Tea Drinking Alleviates Diabetic Symptoms via Upregulating Renal Water Reabsorption Proteins and Downregulating Renal Gluconeogenic Enzymes in db/db Mice

SCOPE

Tea, made from the plant Camellia sinensis, is known to have anti-diabetes effects and different mechanisms of action are proposed. Kidney is a vital organ in managing water reabsorption and glucose metabolism, and is greatly influenced by diabetes. The present study investigates the effects of tea administration on water reabsorption and gluconeogenesis in the kidney of diabetic mice.

METHODS AND RESULTS

Db/db mice are given tea infusion as drinking fluid when they begin to exhibit hyperglycemia. It is found that green tea or black tea infusion potently elevates renal proteins vital for water reabsorption, including protein kinase C-α, aquaporin 2, and urea transporter-A1, as well as increases trafficking of these proteins to apical plasma membrane where they exert water reabsorption function. The treatment also downregulates renal gluconeogenic enzymes, including glucose-6-phosphatase-α and phosphoenolpyruvate carboxykinase. Associated with these biochemical changes are the rectified polyuria, polydipsia, polyphagia, and hyperglycemia, all symptoms of diabetes.

CONCLUSIONS

For the first time, the present study demonstrates that tea has robust effects in enhancing kidney water reabsorption proteins and downregulating gluconeogenic enzymes in db/db mice. It remains to be investigated whether such beneficial effects of tea occur in humans.

Activation of protein kinase C-α/heme oxygenase-1 signaling pathway improves mitochondrial dynamics in lipopolysaccharide-activated NR8383 cells

Mitochondrial function and morphology are dynamically regulated by fusion and fission. Heme oxygenase-1 (HO-1), which may be upregulated by protein kinase C-α (PKC-α), improves mitochondrial dynamics by controlling the balance between fusion and fission in vivo and in vitro. However, whether the PKC-α/HO-1 signaling pathway is one of the underlying mechanisms in adjusting mitochondrial dynamics in lipopolysaccharide (LPS)-activated macrophages has remained elusive. To explore this, NR8383 cells were pre-treated with PKC-α inhibitor Go6976 or PKC-α activator phorbol-12-myristate-13-acetate for 30 min and then stimulated with LPS for 24 h. Next, the expression of PKC-α, HO-1, mitofusin 1 (Mfn1) and mitofusin 2 (Mfn2), optic atrophy 1 (OPA1), dynamin-related protein 1 (Drp1) and fission 1 (Fis1) was detected to evaluate the possible implication of the PKC-α/HO-1 signaling pathway in the LPS-induced NR8383 cells. The results indicated that activation of the PKC-α/HO-1 signaling pathway increased superoxide dismutase activities and the respiratory control ratio (RCR), decreased the levels of malondialdehyde, reactive oxygen species (ROS), Drp1 and Fis1, and simultaneously enhanced the levels of Mfn1, Mfn2 and OPA1. In contrast, the PKC-α inhibitor decreased the expression of RCR, Mfn1, Mfn2 and OPA1, and increased the expression of MDA and ROS in NR8383 cells. The results suggest that activation of the PKC-α/HO-1 signaling pathway is necessary for the balance of mitochondrial dynamics and oxidative stress in macrophages, which provides clues for probing novel strategies against the detrimental effects of sepsis and other disease states.

Listeriolysin O Causes ENaC Dysfunction in Human Airway Epithelial Cells

Pulmonary permeability edema is characterized by reduced alveolar Na⁺ uptake capacity and capillary barrier dysfunction and is a potentially lethal complication of listeriosis. Apical Na⁺ uptake is mainly mediated by the epithelial sodium channel (ENaC) and initiates alveolar liquid clearance. Here we examine how listeriolysin O (LLO), the pore-forming toxin of Listeria monocytogenes, impairs the expression and activity of ENaC. To that purpose, we studied how sub-lytic concentrations of LLO affect negative and positive regulators of ENaC expression in the H441 airway epithelial cell line. LLO reduced expression of the crucial ENaC-α subunit in H441 cells within 2 h and this was preceded by activation of PKC-α, a negative regulator of the channel's expression. At later time points, LLO caused a significant reduction in the phosphorylation of Sgk-1 at residue T256 and of Akt-1 at residue S473, both of which are required for full activation of ENaC. The TNF-derived TIP peptide prevented LLO-mediated PKC-α activation and restored phospho-Sgk-1-T256. The TIP peptide also counteracted the observed LLO-induced decrease in amiloride-sensitive Na⁺ current and ENaC-α expression in H441 cells. Intratracheally instilled LLO caused profound pulmonary edema formation in mice, an effect that was prevented by the TIP peptide; thus indicating the therapeutic potential of the peptide for the treatment of pore-forming toxin-associated permeability edema.

Interfering RNA against PKC-α inhibits TNF-α-induced IP3R1 expression and improves glomerular filtration rate in rats with fulminant hepatic failure

We have reported that tumor necrosis factor-α (TNF-α) is critical for reduction of glomerular filtration rate (GFR) in rats with fulminant hepatic failure (FHF). The present study aims to evaluate the underlying mechanisms of decreased GFR during acute hepatic failure. Rats with FHF induced by d-galactosamine plus lipopolysaccharide (GalN/LPS) were injected intravenously with recombinant lentivirus harboring short hairpin RNA against the protein kinase C-α ( PKC-α) gene (Lenti-shRNA-PKC-α). GFR, serum levels of aminotransferases, creatinine, urea nitrogen, potassium, sodium, chloride, TNF-α, and endothelin-1 (ET-1), as well as type 1 inositol 1,4,5-trisphosphate receptor (IP₃R1) expression in renal tissue were assessed. The effects of PKC-α silencing on TNF-α-induced IP₃R1, specificity protein 1 (SP-1), and c-Jun NH₂-terminal kinase (JNK) expression, as well as cytosolic calcium content were determined in glomerular mesangial cell (GMCs) with RNAi against PKC-α. Renal IP₃R1 overexpression was abrogated by pre-treatment with Lenti-shRNA-PKC-α. The PKC-α silence significantly improved the compromised GFR, reduced Cr levels, and reversed the decrease in glomerular inulin space and the increase in glomerular calcium content in GalN/LPS-exposed rats. TNF-α treatment increased expression of PKC-α, IP₃R1, specificity protein 1 (SP-1), JNK, and p-JNK in GMCs and increased Ca^{2 +} release and binding activity of SP-1 to the IP₃R1 promoter. These effects were blocked by transfection of siRNA against the PKC-α gene, and the PKC-α gene silence also restored cytosolic Ca²⁺ concentration. RNAi targeting PKC-α inhibited TNF-α-induced IP₃R1 overexpression and in turn improved compromised GFR in the development of acute kidney injury during FHF in rats.

A novel tumor necrosis factor-mediated mechanism of direct epithelial sodium channel activation

RATIONALE

Alveolar liquid clearance is regulated by Na(+) uptake through the apically expressed epithelial sodium channel (ENaC) and basolaterally localized Na(+)-K(+)-ATPase in type II alveolar epithelial cells. Dysfunction of these Na(+) transporters during pulmonary inflammation can contribute to pulmonary edema.

OBJECTIVES

In this study, we sought to determine the precise mechanism by which the TIP peptide, mimicking the lectin-like domain of tumor necrosis factor (TNF), stimulates Na(+) uptake in a homologous cell system in the presence or absence of the bacterial toxin pneumolysin (PLY).

METHODS

We used a combined biochemical, electrophysiological, and molecular biological in vitro approach and assessed the physiological relevance of the lectin-like domain of TNF in alveolar liquid clearance in vivo by generating triple-mutant TNF knock-in mice that express a mutant TNF with deficient Na(+) uptake stimulatory activity.

MEASUREMENTS AND MAIN RESULTS

TIP peptide directly activates ENaC, but not the Na(+)-K(+)-ATPase, upon binding to the carboxy-terminal domain of the α subunit of the channel. In the presence of PLY, a mediator of pneumococcal-induced pulmonary edema, this binding stabilizes the ENaC-PIP2-MARCKS complex, which is necessary for the open probability conformation of the channel and preserves ENaC-α protein expression, by means of blunting the protein kinase C-α pathway. Triple-mutant TNF knock-in mice are more prone than wild-type mice to develop edema with low-dose intratracheal PLY, correlating with reduced pulmonary ENaC-α subunit expression.

CONCLUSIONS

These results demonstrate a novel TNF-mediated mechanism of direct ENaC activation and indicate a physiological role for the lectin-like domain of TNF in the resolution of alveolar edema during inflammation.

ENaC activity and expression is decreased in the lungs of protein kinase C-α knockout mice

We used a PKC-α knockout model to investigate the regulation of alveolar epithelial Na(+) channels (ENaC) by PKC. Primary alveolar type II (ATII) cells were subjected to cell-attached patch clamp. In the absence of PKC-α, the open probability (Po) of ENaC was decreased by half compared with wild-type mice. The channel density (N) was also reduced in the knockout mice. Using in vivo biotinylation, membrane localization of all three ENaC subunits (α, β, and γ) was decreased in the PKC-α knockout lung, compared with the wild-type. Confocal microscopy of lung slices showed elevated levels of reactive oxygen species (ROS) in the lungs of the PKC-α knockout mice vs. the wild-type. High levels of ROS in the knockout lung can be explained by a decrease in both cytosolic and mitochondrial superoxide dismutase activity. Elevated levels of ROS in the knockout lung activates PKC-δ and leads to reduced dephosphorylation of ERK1/2 by MAP kinase phosphatase, which in turn causes increased internalization of ENaC via ubiquitination by the ubiquitin-ligase Nedd4-2. In addition, in the knockout lung, PKC-δ activates ERK, causing a decrease in ENaC density at the apical alveolar membrane. PKC-δ also phosphorylates MARCKS, leading to a decrease in ENaC Po. The effects of ROS and PKC-δ were confirmed with patch-clamp experiments on isolated ATII cells in which the ROS scavenger, Tempol, or a PKC-δ-specific inhibitor added to patches reversed the observed decrease in ENaC apical channel density and Po. These results explain the decrease in ENaC activity in PKC-α knockout lung.

Angiotensin II receptor type 1--a novel target for preventing neonatal meningitis in mice by Escherichia coli K1

The increasing incidence of Escherichia coli K1 meningitis due to escalating antibiotic resistance warrants alternate treatment options to prevent this deadly disease. We screened a library of small molecules from the National Institutes of Health clinical collection and identified telmisartan, an angiotensin II receptor type 1 (AT1R) blocker, as a potent inhibitor of E. coli invasion into human brain microvascular endothelial cells (HBMECs). Immunoprecipitation studies revealed that AT1R associates with endothelial cell gp96, the receptor in HBMECs for E. coli outer membrane protein A. HBMECs pretreated with telmisartan or transfected with AT1R small interfering RNA were resistant to E. coli invasion because of downregulation of protein kinase C-α phosphorylation. Administration of a soluble derivative of telmisartan to newborn mice before infection with E. coli prevented the onset of meningitis and suppressed neutrophil infiltration and glial cell migration in the brain. Therefore, telmisartan has potential as an alternate treatment option for preventing E. coli meningitis.

Angiotropic metastatic malignant melanoma in a canine mammary gland

An eleven-year-old spayed female Yorkshire Terrier presented with a sublumbar mass and upon ultrasonographic examination, was revealed to have a mammary gland tumor. Black to reddish colored masses, located in the visceral peritoneum of the sublumbar region was observed on laparotomy with masectomy of the right side. In the laparotomy, we observed reddish masses multifocally located in the serosal membrane of the large intestine. Histopathologic examination of the intestinal and abdominal mass showed highly invasiveness into the muscle and metastasis of melanocytic tumor cells through the blood vessels. The mammary glands showed abnormal hyperplasia of melanocytes, destruction of the normal glands by tumor cells and infiltration of some lymphocytes in the pool of melanocytic cells. We have identified a malignant melanoma containing an angiotumoral complex in which tumor cells occupied a pericytic location along the microvessels with intravasation determined by immunohistochemistry for S100 protein and protein kinase C-α. Histologic findings in this dog lead to a diagnosis of an angiotropic metastatic malignant melanoma.