Biomedical subjects

Akito Maeshima

Publications and source records attributed to Akito Maeshima.

13 recordsLinked to original sources

PubMed2005

Involvement of renal progenitor tubular cells in epithelial-to-mesenchymal transition in fibrotic rat kidneys.

Renal progenitor tubular cells (label-retaining cells [LRC]) were recently identified in normal kidneys by in vivo bromodeoxyuridine (BrdU) labeling. This study was conducted to examine the behavior of LRC in renal fibrosis. BrdU was injected intraperitoneally into normal rats daily for 7 d. After a 2-wk chase period, unilateral ureteral obstruction (UUO) was induced in these rats. In normal and contralateral kidneys, LRC were observed scattering among tubular epithelial cells. After UUO, the number of the LRC significantly increased, and most of them were positive for proliferating cell nuclear antigen (PCNA). In contrast, PCNA+ cells lacking BrdU label were rarely observed. It is interesting that LRC were detected not only in tubules but also in the interstitium after UUO. Laminin staining showed that a number of the LRC were adjacent to the destroyed tubular basement membrane. Some tubules, including LRC, lost the expression of E-cadherin after UUO. A large number of cell populations expressed vimentin, heat shock protein 47, or alpha-smooth muscle actin in the UUO kidneys, and each population contained LRC. None of the LRC was positive for these fibroblastic markers in contralateral kidneys. When renal tubules from BrdU-treated rats were cultured in the gel, some cells protruded from the periphery of the tubules and migrated into the gel. Most of these cells were BrdU+. Neither the total content of BrdU in the kidneys nor the number of LRC in bone marrow significantly changed after UUO. Collectively, these results suggest that LRC is a cell population that proliferates, migrates, and transdifferentiates into fibroblast-like cells during renal fibrosis.

Animals↗

PubMed2004

Crucial role of activin a in tubulogenesis of endothelial cells induced by vascular endothelial growth factor.

The present study was conducted to elucidate the role of activin A in tubulogenesis of vascular endothelial cells. Activin A was produced in bovine aortic endothelial cells (BAEC). These cells also expressed the type I and type II activin receptors. When added to BAEC cultured in a collagen gel, activin A induced capillary formation. Activin A was as potent as vascular endothelial growth factor (VEGF) and markedly enhanced VEGF-induced tubulogenesis. To examine the role of endogenous activin A, we added follistatin, an inhibitor of activin A. Follistatin nearly completely blocked the VEGF-induced tubulogenesis, and the effect of follistatin was reproduced by transfection of the dominant-negative type II activin receptor gene. In BAEC, activin A increased the expression of VEGF and the VEGF receptors, Flt-1 and Flk-1. On the other hand, VEGF increased the production of activin A. Finally, addition of follistatin, which blocks the action of endogenous activin A, reduced the expression of Flt-1 and Flk-1. These results indicate that an autocrine factor activin A amplifies the effect of VEGF by up-regulating VEGF and its receptors. This effect of activin A is critical in the VEGF-induced tubulogenic morphogenesis in BAEC.

Activin Receptors↗

PubMed2004

Assessment of the function of the betaC-subunit of activin in cultured hepatocytes.

We assessed the function of the beta(C)-subunit of activin in hepatocytes. We studied the effect of conditioned medium of Chinese hamster ovary (CHO) cell line stably expressing the beta(C) gene (CHO-beta(C)) on growth of AML12 hepatocytes. We also examined the effect of recombinant activin C and transfection of the beta(C) gene by using adenovirus vector. CHO-beta(C) secreted activin C, a homodimer of the beta(C), as well as precursors of the beta(C). The conditioned medium of CHO-beta(C) increased both [(3)H]thymidine incorporation and the cell number in AML12 cells. It also supported survival of AML12 cells in a serum-free condition. Recombinant human activin C also increased both [(3)H]thymidine incorporation and the number of AML12 cells. Transfection of AML12 cells with the beta(C)-subunit led to the stimulation of [(3)H]thymidine incorporation. Analysis of the conditioned medium revealed that the beta(C)-subunit formed a heterodimer with the endogenous beta(A), the formation of which was dependent on the amount of beta(C) expressed. Recombinant activin C did not affect the binding of (125)I-activin A to its receptor or follistatin. These results indicate that activin C stimulates growth of AML12 cells. The beta(C)-subunit modifies the function of the beta(A)-subunit by multiple mechanisms.

Animals↗

PubMed2004

Activin A is a potent activator of renal interstitial fibroblasts.

The present study was conducted to examine the involvement of the activin-follistatin system in the fibrotic process of the kidney. Immunoreactive activin A was upregulated in tubular cells in the kidneys with unilateral ureteral obstruction but not in normal and contralateral kidneys. Activin A promoted cell proliferation, enhanced the expression of type I collagen mRNA, and induced the production of alpha-smooth muscle actin in a rat kidney fibroblast cell line (NRK-49F cells) as well as in primary cultured renal interstitial fibroblasts. In contrast, activin A did not affect the expressions of alpha-smooth muscle actin and type I collagen in renal epithelial tubular cell lines LLC-PK1, and MDCK. Follistatin, an antagonist of activin A, significantly inhibited cell proliferation in NRK-49F cells. Blockade of activin signaling by overexpression of truncated type II activin receptor, which lacked the intracellular kinase domain, decreased cell proliferation and reduced the expression level of type I collagen mRNA in NRK-49F cells. The expression of activin A was induced by TGF-beta 1 or activin A itself. Induction of type I collagen expression by TGF-beta 1 was reduced by follistatin or by overexpression of truncated type II activin receptor. These results suggest that activin A produced by tubular cells acts as a paracrine factor that activates renal interstitial fibroblasts during the fibrotic processes of the kidney.

Activins↗

PubMed2004

Fluvastatin reduces renal fibroblast proliferation and production of type III collagen: therapeutic implications for tubulointerstitial fibrosis.

BACKGROUND: Accumulating evidence suggests that hydroxymethylglutaryl-CoA reductase inhibitors have many biological effects beyond reducing cholesterol synthesis. In a mouse model of renal interstitial fibrosis induced by unilateral ureteral obstruction, fluvastatin, one of the lipophilic hydroxymethylglutaryl-CoA reductase inhibitors, was shown to ameliorate fibrosis. METHODS: In the present study, we examined the direct effects of fluvastatin on proliferation, matrix and growth factor production by rat kidney fibroblasts (NRK-49F cells). RESULTS: Treatment with fluvastatin reduced proliferation of NRK-49F cells in a dose-dependent manner. The addition of mevalonate or geranylgeranyl pyrophosphate but not farnesyl pyrophosphate to the culture medium almost completely abolished the effect of fluvastatin. Moreover, fluvastatin treatment decreased the expression of activated Rho in NRK-49F cells suggesting that fluvastatin may decrease cell growth through blocking the activation of Rho. The majority of fluvastatin-treated cells were arrested at the G1 phase, associated with down-regulation of cyclin A and up-regulation of cyclin-dependent kinase inhibitor p27kip1, indicating that cell cycle modulation is an important mechanism. Fluvastatin significantly decreased messenger RNA expression of type III collagen and connective tissue growth factor. CONCLUSIONS: Taken together, it is suggested that fluvastatin may prevent tubulointerstitial fibrosis in a variety of progressive renal diseases by inhibiting proliferation of interstitial fibroblasts and their matrix synthesis.

Acute-Phase Proteins↗

PubMed2004

[Activin].

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Activins↗

PubMed2003

Activin A induces cell proliferation of fibroblast-like synoviocytes in rheumatoid arthritis.

OBJECTIVE: To investigate the expression of activin A and its receptors in rheumatoid arthritis (RA) synovial tissues, and to determine the effect of activin A on cultured fibroblast-like synoviocytes (FLS). METHODS: The localization of activin A and activin type II receptor (ARII) in synovial tissues of RA patients was analyzed by immunohistochemistry. The expression of activin A and activin receptors in human cultured FLS was examined by reverse transcriptase-polymerase chain reaction and Western blotting. Enzyme-linked immunosorbent assay was used to measure activin A in culture supernatants. The cell growth of FLS was determined by (3)H-thymidine incorporation and MTT assay. RESULTS: Immunohistochemical analysis confirmed the up-regulation of activin A in rheumatoid synovium as compared with osteoarthritis or normal joint tissues. CD68+ macrophage-lineage cells and vimentin-positive FLS were identified as activin-producing cells in rheumatoid synovium. Both cell types also expressed ARII. The expression of activin A and ARII on cultured FLS was confirmed at the protein and messenger RNA levels. Interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, and transforming growth factor beta activated FLS to secrete activin A. Recombinant activin A accelerated the proliferation of FLS, while follistatin, an endogenous activin antagonist, partially inhibited FLS proliferation induced by IL-1 beta. CONCLUSION: These results suggest that activin A acts as a growth factor of FLS in RA.

Activin Receptors↗

PubMed2003

Activin a produced by ureteric bud is a differentiation factor for metanephric mesenchyme.

The present study was conducted to investigate the role of the activin-follistatin system in the development of metanephros. Organ culture system and cultured metanephric mesenchymal cells were used to address this issue. Activin A was localized in ureteric bud. Activin type II receptor was localized in ureteric bud as well as metanephric mesenchyme. In an organ culture system, exogenous activin A reduced the size of cultured metanephroi, delayed ureteric bud branching, and enlarged the tips of ureteric bud. Follistatin, an antagonist of activin A was used to clarify the role of endogenous activin A. Exogenous follistatin enlarged the size of cultured metanephroi, increased ureteric bud branching, and promoted cell growth in ureteric bud. Blockade of activin signaling by adenoviral transfection of dominantly negative activin mutant receptor mimics the effect of follistatin. In cultured metanephric mesenchymal cells, activin A promoted cell growth; conversely, follistatin induced apoptosis. Furthermore, activin A induced the expressions of epithelial differentiation markers in these cells. These results suggest that activin A produced by ureteric bud is not only an important regulator of ureteric bud branching, but also a differentiation factor for metanephric mesenchyme during kidney development.

Activin Receptors↗

PubMed2003

Identification of renal progenitor-like tubular cells that participate in the regeneration processes of the kidney.

The present study was conducted to explore renal progenitor-like cells that are actively engaged in tubular regeneration after injury. For addressing this issue, the existence of label-retaining cells (LRC; slow-cycling cells) in normal rat kidneys by in vivo bromodeoxyuridine (BrdU) labeling was examined. LRC were scattering among renal epithelial tubular cells of normal rat kidneys. During the recovery after renal ischemia, LRC underwent cell division and most of them became positive for proliferating cell nuclear antigen. In contrast, proliferating cell nuclear antigen-positive but BrdU-negative tubular cells were rarely observed, suggesting that cells proliferating during tubular regeneration are essentially derived from LRC. At an early phase of tubular regeneration, descendants of LRC expressed a mesenchymal marker, vimentin, and eventually became positive for an epithelial marker, E-cadherin, after multiple cell divisions. These findings suggested that LRC function as a source of regenerating cells to replace injured cells. Collectively, it was concluded that LRC are renal progenitor-like tubular cells that provide regenerating cells, which actively proliferate and eventually differentiate into epithelial cell, during tubular regeneration. It may be possible to regenerate renal tubules in vivo through the activation of LRC.

Animals↗

PubMed2002

Activin A: an autocrine regulator of cell growth and differentiation in renal proximal tubular cells.

BACKGROUND: Activin A is involved in tubular regeneration after ischemia/reperfusion injury. The present study was conducted to examine the role of activin A in cell growth, apoptosis and differentiation of tubular cells. METHODS: We performed cell proliferation assays (MTT assay, [3H]-thymidine incorporation) and apoptosis detection assays (nuclear staining, DNA ladder formation, TUNEL staining) using LLC-PK1 cells. Expression of activin and activin receptor in LLC-PK1 cells also were examined by real-time polymerase chain reaction (PCR) and immunostaining. Stable cell lines expressing the truncated type II activin receptor were generated and the phenotype of these cells was analyzed. RESULTS: Activin A inhibited DNA synthesis and cell growth in a dose-dependent manner and induced apoptosis in LLC-PK1 cells. The expression level of mRNA for the activin betaA subunit was markedly increased when the growth was stimulated. The expression of the type II activin receptor was observed in LLC-PK1 cells. The growth rate of cells expressing dominantly negative activin receptor was significantly faster than that of non-transfected cells. The expression level and pattern of cytokeratin and vimentin in these cells were quite different compared to non-transfected cells. When cultured in collagen gel, these cells formed multiple processes, which was not observed in non-transfected cells. Finally, the expression of Pax-2 was markedly elevated in these cells. CONCLUSIONS: Activin A acts as an autocrine inhibitor of cell growth, an inducer of apoptosis, and an important modulator of differentiation in cultured proximal tubular cells.

Activin Receptors, Type II↗

PubMed2002

Involvement of Pax-2 in the action of activin A on tubular cell regeneration.

It has been recently shown that in ischemic rat kidneys activin A is induced in tubular cells and inhibits their regeneration. The present study was conducted to further investigate the action of activin A in tubular cells during regeneration. Among genes thought to be critical for kidney development, Pax-2 was upregulated in tubular cells during regeneration after renal ischemia. Pax-2 protein was localized in nuclei of tubular and interstitial cells, some of which co-expressed a mesenchymal cell marker, vimentin, suggesting that a population of Pax-2-positive cells have properties of immature progenitor-like tubular cells. The Pax-2-expressing cells co-expressed a cell proliferation marker, BrdU, activin A, and the type II activin receptor. Activin A modulated growth of BrdU/Pax-2 double-positive cells since an administration of follistatin increased; conversely, exogenous activin A decreased the number of BrdU/Pax-2 double-positive cells after renal ischemia. Activin A also reduced the expression of Pax-2 in cultured metanephroi. A proximal tubular cell line, LLC-PK(1) cells, was used to further study the mode of action of activin A. The expression of Pax-2 was not detected in quiescent LLC-PK(1) cells, but it was markedly increased when growth was stimulated. Under this condition, activin A significantly inhibited DNA synthesis and reduced the expression of Pax-2 in LLC-PK(1) cells. In contrast, blockade of the activin signaling by overexpressing dominantly negative mutant receptor enhanced the expression level of Pax-2 in LLC-PK(1) cells and induced an immature phenotype. These results suggest that activin A regulates tubular cell growth and differentiation by modulating the expression of Pax-2 during regeneration.

Activin Receptors, Type II↗

PubMed2002

Up-regulation of the expression of activins in the pancreatic duct by reduction of the beta-cell mass.

Activins expressed in progenitor cells of the pancreas regulate differentiation of endocrine cells during development. Neogenesis of beta-cells takes place in adult animals under some conditions, and beta-cells are thought to arise from precursors locating in the pancreatic duct. In the present study, we investigated whether or not activins are expressed in the duct where beta-cell neogenesis is initiated. mRNA for the beta(A)- and beta(B)-subunits was expressed in isolated mouse pancreatic ducts. Immunohistochemically, the beta(A)-subunit was detected in the pancreatic duct and colocalized with cytokeratin, a marker of ductal cells. The beta(A)-subunit was also expressed in nestin-positive cells in the duct. Likewise, the beta(B)-subunit was detected in the pancreatic duct. In addition, mRNA for the type II and type IIB activin receptors was expressed in the duct. Expression of mRNA for two activin subunits was markedly increased after streptozotocin injection. Similarly, the mRNA expression was up-regulated after partial pancreatectomy. These results indicate that activins are expressed in the pancreatic duct and are up-regulated shortly after the reduction of the beta-cell mass. Induction of activins in the duct may be a critical step in the initiation of beta-cell neogenesis.

Activin Receptors↗

PubMed2001

Involvement of the activin-follistatin system in tubular regeneration after renal ischemia in rats.

This study was conducted to investigate the involvement of the activin-follistatin system in renal regeneration after ischemic injury. Expression of mRNA for the activin beta(A) subunit was not detected in normal kidneys but increased markedly after renal ischemia. Immunoreactive beta(A) subunit was detected in tubular cells of the outer medulla in ischemic but not normal kidneys. Expression of mRNA for follistatin, an antagonist of activin A, was abundant in tubular cells of the outer medulla in normal kidneys and decreased significantly after renal ischemia. For assessment of the role of the activin-follistatin system in renal regeneration after ischemic injury, recombinant follistatin was intravenously infused into rats with renal ischemia, at the time of reperfusion. Exogenous follistatin prevented the histologic changes induced by ischemic injury, reduced apoptosis in tubular cells, and accelerated tubular cell proliferation. Serum levels of creatinine and blood urea nitrogen were significantly lower in follistatin-treated rats. Conversely, intravenous administration of recombinant activin A inhibited tubular cell proliferation after ischemic injury. These results indicate that the activin-follistatin system participates in renal regeneration after ischemic injury. Follistatin administered intravenously accelerates renal regeneration after renal ischemia, presumably by blocking the actions of endogenous activin.

Activin Receptors↗