target of KRAS-ERK signaling involved in the development of pancreatic cancer.

BACKGROUND: The KRAS mutation is the driving force of pancreatic ductal adenocarcinoma (PDAC). Downstream effectors of KRAS signal pathways are crucial to the development of PDAC. The purpose of this study was to investigate the relationship between KRAS mutation and transgelin-2. Transgelin-2 is highly expressed in PDAC tissues compared with adjacent normal tissues. The underlying mechanism for upregulating transgelin-2 is largely unknown. METHODS: Expression of transgelin-2 was analyzed by microarray data and qRT-PCR. The effect of KRAS signaling on transgelin-2 expression was examined in PDAC cells in the presence or absence of the ERK inhibitor. The interaction of transgelin-2 with ERK was confirmed by immunoprecipitation. ERK-mediated Phosphorylation of transglein-2 was detected by in vivo and in vitro kinase assays. The gain-of-function and loss-of-function approaches were used to examine the role of phosphorylation of transgelin-2 on cell proliferation. Phosphorylation of transgelin-2 was detected by immunohistochemistry in PDAC tissues. RESULTS: Here we found transgelin-2 expression was induced by KRAS mutation. In the case of KRAS mutation, ERK2 interacted with 29-31 amino acids of transgelin-2 and subsequently phosphorylated the S145 residue of transgelin-2. S145 phosphorylation of transgelin-2 played important roles in cell proliferation and tumorigenesis of PDAC. In addition, S145 phosphorylation of transgelin-2 was associated with a poor prognosis in patients with PDAC. CONCLUSIONS: This study indicated that KRAS-ERK-mediated transeglin-2 phosphorylation played an important role in the development of PDAC. Inhibition of transgelin-2 phosphorylation may be a potential therapeutic strategy for targeting PDAC with KRAS mutation.

Role of transgelin-2 in diabetes-associated pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with poor prognosis. Diabetes is a significant risk factor for PDAC and >50% of PDAC patients have concomitant diabetes. How diabetes influences the initiation and progression of PDAC remains elusive. Here, we show that transgelin-2 is dominantly expressed in PDAC tissues compared with adjacent normal tissues. The high level of transgelin-2 indicates poor survival of patients with PDAC. Remarkably, transgelin-2 expression is correlated with diabetic status. Hyperinsulinemia is frequently observed in type 2 diabetes. Our results indicate that upregulation of transgelin-2 is induced by insulin via sterol regulatory element-binding protein (SREBP)-1-mediated transcription in PDAC cells. Transgelin-2 is a novel target of SREBP-1. Our data support a novel mechanism in diabetes-associated PDAC by which transgelin-2 mediates proliferation of PDAC cells upon insulin stimulation. The insulin/SREBP-1/transgelin-2 network should be further explored as a diagnostic marker or a novel therapeutic target for diabetes-associated PDAC.

Phosphorylation of Ser6 in hnRNPA1 by S6K2 regulates glucose metabolism and cell growth in colorectal cancer.

Abnormal glucose metabolism is critical in colorectal cancer (CRC) development. Expression of the pyruvate kinase (PK) M2 isoform, rather than the PKM1 isoform, serves important functions in reprogramming the glucose metabolism of cancer cells. Preferential expression of PKM2 is primarily driven by alternative splicing, which is coordinated by a group of splicing factors including heterogeneous nuclear ribonucleoprotein (hnRNP)A1, hnRNPA2 and RNA binding motif containing. However, the underlying molecular mechanisms associated with cancer cell expression of PKM2, instead of PKM1, remain unknown. The mRNA levels of PKM isoform and glucose metabolism were analyzed in CRC cells. The results of the present study indicated that S6 kinase 2 (S6K2) promotes glycolysis and growth of CRC cells by regulating alternative splicing of the PKM gene. In addition, chromatin immunoprecipitation assay indicated that S6K2 phosphorylation of Ser6 of hnRNPA1 facilitated hnRNPA1 binding to the splicing site of the PKM gene. As a result, cancer cells preferentially expressed the PKM2 isoform, instead of the PKM1 isoform. Furthermore, Cox regression analysis demonstrated that the phosphorylation of Ser6 of hnRNPA1 was a predictor of poor prognosis for patients with CRC. Therefore, the results of the present study revealed that the phosphorylation of Ser6 in hnRNPA1 by S6K2 was a novel mechanism underlying glucose metabolic reprogramming, and suggested that S6K2 is a potential therapeutic target for CRC treatment.

SREBP1 regulates tumorigenesis and prognosis of pancreatic cancer through targeting lipid metabolism.

Sterol regulatory element-binding protein 1 (SREBP1) is a known transcription factor of lipogenic genes, which plays important roles in regulating de novo lipogenesis. Accumulating evidences indicate SREBP1 is involved in tumorigenesis, yet its role in pancreatic cancer remains unclear. Here, we explored the expression characteristic and function of SREBP1 in pancreatic cancer. Analysis of 60 patients with pancreatic ducat cancer showed that SREBP1 level was significantly higher in pancreatic cancer than that in adjacent normal tissues. High expression of SREBP1 predicted poor prognosis in patients with pancreatic cancer. Multivariate analysis revealed that SREBP1 was an independent factor affecting overall survival. SREBP1 silencing resulted in proliferation inhibition and induction of apoptosis in pancreatic cancer cells. Mechanistically, lipogenic genes (acetyl-CoA carboxylase (ACC), fatty acid synthase (FASN), and stearoyl-CoA desaturase-1 (SCD1)) and de novo lipogenesis were promoted by SREBP1. Inhibition of lipogenic genes through specific inhibitors ablated SREBP1-mediated growth regulation. Furthermore, depletion of SREBP1 could suppress lipid metabolism and tumor growth in vivo. Our results indicate that SREBP1 had important role in tumor progression and appears to be a novel prognostic marker for pancreatic cancer.

The pro-apoptotic role of the regulatory feedback loop between miR-124 and PKM1/HNF4α in colorectal cancer cells.

Accumulating evidence indicates that miRNA regulatory circuits play important roles in tumorigenesis. We previously reported that miR-124 is correlated with prognosis of colorectal cancer due to PKM-dependent regulation of glycolysis. However, the mechanism by which miR-124 regulates apoptosis in colorectal cancer remains largely elusive. Here, we show that miR-124 induced significant apoptosis in a panel of colorectal cancer cell lines. The mitochondrial apoptosis pathway was activated by miR-124. Furthermore, the pro-apoptotic role of miR-124 was dependent on the status of PKM1/2 level. PKM1 was required for miR-124-induced apoptosis. Via direct protein-protein interaction, PKM1 promoted HNF4α binding to the promoter region of miR-124 and transcribing miR-124. Moreover, HNF4α or PKM1 had a more dramatic effect on colorectal cancer cell apoptosis in the presence of miR-124. However, inhibition of miR-124 blocked cell apoptosis induced by HNF4α or PKM1. These data indicate that miR-124 not only alters the expression of genes involved in glucose metabolism but also stimulates cancer cell apoptosis. In addition, the positive feedback loop between miR-124 and PKM1/HNF4α plays an important role in colorectal cancer cell apoptosis; it suggests that disrupting this regulatory circuit might be a potential therapeutic tool for colorectal cancer treatment.