Role of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission in oxygen sensing and constriction of the ductus arteriosus.

RATIONALE: Closure of the ductus arteriosus (DA) is essential for the transition from fetal to neonatal patterns of circulation. Initial PO2-dependent vasoconstriction causes functional DA closure within minutes. Within days a fibrogenic, proliferative mechanism causes anatomic closure. Though modulated by endothelial-derived vasodilators and constrictors, O2 sensing is intrinsic to ductal smooth muscle cells and oxygen-induced DA constriction persists in the absence of endothelium, endothelin, and cyclooxygenase mediators. O2 increases mitochondrial-derived H2O2, which constricts ductal smooth muscle cells by raising intracellular calcium and activating rho kinase. However, the mechanism by which oxygen changes mitochondrial function is unknown. OBJECTIVE: The purpose of this study was to determine whether mitochondrial fission is crucial for O2-induced DA constriction and closure. METHODS AND RESULTS: Using DA harvested from 30 term infants during correction of congenital heart disease, as well as DA from term rabbits, we demonstrate that mitochondrial fission is crucial for O2-induced constriction and closure. O2 rapidly (<5 minutes) causes mitochondrial fission by a cyclin-dependent kinase- mediated phosphorylation of dynamin-related protein 1 (Drp1) at serine 616. Fission triggers a metabolic shift in the ductal smooth muscle cells that activates pyruvate dehydrogenase and increases mitochondrial H2O2 production. Subsequently, fission increases complex I activity. Mitochondrial-targeted catalase overexpression eliminates PO2-induced increases in mitochondrial-derived H2O2 and cytosolic calcium. The small molecule Drp1 inhibitor, Mdivi-1, and siDRP1 yield concordant results, inhibiting O2-induced constriction (without altering the response to phenylephrine or KCl) and preventing O2-induced increases in oxidative metabolism, cytosolic calcium, and ductal smooth muscle cells proliferation. Prolonged Drp1 inhibition reduces DA closure in a tissue culture model. CONCLUSIONS: Mitochondrial fission is an obligatory, early step in mammalian O2 sensing and offers a promising target for modulating DA patency.

Patient satisfaction of BRCA1/2 genetic testing by women at high risk for breast cancer participating in a prevention trial.

With the increasing availability of cancer risk counseling and genetic testing, we need to determine the most effective way to provide complex and sensitive information to patients. This study was designed to determine the satisfaction of results delivery in women who participated in a breast cancer prevention trial and chose to undergo free and confidential BRCA1/2 genetic testing. Self-selected women at high-risk for breast cancer who were eligible to participate in a phase II chemoprevention trial, were offered free and confidential pre-test counseling and BRCA1/2 full sequencing. Subjects were not randomized but rather had the option of in person or telephone results disclosure. Those subjects with an identified germline alteration were required to follow-up with an in person consultation; this was optional for those with a negative result. A satisfaction survey was mailed to subjects after receiving their results. Ninety-seven percent (116/119) of the eligible subjects underwent genetic testing. Ninety-one percent (105/116) of those women tested responded to the follow-up survey. Twenty-four of the 26 women with an identified germline alteration responded. Nearly all of the responders were satisfied with the counseling and testing process. All of the respondents felt they made a wise decision in having the testing and would recommend that other women in a similar situation undergo genetic testing. We found that the majority of women at high risk for breast cancer participating in a prevention trial will choose to undergo anonymous and free BRCA1/2 genetic testing, be informed of the results, and are accepting of receiving results initially by phone.