Neonatal lead exposure impairs development of rodent barrel field cortex

Childhood exposure to low-level lead can permanently reduce intelligence, but the neurobiologic mechanism for this effect is unknown. We examined the impact of lead exposure on the development of cortical columns, using the rodent barrel field as a model. In all areas of mammalian neocortex, cortical columns constitute a fundamental structural unit subserving information processing. Barrel field cortex contains columnar processing units with distinct clusters of layer IV neurons that receive sensory input from individual whiskers. In this study, rat pups were exposed to 0, 0.2, 1, 1.5, or 2 g/liter lead acetate in their dam's drinking water from birth through postnatal day 10. This treatment, which coincides with the development of segregated columns in the barrel field, produced blood lead concentrations from 1 to 31 μg/dl. On postnatal day 10, the area of the barrel field and of individual barrels was measured. A dose-related reduction in barrel field area was observed (Pearson correlation = −0.740; P < 0.001); mean barrel field area in the highest exposure group was decreased 12% versus controls. Individual barrels in the physiologically more active caudoventral group were affected preferentially. Total cortical area measured in the same sections was not altered significantly by lead exposure. These data support the hypothesis that lead exposure may impair the development of columnar processing units in immature neocortex. We demonstrate that low levels of blood lead, in the range seen in many impoverished inner-city children, cause structural alterations in a neocortical somatosensory map.

Neonatal gene transfer leads to widespread correction of pathology in a murine model of lysosomal storage disease

For many inborn errors of metabolism, early treatment is critical to prevent long-term developmental sequelae. We have used a gene-therapy approach to demonstrate this concept in a murine model of mucopolysaccharidosis type VII (MPS VII). Newborn MPS VII mice received a single intravenous injection with 5.4 × 106 infectious units of recombinant adeno-associated virus encoding the human β-glucuronidase (GUSB) cDNA. Therapeutic levels of GUSB expression were achieved by 1 week of age in liver, heart, lung, spleen, kidney, brain, and retina. GUSB expression persisted in most organs for the 16-week duration of the study at levels sufficient to either reduce or prevent completely lysosomal storage. Of particular significance, neurons, microglia, and meninges of the central nervous system were virtually cleared of disease. In addition, neonatal treatment of MPS VII mice provided access to the central nervous system via an intravenous route, avoiding a more invasive procedure later in life. These data suggest that gene transfer mediated by adeno-associated virus can achieve therapeutically relevant levels of enzyme very early in life and that the rapid growth and differentiation of tissues does not limit long-term expression.

Backtracking leukemia to birth: Identification of clonotypic gene fusion sequences in neonatal blood spots

Epidemiological evidence has suggested that some pediatric leukemias may be initiated in utero and, for some pairs of identical twins with concordant leukemia, this possibility has been strongly endorsed by molecular studies of clonality. Direct evidence for a prenatal origin can only be derived by prospective or retrospective detection of leukemia-specific molecular abnormalities in fetal or newborn samples. We report a PCR-based method that has been developed to scrutinize neonatal blood spots (Guthrie cards) for the presence of numerically infrequent leukemic cells at birth in individuals who subsequently developed leukemia. We demonstrate that unique or clonotypic MLL-AF4 genomic fusion sequences are present and detectable in neonatal blood spots from individuals who were diagnosed with acute lymphoblastic leukemia at ages 5 months to 2 years and, therefore, have arisen during fetal hematopoiesis in utero. This result provides unequivocal evidence for a prenatal initiation of acute leukemia in young patients. The method should be applicable to other fusion genes in children with common subtypes of leukemia and will be of value in attempts to unravel the natural history and etiology of this major subtype of pediatric cancer.

Annual league tables of mortality in neonatal intensive care units: longitudinal study

Objective: To assess whether crude league tables of mortality and league tables of risk adjusted mortality accurately reflect the performance of hospitals.

Activation of NF-κB is required for hypertrophic growth of primary rat neonatal ventricular cardiomyocytes

The transcription factor NF-κB regulates expression of genes that are involved in inflammation, immune response, viral infection, cell survival, and division. However, the role of NF-κB in hypertrophic growth of terminally differentiated cardiomyocytes is unknown. Here we report that NF-κB activation is required for hypertrophic growth of cardiomyocytes. In cultured rat primary neonatal ventricular cardiomyocytes, the nuclear translocation of NF-κB and its transcriptional activity were stimulated by several hypertrophic agonists, including phenylephrine, endothelin-1, and angiotensin II. The activation of NF-κB was inhibited by expression of a “supersuppressor” IκBα mutant that is resistant to stimulation-induced degradation and a dominant negative IκB kinase (IKKβ) mutant that can no longer be activated by phosphorylation. Furthermore, treatment with phenylephrine induced IκBα degradation in an IKK-dependent manner, suggesting that NF-κB is a downstream target of the hypertrophic agonists. Importantly, expression of the supersuppressor IκBα mutant or the dominant negative IKKβ mutant blocked the hypertrophic agonist-induced expression of the embryonic gene atrial natriuretic factor and enlargement of cardiomyocytes. Conversely, overexpression of NF-κB itself induced atrial natriuretic factor expression and cardiomyocyte enlargement. These findings suggest that NF-κB plays a critical role in the hypertrophic growth of cardiomyocytes and may serve as a potential target for the intervention of heart disease.

Complete Cytolysis and Neonatal Lethality in Keratin 5 Knockout Mice Reveal Its Fundamental Role in Skin Integrity and in Epidermolysis Bullosa Simplex

In human patients, a wide range of mutations in keratin (K) 5 or K14 lead to the blistering skin disorder epidermolysis bullosa simplex. Given that K14 deficiency does not lead to the ablation of a basal cell cytoskeleton because of a compensatory role of K15, we have investigated the requirement for the keratin cytoskeleton in basal cells by inactivating the K5 gene in mice. We report that the K5−/− mice die shortly after birth, lack keratin filaments in the basal epidermis, and are more severely affected than K14−/− mice. In contrast to the K14−/− mice, we detected a strong induction of the wound-healing keratin K6 in the suprabasal epidermis of cytolyzed areas of postnatal K5−/− mice. In addition, K5 and K14 mice differed with respect to tongue lesions. Moreover, we show that in the absence of K5 and other type II keratins, residual K14 and K15 aggregated along hemidesmosomes, demonstrating that individual keratins without a partner are stable in vivo. Our data indicate that K5 may be the natural partner of K15 and K17. We suggest that K5 null mutations may be lethal in human epidermolysis bullosa simplex patients.