A technique for eliminating allele specific amplification failure during DNA amplification of heterozygous cells for preimplantation diagnosis

Advances in techniques of molecular biology have made possible the amplification of specific genes from single cells. This has a major clinical application in preimplantation diagnosis of monogenic disorders. However, the incidence of allele specific amplification failure (allele drop out) in heterozygous single cells can lead to misdiagnosis and the transfer of affected embryos. Few studies have been done to investigate the actual cause of allele drop out, although some investigators have succeeded in reducing but not eliminating it. Here we report the efficiency of amplifying both alleles in heterozygous cells lysed according to two different protocols. A total of 177 heterozygous cells from carriers of cystic fibrosis (CF) and haemoglobin C (HbC) were lysed using two different lysis buffers. Interestingly none of the cells that were lysed with sodium dodecyl sulphate/proteinase K showed any example of allele specific amplification failure whereas in those lysed by KOH/dithiothreitol it was present in 17.6 and 4.7% of the CF and HbC cells respectively. Our results suggest that the phenomenon of allele specific amplification failure is at least in part dependent on the lysis buffer used.      

Interferon-gamma-Jak-Stat signaling in pulmonary lymphangioleiomyomatosis and renal angiomyolipoma: a potential therapeutic target

Pulmonary lymphangioleiomyomatosis (LAM) and renal angiomyolipoma (AML) are proliferative lesions that occur in sporadic patients, and at much higher frequency in patients with tuberous sclerosis (TSC). The TSC1 and TSC2 genes play a critical role in their pathogenesis. Here we report a marked decrease in interferon (IFN)-gamma expression in both sporadic and TSC-associated AML and LAM. A marked increase in Stat1 expression and phosphorylation at Ser 727, and in phospho-Tyr705-Stat3 levels, was also seen in both AML and LAM tissues. Our results demonstrate that the IFN-gamma-Jak-Stat pathway is perturbed in TSC-related and sporadic LAM and AML, and suggest that IFN-gamma has potential therapeutic benefit for treatment of those lesions.     

Mutation in TSC2 and activation of mammalian target of rapamycin signalling pathway in renal angiomyolipoma

Mutations that inactivate either TSC1 or TSC2 cause tuberous sclerosis. We have used immunoblotting and immunohistochemical analysis to see whether there is phosphorylation of p70 S6 kinase, and the ribosomal S6 protein in angiomyolipomas occurring in tuberous scierosis. Hamartin (encoded by TSC1) and S6K was expressed in all samples. Tuberin (TSC2) was weak or absent in angiomyolipomas, but present in healthy kidney, whereas, phosphorylated p70 S6 kinase and p56 were present only in angiomyolipomas. Our results indicate activation of a mammalian target of rapamycin metabolic pathway in tuberous sclerosis lesions, which contributes to their growth. We suggest that treatment with rapamycin and its analogues could benefit such patients.     

Estrogen enhances whereas tamoxifen retards development of Tsc mouse liver hemangioma: a tumor related to renal angiomyolipoma and pulmonary lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis and abdominal angiomyolipoma are related lesions for which there is no authentic animal model. Both of these proliferative lesions occur in sporadic patients, and at much higher frequency in patients with tuberous sclerosis, which is due to mutations in the TSC1 and TSC2 genes. Tsc1+/- and Tsc2+/- mice frequently develop liver hemangioma. We found that the Tsc mouse liver hemangioma are composed predominantly of endothelial cells but with a smooth muscle component, and express HMB45 antigen, estrogen receptor, and progesterone receptor, similar to lymphangioleiomyomatosis and angiomyolipoma. Estrogen treatment significantly accelerated the development of liver hemangioma in Tsc1+/- female mice, with 91% having liver hemangioma and 55% having severe lesions by 7 months of age. Similarly, an increased frequency and severity of liver hemangiomas was seen in Tsc1+/- males treated with estrogen. In contrast, tamoxifen treatment for 9 months significantly reduced the frequency and severity of hemangiomas in Tsc1+/- female mice. In addition, estrogen treatment significantly increased serum vascular endothelial growth factor levels in Tsc1+/- mice, whereas tamoxifen reduced vascular endothelial growth factor levels. These mouse model observations indicate the importance of estrogen signaling in vivo for the growth of tuberous sclerosis lesions, suggesting the possible benefits of tamoxifen therapy for the treatment of angiomyolipoma and lymphangioleiomyomatosis.     

Loss of Tsc1 or Tsc2 induces vascular endothelial growth factor production through mammalian target of rapamycin

Mutation in either TSC1 or TSC2 causes the autosomal dominant disorder tuberous sclerosis, in which widespread hamartomas are seen, some of which have a high level of vascularization. Tuberous sclerosis complex (TSC) gene products negatively regulate mammalian target of rapamycin (mTOR) activity. We found that vascular endothelial growth factor (VEGF) is secreted by Tsc1- or Tsc2-null fibroblasts at high levels compared with wild-type cells. In Tsc1+/- mice, serum levels of VEGF were increased and appeared to be associated with the extent of tumor development. Rapamycin, a mTOR inhibitor, reduced the production of VEGF by Tsc1- and Tsc2-null fibroblasts to normal levels. Moreover, short-term treatment of Tsc1+/- mice with rapamycin at 20 mg/kg led to some changes in tumor morphology and a reduction in serum VEGF levels. These observations have three implications. First, TSC gene products regulate VEGF production through a mTOR signaling pathway. Second, serum VEGF levels may be a useful clinical biomarker to monitor the progression of TSC-associated lesions. Last, rapamycin or related inhibitors of mTOR may have therapeutic benefit in TSC both by direct tumor cell killing and by inhibiting the development of TSC lesions through impairment of VEGF production.     

Efficacy of a rapamycin analog (CCI-779) and IFN-gamma in tuberous sclerosis mouse models

Tuberous sclerosis complex (TSC) is a familial tumor disorder for which there is no effective medical therapy. Disease-causing mutations in the TSC1 or TSC2 gene lead to increased mammalian target of rapamycin (mTOR) kinase activity in the conserved mTOR signaling pathway, which regulates nutrient uptake, cell growth, and protein translation. The normal function of TSC1 and TSC2 gene products is to form a complex that reduces mTOR kinase activity. Thus, mTOR kinase inhibition may be a useful targeted therapeutic approach. Elevated interferon-gamma (IFN-gamma) expression is associated with decreased severity of kidney tumors in TSC patients and mouse models; therefore, IFN-gamma also has therapeutic potential. We studied cohorts of Tsc2+/- mice and a novel mouse model of Tsc2-null tumors in order to evaluate the efficacy of targeted therapy for TSC. We found that treatment with either an mTOR kinase inhibitor (CCI-779, a rapamycin analog) or with IFN-gamma reduced the severity of TSC-related disease without significant toxicity. These results constitute definitive preclinical data that justify proceeding with clinical trials using these agents in selected patients with TSC and related disorders.