Tight junction channel regulation by interclaudin interference.

Tight junctions form selectively permeable seals across the paracellular space. Both barrier function and selective permeability have been attributed to members of the claudin protein family, which can be categorized as pore-forming or barrier-forming. Here, we show that claudin-4, a prototypic barrier-forming claudin, reduces paracellular permeability by a previously unrecognized mechanism. Claudin-4 knockout or overexpression has minimal effects on tight junction permeability in the absence of pore-forming claudins. However, claudin-4 selectively inhibits flux across cation channels formed by claudins 2 or 15. Claudin-4-induced loss of claudin channel function is accompanied by reduced anchoring and subsequent endocytosis of pore-forming claudins. Analyses in nonepithelial cells show that claudin-4, which is incapable of independent polymerization, disrupts polymeric strands and higher order meshworks formed by claudins 2, 7, 15, and 19. This process of interclaudin interference, in which one claudin disrupts higher order structures and channels formed by a different claudin, represents a previously unrecognized mechanism of barrier regulation.

Central environmental inspection and corporate environmental investment: evidence from Chinese listed companies.

As a new type of environmental policy, the central environmental inspection (CEI) policy is an important innovative strategy in economic transition. Using the panel data of Chinese listed companies from 2011 to 2018, we apply the extended STIRPAT model to examine the direct impact of CEI policy on corporate environmental investment and its heterogeneity effects. The main findings are as follows: (1) The CEI policy has a positive influence on the environmental investment of all listed companies. (2) The promotion effect of CEI policy is quite different among five-round campaigns; while companies in later rounds fails to learn some experiences and lessons from the earlier rounds. (3) Due to the differences in property rights, industries, and environmental situations, the positive effect of CEI policy will be more significant in non-SOEs, companies in non-heavy-pollution industries, and companies in provinces with poor environment performance. This study supplements the research of environmental regulations, potentially contributing to the next stage of green and sustainable development in China.

Plasma lipidomic signatures of spontaneous obese rhesus monkeys.

BACKGROUND: Obesity plays crucial roles in the pathogenesis of metabolic diseases such as hyperlipidemia, nonalcoholic fatty liver disease (NAFLD), and type 2 diabetes (T2D). The underlying mechanisms linking obesity to metabolic diseases are still less understandable. METHODS: Previously, we screened a group of spontaneously obese rhesus monkeys. Here, we performed a plasma lipidomic analysis of normal and obese monkeys using gas chromatography/mass spectroscopy (GC/MS) and ultra-high performance liquid chromatography/mass spectroscopy (UPLC/MS). RESULTS: In total, 143 lipid species were identified, quantified, and classified into free fatty acids (FFA), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylglycerol (PG), lysophosphatidylcholine (LPC), lysophosphatidic acid (LPA), and sphingomyelin (SM). Data analysis showed that the obese monkeys had increased levels of fatty acids palmitoleic acid (C16:1) and arachidonic acid (C20:4), FFA especially palmitic acid (C16:0), as well as certain PC species and SM species. Surprisingly, the plasma level of LPA-C16:0 was approximately four-fold greater in the obese monkeys. Conversely, the levels of most PE species were obviously reduced in the obese monkeys. CONCLUSION: Collectively, our work suggests that lipids such as FFA C16:0 and 16:0-LPA may be potential candidates for the diagnosis and study of obesity-related diseases.

Zinc ions regulate opening of tight junction favouring efflux of macromolecules via the GSK3ß/snail-mediated pathway.

Zinc is an essential trace element presenting in particularly high concentration in the brain. In some regions, e.g. lateral amygdala, subiculum and hippocampus, rapidly-exchangeable zinc may transiently reach even up to 600 µM. To explore the possible roles of high-concentration Zn2+ in regulating the blood-brain barrier (BBB), we investigated the effects of Zn2+ on the functions and structures of the tight junction (TJ) with an in vitro model of a Madin-Darby canine kidney (MDCK) cell monolayer. The experimental results indicated that high concentrations (>200 µM) of Zn2+ can affect the TJ integrity in a polarized manner. Basolateral addition of Zn2+ led to reversible TJ opening with pore paths of r ∼ 2 nm or more depending on Zn2+ concentration. The efflux/influx ratios of different sized probes were found to be ∼4.6 for FD4 (MW 4000) and ∼1.8 for Eu-DTPA (MW 560), suggesting that the Zn2+-induced paracelluar channels favour efflux especially for macromolecules. Further mechanistic studies revealed that the elevated intracellular Zn2+ taken from the basolateral side can increase phosphorylation of glycogen synthase kinase (GSK) 3ß, primarily due to the inhibition of calcineurin (CaN), thus resulting in the elevation of the snail transcriptional repressors. Subsequently, Zn2+ can cause the down-regulation of claudin-1, breakage of occludin and ZO-1 rings, and collapse of basolateral F-actin structures. These overall factors result in the formation of a trumpet-like paracellular channel, which allows asymmetric solute permeation. The ERK1/2 and JNK1/2 pathways may also be involved in the Zn2+-induced TJ opening process, while the activation of matrix metalloproteinase was not observed. Our results may suggest a potential role of zinc in regulation of BBB permeability associated with brain clearance of metabolites through the glymphatic system.

Kudinoside-D, a triterpenoid saponin derived from Ilex kudingcha suppresses adipogenesis through modulation of the AMPK pathway in 3T3-L1 adipocytes.

The leaves of Ilex Kudingcha, locally named "Kudingcha" in China, has been traditionally applied for treating obesity. Studies have demonstrated that the ethanol extract of Ilex kudingcha have anti-adipogenic effects. However, the constituent which was responsible for its anti-obesity and its underlying molecular mechanism has not yet been elucidated. This research explored the anti-obesity effect of kudinoside-D which was a main natural component of triterpenoid saponin from the ethanol extract of Ilex kudingcha, on lipid accumulation and the potential mechanism of action of adipogenesis in 3T3-L1 adipocytes. The adipocytes were treated with various concentrations of kudinoside D (0 to 40µM) during differentiation. The image-based Oil Red O staining analyses revealed that KD-D, dose dependently reduced cytoplasmic lipid droplet in 3T3-L1 adipocytes with the IC50 is 59.49µM. Meanwhile, major adipogenic transcription factor peroxisome proliferator-activated receptor γ (PPARγ), CCAAT/enhancer binding protein-α (C/EBPα) and sterol regulatory element-binding protein 1c (SREBP-1c) were significantly repressed as well as their target genes. The phosphorylation of AMP-activated protein kinase (AMPK) and its downstream target phosphorylated-acetyl CoA carboxylase (ACC) expression were also increased. In addition, the inhibitory effects of KD-D on the expressions of PPARγ and C/EBPα were weakened when cells were cotreated with AMPK inhibitor Compound C. These results indicated KD-D exerts anti-adipogenic effects through modulation of adipogenic transcription factors via AMPK signaling pathway. And the current findings demonstrated that KD-D was a potential therapeutic candidate for alleviating obesity and hyperlipidemia.

Transcriptome Profile Reveals that Pu-Erh Tea Represses the Expression of Vitellogenin Family to Reduce Fat Accumulation in Caenorhabditis elegans.

Due to misbalanced energy surplus and expenditure, obesity has become a common chronic disorder that is highly associated with many metabolic diseases. Pu-erh tea, a traditional Chinese beverage, has been believed to have numerous health benefits, such as anti-obesity. However, the underlying mechanisms of its anti-obesity effect are yet to be understood. Here, we take the advantages of transcriptional profile by RNA sequencing (RNA-Seq) to view the global gene expression of Pu-erh tea. The model organism Caenorhabditis elegans was treated with different concentrations of Pu-erh tea water extract (PTE, 0 g/mL, 0.025 g/mL, and 0.05 g/mL). Compared with the control, PTE indeed decreases lipid droplets size and fat accumulation. The high-throughput RNA-Sequence technique detected 18073 and 18105 genes expressed in 0.025 g/mL and 0.05 g/mL PTE treated groups, respectively. Interestingly, the expression of the vitellogenin family (vit-1, vit-2, vit-3, vit-4 and vit-5) was significantly decreased by PTE, which was validated by qPCR analysis. Furthermore, vit-1(ok2616), vit-3(ok2348) and vit-5(ok3239) mutants are insensitive to PTE triggered fat reduction. In conclusion, our transcriptional profile by RNA-Sequence suggests that Pu-erh tea lowers the fat accumulation primarily through repression of the expression of vit(vitellogenin) family, in addition to our previously reported (sterol regulatory element binding protein) SREBP-SCD (stearoyl-CoA desaturase) axis.

Tree shrew (Tupaia belangeri chinensis), a novel non-obese animal model of non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is becoming a severe public health problem that is affecting a large proportion of the world population. Generally, NAFLD in patients is usually accompanied by obesity, hyperglycemia, insulin resistance (IR) and type 2 diabetes (T2D), for which numerous animal models have been generated in order to explore the pathogenesis and therapies of NAFLD. On the contrary, quite a number of NAFLD subjects, especially in Asian regions, are non-obese and non-diabetic; however, few animal models are available for the research of non-obese NAFLD. Here, four approaches (here called approach 1 to 4) corresponding to the variable compositions of diets were used to treat tree shrews (Tupaia belangeri chinensis), which have a closer evolutionary relationship to primates than rodents. Analysis of plasma biochemical parameters, hepatic histology, and the expression of hepatic lipid metabolic genes revealed that all four approaches led to hepatic lipid accumulation, liver injury and hypercholesterolemia, but had no effect on body weight and adipose tissue generation, or glycemia. Hepatic gene expression in tree shrews treated by approach 4 might suggest a different or non-canonical pathway leading to hepatic steatosis. In conclusion, the tree shrew displays hepatic steatosis and dyslipidemia, but remains non-obese and non-diabetic under high energy diets, which suggests that the tree shrew may be useful as a novel animal model for the research of human non-obese NAFLD.

The Molecular Mechanisms and Rational Design of Anti-Diabetic Vanadium Compounds.

Vanadium compounds are promising anti-diabetic agents. Although BEOV was not able to succeed in phase II clinical trial, great progresses have been made in the past three decades on the discovery and development of anti-diabetic vanadium compounds. A vast of knowledge has been obtained on the molecular mechanisms of both the pharmacological and toxicological effects of vanadium complexes. It has been revealed that vanadium compounds exert insulin enhancement effects and cell protection via a multiple mechanism involving inhibition of PTP1B, activation of PPARs- AMPK signaling, regulation of unfolded protein responses (UPRs), and stimulation of antioxidant enzymes, while vanadium-induced oxidative stress and inflammatory response could primarily be attributed to vanadium toxicity. Based on the present results concerning the relationship between structures, biological activities and biochemical properties, the rationale for future design of anti-diabetic vanadium compounds has been discussed.

The permeability and transport mechanism of graphene quantum dots (GQDs) across the biological barrier.

As an emerging nanomaterial, graphene quantum dots (GQDs) have shown enormous potential in theranostic applications. However, many aspects of the biological properties of GQDs require further clarification. In the present work, we prepared two sizes of GQDs and for the first time investigated their membrane permeabilities, one of the key factors of all biomedical applications, and transport mechanisms on a Madin Darby Canine Kidney (MDCK) cell monolayer. The experimental results revealed that under ∼300 mg L(-1), GQDs were innoxious to MDCK and did not affect the morphology and integrity of the cell monolayer. The Papp values were determined to be 1-3 × 10(-6) cm s(-1) for the 12 nm GQDs and 0.5-1.5 × 10(-5) cm s(-1) for the 3 nm GQDs, indicating that the 3 nm GQDs are well-transported species while the 12 nm GQDs have a moderate membrane permeability. The transport and uptake of GQDs by MDCK cells were both time and concentration-dependent. Moreover, the incubation of cells with GQDs enhanced the formation of lipid rafts, while inhibition of lipid rafts with methyl-ß-cyclodextrin almost eliminated the membrane transport of GQDs. Overall, the experimental results suggested that GQDs cross the MDCK cell monolayer mainly through a lipid raft-mediated transcytosis. The present work has indicated that GQDs are a novel, low-toxic, highly-efficient general carrier for drugs and/or diagnostic agents in biomedical applications.