Early changes in retinal structure and BMP2 expression in the retina and crystalline lens of streptozotocin-induced diabetic pigs / 한국실험동물학회지

PURPOSE: This study aims to evaluate early changes in retinal structure and BMP2 expression in the retina and crystalline lens by comparing streptozotocin-induced diabetic pigs and normal control group pigs. METHODS: Five eye samples from five diabetic Micro-pigs (Medikinetics, Pyeongtaek, Korea) and five eye samples from five control pigs bred in a specific pathogen-free area were used. Diabetes was developed through intravenous injection of nicotinamide and streptozotocin, and the average fasting glucose level was maintained at 250 mg/dL or higher for 16 weeks. To evaluate BMP2 expression in the retina and crystalline lens, Western blotting was performed. RESULTS: In Hematoxylin and Eosin staining, most diabetic pigs showed structural abnormalities in the inner plexiform layer. The number of nuclei in the ganglion cell layer within the range of 10⁴µm² was 3.78±0.60 for diabetic pigs and 5.57±1.07 for control group pigs, showing a statistically significant difference. In immunohistochemical staining, diabetic retinas showed an overall increase in BMP2 expression. In Western blotting, the average BMP2/actin level of diabetic retinas was 1.19±0.05, showing a significant increase compared to the 1.06±0.03 of the control group retinas (P=0.016). The BMP2/actin level of diabetic crystalline lenses was similar to the control group crystalline lenses (P=0.730). CONCLUSIONS: Compared to control group pigs, the number of nuclei in the inner nuclear layer of retinas from streptozotocin-induced diabetic pigs decreased, while an increase in BMP2 expression was observed in the retina of diabetic pigs.

Development of a type II diabetic mellitus animal model using Micropig(R) / 한국실험동물학회지

Diabetes, which has shown an explosive increase in terms of its incidence, is regarded as a serious disease that must be overcome for the sake of human life. Among animal models used for testing of drug efficacy, the mini-pig model has shown a rapid upload due to its many similarities with human, particularly concerning the pharmacokinetics of compounds after subcutaneous administration, the structure and function of the gastrointestinal tract, the morphology of the pancreas, and overall metabolic status. Based on these various advantages, we sought to develop an animal model of type II diabetic mellitus using the Micro-pig, which differs from other miniature pigs. We used six male Micro-pigs for induction of a moderate insulin deficient model with nicotinamide (NIA)/streptozotocin (STZ) treatment and three animals for control. For evaluation of incidence of type II diabetes, we measured blood glucose level, and performed oral glucose tolerance test and immunohistochemistry on pancreatic tissue using insulin antibody. Compared to control animals, all animals treated with NIA/STZ showed high levels of glucose and low levels of insulin. In addition, we observed the partially destroyed beta cell population from tissue of the pancreas in treated animals. Based on these results, we report that the Micro-pig model developed in this study can be used for testing of the efficacy of therapeutic agents for treatment of Type 2 diabetic mellitus.

Co-localization and interaction of human organic anion transporter 4 with caveolin-1 in primary cultured human placental trophoblasts

The human organic anion transporter 4 (hOAT4) has been identified as the fourth isoform of OAT family. hOAT4 contributes to move several negatively charged organic compounds between cells and their extracellular milieu. The functional characteristics and regulatory mechanisms of hOAT4 remain to be elucidated. It is well known that caveolin plays a role in modulating proteins having some biological functions. To address this issue, we investigated the co-localization and interaction between hOAT4 and caveolin-1. hOAT4 and caveolin-1 (mRNA and protein expression) were observed in cultured human placental trophoblasts isolated from placenta. The confocal microscopy of immuno-cytochemistry using primary cultured human trophoblasts showed hOAT4 and caveolin-1 were co-localized at the plasma membrane of the cell. This finding was confirmed by Western blot analysis using isolated caveolae-enriched membrane fractions and immune-precipitates from the trophoblasts. When synthesized cRNA of hOAT4 along with scrambled- or antisense-oligodeoxynucleotide (ODN) of Xenopus caveolin-1 were co-injected to Xenopus oocytes, the [3H]estrone sulfate uptake was significantly decreased by the co-injection of antisense ODN but not by scrambled ODN. These findings suggest that hOAT4 and caveolin-1 share a cellular expression in the plasma membrane and caveolin-1 up-regulates the organic anionic compound uptake by hOAT4 under the normal physiological condition.

Identification of a kidney-specific mouse organic cation transporter like-1 (mOCTL1)

Organic ion transporters are expressed in various tissues that transport endogenous and exogenous compounds including their metabolites. There are organic anion transporter (OAT), organic cation transporter (OCT), organic anion transporter like protein (OATLP) and organic cation transporter like (OCTL). Considering the variety of charged organic ionic compounds, the existence of numerous isoforms of organic ion transporters can be assumed. In the present study, we have searched for a new isoform in the expressed sequence tag (EST) database using human organic anion transporter 4 (hOAT4) amino acid sequence as a "query". We found a candidate clone (BC021449) from the mouse kidney cDNA library. This clone was identified as an ortholog of ORCTL3 or OCTL-1. The mOCTL1 cDNA consists of 2016 base pairs encoding 551 amino acid residues with 12 putative transmembrane domains. The deduced amino acid sequence of mOCTL1 showed 35 to 40% identity to those of the other members of the OATs and OCTs. According to the tissue distribution, examined by Northern blot analysis, about a 2.4-kb transcript of mOCTL1 was observed in the kidney. About a 90-kDa band was detected when Western blot analysis in the mouse kidney was done by using antibody against synthesized oligopeptide of mOCTL1. The immunohistochemical result showed that mOCTL1 was stained at the glomerulus (the parietal epithelial cells and podocytes), pars recta of proximal tubule, distal convoluted tubules, connecting tubules and collecting tubules. From these results, we conclude that mOCTL1 may be a candidate for an organic ion transporter isoform in the mouse kidney.

Evidence for Cyclooxygenase-2 Association with Caveolin-3 in Primary Cultured Rat Chondrocytes

The purpose of this study was to demonstrate the cellular localization of cyclooxygenase-2 (COX-2) and caveolin-3 (Cav-3) in primarily cultured rat chondrocytes. In normal rat chondrocytes, we observed relatively high levels of Cav-3 and a very low level of COX-2 mRNA and protein. Upon treating the chondrocytes with 5 microM of CdCl2 (Cd) for 6 hr, the expressions of COX-2 mRNA and protein were increased with the decreased Cav-3 mRNA and protein expressions. The detergent insoluble caveolae-rich membranous fractions that were isolated from the rat chondrocytes and treated with Cd contained the both proteins of both COX-2 and Cav-3 in a same fraction. The immuno-precipitation experiments showed complex formation between the COX-2 and Cav-3 in the rat chondrocytes. Purified COX-2 with glutathione S-transferase-fused COX-2 also showed complex formation with Cav-3. Confocal and electron microscopy also demonstrated the co-localization of COX-2 and Cav-3 in the plasma membrane. The results from our current study show that COX-2 and Cav-3 are co-localized in the caveolae of the plasma membrane, and they form a protein-protein complex. The co-localization of COX-2 with Cav-3 in the caveolae suggests that the caveolins might play an important role for regulating the function of COX-2.

Identification of a novel murine organic anion transporter like protein 1 (OATLP1) expressed in the kidney

The organic anion transporters (OATs) are expressed in various tissues, primarily in the kidney and liver, but they are also expressed in the placenta, small intestine, and the choroid plexus, which are all epithelial tissues that transport xenobiotics. Six isoforms of OATs are currently known. Considering the variety of organic anionic compounds, other OATs isoforms can be assumed. In this connection, we have searched for a new isoform in the expressed sequence tag (EST) database. We found the new candidate clone AK052752 in the mouse kidney cDNA library and we named it mouse organic anion transporter like protein 1 (mOATLP1). The mOATLP1 cDNA consisted of 2221 base pairs that encoded a 552 amino acid residue protein with 12 putative transmembrane domains. The deduced amino acid sequence of mOATLP1 showed 37 to 63% identity to other members of the OAT family. According to the tissue distribution based on Northern blot analysis, 2.7 kb and 2.9 kb mOATLP1 transcripts (approximate sizes) were observed in the kidney and liver. An 85-kDa band (approximate) was detected using Western blot analysis of mouse kidney performed with a synthesized oligopeptide-induced mOATLP1 antibody. Immunohistochemical results showed mOATLP1 was stained in the blood vessels, glomeruli (the parietal epithelial cells and podocytes), distal convoluted tubules, connecting tubules, and inner medullary collecting tubules. mOATLP1 appears to be a novel candidate for an organic anion transporter isoform identified in the kidney.

Introduction of Organic Anion Transporters (SLC22A) and a Regulatory Mechanism by Caveolins

The kidney is an important organ for controlling the volume of body fluids, electrolytic balance and excretion/reabsorption of endogenous and exogenous compounds. Among these renal functions, excretion/reabsorption of endogenous and exogenous substance is very important for the maintenance of physiological homeostasis in the body. Recently discovered organic anion transporters (OAT or SLC22A) have important roles for renal functions. It is well known as drug transporter. Several isoforms belong to SLC22A family. They showed different transport substrate spectrums and different localizations within the kidney. Their gene expressions are changed by some stimulus. The functional transport properties are regulated by protein kinase C. In addition, the function of organic anion transporters are also regulated by protein-protein interaction, such as caveolin which is compositional protein of caveolae structure. In this review, we will give an introduction of organic anion transporters and its regulatory mechanisms.