Expression of active B-Raf proto-oncogene in kidney collecting ducts induces cyst formation in normal mice and accelerates cyst growth in mice with polycystic kidney disease.

Polycystic kidney disease (PKD) is characterized by the formation and progressive enlargement of fluid-filled cysts due to abnormal cell proliferation. Cyclic AMP agonists, including arginine vasopressin, stimulate ERK-dependent proliferation of cystic cells, but not normal kidney cells. Previously, B-Raf proto-oncogene (BRAF), a MAPK kinase kinase that activates MEK-ERK signaling, was shown to be a central intermediate in the cAMP mitogenic response. However, the role of BRAF on cyst formation and enlargement in vivo had not been demonstrated. To determine if active BRAF induces kidney cyst formation, we generated transgenic mice that conditionally express BRAFV600E, a common activating mutation, and bred them with Pkhd1-Cre mice to express active BRAF in the collecting ducts, a predominant site for cyst formation. Collecting duct expression of BRAFV600E (BRafCD) caused kidney cyst formation as early as three weeks of age. There were increased levels of phosphorylated ERK (p-ERK) and proliferating cell nuclear antigen, a marker for cell proliferation. BRafCD mice developed extensive kidney fibrosis and elevated blood urea nitrogen, indicating a decline in kidney function, by ten weeks of age. BRAFV600E transgenic mice were also bred to Pkd1RC/RC and pcy/pcy mice, well-characterized slowly progressive PKD models. Collecting duct expression of active BRAF markedly increased kidney weight/body weight, cyst number and size, and total cystic area. There were increased p-ERK levels and proliferating cells, immune cell infiltration, interstitial fibrosis, and a decline in kidney function in both these models. Thus, our findings demonstrate that active BRAF is sufficient to induce kidney cyst formation in normal mice and accelerate cystic disease in PKD mice.

Periostin overexpression in collecting ducts accelerates renal cyst growth and fibrosis in polycystic kidney disease.

In polycystic kidney disease (PKD), persistent activation of cell proliferation and matrix production contributes to cyst growth and fibrosis, leading to progressive deterioration of renal function. Previously, we showed that periostin, a matricellular protein involved in tissue repair, is overexpressed by cystic epithelial cells of PKD kidneys. Periostin binds αVß3-integrins and activates integrin-linked kinase (ILK), leading to Akt/mammalian target of rapamycin (mTOR)-mediated proliferation of human PKD cells. By contrast, periostin does not stimulate the proliferation of normal human kidney cells. This difference in the response to periostin is due to elevated expression of αVß3-integrins by cystic cells. To determine whether periostin accelerates cyst growth and fibrosis, we generated mice with conditional overexpression of periostin in the collecting ducts (CDs). Ectopic CD expression of periostin was not sufficient to induce cyst formation or fibrosis in wild-type mice. However, periostin overexpression in pcy/pcy ( pcy) kidneys significantly increased mTOR activity, cell proliferation, cyst growth, and interstitial fibrosis; and accelerated the decline in renal function. Moreover, CD-specific overexpression of periostin caused a decrease in the survival of pcy mice. These pathological changes were accompanied by increased renal expression of vimentin, α-smooth muscle actin, and type I collagen. We also found that periostin increased gene expression of pathways involved in repair, including integrin and growth factor signaling and ECM production, and it stimulated focal adhesion kinase, Rho GTPase, cytoskeletal reorganization, and migration of PKD cells. These results suggest that periostin stimulates signaling pathways involved in an abnormal tissue repair process that contributes to cyst growth and fibrosis in PKD.

Integrin-Linked Kinase Signaling Promotes Cyst Growth and Fibrosis in Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by innumerous fluid-filled cysts and progressive deterioration of renal function. Previously, we showed that periostin, a matricellular protein involved in tissue repair, is markedly overexpressed by cyst epithelial cells. Periostin promotes cell proliferation, cyst growth, interstitial fibrosis, and the decline in renal function in PKD mice. Here, we investigated the regulation of these processes by the integrin-linked kinase (ILK), a scaffold protein that links the extracellular matrix to the actin cytoskeleton and is stimulated by periostin. Pharmacologic inhibition or shRNA knockdown of ILK prevented periostin-induced Akt/mammalian target of rapamycin (mTOR) signaling and ADPKD cell proliferation in vitro Homozygous deletion of ILK in renal collecting ducts (CD) of Ilkfl/fl ;Pkhd1-Cre mice caused tubule dilations, apoptosis, fibrosis, and organ failure by 10 weeks of age. By contrast, Ilkfl/+ ;Pkhd1-Cre mice had normal renal morphology and function and survived >1 year. Reduced expression of ILK in Pkd1fl/fl ;Pkhd1-Cre mice, a rapidly progressive model of ADPKD, decreased renal Akt/mTOR activity, cell proliferation, cyst growth, and interstitial fibrosis, and significantly improved renal function and animal survival. Additionally, CD-specific knockdown of ILK strikingly reduced renal cystic disease and fibrosis and extended the life of pcy/pcy mice, a slowly progressive PKD model. We conclude that ILK is critical for maintaining the CD epithelium and renal function and is a key intermediate for periostin activation of signaling pathways involved in cyst growth and fibrosis in PKD.

Is age-related macular degeneration a microvascular disease?

Age-related macular degeneration (AMD) is a common, degenerative disease of the central retina affecting millions of elderly in the USA alone and many more worldwide. A better understanding of the pathophysiology of AMD will be essential for developing new treatments. In this review, we discuss the potential impact of complement complex deposition at the choriocapillaris of aging eyes and the relationship between choriocapillaris loss and drusen formation. We further propose a model that integrates genetic and anatomical findings in AMD and suggest the implications of these findings for future therapies.

A Cross-sectional Study on Hepatitis B Vaccination Status and Post-exposure Prophylaxis Practices Among Health Care Workers in Teaching Hospitals of Mangalore.

BACKGROUND: Health care workers (HCWs) are at high risk for acquiring hepatitis B virus infection because of needle stick injury (NSI) and occupational exposures to potentially infectious bodily fluids. Hepatitis B vaccination confers protection against the infection. Very little information is available in India about current vaccination status and postexposure prophylaxis (PEP) practices among HCWs. OBJECTIVES: This study had 2 objectives. The first was to characterize current vaccination coverage among HCWs, and the second was to define PEP practices among HCWs after NSI and exposures to potentially infectious bodily fluids. METHODS: A questionnaire-based, cross-sectional study was conducted in hospitals attached to Kasturba Medical College, Mangalore. We selected 297 individuals. A pretested, semistructured questionnaire was devised to collect information from study participants. After obtaining permission from the Institutional Ethics Committee, data were collected by interviewing HCWs in the hospitals. Analysis was done using SPSS. FINDINGS: Nearly all (93.8%) of the HCWs surveyed had taken 1 dose of hepatitis B vaccine. However, only 57.1% completed the primary series of 3 doses and only 26.4% had taken 1 or more booster doses. Of the HCWs questioned, 24.8% had experienced NSIs, exposure to potentially infectious bodily fluids, or both. Local measures were the PEP practices most commonly used (85.5%) by the HCWs. CONCLUSION: The present study demonstrated that there is a need in Mangalore to improve the vaccination coverage and train HCWs in appropriate PEP practices. This will protect the workers from acquiring hepatitis B infection.

Structural and biochemical analyses of choroidal thickness in human donor eyes.

PURPOSE: The choroid plays a vital role in the health of the outer retina. While measurements of choroid using optical coherence tomography show altered thickness in aging and macular disease, detailed histopathologic and proteomic analyses are lacking. In this study we sought to evaluate biochemical differences in human donor eyes between very thin and thick choroids. METHODS: One hundred forty-one eyes from 104 donors (mean age ± standard deviation, 81.5 ± 12.2) were studied. Macular sections were collected, and the distance between Bruch's membrane and the inner surface of the sclera was measured in control, early/dry age-related macular degeneration (AMD), neovascular AMD, and geographic atrophy eyes. Proteins from the RPE-choroid of eyes with thick and thin choroids were analyzed using two-dimensional electrophoresis and/or mass spectrometry. Two proteins with altered abundance were confirmed using Western blot analysis. RESULTS: Donor eyes showed a normal distribution of thicknesses. Eyes with geographic atrophy had significantly thinner choroids than age-matched controls or early AMD eyes. Proteomic analysis showed higher levels of the serine protease SERPINA3 in thick choroids and increased levels of tissue inhibitor of metalloproteinases-3 (TIMP3) in thin choroids. CONCLUSIONS: Consistent with clinical imaging observations, geographic atrophy was associated with choroidal thinning. Biochemical data suggest an alteration in the balance between proteases and protease inhibitors in eyes that lie at the extremes of choroidal thickness. An improved understanding of the basic mechanisms associated with choroidal thinning may guide the development of new therapies for AMD.

Bradykinetic alcohol dehydrogenases make yeast fitter for growth in the presence of allyl alcohol.

Previous studies showed that fitter yeast (Saccharomyces cerevisiae) that can grow by fermenting glucose in the presence of allyl alcohol, which is oxidized by alcohol dehydrogenase I (ADH1) to toxic acrolein, had mutations in the ADH1 gene that led to decreased ADH activity. These yeast may grow more slowly due to slower reduction of acetaldehyde and a higher NADH/NAD(+) ratio, which should decrease the oxidation of allyl alcohol. We determined steady-state kinetic constants for three yeast ADHs with new site-directed substitutions and examined the correlation between catalytic efficiency and growth on selective media of yeast expressing six different ADHs. The H15R substitution (a test for electrostatic effects) is on the surface of ADH and has small effects on the kinetics. The H44R substitution (affecting interactions with the coenzyme pyrophosphate) was previously shown to decrease affinity for coenzymes 2-4-fold and turnover numbers (V/Et) by 4-6-fold. The W82R substitution is distant from the active site, but decreases turnover numbers by 5-6-fold, perhaps by effects on protein dynamics. The E67Q substitution near the catalytic zinc was shown previously to increase the Michaelis constant for acetaldehyde and to decrease turnover for ethanol oxidation. The W54R substitution, in the substrate binding site, increases kinetic constants (Ks, by >10-fold) while decreasing turnover numbers by 2-7-fold. Growth of yeast expressing the different ADHs on YPD plates (yeast extract, peptone and dextrose) plus antimycin to require fermentation, was positively correlated with the log of catalytic efficiency for the sequential bi reaction (V1/KiaKb=KeqV2/KpKiq, varying over 4 orders of magnitude, adjusted for different levels of ADH expression) in the order: WT≈H15R>H44R>W82R>E67Q>W54R. Growth on YPD plus 10mM allyl alcohol was inversely correlated with catalytic efficiency. The fitter yeast are "bradytrophs" (slow growing) because the ADHs have decreased catalytic efficiency.