Postoperative fibromatosis-type fibromas in the Bhd gene mutant (Nihon) rat.

Fibromatosis-type fibromas were found to develop at abdominal surgical sites in 4 heterozygous Nihon rats, a model for the human Birt-Hogg-Dubé syndrome. In all 4 rats, solitary and firm nodules were located within the lateral abdominal musculature involving the full thickness of the abdominal wall at the sites of laparotomy. Histologically, the nodules consisted of well-differentiated fibroblastic spindle-shaped cells. These cells were surrounded by large amounts of collagen fibers, and appeared to infiltrate within the abdominal musculature. A portion of the spindle-shaped cells showed features of myofibroblasts. These characteristics are consistent with desmoid tumors in human. Although the etiology of desmoid tumors in human remains unclear, they are known to occur in association with hormonal factors, surgical trauma, and familial adenomatous polyposis. In animals, they have been reported in dogs, cats, horses, and genetically modified mouse models for human familial adenomatous polyposis. The development of the tumors in the Nihon rats was apparently associated with surgical incisions. Genetic factor should be involved in the occurrence of the tumor, since it was found only in the Nihon rats among many rats. Our present data suggest that Bhd gene mutation is not likely to be a candidate.

Natural history of the Nihon (Bhd gene mutant) rat, a novel model for human Birt-Hogg-Dubé syndrome.

In the Nihon rat, an established model of hereditary renal cell carcinoma (RCC), the propensity for tumor development, is inherited as an autosomal dominant trait due to a single germline nucleotide insertion mutation in the rat Bhd ortholog. The Birt-Hogg-Dubé (BHD) syndrome is a rare autosomal dominant disease characterized by fibrofolliculoma, pulmonary cysts, spontaneous pneumothorax, and renal neoplasm. The renal lesions of the Nihon rat are characterized, and extrarenal lesions are also described in this work. The earliest lesion of the RCC was identified as an altered tubule at as early as 3 weeks of age and rapidly progressed through adenoma to carcinoma with the primary cell type being clear/acidophilic where some similarities were evident to RCCs in BHD syndrome. The Nihon rats demonstrate a heterotopic ossification within RCCs and three extrarenal lesions, clear cell hyperplasia/adenoma of the endometrium, clear cell change of the epithelium of striated portions of salivary glands, and cardiac rhabdomyomatosis. This rat model of hereditary RCC provides a useful tool for analyzing the series of events leading to renal tumorigenesis and for studying BHD gene functions.

Gene expression analysis of the rat testis after treatment with di(2-ethylhexyl) phthalate using cDNA microarray and real-time RT-PCR.

To investigate the effects of di(2-ethylhexyl) phthalate (DEHP) on gene expression in rat testis, 6-week-old male Sprague-Dawley rats were given a single oral dose of 20 or 2000 mg/kg and euthanized 3, 6, 24, or 72 h thereafter. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells were significantly increased in the testis at 24 and 72 h after the exposure to 2000 mg/kg of DEHP. On cDNA microarray analysis, in addition to apoptosis-related genes, genes associated with atrophy, APEX nuclease, MutS homologue (E. coli), testosterone-repressed-prostatic-message-2 (TRPM-2), connective tissue growth factor, collagen alpha 2 type V, and cell adhesion kinase were differentially expressed. To investigate the relationship between histopathological alteration and gene expression, we selected genes associated with apoptosis and analyzed their expression by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). With 20 mg/kg of DEHP treatment, bcl-2, key gene related to apoptosis, was increased. Up-regulation of bcl-2, inhibitor of Apaf-1/caspase-9/caspase-2 cascade of apoptosis, may be related to the fact that no morphological apoptotic change was induced after dosing of 20 mg/kg DEHP. With 2000 mg/kg of DEHP treatment, the apoptotic activator cascade, Fas/FasL, FADD/caspase-8/caspase-3 cascade, and Apaf-1/caspase-9/caspase-2 cascade were increased and bcl-2 was decreased. Thus, these gene regulations might lead the cells into apoptosis in the case of high exposure to DEHP. In contrast, FADD/caspase-10/caspase-6 cascade and caspase-11/caspase-3 cascade were not increased. These results indicate that the cascades of FADD/caspase-10/caspase-6 and caspase-11/caspase-3 are not related to apoptosis with DEHP treatment.

Mechanism of clobazam-induced thyroidal oncogenesis in male rats.

In order to elucidate the mechanisms by which long-term treatment with clobazam (CLB), 1,5-benzodiazepine, induces thyroid follicular cell tumors in male rats, male Sprague-Dawley (SD) rats were treated orally with 400 mg/kg of CLB for up to 4 weeks, and the contribution of feedback through elevated thyroid stimulating hormone (TSH) was investigated. Measurements taken after 1, 2, and 4 weeks of treatment revealed that thyroxine (T4)-UDP-glucuronosyltransferase (T4-UDPGT) activity was higher than that of untreated animals. This change was accompanied by increase in liver weights and centrilobular hepatocyte hypertrophy. In addition, plasma total triiodothyronine (T3) and T4 levels were lower than in the untreated rats when measured after 1 week of treatment. However, a high plasma TSH level was sustained throughout the 4-week treatment. Thyroid follicular cell hypertrophy began after 1 week of treatment, followed by increased thyroid weight after 2 weeks. Clearance of exogenous [125I] T4 from the blood of treated rats, determined after 4 weeks of treatment, was significantly faster than that in untreated rats, whereas iodine uptake and organification in the thyroid glands were not affected. These results suggest that CLB increases hepatic T4-UDPGT activity leading to acceleration of T4-clearance, which results in decreased plasma thyroidal hormones followed by compensatory increase of TSH biosynthesis and secretion. Chronic high levels of TSH would exert a continuous growth pressure on the thyroid, under which hypertrophic follicular cells can ultimately progress to frank neoplasms.