Corticoadrenal activity regulates in rat betaine-homocysteine <Emphasis Type="Italic">S</Emphasis>-methyltransferase expression with opposites effects in liver and kidney

Betaine-homocysteine S-methyltransferase (BHMT) is an enzyme that converts homocysteine (Hcy) to methionine using betaine as a methyl donor. Betaine also acts as osmolyte in kidney medulla, protecting cells from high extracellular osmolarity. Hepatic BHMT expression is regulated by salt intake. Hormones, particularly corticosteroids, also regulate BHMT expression in rat liver. We investigated to know whether the corticoadrenal activity plays a role in kidney BHMT expression. BHMT activity in rat kidneys is several orders of magnitude lower than in rat livers and only restricted to the renal cortex. This study confirms that corticosteroids stimulate BHMT activity in the liver and, for the first time in an animal model, also up-regulate the BHMT gene expression. Besides, unlike the liver, corticosteroids in rat kidney down-regulate BHMT expression and activity. Given that the classical effect of adrenocortical activity on the kidney is associated with sodium and water re-absorption by the distal tubule leading to volume expansion, by promoting lesser use of betaine as a methyl donor, corticosteroids would preserve betaine for its other role as osmoprotectant against changes in the extracellular osmotic conditions. We conclude that corticosteroids are, at least in part, responsible for the inhibition of BHMT expression and activity in rat kidneys.     

High sodium chloride intake decreases betaine-homocysteine S-methyltransferase expression in guinea pig liver and kidney

Betaine-homocysteine S-methyltransferase (BHMT) is the only enzyme known to catabolize betaine. In addition to being a substrate for BHMT, betaine also functions as an osmoprotectant that accumulates in the kidney medulla under conditions of high extracellular osmolarity. The mechanisms that regulate the partitioning of betaine between its use as a methyl donor and its accumulation as an osmoprotectant are not completely understood. The aim of this study was to determine whether BHMT expression is regulated by salt intake. This report shows that guinea pigs express BHMT in the liver, kidney, and pancreas and that the steady-state levels of BHMT mRNA in kidney and liver decrease 68% and 93% in guinea pigs consuming tap water containing high levels of salt compared with animals provided untreated tap water. The animals consuming the salt water also had approximately 50% less BHMT activity in the liver and kidney, and steady-state protein levels decreased approximately 30% in both organs. Pancreatic BHMT activity and protein levels were unaffected by the high salt treatment. The complex mechanisms involved in the downregulation of hepatic and renal BHMT expression in guinea pigs drinking salt water remain to be clarified, but the physiological significance of this downregulation may be to expedite the transport and accumulation of betaine into the kidney medulla under conditions of high extracellular osmolarity.     

A monoclonal antibody against human kidney gamma-glutamyl transpeptidase: preparation, immunochemical, and immunohistochemical characterization

To perform immunohistochemical study of the distribution of gamma-glutamyl transpeptidase in human organs, a highly specific antibody against the human enzyme is required. We prepared monoclonal antibody against gamma-glutamyl transpeptidase from human kidney, using the hybridoma technique. The antibody was of the IgG1 type and the light chain belonged to the kappa class. The antibody reacted specifically with the 63 KD heavy subunit of the enzyme. Examination of the specificity of the antibody performed by immunohistochemical staining of human kidney sections revealed that the antigen was localized on the brush border and along the basolateral membrane of the epithelial cells of both the convoluted and the straight portions of the proximal tubule. This antibody was also reactive in several human organs other than kidney, including epididymis, prostate, seminal vesicle, pancreas, and normal liver, and in human hepatoma. These findings indicate the existence of an antigenic determinant common to human kidney and other organs. The monoclonal antibody did not crossreact with mouse, rat, guinea pig, rabbit, or pig kidney.     

The activities and intracellular distribution of nicotinamide-adenine dinucleotide phosphate-malate dehydrogenase, phosphoenolpyruvate carboxykinase and pyruvate carboxylase in rat, guinea-pig and rabbit tissues.

1. Measurements are presented of the activity and intracellular distribution of phosphoenolypruvate carboxykinase, pyruvate carboxylase and NADP-malate dehydrogenase in rat, guinea-pig and rabbit liver and kidney cortex, together with previously obtained measurements of these enzymes in adipose tissue. 2. In all three tissues pyruvate carboxylase activity was greatest in the rat and lowest in the rabbit. 3. Guinea pig and rabbit were very similar to each other with respect to the extramitochondrial-mitochondrial distribution of phosphoenolpyruvate carboxykinase in all three tissues. 4. NADP-malate dehydrogenase was present in all three tissues in the rat, present in kidney cortex and adipose tissue in the guinea pig and absent from all tissues examines in the rabbit.     

VEGF-C and VEGF-D expression in neuroendocrine cells and their receptor, VEGFR-3, in fenestrated blood vessels in human tissues.

Recently, vascular endothelial growth factor receptor 3 (VEGFR-3) has been shown to provide a specific marker for lymphatic endothelia in certain human tissues. In this study, we have investigated the expression of VEGFR-3 and its ligands VEGF-C and VEGF-D in fetal and adult tissues. VEGFR-3 was consistently detected in the endothelium of lymphatic vessels such as the thoracic duct, but fenestrated capillaries of several organs including the bone marrow, splenic and hepatic sinusoids, kidney glomeruli and endocrine glands also expressed this receptor. VEGF-C and VEGF-D, which bind both VEGFR-2 and VEGFR-3 were expressed in vascular smooth muscle cells. In addition, intense cytoplasmic staining for VEGF-C was observed in neuroendocrine cells such as the alpha cells of the islets of Langerhans, prolactin secreting cells of the anterior pituitary, adrenal medullary cells, and dispersed neuroendocrine cells of the gastrointestinal tract. VEGF-D was observed in the innermost zone of the adrenal cortex and in certain dispersed neuroendocrine cells. These results suggest that VEGF-C and VEGF-D have a paracrine function and perhaps a role in peptide release from secretory granules of certain neuroendocrine cells to surrounding capillaries.     

石蜡切片行免疫荧光染色后再行PAS或HE染色确定NPR-A蛋白在肾脏的定位

目的 介绍一种新方法来明确NPR-A蛋白在大鼠肾组织的定位.方法 采用肾脏石蜡切片先行NPR-A免疫荧光染色,然后再行PAS或HE染色.结果 NPR-A免疫阳性物在大鼠肾组织主要沉积于皮质的近端小管、外髓的髓袢升支粗段以及内髓集合管,直小血管、肾小球、远曲小管和细段也有一定量的表达,而皮质及外髓集合管仅有少量的表达.结论 研究采用石蜡切片先行免疫荧光染色后再行PAS或HE染色,在不用或少用特异性抗体的情况下,成功的解决了NPR-A蛋白在大鼠肾组织表达的分布位置及细胞定位的难题.     

T-cell-activating monoclonal antibodies, reacting with both leukocytes and erythrocytes, recognize the guinea pig Thy-1 differentiation antigen: characterization and cloning of guinea pig CD90

A glycophosphatidylinositol (GPI)-linked differentiation antigen expressed on guinea pig T and B lymphocytes was identified by several monoclonal antibodies; it has been shown previously that this membrane protein induced strong polyclonal T cell proliferation upon antibody binding and costimulation by PMA. Purification by immunoadsorption and microsequencing revealed that this T-cell-activating protein is the homologue of Thy-1 or CD90. In contrast to the Thy-1 antigen of most other species, guinea pig Thy-1 has a much higher molecular weight, which is due to a more extensive N-linked glycosylation, bringing the molecular weight of the total antigen up to 36 kDa. Molecular cloning of guinea pig Thy-1 indicated that the deduced molecular weight of the protein backbone is 12,777 after removal of an N-terminal 19-amino-acid leader peptide and cleavage of the 31 amino acids for GPI anchoring the C-terminal end. Sequence comparison showed that guinea pig Thy-1 has an 82% homology to human and a 72% homology to mouse Thy-1 on the amino acid level. Immunohistological staining of cryostat sections revealed intensive staining with the monoclonal antibody H154 on fibroblasts, fibrocytes, Kupffer cells, alveolar macrophages, and mesangial cells. As observed in the human, mouse, and rat, Thy-1 is abundant in the guinea pig brain. Unlike Thy-1 expression in other species, guinea pig Thy-1 is strongly expressed on most resting, nonactivated B cells and, to a lesser extent, on erythrocytes. While treatment of erythrocytes and lymphocytes with GPI-specific phospholipase C largely decreased reactivity with mAb H154, T cells retained the proliferative response to antibody and phorbol esters.     

AQP5 is expressed in type-B intercalated cells in the collecting duct system of the rat, mouse and human kidney

We screened human kidney-derived multipotent CD133+/CD24+ ARPCs for the possible expression of all 13 aquaporin isoforms cloned in humans. Interestingly, we found that ARPCs expressed both AQP5 mRNA and mature protein. This novel finding prompted us to investigate the presence of AQP5 in situ in kidney. We report here the novel finding that AQP5 is expressed in human, rat and mouse kidney at the apical membrane of type-B intercalated cells. AQP5 is expressed in the renal cortex and completely absent from the medulla. Immunocytochemical analysis using segment- and cell type-specific markers unambiguously indicated that AQP5 is expressed throughout the collecting system at the apical membrane of type-B intercalated cells, where it co-localizes with pendrin. No basolateral AQPs were detected in type-B intercalated cells, suggesting that AQP5 is unlikely to be involved in the net trans-epithelial water reabsorption occurring in the distal tubule. An intriguing hypothesis is that AQP5 may serve an osmosensor for the composition of the fluid coming from the thick ascending limb. Future studies will unravel the physiological role of AQP5 in the kidney.     

Localization of a brain sulfotransferase, SULT4A1, in the human and rat brain: an immunohistochemical study.

Cytosolic sulfotransferases are believed to play a role in the neuromodulation of certain neurotransmitters and drugs. To date, four cytosolic sulfotransferases have been shown to be expressed in human brain. Recently, a novel human brain sulfotransferase has been identified and characterized, although its role and localization in the brain are unknown. Here we present the first immunohistochemical (IHC) localization of SULT4A1 in human brain using an affinity-purified polyclonal antibody raised against recombinant human SULT4A1. These results are supported and supplemented by the IHC localization of SULT4A1 in rat brain. In both human and rat brains, strong reactivity was found in several brain regions, including cerebral cortex, cerebellum, pituitary, and brainstem. Specific signal was entirely absent on sections for which preimmune serum from the corresponding animal, processed in the same way as the postimmune serum, was used in the primary screen. The findings from this study may assist in determining the physiological role of this SULT isoform.     

The subcellular location of isozymes of NADP-isocitrate dehydrogenase in tissues from pig, ox and rat

Antibodies against purified NADP-isocitrate dehydrogenase from pig liver cytosol and pig heart were raised in rabbits. The purified enzymes from these sources are different proteins, as demonstrated by differences in electrophoretic mobility and absence of crossreactivity by immunotitration and immunodiffusion. The NADP-isocitrate dehydrogenase in the soluble supernatant homogenate fraction from pig liver, kidney cortex, brain and erythrocyte hemolyzate was identical with the purified enzyme from pig liver cytosol, as determined by electrophoretic mobility and immunological techniques. The enzyme in extracts of mitochondria from pig heart, kidney, liver and brain was identical with the purified pig heart enzyme by the same criteria. However, the 'mitochondrial' isozyme was the major component also in the soluble supernatant fraction of pig heart homogenate. The 'cytosolic' isozyme accounted for only 1-2% of total NADP-isocitrate dehydrogenase in pig heart, as determined by separation of the isozymes with agarose gel electrophoresis and immunotitration. The mitochondrial isozyme was also the predominant NADP-isocitrate dehydrogenase in porcine skeletal muscle. The ratio of cytosolic/mitochondrial isozyme for porcine whole tissue extract, determined by immunotitration, was about 2 for liver and 1 for kidney cortex and brain. The distribution of isozymes in cell homogenate fractions from ox and rat tissues corresponded to that observed in organs of porcine origin. The mitochondrial and cytosolic isozymes from ox and rat tissues exhibited crossreactivity with the antibodies against the pig heart and pig liver cytosol enzyme, respectively, and the electrophoretic migration patterns were similar qualitatively to those found for the isozymes in porcine tissues. Nevertheless, there were species specific differences in the characteristics of each of the corresponding isozymes. NAD-isocitrate dehydrogenase was not inhibited by the antibodies, confirming that the protein is distinct from that of either isozyme of NADP-isocitrate dehydrogenase.     

Isoforms of alanine aminotransferases in human tissues and serum--differential tissue expression using novel antibodies

Serum alanine aminotransferase (ALT) is used as a clinical marker of hepatotoxicity. Two forms of ALT have been identified, ALT1 and ALT2, encoded by separate genes. The cellular and tissue distribution of the different ALT proteins has not been characterized in humans, and their relative contribution to serum is unknown. Here, we describe the development of novel isoenzyme specific ALT1 and ALT2 antibodies and the expression of the enzymes in human cells and organs. In normal human tissue, high expression of ALT1 was found in liver, skeletal muscle and kidney and low levels in heart muscle and not detectable in pancreas. High ALT2 reactivity was detected in heart and skeletal muscle, while no ALT2 expression was found in liver or kidney. Using immunohistochemistry, strong ALT1 reactivity was found in hepatocytes, renaltubular epithelial cells and in salivary gland epithelial cells, while ALT2 was expressed in adrenal gland cortex, neuronal cell bodies, cardiac myocytes, skeletal muscle fibers and endocrine pancreas. Immunoprecipitation using ALT antibodies on normal human serums showed ALT1 to be mainly responsible for basal ALT activity. Together, the results points to a differential expression of ALT1 and ALT2 in human organs and substantiate a need for investigations regarding the possible impacts on ALT measurements.     

Expression of cytochrome P-450 4 enzymes in the kidney and liver: Regulation by PPAR and species-difference between rat and human

Members of the cytochrome P-450 4 (CYP4) family catalyze the ω-hydroxylation of fatty acids, and some of them have the PPAR response element in the promoter area of the genes. The localization of CYP4A and PPAR isoforms and the effect of PPAR agonists on CYP4A protein level and activity were determined in rat kidney and liver. Immunoblot analysis showed that CYP4A was expressed in the liver and proximal tubule, with lower expression in the preglomerular microvessel, glomerulus and thick ascending limb (TAL), but the expression was not detected in the collecting duct. PPARα was expressed in the liver, proximal tubule and TAL. PPARγ was expressed in the collecting duct, with lower expression in the TAL, but no expression in the proximal tubule and liver. The PPARα agonist clofibrate induced CYP4A protein levels and activity in the renal cortex and liver. The PPARγ agonist pioglitazone did not modulate them in these tissues. The localization of CYP4A and CYP4F were further determined in human kidney and liver by immunohistochemical technique. Immunostainings for CYP4A and CYP4F were observed in the hepatocytes of the liver lobule and the proximal tubules, with lower stainings in the TALs and collecting ducts, but no staining in the glomeruli or renal vasculatures. These results indicate that the inducibility of CYP4A by PPAR agonists in the rat tissues correlates with the expression of the respective PPAR isoforms, and that the localization of CYP4 in the kidney has a species-difference between rat and human.     

Localization of S-adenosylhomocysteine hydrolase in the rat kidney.

S-adenosylhomocysteine (SAH) hydrolase is a cytosolic enzyme present in the kidney. Enzyme activities of SAH hydrolase were measured in the kidney in isolated glomeruli and tubules. SAH hydrolase activity was 0.62 +/- 0.02 mU/mg in the kidney, 0.32 +/- 0.03 mU/mg in the glomeruli, and 0.50 +/- 0.02 mU/mg in isolated tubules. Using immunohistochemical methods, we describe the localization of the enzyme SAH hydrolase in rat kidney with a highly specific antibody raised in rabbits against purified SAH hydrolase from bovine kidney. This antibody crossreacts to almost the same extent with the SAH hydrolase from different species such as rat, pig, and human. Using light microscopy, SAH hydrolase was visualized by the biotin-streptavidin-alkaline phosphatase immunohistochemical procedure. SAH hydrolase immunostaining was observed in glomeruli and in the epithelium of the proximal and distal tubules. The collecting ducts of the cortex and medulla were homogeneously stained. By using double immunofluorescence staining and two-channel immunofluorescence confocal laser scanning microscopy, we differentiated the glomerular cells (endothelium, mesangium, podocytes) and found intensive staining of podocytes. Our results show that the enzyme SAH hydrolase is found ubiquitously in the rat kidney. The prominent staining of SAH hydrolase in the podocytes may reflect high rates of transmethylation. (J Histochem Cytochem 48:211-218, 2000)     

A monoclonal antibody against insect CALNUC recognizes the prooncoprotein EWS specifically in mammalian cells. Immunohistochemical and biochemical studies of the antigen in rat tissues

A monoclonal antibody against insect CALNUC was shown to recognize an 85-kDa nuclear protein specifically in mammalian cells. Amino acid sequencing of the protein purified from rat liver revealed it to be EWS, a prooncoprotein for Ewing sarcomas and related tumors. Using the antibody, distribution of EWS was studied in rat tissues fixed with 4% paraformaldehyde by immunohistochemical methods. On thaw-fixed cryosections or those of perfusion-fixed tissues, almost all cell nuclei showed the specific staining. In immersion-fixed tissues, the staining unexpectedly disappeared in particular tissues (kidney cortex, liver, etc.), although it was recovered by autoclaving the cryosections. Western blotting also demonstrated the ubiquitous expression of EWS in the tissues. In extracts from the liver, the 85-kDa band rapidly disappeared in a Ca(2+)-dependent manner, but never in the testis. The antigen was very labile in kidney homogenates even without Ca2+. Biochemical studies with digoxigenin-labeled EWS showed that the Ca(2+)-dependent disappearance was associated with upward mobility shifts of EWS. These suggested that EWS was ubiquitously expressed in rat tissues, and that the antigen was masked in particular tissues during the immersion fixation.