Brain-derived neurotrophic factor (BDNF) is thought to be involved in neuronal survival, migration, morphological and biochemical differentiation, and modulation of synaptic function in the CNS. In the rodent cortex, postnatal BDNF expression is initially low but subsequently increases to reach maximal levels around weaning. Thus, BDNF expression peaks at a time when both structural and functional maturation of cortical circuitry occurs. Although the function of BDNF has been probed using many approaches, its requirements during this phase of life have not previously been examined genetically. To test the in vivo requirements for BDNF during this important phase of development we generated early-onset forebrain-specific BDNF mutant mice. Although these mice undergo forebrain-restricted deletion of BDNF by Cre-mediated recombination during embryogenesis, they are healthy, and we did not detect the loss of specific cortical excitatory or inhibitory neurons. However, the neocortex of 5-week-old mice was thinner, attributable at least partly to neuronal shrinkage. Importantly, although visual cortical layer 2/3 neurons in the mutants initially developed normal dendrite structure, dendritic retraction became apparent by 3 weeks of age. Thus, our observations suggest that cortically expressed BDNF functions to support the maintenance of cortical neuron size and dendrite structure rather than the initial development of these features. This is consistent with a role for BDNF in stabilizing the "survival" of circuitry during the phase of activity-dependent reorganization of cortical connectivity.

The ␣7␤1 integrin is a laminin receptor that has been implicated in muscle disease and the development of neuromuscular and myotendinous junctions. Studies have shown the ␣7␤1 integrin is also expressed in nonskeletal muscle tissues. To identify the expression pattern of the ␣7 integrin in these tissues during embryonic development, ␣7 integrin chain knockout mice were generated by a LacZ knockin strategy. In these mice, expression from the ␣7 promoter is reported by ␤-galactosidase. From embryonic day (ED) 11.5 to ED14.5, ␤-galactosidase was detected in the developing central and peripheral nervous systems and vasculature. The loss of the ␣7 integrin gene resulted in partial embryonic lethality. Several ␣7 null embryos were identified with cerebrovascular hemorrhages and showed reduced vascular smooth muscle cells and cerebral vascularization. The ␣7 null mice that survived to birth exhibited vascular smooth muscle defects, including hyperplasia and hypertrophy. In addition, altered expression of ␣5 and ␣6B integrin chains was detected in the cerebral arteries of ␣7 null mice, which may contribute to the vascular phenotype. Our results demonstrate for the first time that the ␣7␤1 integrin is important for the recruitment or survival of cerebral vascular smooth muscle cells and that this integrin plays an important role in vascular development and integrity. Developmental Dynamics 234:11-21, 2005.

Redox homeostasis regulates key cellular signaling pathways in both physiology and pathology. The cell's antioxidant response provides a defense against oxidative stress and establishes a redox tone permissive for cell signaling. The molecular regulation of the well-known Keap1/Nrf2 system acts as sensor responding to changes in redox homeostasis and is poorly studied in the heart. Importantly, it is not yet known whether Nrf2 alone can serve as a master regulator of cellular redox homeostasis without compensation of the transcriptional regulation of antioxidant response element (ARE) genes through alternate mechanisms. Here, we addressed this question using cardiac-specific transgenic expression at two different levels of constitutively active nuclear erythroid related factor 2 (caNrf2) functioning independently of Keap1. The caNrf2 mice showed augmentation of glutathione (GSH), the key regulator of the cellular thiol redox state. The Trans-AM assay for Nrf2-binding to the antioxidant response element (ARE) showed a dose-dependent increase associated with upregulation of several major antioxidant genes and proteins. This was accompanied by a significant decrease in dihydroethidium staining and malondialdehyde (MDA) in the caNrf2-TG mice myocardium. Interestingly, caNrf2 gene-dosage dependent redox changes were noted resulting in generation of a multi-stage model of pro-reductive and reductive conditions in the myocardium of TG-low and TG-high mice, respectively. These data clearly show that Nrf2 levels alone are capable of serving as the master regulator of the ARE. These models provide an important platform to investigate the impact of the Nrf2 system independent of the need to regulate the activity of Keap1 and the consequent exposure to pro-oxidants or electrophiles, which have numerous off-target effects.

Background— Recent evidence suggests that chloride channels may be involved in ischemic preconditioning (IPC). In this study, we tested whether the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels, which are expressed in the heart and activated by protein kinase A and protein kinase C, are important for IPC in isolated heart preparations from wild-type (WT) and CFTR knockout (CFTR −/− ) mice. Methods and Results— Hearts were isolated from age-matched WT or CFTR −/− (B6.129P2-Cftr tm1Unc and STOCKCftr tm1Unc -TgN 1Jaw) mice and perfused in the Langendorff or working-heart mode. All hearts were allowed to stabilize for 10 minutes before they were subjected to 30 or 45 minutes of global ischemia followed by 40 minutes of reperfusion (control group) or 3 cycles of 5 minutes of ischemia and reperfusion (IPC group) before 30 or 45 minutes of global ischemia and 40 minutes of reperfusion. Hemodynamic indices were recorded to evaluate cardiac functions. Release of creatine phosphate kinase (CPK) in the samples of coronary effluent and infarct size of the ventricles were used to estimate myocardial tissue injury. In WT adult hearts, IPC protected cardiac function during reperfusion and significantly decreased ischemia-induced CPK release and infarct size. A selective CFTR channel blocker, gemfibrozil, abrogated the protective effect of IPC. Furthermore, targeted inactivation of the CFTR gene in 2 different strains of CFTR −/− mice also prevented IPC’s protection of cardiac function and myocardial injury against sustained ischemia. Conclusions— CFTR Cl − channels may serve as novel and crucial mediators in mouse heart IPC.