Diagnóstico genético pré-implantacional: uma ferramenta importante para a rotina de fertilização in vitro? / Preimplantation genetic diagnosis: an important tool for the in vitro fertilization routine?

Erros cromossômicos numéricos são comuns durante as primeiras etapas do desenvolvimento embrionário humano, contribuem significativamente com processos de falta de implantação e são causadores da perda gestacional recorrente em pelo menos 50 por cento dos abortos ocorridos no primeiro trimestre. Tradicionalmente, a prevenção das anomalias genéticas cromossômicas em pacientes de alto risco é realizada por exames pré-natais, como a biópsia do vilo coriônico, aminiocentese e a cordocentese. Uma vez diagnosticada a anomalia, não existe tratamento eficaz para portadores de aberrações genéticas e a interrupção da gestação nestes casos ainda é ética e legalmente questionável. O diagnóstico genético pré-implantacional (DGPI) representa uma ferramenta valiosa aos casais de alto risco, por permitir a seleção de embriões saudáveis obtidos através de programas de fertilização in vitro antes de estes serem transferidos para um útero materno. Os primeiros relatos da utilização do DGPI datam da década de 90, quando eram utilizadas metodologias da reação em cadeia da polimerase para determinação do sexo do embrião, permitindo desta maneira transferir embriões que não fossem portadores de doenças ligadas ao cromossomo X. O DGPI é uma técnica extremamente eficaz, que analisa uma única célula do embrião que é biopsiado a partir do terceiro dia de desenvolvimento. Esta metodologia tem como finalidade identificar embriões gerados por processos de reprodução assistida, os quais sejam portadores de aberrações cromossômicas numéricas que envolvam os cromossomos X, Y, 13, 16, 18, 21 e 22. A metodologia mais utilizada para a realização do DGPI é a técnica de hibridização in situ, utilizando-se sondas fluorescentes para os cromossomos citados. Este é um método eficiente e que deve ser discutido com casais cuja idade da mulher seja acima dos 39 anos, casais com cariótipo alterado ou ainda casais com histórico familiar de presença de portadores de cromossomopatias. A eficiência...

The potential transmission of genetic disorders to the offspring has been a major problem for many couples when contemplating pregnancy. Numerical chromosomes errors are common during the first stages of the human embryonic development and contribute significantly with processes of implantation failure and it is also related to recurrent miscarriage, in at least 50 percent of the abortions occurred in the first trimester. Traditionally, the prevention of genetic chromosomal abnormalities in high risk patients is achieved by pre-natal examinations such as biopsy of the chorionic villi, aminiocentese of cordocentesis. Once diagnosed the genetic error, there is no effective treatment for patients with genetic aberrations and the interruption of pregnancy in these cases are ethically and legally questionable. The risk has been greatly decreases by the evaluation of the family history of the age of the mother, and the implementation of prenatal diagnosis in those couples in which the risk was increased compared to the general population. An alternative approach that is available with assisted reproductive technologies is the preimplantation genetic diagnosis (PGD), which it is possible to observe X, Y, 13, 16, 18, 21 and 22 chromosomes or to perform gene screen by PCR for knowing genetic diseases before the corresponding embryo is transferred to the uterus of the mother. PGD was first clinically applied in the early nineties, and was initially used in sexing cases for couples who were at risk of transmitting an X-linked recessive disorder. PGD involves the analysis of either polar bodies, extruded from oocytes during meiosis, or single cells (blastomeres) biopsied from embryos after fertilization. PGD tests have largely focused on two methodologies: fluorescent in situ hybridization and polymerase chain reaction. The efficiency of the method is about 98 percent and its extremely invasive technique demands high level professional.

Tumor necrosis factor-á signaling cascades in apoptosis, necrosis, necroptosis and cell proliferation

Tumor necrosis factor-á (TNF-á) is a multifunctional cytokine involved in host defense, inflammation, apoptosis, autoimmunity, organogenesis and lymphoid microarchitecture. Many of these activities may be explained by the ability of this cytokine to induce distinct signal transduction pathways that recruit regulatory proteins involved in differentiation, cell death or cell proliferation. In this review, we discuss the contribution of caspases -3, -6, -7 and -8, and of cyclin-dependent kinases (CDKs), cyclin B and cyclin-dependent kinase inhibitors (CKI p21 and p27), as well as retinoblastoma tumor suppressor in the signaling cascades triggered by TNF-á to induce apoptosis, necrosis and cellular proliferation in the murine cell lines NIH3T3 and WEHI-164 and the human cervical carcinoma cell line HeLa-S3. Based on the findings of many literature reports and our own data, we discussed a model in which caspases are continuously activated throughout the cell cycle and kept at a critical threshold level by IAP (inhibitor of apoptosis) antagonists. Following the release of Smac/Diablo and HtrA2/OMI from mitochondria in response to diverse stimuli, this threshold is overcome and results in amplified caspase activation and cell death. An alternative, caspase-independent mechanism of cell death is induced in NIH3T3 fi broblasts by a combination of TNF and the pan-caspase inhibitor z-VADfmk. This cell death phenotype, known as necroptosis, displays some morphological features of apoptosis and necrosis. Although caspases are critical regulators of the TNF signaling pathway during cellular life and death, the mechanisms involved in the fine regulation of their dual effects remain to be fully elucidated.