Genetic modifiers modulate phenotypic expression of tafazzin deficiency in a mouse model of Barth syndrome.

Barth syndrome is an X-linked disorder caused by loss-of-function mutations in Tafazzin (TAZ), an acyltransferase that catalyzes remodeling of cardiolipin, a signature phospholipid of the inner mitochondrial membrane. Patients develop cardiac and skeletal muscle weakness, growth delay and neutropenia, although phenotypic expression varies considerably between patients. Taz knockout mice recapitulate many of the hallmark features of the disease. We used mouse genetics to test the hypothesis that genetic modifiers alter the phenotypic manifestations of Taz inactivation. We crossed TazKO/X females in the C57BL6/J inbred strain to males from eight inbred strains and evaluated the phenotypes of first-generation (F1) TazKO/Y progeny, compared to TazWT/Y littermates. We observed that genetic background strongly impacted phenotypic expression. C57BL6/J and CAST/EiJ[F1] TazKO/Y mice developed severe cardiomyopathy, whereas A/J[F1] TazKO/Y mice had normal heart function. C57BL6/J and WSB/EiJ[F1] TazKO/Y mice had severely reduced treadmill endurance, whereas endurance was normal in A/J[F1] and CAST/EiJ[F1] TazKO/Y mice. In all genetic backgrounds, cardiolipin showed similar abnormalities in knockout mice, and transcriptomic and metabolomic investigations identified signatures of mitochondrial uncoupling and activation of the integrated stress response. TazKO/Y cardiac mitochondria were small, clustered and had reduced cristae density in knockouts in severely affected genetic backgrounds but were relatively preserved in the permissive A/J[F1] strain. Gene expression and mitophagy measurements were consistent with reduced mitophagy in knockout mice in genetic backgrounds intolerant of Taz mutation. Our data demonstrate that genetic modifiers powerfully modulate phenotypic expression of Taz loss-of-function and act downstream of cardiolipin, possibly by altering mitochondrial quality control.

Personalized Prognosis of Uveal Melanoma Based on Cytogenetic Profile in 1059 Patients over an 8-Year Period: The 2017 Harry S. Gradle Lecture.

PURPOSE: To determine the personalized rate of uveal melanoma-related metastasis on the basis of individual tumor cytogenetic profile. DESIGN: Retrospective case series. PARTICIPANTS: A total of 1059 patients with uveal melanoma. METHODS: Fine-needle aspiration biopsy (FNAB) for DNA amplification and whole genome array-based assay were performed for analysis of chromosomes 3, 6, and 8. MAIN OUTCOME MEASURES: Melanoma-related metastasis. RESULTS: The mean patient age was 57 years, and most were white (1026/1059, 97%). The melanoma involved the choroid (938/1059, 89%), ciliary body (85/1059, 8%), or iris (36/1059, 3%), with 19% being macular in location. The mean largest basal diameter was 11 mm (median, 12 mm; range, 3-24 mm), and mean thickness was 5 mm (median, 4 mm; range, 1-20 mm). On the basis of individual chromosomal mutations, risk for metastasis was increased for chromosome 3 partial monosomy (hazard ratio [HR], 2.84; P = 0.001), 3 complete monosomy (HR, 6.7, P < 0.001), 6q loss (HR, 3.1, P = 0.003), 8p loss (HR, 21.5, P < 0.001), and 8q gain (HR, 9.8, P < 0.001). Kaplan-Meier estimate for melanoma-related metastasis in 1, 3, 5, and 7 years for 3 partial monosomy was 1%, 5%, 14%, and 17%; for 3 complete monosomy was 3%, 19%, 28%, and 37%; for 6q loss was 8%, 23%, 49%, and 49%; for 8p loss was 8%, 29%, not estimable (NE), and NE; and for 8q gain was 6%, 21%, 35%, 48%, respectively. On the basis of personalized cytogenetic profiles, Kaplan-Meier estimates (1, 3, and 5 years) for melanoma-related metastasis for 3, 6, and 8 disomy (1%, 1%, 4% [HR, 1]) were low compared with the higher-risk combinations of 3 complete monosomy, 6p gain, and 8q gain (0%, 29%, 29% [HR, 10.6, P = 0.02]); 3 complete monosomy, 6 disomy, 8q gain, and 8p gain (14%, 14%, NE [HR, 18.3, P = 0.02]); 3 complete monosomy, 6 disomy, and 8q gain (8%, 27%, 39% [HR, 19.5, P < 0.001]); and 3 complete monosomy, 6 disomy, 8q gain, and 8p loss (3%, 28%, NE [HR, 31.6, P < 0.001]), respectively. CONCLUSIONS: Risk for melanoma-related metastasis strongly correlates with personalized cytogenetic profiles, with 5-year Kaplan-Meier estimates ranging from 4% with chromosomes 3, 6, and 8 disomy up to 39% for 3 complete monosomy, 6 disomy, and 8q gain.

A new murine model of Barth syndrome neutropenia links TAFAZZIN deficiency to increased ER stress-induced apoptosis.

Barth syndrome is an inherited X-linked disorder that leads to cardiomyopathy, skeletal myopathy, and neutropenia. These symptoms result from the loss of function of the enzyme TAFAZZIN, a transacylase located in the inner mitochondrial membrane that is responsible for the final steps of cardiolipin production. The link between defective cardiolipin maturation and neutropenia remains unclear. To address potential mechanisms of neutropenia, we examined myeloid progenitor development within the fetal liver of TAFAZZIN knockout (KO) animals as well as within the adult bone marrow of wild-type recipients transplanted with TAFAZZIN-KO hematopoietic stem cells. We also used the ER-Hoxb8 system (estrogen receptor fused to Hoxb8) of conditional immortalization to establish a new murine model system for the ex vivo study of TAFAZZIN-deficient neutrophils. The TAFAZZIN-KO cells demonstrated the expected dramatic differences in cardiolipin maturation that result from a lack of TAFAZZIN enzyme activity. Contrary to our hypothesis, we did not identify any significant differences in neutrophil development or neutrophil function across a variety of assays including phagocytosis and the production of cytokines or reactive oxygen species. However, transcriptomic analysis of the TAFAZZIN-deficient neutrophil progenitors demonstrated an upregulation of markers of endoplasmic reticulum stress and confirmatory testing demonstrated that the TAFAZZIN-deficient cells had increased sensitivity to certain ER stress-mediated and non-ER stress-mediated triggers of apoptosis. Although the link between increased sensitivity to apoptosis and the variably penetrant neutropenia phenotype seen in some patients with Barth syndrome remains to be clarified, our studies and new model system set a foundation for further investigation.

Membrane potential (Vmem) measurements during mesenchymal stem cell (MSC) proliferation and osteogenic differentiation.

BACKGROUND: Electrochemical signals play an important role in cell communication and behavior. Electrically charged ions transported across cell membranes maintain an electrochemical imbalance that gives rise to bioelectric signaling, called membrane potential or Vmem. Vmem plays a key role in numerous inter- and intracellular functions that regulate cell behaviors like proliferation, differentiation and migration, all playing a critical role in embryonic development, healing, and regeneration. METHODS: With the goal of analyzing the changes in Vmem during cell proliferation and differentiation, here we used direct current electrical stimulation (EStim) to promote cell proliferation and differentiation and simultaneously tracked the corresponding changes in Vmem in adipose derived mesenchymal stem cells (AT-MSC). RESULTS: We found that EStim caused increased AT-MSC proliferation that corresponded to Vmem depolarization and increased osteogenic differentiation that corresponded to Vmem hyperpolarization. Taken together, this shows that Vmem changes associated with EStim induced cell proliferation and differentiation can be accurately tracked during these important cell functions. Using this tool to monitor Vmem changes associated with these important cell behaviors we hope to learn more about how these electrochemical cues regulate cell function with the ultimate goal of developing new EStim based treatments capable of controlling healing and regeneration.

Inconsistent diagnostic criteria for convergence insufficiency.

BACKGROUND: Convergence insufficiency (CI) is a common entity but seems to be an ill-defined diagnosis that incorporates many near-vision symptoms. The current literature often varies in its criteria for diagnosis. Without a clear definition and standardization of the clinical examination, there is the potential for misdiagnosis and/or the inclusion of other diagnoses as CI. The purpose of this study was to assess the uniformity of diagnostic criteria in a well-defined practice environment. METHODS: The medical records of individuals diagnosed with CI between June 2007 and November 2014 who were patients of 6 fellowship-trained strabismologists in private practices and at Wills Eye Hospital clinics were reviewed retrospectively. Exclusion criteria included any previous treatments for CI, prior strabismus surgery, or other causes for strabismus, including cranial nerve palsies. The following data were collected: age, sex, race, age at diagnosis, past medical and family history, relevant symptoms, visual acuity, near point of convergence (NPC), strabismus measurements, and fusional amplitudes at distance with base-out and base-in prisms. RESULTS: A total of 387 patients fit our inclusion criteria and were analyzed in our study. There was no uniformity across clinicians in the clinical evaluation and diagnosis of patients with CI. The amplitude of the NPC was highly variable, and most clinicians did not assess the quality of the convergence movement or perform convergence fusional amplitude testing in making the diagnosis of CI. CONCLUSIONS: Our review has demonstrated the range of criteria within one group of practitioners to diagnose CI. This may reflect our current understanding and the need for an evidence-based definition of the disease and its diagnosis.