Regulation of hepatic insulin signaling and glucose homeostasis by sphingosine kinase 2.

Sphingolipid dysregulation is often associated with insulin resistance, while the enzymes controlling sphingolipid metabolism are emerging as therapeutic targets for improving insulin sensitivity. We report herein that sphingosine kinase 2 (SphK2), a key enzyme in sphingolipid catabolism, plays a critical role in the regulation of hepatic insulin signaling and glucose homeostasis both in vitro and in vivo. Hepatocyte-specific Sphk2 knockout mice exhibit pronounced insulin resistance and glucose intolerance. Likewise, SphK2-deficient hepatocytes are resistant to insulin-induced activation of the phosphoinositide 3-kinase (PI3K)-Akt-FoxO1 pathway and elevated hepatic glucose production. Mechanistically, SphK2 deficiency leads to the accumulation of sphingosine that, in turn, suppresses hepatic insulin signaling by inhibiting PI3K activation in hepatocytes. Either reexpressing functional SphK2 or pharmacologically inhibiting sphingosine production restores insulin sensitivity in SphK2-deficient hepatocytes. In conclusion, the current study provides both experimental findings and mechanistic data showing that SphK2 and sphingosine in the liver are critical regulators of insulin sensitivity and glucose homeostasis.

Parthenolide induces gallbladder cancer cell apoptosis via MAPK signalling.

Objective: Parthenolide (PTL) has a wide range of clinical applications owing to its anti-inflammatory and antitumor effects. To date, the antitumor effect of PTL on gallbladder cancer (GBC) remains largely unknown. Therefore, we aimed to investigate the biological effects of PTL on GBC. Methods: The cellular viability and proliferation of GBC-SD and NOZ cell lines after treatment with different concentrations of PTL were analyzed using the Cell Counting Kit-8 (CCK8)assay and colony formation assay. Apoptosis analysis was performed using flow cytometry. Hoechst staining was performed. RNA sequencing (RNA-seq) was performed to identify PTL-related genes and signalling pathways. Furthermore, we confirmed the involvement of these signalling pathways by qRT-PCR and western blotting. For the in-vivo experiments, a xenograft model was used to evaluate the effects of PTL on the proliferation of NOZ cells. Results: PTL significantly inhibited GBC cell growth in vitro and induced apoptosis in the GBC-SD and NOZ cell lines in a dose-dependent manner. RNA sequencing data showed that the immune response and mitogen-activated protein kinase (MAPK) signalling pathways are closely associated with PTL-induced gallbladder cancer cell apoptosis. PTL upregulated BAX, cleaved PARP-1, cleaved caspase-3, cleaved caspase-9, P53 and decreased the expression of BCL-2, phosphorylated ERK, and phosphorylated MEK in vitro. Tumour volume and weight were also suppressed by PTL in vivo. Moreover, the effects of PTL on GBC cells might be mediated by the MAPK pathway. Conclusion: PTL significantly inhibits gallbladder cancer cell proliferation and induces apoptosis through the MAPK pathway, which is a potential molecular reagent for treating GBC. However, further exploration is needed to verify the antitumor effects of PTL and its intracellular signalling mechanism.

Sphingosine kinase 2 regulates insulin receptor trafficking in hepatocytes.

Disturbed insulin receptor (InsR) trafficking is associated with impaired insulin signaling and the development of diabetes. Sphingosine kinase (SphK), including SphK1 and SphK2, is a key enzyme of sphingolipid metabolism, which has been implicated in the regulation of membrane trafficking. More recently, we have reported that SphK2 is a key regulator of hepatic insulin signaling and glucose homeostasis. However, the role of SphK in InsR trafficking is still undefined. Huh7 cells were treated with specific SphK1 and SphK2 inhibitors or SphK1- and SphK2-specific small interfering RNA (siRNA) in the presence or absence of insulin. Flow cytometry and immunofluorescence assays were carried out to investigate the role of SphK in InsR trafficking. InsR endocytosis, recycling, and insulin signaling were analyzed. Inhibition of SphK2, but not SphK1, by either specific pharmaceutic inhibitors or siRNA, significantly suppressed InsR endocytosis and recycling following insulin stimulation. Consequently, the insulin-stimulated Akt activation was significantly attenuated by SphK2 inhibition in hepatocytes. Moreover, the effect of SphK2 on InsR trafficking was mediated via the clathrin-dependent mechanism. Thus, our results show that SphK2 is able to regulate InsR trafficking. These findings suggest that SphK2 may impinge on hepatic insulin signaling by regulating InsR trafficking, providing further mechanistic evidence that SphK2 could serve as a potential intervention target against insulin resistance and T2D (type 2 diabetes).

Thyroid Peroxidase Antibody is Associated with Plasma Homocysteine Levels in Patients with Graves' Disease.

PURPOSE: Homocysteine is associated with cardiovascular, inflammation and autoimmune diseases. Previous studies have shown that thyroid peroxidase antibody is associated with homocysteine levels in hypothyroidism. The relationship between thyroid antibodies and homocysteine in hyperthyroidism remains unclear. In this study, we aimed to investigate the association of thyroid antibodies with homocysteine in patients with Graves' disease. METHODS: This was a cross-sectional study including 478 Graves' disease patients who were consecutively admitted and underwent radioiodine therapy. Homocysteine, thyroid hormones, thyroid antibodies, glucose and lipids were measured. RESULTS: Patients with homocysteine levels above the median were older and had unfavorable metabolic parameters compared to patients with homocysteine levels below the median. Thyroglobulin antibody or thyroid peroxidase antibody was associated with homocysteine levels (ß=0.56, 95%CI 0.03-1.08, p=0.04; ß=0.75, 95%CI 0.23-1.27, p=0.005). The relationship between thyroid peroxidase antibody and homocysteine remained significant when additionally adjusting for free triiodothyronine (ß=0.76, 95%CI 0.24-1.28, p=0.004). The presence of a homocysteine level above the median increased significantly with increasing thyroid peroxidase antibody quartiles in the logistic regression (OR=1.74, 95%CI 1.27-2.39, P for trend=0.001). Homocysteine levels increased significantly with increasing thyroid peroxidase antibody quartiles (p=0.005). Thyroid peroxidase antibody had no significant effect on other traditional cardiovascular risk factors. CONCLUSIONS: Thyroid peroxidase antibody is independently and positively associated with homocysteine levels in patients with Graves' disease. Thyroid peroxidase antibody may be associated with the cardiovascular risk of patients with Graves' disease through its effect on homocysteine.

Role of Sphingosine Kinase in Type 2 Diabetes Mellitus.

Sphingolipids are a class of essential lipids, functioning as both cell membrane constituents and signaling messengers. In the sphingolipid metabolic network, ceramides serve as the central hub that is hydrolyzed to sphingosine, followed by phosphorylation to sphingosine 1-phosphate (S1P) by sphingosine kinase (SphK). SphK is regarded as a "switch" of the sphingolipid rheostat, as it catalyzes the conversion of ceramide/sphingosine to S1P, which often exhibit opposing biological roles in the cell. Besides, SphK is an important signaling enzyme that has been implicated in the regulation of a wide variety of biological functions. In recent years, an increasing body of evidence has suggested a critical role of SphK in type 2 diabetes mellitus (T2D), although a certain level of controversy remains. Herein, we review recent findings related to SphK in the field of T2D research with a focus on peripheral insulin resistance and pancreatic ß-cell failure. It is expected that a comprehensive understanding of the role of SphK and the associated sphingolipids in T2D will help to identify druggable targets for future anti-diabetes therapy.

Upregulation of PCP4 in human aldosterone-producing adenomas fosters human adrenocortical tumor cell growth via AKT and AMPK pathway.

Primary aldosteronism (PA) is characterized by aldosterone hypersecretion and adrenal hyperplasia and ranks as one of the most common causes of secondary hypertension. However, the molecular mechanism involved in adrenal hyperplasia and tumorigenesis is largely unknown. Dysregulation of Purkinji cell protein 4 (PCP4) is involved in the development and progression of neoplasia and aldosterone secretion, but little is known about the effect of PCP4 on human adrenocortical tumorigenesis. We investigated the expression pattern of PCP4 in different adrenal tissues and studied whether PCP4 is involved in cell growth in human adrenal cell lines. The mRNA levels of PCP4 were measured by real-time PCR in tissues from aldosterone-producing adenomas (APAs), idiopathic hyperaldosteronism (IHA) tissues, and normal adrenal (NA) tissues. In vitro siRNA knockdown of PCP4 in NCI-H295R and SW13 cell lines was used to determine the effect of PCP4 on cellular growth. Our results show that the mRNA level of PCP4 is upregulated in APAs and IHA compared with that in NA. The PCP4 mRNA expression level was positively correlated with tumor size in APAs. Knockdown of PCP4 decreased cell proliferation. Flow cytometry analysis showed that PCP4 knockdown fosters apoptosis. Finally, PCP4 knockdown inhibited phosphorylation of AKT308 and AMPKThr172. Our data suggest that PCP4 may represent a key player in the development and pathophysiology of PA via targeting the AKT and AMPK signaling pathways and thus may be a promising therapeutic target for PA.

Endocrinal description of two Chinese Kennedy's disease pedigrees.

Kennedy's disease (KD), also known as X-linked spinal and bulbar muscular atrophy (SBMA), is caused by the expansion of cytosine-adenine-guanine (CAG) repeats in the first exon of the androgen receptor (AR) gene. KD is a late-onset neural-endocrinal disease that is characterized by the degeneration of motor neurons in the brainstem and spinal cord. In addition, partial androgen insensitivity is an important manifestation of KD. Here, we report two Chinese KD pedigrees that reveal the clinical and genetic manifestations and fully elaborate the endocrinal characteristics of KD patients. The proband in pedigree 1 was referred to an endocrinologist for gynaecomastia and sexual dysfunction. A gene analysis of this patient revealed that there were 53 CAG repeats in the AR gene. A family survey identified an additional two KD patients in pedigree 1. The proband in pedigree 2 was diagnosed by a neurologist and did not have gynaecomastia or sexual dysfunction. A family survey identified an additional subclinical patient, and both patients exhibited partial androgen insensitivity at a hormonal level. We therefore suggest that a family survey and hormone tests should be routinely performed in KD patients and that physicians should increase their understanding of the different symptoms of KD to achieve correct diagnoses in affected patients.