Description: PALB2 links BRCA1 and BRCA2 in homologous recombinational repair of DNA double strand breaks (DSBs). Mono-allelic mutations in PALB2 increase the risk of breast, pancreatic, and other cancers, and biallelic mutations cause Fanconi anemia (FA). Like Brca1 and Brca2, systemic knock-out of Palb2 in mice results in embryonic lethality. In this study, we generated a hypomorphic Palb2 allele expressing a mutant PALB2 protein unable to bind BRCA1. Consistent with an FA-like phenotype, cells from the mutant mice showed hypersensitivity and chromosomal breakage when treated with mitomycin C, a DNA interstrand crosslinker. Moreover, mutant males showed reduced fertility due to impaired meiosis and increased apoptosis in germ cells. Interestingly, mutant meiocytes showed a significant defect in sex chromosome synapsis, which likely contributed to the germ cell loss and fertility defect. Our results underscore the in vivo importance of the PALB2-BRCA1 complex formation in DSB repair and male meiosis.

Description: Background— Fetal hypoxia has been implicated in the abnormal brain development seen in newborns with congenital heart disease (CHD). New magnetic resonance imaging technology now offers the potential to investigate the relationship between fetal hemodynamics and brain dysmaturation. Methods and Results— We measured fetal brain size, oxygen saturation, and blood flow in the major vessels of the fetal circulation in 30 late-gestation fetuses with CHD and 30 normal controls using phase-contrast magnetic resonance imaging and T2 mapping. Fetal hemodynamic parameters were calculated from a combination of magnetic resonance imaging flow and oximetry data and fetal hemoglobin concentrations estimated from population averages. In fetuses with CHD, reductions in umbilical vein oxygen content ( P 〈0.001) and failure of the normal streaming of oxygenated blood from the placenta to the ascending aorta were associated with a mean reduction in ascending aortic saturation of 10% ( P 〈0.001), whereas cerebral blood flow and cerebral oxygen extraction were no different from those in controls. This accounted for the mean 15% reduction in cerebral oxygen delivery ( P =0.08) and 32% reduction cerebral V o 2 in CHD fetuses ( P 〈0.001), which were associated with a 13% reduction in fetal brain volume ( P 〈0.001). Fetal brain size correlated with ascending aortic oxygen saturation and cerebral V o 2 ( r =0.37, P =0.004). Conclusions— This study supports a direct link between reduced cerebral oxygenation and impaired brain growth in fetuses with CHD and raises the possibility that in utero brain development could be improved with maternal oxygen therapy.

Description: Despite being a major health problem, respiratory syncytial virus (RSV) infections remain without specific therapy. Identification of novel host cellular responses that play a role in the pathogenesis of RSV infection is needed for therapeutic development. The endoplasmic reticulum (ER) stress response is an evolutionarily conserved cellular signaling cascade that has been implicated in multiple biological phenomena, including the pathogenesis of some viral infections. In this study, we investigate the role of the ER stress response in RSV infection using an in vitro A549 cell culture model. We found that RSV infection induces a non-canonical ER stress response with preferential activation of the inositol-requiring enzyme 1 (IRE1) and activated transcription factor 6 (ATF6) pathways with no concomitant significant activation of the protein kinase R-like ER kinase (PERK) pathway. Furthermore, we discovered that IRE1 has an inhibitory effect on RSV replication. Our data characterize, for the first time, the nature of the ER stress response in the setting of RSV infection and identify the IRE1 stress pathway as a novel cellular anti-RSV defense mechanism.

Description: Rationale: Efficient clearance of apoptotic cells (efferocytosis) is a prerequisite for inflammation resolution and tissue repair. After myocardial infarction, phagocytes are recruited to the heart and promote clearance of dying cardiomyocytes. The molecular mechanisms of efferocytosis of cardiomyocytes and in the myocardium are unknown. The injured heart provides a unique model to examine relationships between efferocytosis and subsequent inflammation resolution, tissue remodeling, and organ function. Objective: We set out to identify mechanisms of dying cardiomyocyte engulfment by phagocytes and, for the first time, to assess the causal significance of disrupting efferocytosis during myocardial infarction. Methods and Results: In contrast to other apoptotic cell receptors, macrophage myeloid-epithelial-reproductive tyrosine kinase was necessary and sufficient for efferocytosis of cardiomyocytes ex vivo. In mice, Mertk was specifically induced in Ly6c LO myocardial phagocytes after experimental coronary occlusion. Mertk deficiency led to an accumulation of apoptotic cardiomyocytes, independently of changes in noncardiomyocytes, and a reduced index of in vivo efferocytosis. Importantly, suppressed efferocytosis preceded increases in myocardial infarct size and led to delayed inflammation resolution and reduced systolic performance. Reduced cardiac function was reproduced in chimeric mice deficient in bone marrow Mertk ; reciprocal transplantation of Mertk +/+ marrow into Mertk –/– mice corrected systolic dysfunction. Interestingly, an inactivated form of myeloid-epithelial-reproductive tyrosine kinase, known as solMER, was identified in infarcted myocardium, implicating a natural mechanism of myeloid-epithelial-reproductive tyrosine kinase inactivation after myocardial infarction. Conclusions: These data collectively and directly link efferocytosis to wound healing in the heart and identify Mertk as a significant link between acute inflammation resolution and organ function.

Description: Background— Multiple echocardiographic methods are used to measure left ventricular size and function. Clinical management is based on individual evaluations and longitudinal trends. The Pediatric Heart Network VVV study (Ventricular Volume Variability) in pediatric patients with dilated cardiomyopathy has reported reproducibility of several of these measures, and how disease state and number of beats impact their reproducibility. In this study, we investigated the impact of observer and sonographer variation on reproducibility of dimension, area, and volume methods to determine the best method for both individual and sequential evaluations. Methods and Results— In 8 centers, echocardiograms were obtained on 169 patients prospectively. During the same visit, 2 different sonographers acquired the same imaging protocol on each patient. Each acquisition was analyzed by 2 different observers; first observer analyzed the first acquisition twice. Intraobserver, interobserver, interacquisition, and interobserver-acquisition (different observers and different acquisition) reproducibility were assessed on measurements of left ventricular end-diastolic dimension, area, and volume. Left ventricular shortening fraction, ejection fraction, mass, and fractional area change were calculated. Percent difference was calculated as (interobservation difference/mean) x 100. Interobserver reproducibility for both acquisitions was better for both volume and dimension measurements ( P ≤0.002) compared with area measurements, whereas intraobserver, interacquisition (for both observers), and interobserver-acquisition reproducibilities (for both observer-acquisition sets) were best for volume measurements ( P ≤0.01). Overall, interobserver-acquisition percent differences were significantly higher than interobserver and interacquisition percent differences ( P 〈0.001). Conclusions— In pediatric patients with dilated cardiomyopathy, compared with dimension and area methods, left ventricular measurements by volume method have the best reproducibility in settings where assessment is not performed by the same personnel. Clinical Trial Registration— URL: https://www.clinicaltrials.gov . Unique identifier: NCT00123071.

Description: Alzheimer disease (AD) is a progressive neurodegenerative disease leading to memory loss. Numerous lines of evidence suggest that amyloid-β (Aβ), a neurotoxic peptide, initiates a cascade that results in synaptic dysfunction, neuronal death, and eventually cognitive deficits. Aβ is generated by the proteolytic processing of the amyloid precursor protein (APP), and alterations to this processing can result in Alzheimer disease. Using in vitro and in vivo models, we identified cyclopamine as a novel regulator of γ-secretase-mediated cleavage of APP. We demonstrate that cyclopamine decreases Aβ generation by altering APP retrograde trafficking. Specifically, cyclopamine treatment reduced APP-C-terminal fragment (CTF) delivery to the trans-Golgi network where γ-secretase cleavage occurs. Instead, cyclopamine redirects APP-CTFs to the lysosome. These data demonstrate that cyclopamine treatment decreases γ-secretase-mediated cleavage of APP. In addition, cyclopamine treatment decreases the rate of APP-CTF degradation. Together, our data demonstrate that cyclopamine alters APP processing and Aβ generation by inducing changes in APP subcellular trafficking and APP-CTF degradation.

Description: The number of patients surviving with congenital heart disease (CHD) has soared over the last 3 decades. Adults constitute the fastest-growing segment of the CHD population, now outnumbering children. Research to date on the heart-brain intersection in this population has been focused largely on neurodevelopmental outcomes in childhood and adolescence. Mutations in genes that are highly expressed in heart and brain may cause cerebral dysgenesis. Together with altered cerebral perfusion in utero, these factors are associated with abnormalities of brain structure and brain immaturity in a significant portion of neonates with critical CHD even before they undergo cardiac surgery. In infancy and childhood, the brain may be affected by risk factors related to heart disease itself or to its interventional treatments. As children with CHD become adults, they increasingly develop heart failure, atrial fibrillation, hypertension, diabetes mellitus, and coronary disease. These acquired cardiovascular comorbidities can be expected to have effects similar to those in the general population on cerebral blood flow, brain volumes, and dementia. In both children and adults, cardiovascular disease may have adverse effects on achievement, executive function, memory, language, social interactions, and quality of life. Against the backdrop of shifting demographics, risk factors for brain injury in the CHD population are cumulative and synergistic. As neurodevelopmental sequelae in children with CHD evolve to cognitive decline or dementia during adulthood, a growing population of CHD can be expected to require support services. We highlight evidence gaps and future research directions.

Description: Salmonella enterica serovar typhimurium translocates a glycerophospholipid:cholesterol acyltransferase (SseJ) into the host cytosol after its entry into mammalian cells. SseJ is recruited to the cytoplasmic face of the host cell phagosome membrane where it is activated upon binding the small GTPase, RhoA. SseJ is regulated similarly to cognate eukaryotic effectors, as only the GTP-bound form of RhoA family members stimulates enzymatic activity. Using NMR and biochemistry, this work demonstrates that SseJ competes effectively with Rhotekin, ROCK, and PKN1 in binding to a similar RhoA surface. The RhoA surface that binds SseJ includes the regulatory switch regions that control activation of mammalian effectors. These data were used to create RhoA mutants with altered SseJ binding and activation. This structure-function analysis supports a model in which SseJ activation occurs predominantly through binding to residues within switch region II. We further defined the nature of the interaction between SseJ and RhoA by constructing SseJ mutants in the RhoA binding surface. These data indicate that SseJ binding to RhoA is required for recruitment of SseJ to the endosomal network and for full Salmonella virulence for inbred susceptible mice, indicating that regulation of SseJ by small GTPases is an important virulence strategy of this bacterial pathogen. The dependence of a bacterial effector on regulation by a mammalian GTPase defines further how intimately host pathogen interactions have coevolved through similar and divergent evolutionary strategies.

Description: The microtubule-associated protein targeting protein for Xenopus kinesin-like protein 2 (TPX2) plays a key role in spindle assembly and is required for mitosis in human cells. In interphase, TPX2 is actively imported into the nucleus to prevent its premature activity in microtubule organization. To date, no function has been assigned to nuclear TPX2. We now report that TPX2 plays a role in the cellular response to DNA double strand breaks induced by ionizing radiation. Loss of TPX2 leads to inordinately strong and transient accumulation of ionizing radiation-dependent Ser-139-phosphorylated Histone 2AX (γ-H2AX) at G0 and G1 phases of the cell cycle. This is accompanied by the formation of increased numbers of high intensity γ-H2AX ionizing radiation-induced foci. Conversely, cells overexpressing TPX2 have reduced levels of γ-H2AX after ionizing radiation. Consistent with a role for TPX2 in the DNA damage response, we found that the protein accumulates at DNA double strand breaks and associates with the mediator of DNA damage checkpoint 1 (MDC1) and the ataxia telangiectasia mutated (ATM) kinase, both key regulators of γ-H2AX amplification. Pharmacologic inhibition or depletion of ATM or MDC1, but not of DNA-dependent protein kinase (DNA-PK), antagonizes the γ-H2AX phenotype caused by TPX2 depletion. Importantly, the regulation of γ-H2AX signals by TPX2 is not associated with apoptosis or the mitotic functions of TPX2. In sum, our study identifies a novel and the first nuclear function for TPX2 in the cellular responses to DNA damage.