Biomedical subjects

Tatsuo Sakai

Publications and source records attributed to Tatsuo Sakai.

26 records · Page 2Linked to original sources

PubMed2003

Cloning of rat homologue of podocin: expression in proteinuric states and in developing glomeruli.

Podocin is identified as a product of the gene mutated in a patient with autosomal recessive steroid-resistant nephrotic syndrome. Although podocin is reported to be located at the slit diaphragm area, the precise role of podocin for maintaining the barrier function of the slit diaphragm has not been clearly elucidated. A rat homologue of podocin was cloned, and the expression of podocin was investigated and then compared with the nephrin and the ZO-1 expressions in rat experimental proteinuric models and in developing glomeruli. Amino acid sequences of rat and human podocin are highly homologous (84.3% identity). The domain structure of podocin is also highly conserved between rat and human. The mRNA expression for podocin was detected in glomeruli and the nerve tissues. The localization of podocin has close proximity to that of nephrin in normal adult rat glomeruli. Podocin staining was restricted to the basal side of the podocyte of the early developing stage, whereas nephrin staining was detected on the basolateral surface of podocyte. The redistribution of podocin was observed in the anti-nephrin antibody (ANA)-induced nephropathy and puromycin aminonucleoside (PAN) nephropathy. The redistribution of podocin paralleled with nephrin in ANA nephropathy but not in PAN nephropathy. Podocin is observed at the site of tight junction newly formed in proteinuric state in PAN nephropathy. It is postulated that podocin is one of the critical components of a slit diaphragm for maintaining the barrier function of the glomerular capillary wall.

Aging↗

PubMed2003

Actin filament organization of foot processes in rat podocytes.

The foot processes of podocytes possess abundant microfilaments and modulate glomerular filtration. We investigated the actin filament organization of foot processes in adult rat podocytes and the formation of the actin cytoskeletal system of immature podocytes during glomerulogenesis. Electron microscopy revealed two populations of actin cytoskeletons in foot processes of adult podocytes. One is the actin bundle running above the level of slit diaphragms and the other is the cortical actin network located beneath the plasmalemma. Immunogold labeling for actin-binding proteins demonstrated that alpha-actinin and synaptopodin were localized in the actin bundle, whereas cortactin was in the cortical actin network. Immunofluorescence labeling for actin-binding proteins in immature podocyte showed that alpha-actinin was localized at the level of the junctional complex, whereas cortactin was distributed beneath the entire plasmalemma. Synaptopodin was first observed along the basal plasmalemma from the advanced S-shaped body to the capillary loop stage. We conclude that foot processes have specialized actin filamentous organization and that its establishment is associated with the expression and redistribution of actin-binding proteins during development.

Actin Cytoskeleton↗

PubMed2003

Angiotensin II blockade restores albumin reabsorption in the proximal tubules of diabetic rats.

The kidney plays an important role in protein metabolism. The albumin reabsorption in the proximal tubule is disturbed in the early stage of diabetic nephropathy. We evaluated the effects of angiotensin converting enzyme inhibitor (ACEI) and angiotensin III type 1 receptor blocker (ARB) on albumin reabsorption and expression of megalin, an endocytosis receptor for albumin, in proximal tubules of streptozotocin (STZ)-induced diabetic-rats. Diabetic rats at the second week after STZ injection were treated with quinapril (3 mg/kg/day) or candesartan (0.05 mg/kg/day) for 2 weeks. The tubular reabsorption of fluorescein isothiocyanate (FITC)-labeled albumin was evaluated by immunogold electron microscopy, and megalin expression was investigated by immunohistochemistry and Western blotting. Reabsorption of FITC-labeled albumin and megalin expression were prominently inhibited in the proximal convoluted tubules of diabetic rats compared to the controls. Both quinapril and candesartan restored albumin reabsorption in the proximal tubule due to normalization of megalin expression. Urinary albumin excretion was significantly reduced by both ACEI and ARB treatment. Angiotensin II infusion decreased megalin expression and albumin reabsorption in the proximal tubule. In conclusion, angiotensin II blockade restored albumin reabsorption via amelioration of megalin expression in the proximal tubules of early stage diabetic rats.

Albuminuria↗

PubMed2003

The ultrastructure of periductal connective tissue and distinctive populations of collagen fibrils associated with ductal epithelia of exocrine glands.

The ultrastructure of the connective tissue around the intraglandular ducts was observed in rat exocrine glands. Connective tissue with a dense population of collagen fibrils was found either around the ducts and blood vessels (perivasculoductal connective tissue; PVDCT) as in the lacrimal and salivary glands and liver, or solely surrounding the ducts (periductal connective tissue; PDCT) as in the exocrine pancreas, whereas the interlobular and intralobular interstitium of the glands-except for the liver-contained substantially fluid-filled spaces without collagen fibrils. The PVDCT and PDCT of these glands contained two populations of collagen fibrils-fibroblast-associated and epithelium-associated-although the development and density of these fibrils varied considerably in individual glands. Both populations of collagen fibrils were most developed in the lacrimal glands, in which the basal aspects of the ductal epithelium and the basement membrane showed considerable undulation associated with a distinctive peribasement membrane zone with amorphous matter and a small population of the fibrils. In the parotid and submandibular glands, both populations were distinct, though poorly developed. In the exocrine pancreas and hepatic Glisson's sheath, the two populations of collagen fibrils were moderately developed, and the basal aspects of the ductal epithelium were characterized by prominent invaginations in which the multilaminar basement membranes and the epithelium-associated collagen fibrils were frequently engulfed. These observations provide evidence that the two populations of collagen fibrils around the ducts are found universally in exocrine glands, and support the hypothesis of the collagen fibril-synthesizing and -secreting ability of ductal epithelial cells.

Animals↗

PubMed2003

[Galen " On the anatomy of nerves": Translation from the Greek text and discussion].

Galen's treatise "On the Anatomy of Nerves" was translated literally from the Greek text (Kuhn's edition, vol. 2, pp. 831-856) into Japanese, utilizing the knowledge of anatomy. The previous Latin and English translations, as well as the descriptions of the nervous system in the other Galenic texts such as "Anatomical Procedures" and "On the Usefulness of the Parts of the Body," were utilized as references for the present translation, but it became evident from the present study that the previous translations contained an abundance of immature and erroneous understandings of the Galenic text. The present study has made it clear that the third cranial nerve referred to by Galen contains the most branches of the trigeminal nerve, and that the fourth cranial nerve represents the sympathetic trunk and the palatine nerves. The Galenic texts which were translated into Latin mainly in the 16th century before development of anatomical knowledge contain misunderstandings peculiar to the age. Thus the modern translations inherit some misunderstandings found in those Latin translations. Descriptions in the Galenic "On the Anatomy of Nerves" appear vague at first sight, but the described structures can be identified in most cases without doubt on the basic of anatomical knowledge. Furthermore we can estimate how Galen developed the preceding understanding of the nervous system made by Marinus on the basis of his own observations.

Anatomy↗

PubMed2002

Nectin couples cell-cell adhesion and the actin scaffold at heterotypic testicular junctions.

Actin-based cell-cell adherens junctions (AJs) are crucial not only for mechanical adhesion but also for cell morphogenesis and differentiation. While organization of homotypic AJs is attributed mostly to classic cadherins, the adhesive mechanism of heterotypic AJs in more complex tissues remains to be clarified. Nectin, a member of a family of immunoglobulin-like adhesion molecules at various AJs, is a possible organizer of heterotypic AJs because of its unique heterophilic trans-interaction property. Recently, nectin-2 (-/-) mice have been shown to exhibit the defective sperm morphogenesis and the male-specific infertility, but the role of nectin in testicular AJs has not been investigated. We show here the heterotypic trans-interaction between nectin-2 in Sertoli cells and nectin-3 in spermatids at Sertoli-spermatid junctions (SspJs), heterotypic AJs in testes. Moreover, each nectin-based adhesive membrane domain exhibits one-to-one colocalization with each actin bundle underlying SspJs. Inactivation of the mouse nectin-2 gene causes not only impaired adhesion but also loss of the junctional actin scaffold at SspJs, resulting in aberrant morphogenesis and positioning of spermatids. Localization of afadin, an adaptor protein of nectin with the actin cytoskeleton, is also nectin-2 dependent at SspJs. These results indicate that the nectin-afadin system plays essential roles in coupling cell-cell adhesion and the cortical actin scaffold at SspJs and in subsequent sperm morphogenesis.

Actins↗

PubMed2002

Involvement of ASIP/PAR-3 in the promotion of epithelial tight junction formation.

The mammalian protein ASIP/PAR-3 interacts with atypical protein kinase C isotypes (aPKC) and shows overall sequence similarity to the invertebrate proteins C. elegans PAR-3 and Drosophila Bazooka, which are crucial for the establishment of polarity in various cells. The physical interaction between ASIP/PAR-3 and aPKC is also conserved in C. elegans PAR-3 and PKC-3 and in Drosophila Bazooka and DaPKC. In mammals, ASIP/PAR-3 colocalizes with aPKC and concentrates at the tight junctions of epithelial cells, but the biological meaning of ASIP/PAR-3 in tight junctions remains to be clarified. In the present study, we show that ASIP/PAR-3 staining distributes to the subapical domain of epithelial cell-cell junctions, including epithelial cells with less-developed tight junctions, in clear contrast with ZO-1, another tight-junction-associated protein, the staining of which is stronger in cells with well-developed tight junctions. Consistently, immunogold electron microscopy revealed that ASIP/PAR-3 concentrates at the apical edge of tight junctions, whereas ZO-1 distributes alongside tight junctions. To clarify the meaning of this characteristic localization of ASIP, we analyzed the effects of overexpressed ASIP/PAR-3 on tight junction formation in cultured epithelial MDCK cells. The induced overexpression of ASIP/PAR-3, but not its deletion mutant lacking the aPKC-binding sequence, promotes cell-cell contact-induced tight junction formation in MDCK cells when evaluated on the basis of transepithelial electrical resistance and occludin insolubilization. The significance of the aPKC-binding sequence in tight junction formation is also supported by the finding that the conserved PKC-phosphorylation site within this sequence, ASIP-Ser827, is phosphorylated at the most apical tip of cell-cell contacts during the initial phase of tight junction formation in MDCK cells. Together, our present data suggest that ASIP/PAR-3 regulates epithelial tight junction formation positively through interaction with aPKC.

Adaptor Proteins, Signal Transducing↗

PubMed2002

Fibroblasts and antigen-presenting cells in the renal interstitium of streptozotocin-induced diabetic rats on a high cholesterol diet.

The cortical peritubular interstitium of the normal kidney contains both fibroblasts and antigen-presenting dendritic cells. Characteristics of these interstitial cells were analyzed in an overnutrition model by electron microscopy after the cold-dehydration technique and immunohistochemistry for antigen-presenting cells. In control rats, fibroblasts and dendritic cells were clearly identified by electron microscopy on the basis of their distinct ultrastructures. Fibroblasts possessed slender cell processes, and contained an abundance of actin filament bundles occasionally anchoring to surrounding structures, whereas dendritic cells possessed irregularly-shaped cell processes with a clear cytoplasm and a paucity of actin filament bundles. In the experimental kidney from diabetic rats given a high cholesterol diet, the peritubular interstitium contained fibroblasts and vacuolated cells, and the extracellular matrices such as collagen bundles were distinctly increased compared with the control rat kidney. Immunohistochemical staining with OX6 and ED1 revealed that the peritubular interstitium in the control rat kidney contained dendritic cells, while that in the experimental rats was occupied by macrophages. The present study provides the first evidence indicating that overnutrition may dramatically affect the immune cells in nonlymphoid tissue.

Animals↗