Immunocytochemical studies on the localization of plasma and of cellular retinol-binding proteins and of transthyretin (prealbumin) in rat liver and kidney.

Abstract

The immunocytochemical localization of cellular retinol-binding protein (CRBP), of plasma retinol-binding protein (RBP), and of plasma transthyretin (TTR) was studied in rat liver and kidney. The studies employed normal rats, retinol-deficient rats, and rats fed excess retinol . Antisera were prepared in rabbits against purified rat CRBP, RBP, and TTR . The primary antibodies and goat anti-rabbit IgG were purified by immunosorbent affinity chromatography, using the respective pure antigen coupled to Sepharose as the immunosorbent . This procedure effectively removed cross-reactive and heterophile antibodies, which permitted the specific staining and localization of each antigen by the unlabeled peroxidase-antiperoxidase method . CRBP was found to be localized in two cell types in the liver, the parenchymal cells and the fat-storing cells . Diffuse cytoplasmic staining for CRBP was seen in all the parenchymal cells . Much more intense staining for CRBP was seen in the fat-storing cells . The prominence of the CRBP-positive fat-storing cells changed markedly with vitamin A status . Thus, these cells were most prominent, and appeared most numerous, in liver from rats fed excess retinol . Both RBP and TTR were localized within liver parenchymal cells . The intensity of RBP staining increased markedly in retinol-deficient rat liver, consistent with previous biochemical observations . With the methods employed, specific staining for RBP or TTR was not seen in cells other than the parenchymal cells . In the kidney, all three proteins (CRBP, RBP, and TTR) were localized in the proximal convoluted tubules of the renal cortex . Staining for RBP was much more intense in normal kidney than in kidney from retinol-deficient rats. These findings reflect the fact that RBP in the tubules represents filtered and reabsorbed RBP . The pattern of specific staining for CRBP among the various tubules was very similar to that seen for RBP on adjacent, serial sections of kidney . The function of CRBP in the kidney is not known .It is now well established that specific binding proteins for retinol exist in plasma and in the intracellular compartment in a number of tissues. These proteins play important roles in the metabolism of vitamin A. Thus, retinol-binding protein (RBP)`, the specific plasma transport protein for vitamin A, transports retinol from its storage site in the liver to peripheral target tissues in the body. A different protein, cellular retinolbinding protein (CRBP) is found within cells in many tissues.Since the initial isolation of human RBP in 1968 (1), 'Abbreviations used in this paper are : CRBP, cellular retinol-binding protein ; RBP, retinol-binding protein ; TTR, transthyretin . 1696extensive studies in many laboratories have provided considerable information about the structure, metabolism, and biological roles of RBP (see references 2-4 for recent reviews) . RBP, with a molecular weight close to 21,000 and one binding site for retinol, is synthesized in (5) and secreted by the liver . RBP in plasma stro...

The distribution of vitamin A and retinol-binding protein in the blood plasma, urine, liver and kidneys of carnivores

“…In rats, vitamin A deficiency blocks the secretion of RBP from the liver, so that plasma RBP concentrations fall and liver RBP levels rise [1,7]. These observations are consistent with a much stronger intensity of staining for immunoreactive RBP in the liver of vitamin A deficient rats [9].…”

“…Consequently, immunoreactive RBP could be detected in the proximal convoluted tubules as described in human and rat kidneys [8,9]. This result and the high vitamin A concentrations in the kidneys of raccoon dogs and silver foxes despite low vitamin A concentrations in the livers suggest a specific function of the canine kidney in contributing plasma retinol and retinyl esters in addition to the excretion of vitamin A with the urine [27].…”

Cellular Retinol-Binding Protein-1 Expression and Modulation during In Vivo and In Vitro Myofibroblastic Differentiation of Rat Hepatic Stellate Cells and Portal Fibroblasts

“…2a). CRBP-1 was expressed at a high level in HSC and slightly in hepatocytes as previously described (Kato et al, 1984); in the parenchyma, the distribution of CRBP-1-expressing HSC was homogeneous. In portal areas, the fibroblastic cells did not express CRBP-1 (Fig.…”

“…Several studies have examined the expression of CRBP-1 in the different cell types of the liver Blomhoff et al, 1985;Kato et al, 1984). Hepatocytes and HSC contain large amounts of CRBP-1.…”

Plasma turnover of 3,4-didehydroretinol (vitamin A2) increases in vitamin A-deficient rats fed low versus high dietary fat

“…Nagy et al (19) reported that very few lipid droplet containing stellate cells were found in the interstitial regions of kidney cortex regardless of whether animals were fed a vitamin Asufficient or excessive diet suggesting that in the vitamin Adeficient rats, little R, RE, and presumably DR and DRE were stored in renal stellate cell lipid droplets. Kato, Kato, and Goodman (53) reported that RBP traveled to the apical portions of the proximal convoluted tubular cells, and this represented RBP that had already undergone glomerular filtration and tubular reabsorption. This report of RBPʼs renal cellular location suggests that R may colocalize there.…”