Congenic strain differences of renal malformations in ACI/Mna rats by introgression of the chromosomal region of BUF/Mna rats containing Pur1.

The ACI rats developed hereditary renal malformations including agenesis and hydronephrosis at moderate penetrance. During construction of a variety of congenic strains based on ACI/Mna (ACI), BUF/Mna (BUF), and WKY/NCrj (WKY) rats, we found that the renal malformations were significantly suppressed by introgression of a segment of chromosome 13 of BUF rats containing Pur1 locus. It is plausible that this region contain a modifier locus influencing development of renal malformations.

Phosphate overload induces podocyte injury via type III Na-dependent phosphate transporter.

Uptake of P(i) at the cellular membrane is essential for the maintenance of cell viability. However, phosphate overload is also stressful for cells and can result in cellular damage. In the present study, we investigated the effects of the transgenic overexpression of type III P(i) transporter Pit-1 to explore the role of extracellular P(i) in glomerular sclerosis during chronic renal disease. Pit-1 transgenic (TG) rats showed progressive proteinuria associated with hypoalbuminemia and dyslipidemia. Ultrastructural analysis of TG rat kidney by transmission electron microscopy showed a diffuse effacement of the foot processes of podocytes and a thickening of the glomerular basement membrane, which were progressively exhibited since 8 wk after birth. TG rats died at 32 wk of age due to cachexia. At this time, more thickening of the glomerular basement membrane and segmental sclerosis were observed in glomeruli of the TG rats. Immunohistochemical examination using anti-connexin 43 and anti-desmin antibodies suggested the progressive injury of podocytes in TG rats. TG rats showed higher P(i) uptake in podocytes than wild-type rats, especially under low P(i) concentration. When 8-wk-old wild-type and TG rats were fed a 0.6% normal phosphate (NP) or 1.2% phosphate (HP) diet for 12 wk, HP diet-treated TG rats showed more progressive proteinuria and higher serum creatinine levels than NP diet-treated TG rats. In conclusion, our findings suggest that overexpression of Pit-1 in rats induces phosphate-dependent podocyte injury and damage to the glomerular barrier, which result in the progression of glomerular sclerosis in the kidney.

Cervical thymuses exist, but no cervical thymomas develop in thoracic thymoma-prone BUF rats.

To confirm the existence of the cervical thymus and the development of cervical thymoma in thymoma-prone BUF/Mna (BUF) rats, we examined cervical organs and adjacent tissues, and thoracic thymic tissues of the three inbred strains, BUF, ACI/NMna (ACI), and WKY/NCrj (WKY), and 11 congenic strains, in which genetic regions of rat nude (Rnu), thymus enlargement-1 and thymus enlargement-2 (Ten1 and Ten2), thymoma susceptibility of rat-1 (Tsr1), atrophy of fast-twitch muscles-1 (Aftm1) and proteinuria of rat-1 (Pur1) were transferred into BUF, ACI or WKY rats. These organs and tissues were fixed en block in 10% formalin and cut coronally into four to six slices of 3-mm thickness, depending on the age of the rat, and embedded together in one block for each rat. Sections were cut and stained with haematoxylin and eosin and examined microscopically. Cervical thymuses were detected in 12-21% of rats from these inbred and congenic strains. No cervical thymuses were found in BUF-Rnu/Rnu rats, which were athymic. All of 42 BUF, 2 of 55 BUF-Rnu/+ and 28 of 33 ACI-Tsr1/Tsr1 rats survived more than 52 weeks, and developed thoracic thymoma, but no cervical thymomas did. It is therefore clear that cervical thymuses behave differently from thoracic thymuses in spontaneous thymomagenesis in BUF rats.

Hepatocellular carcinoma arising from ectopic liver tissue in the spleen producing insulin-like growth factor II.

We report a case of splenic tumor associated with severe hypoglycemia. The patient was a 69-year-old man with a large splenic tumor. He had suffered from relapsing hypoglycemic attacks and the lowest serum glucose level (4 mg/dl). He died 34 months after the onset of symptoms of left abdominal pain. Autopsy revealed large tumors in the spleen, 3 medium sized tumors in the lungs, and several small tumors in the liver. Microscopic studies of the splenic tumors revealed a hepatocellular carcinoma which showed a strongly positive reaction against anti-PIVKA-II and anti-"hepatocyte" antibodies. Several bile ductules thought to be heterotopic remnants of the liver tissues were found in the capsule of the spleen, adjoining the splenic tumor. It was suggested that the tumor originated from one of these ductules. Electron microscopic analysis showed numerous endocrine-like granules of every tumor cell, and 87-165 times stronger mRNA expression of insulin-like growth factor-II was measured in the tumor tissues when compared with normal liver tissue. Owing to these results, we believe that this is the first report of hepatocellular carcinoma that had developed from a liver tissue in the spleen.

Characterization of T cell maturity in thymic epithelial cell tumors from BUF/Mna spontaneous thymoma rats and BUF/Mna-Rnu/+ rats showing delayed thymomagenesis.

BUF/Mna rats develop thymomas spontaneously, which histologically mimic human thymomas. Although neoplasms in this rat strain contain a large number of immature lymphocytes, the phenotype has not been sufficiently assessed. We characterized T cell phenotypes in tumors from BUF/Mna rats in the present study. We also analyzed BUF/Mna-Rnu/+ rats, a heterozygous strain with suppressive thymomagenesis, and compared the histology and T cell maturation with those from the BUF/Mna rats. A total of 11 BUF/Mna and 10 BUF/Mna-Rnu/+ rats were used. Three-color flow cytometry was performed with anti-CD3, CD4, and CD8 antibodies to identify infiltrated lymphocytes, while tumor histology was evaluated with hematoxylin-eosin staining. The weight ratios of the entire thymic tissue including thymoma as compared to the BUF/Mna and BUF/Mna-Rnu/+ rat bodies were 0.8+/-0.8% and 1.2+/-1.8%, respectively. Histological findings for both rat congenic strains showed abundant lymphocytes surrounding large polygonal neoplastic thymic epithelia, which was compatible with the type B1 classification of the World Health Organization for human thymoma. CD4+CD8+ T cells accounted for 73.7+/-8.0% of the cells in tumors from BUF/Mna and 67.2+/-9.4% in those from BUF/Mna-Rnu/+ rats. Further, CD3-CD4-CD8+ T cells, intermediate between CD4-CD8-and CD4+CD8+ cells, accounted for 47.7+/-17.5% and 38.0+/-14.0% of the cells in tumors from the BUF/Mna and BUF/Mna-Rnu/+ strains, respectively. Thus, the proportion of developing thymic lymphocytes in and histology of thymomas from BUF/Mna and BUF/Mna-Rnu/+ rats were similar. These results suggest that both BUF/Mna and BUF/ Mna-Rnu/+ strains are suitable animal models for human thymoma to understand the development of immature thymic lymphocytes.

Establishment of thymoma-prone congenic rat strain, ACI.BUF/Mna-Tsr1/Tsr1.

PURPOSE: To confirm the presence of the susceptible gene for the thymoma development in the region that was assumed by the previous linkage study by Oyabu et al. (J Natl Cancer Inst 91:279-282, 1999), we tried to establish a congenic strain of rats. METHODS: Backcrossings between the BUF/Mna strain as a donor strain and the ACI/NMna strain as an inbred partner were repeated for 12 generations, examining whether rats had the thymoma development region, and then homozygous rats were yielded by mating among the heterozygotes. To detect the phenotypic expression, heterozygous ACI.BUF/Mna-Tsr1/+ (ACI-Tsr1/+) rats were generated by crossing female ACI.BUF/Mna-Tsr1/Tsr1 (ACI-Tsr1/Tsr1) rats with male ACI/NMna rats and were maintained for 24 months. RESULTS: These ACI-Tsr1/+ rats produced thymoma in 71%, showing a dominant trait. The thymomas were of the lymphocyte predominant type, as those developed in rats of the original BUF/Mna strain. CONCLUSIONS: Thus, a new rat congenic strain, ACI-Tsr1/Tsr1, was established, revealing that thymoma develops in the dominant trait in ACI-Tsr1/+ rats.

Actin -related protein 3 (Arp3) is mutated in proteinuric BUF/Mna rats.

The BUF/Mna strain of rat is a model of focal and segmental glomerulosclerosis (FSGS) in which a quantitative trait locus (QTL) for proteinuria, Pur1, has been identified. The aim of the present study was to identify candidates for the Pur1 gene. To narrow the Pur1 QTL, we performed fine QTL mapping and single nucleotide polymorphism (SNP) genotyping. To identify candidate genes, sequencing and gene-expression analyses of all genes contained in the narrowed locus were conducted. The narrowed Pur1 region contained 25 genes. Among these genes, only the Arp3 gene was mutated in the BUF/Mna strain; it contained a missense mutation that caused an (L)111(F) substitution. This leucine is conserved across species. Gene-expression analysis failed to identify any other candidate genes for Pur1. Arp3-mediated actin assembly abnormalities were visible in immunohistochemical and electron microscopic examinations of podocytes in old BUF/Mna rats. Taken together, these data suggest that Arp3 is a candidate for the Pur1 gene. This observation is consistent with our growing recognition that abnormal signaling-induced assembly of actin in podocytes leads to the development of FSGS.

Composite tumor of mucinous cystadenoma and somatostatinoma of the kidney.

Approximately 30 cases of carcinoid tumor of the kidney have been reported in the English literature, including three cases found as components of teratomas. Renal composite tumors associated with somatostatinoma have not been described. A 53-year-old female presented with an incidentally found right renal cystic lesion. Computed tomography demonstrated a cystic lesion associated with a solid nodule in the right kidney and postcontrast dynamic MRI revealed enhancement of the solid nodule. The patient underwent radical nephrectomy for the kidney lesion and is now well without recurrence 21 months after the operation. From the histopathological findings we diagnosed the cystic lesion as a composite tumor composed of mucinous cystadenoma and carcinoid tumor. Immunohistochemistry demonstrated the majority of cells of in carcinoid portion to be positive for antisomatostatin staining. The present case is the first documented composite tumor of mucinous cystadenoma and somatostatinoma of the kidney.