BDNF/TrkB signaling endosomes in axons coordinate CREB/mTOR activation and protein synthesis in the cell body to induce dendritic growth in cortical neurons.

Brain-derived neurotrophic factor (BDNF) and its receptors tropomyosin kinase receptor B (TrkB) and the p75 neurotrophin receptor (p75) are the primary regulators of dendritic growth in the CNS. After being bound by BDNF, TrkB and p75 are endocytosed into endosomes and continue signaling within the cell soma, dendrites, and axons. We studied the functional role of BDNF axonal signaling in cortical neurons derived from different transgenic mice using compartmentalized cultures in microfluidic devices. We found that axonal BDNF increased dendritic growth from the neuronal cell body in a cAMP response element-binding protein (CREB)-dependent manner. These effects were dependent on axonal TrkB but not p75 activity. Dynein-dependent BDNF-TrkB-containing endosome transport was required for long-distance induction of dendritic growth. Axonal signaling endosomes increased CREB and mTOR kinase activity in the cell body, and this increase in the activity of both proteins was required for general protein translation and the expression of Arc, a plasticity-associated gene, indicating a role for BDNF-TrkB axonal signaling endosomes in coordinating the transcription and translation of genes whose products contribute to learning and memory regulation.

Effects of cardiopulmonary bypass on the development of lymphopenia and sepsis after cardiac surgery in children with congenital cardiopathy.

The objective of the present study was to investigate whether lymphopenia occurring after heart surgery with cardiopulmonary bypass (CPB) is related to apoptosis and or sepsis in children. The design was a prospective cohort study in a third level care hospital in Mexico City. In total, 68 children (31 girls and 37 boys) with congenital cardiopathy who needed corrective cardiac surgery with or without CPB were included. The samples were obtained from central blood before, immediately after and 24 h after surgery. Complete blood counts and lymphocyte apoptosis were analyzed. Systemic inflammatory response syndrome (SIRS), sepsis and the type of microorganism were recorded. A total of 53 patients received CPB and 15 did not. Lymphocyte count decreased after surgery in both groups (P<0.001). However, neutrophil count increased markedly in both groups. Apoptosis of B (CD19+) lymphocytes was higher in the non-CPB group (14, 2 and 21% before, immediately after and 24 h after surgery, respectively) than the CPB group (0, 2 and 3%, respectively), but apoptosis of cytotoxic T lymphocytes (CD8+) was higher in the CPB group (5, 4 and 3% before, immediately after and 24 h after surgery, respectively) than in the non-CPB group (2, 3 and 2%, respectively). However, the extent of apoptosis of T and B lymphocytes after surgery did not differ between groups. The CPB group had more complications than the non-CPB group [38 (71.7%) vs. 9 (60.0%)]. In conclusion, the decrease in lymphocyte count may be related to apoptosis of cytotoxic T lymphocytes in children receiving cardiac surgery with CPB and to apoptosis of B lymphocytes in those not receiving CPB. The decreased lymphocyte counts in both groups suggested that CPB is not the main cause of this decrease. Children who received CPB during surgery had more complications, such as sepsis and cardiogenic shock than did those who did not receive CPB.

Enhanced nuclear protein export in premature aging and rescue of the progeria phenotype by modulation of CRM1 activity.

The study of Hutchinson-Gilford progeria syndrome (HGPS) has provided important clues to decipher mechanisms underlying aging. Progerin, a mutant lamin A, disrupts nuclear envelope structure/function, with further impairment of multiple processes that culminate in senescence. Here, we demonstrate that the nuclear protein export pathway is exacerbated in HGPS, due to progerin-driven overexpression of CRM1, thereby disturbing nucleocytoplasmic partitioning of CRM1-target proteins. Enhanced nuclear export is central in HGPS, since pharmacological inhibition of CRM1 alleviates all aging hallmarks analyzed, including senescent cellular morphology, lamin B1 downregulation, loss of heterochromatin, nuclear morphology defects, and expanded nucleoli. Exogenous overexpression of CRM1 on the other hand recapitulates the HGPS cellular phenotype in normal fibroblasts. CRM1 levels/activity increases with age in fibroblasts from healthy donors, indicating that altered nuclear export is a common hallmark of pathological and physiological aging. Collectively, our findings provide novel insights into HGPS pathophysiology, identifying CRM1 as potential therapeutic target in HGPS.

Neuronal Nitric Oxide Synthase in Cultured Cerebellar Bergmann Glia: Glutamate-Dependent Regulation.

Glutamate exerts its actions through the activation of membrane receptors expressed in neurons and glia cells. The signaling properties of glutamate transporters have been characterized recently, suggesting a complex array of signaling transactions triggered by presynaptic released glutamate. In the cerebellar molecular layer, glutamatergic synapses are surrounded by Bergmann glia cells, compulsory participants of glutamate turnover and supply to neurons. Since a glutamate-dependent increase in cGMP levels has been described in these cells and the nitric oxide-cGMP signaling cascade increases their glutamate uptake activity, we describe here the Bergmann glia expression of neuronal nitric oxide synthetase. An augmentation of neuronal nitric oxide synthase was found upon glutamate exposure. This effect is mediated by glutamate transporters and is related to an increase in the stability of the enzyme. These results strengthen the notion of a complex regulation of glial glutamate uptake that supports neuronal glutamate signaling.

The intracellular domain of ß-dystroglycan mediates the nucleolar stress response by suppressing UBF transcriptional activity.

ß-dystroglycan (ß-DG) is a key component of multiprotein complexes in the plasma membrane and nuclear envelope. In addition, ß-DG undergoes two successive proteolytic cleavages that result in the liberation of its intracellular domain (ICD) into the cytosol and nucleus. However, stimuli-inducing ICD cleavage and the physiological relevance of this proteolytic fragment are largely unknown. In this study we show for the first time that ß-DG ICD is targeted to the nucleolus where it interacts with the nuclear proteins B23 and UBF (central factor of Pol I-mediated rRNA gene transcription) and binds to rDNA promoter regions. Interestingly DG silencing results in reduced B23 and UBF levels and aberrant nucleolar morphology. Furthermore, ß-DG ICD cleavage is induced by different nucleolar stressors, including oxidative stress, acidosis, and UV irradiation, which implies its participation in the response to nucleolar stress. Consistent with this idea, overexpression of ß-DG elicited mislocalization and decreased levels of UBF and suppression of rRNA expression, which in turn provoked altered ribosome profiling and decreased cell growth. Collectively our data reveal that ß-DG ICD acts as negative regulator of rDNA transcription by impeding the transcriptional activity of UBF, as a part of the protective mechanism activated in response to nucleolar stress.

Glutamate-Dependent Translational Control of Glutamine Synthetase in Bergmann Glia Cells.

Glutamate is the major excitatory transmitter of the vertebrate brain. It exerts its actions through the activation of specific plasma membrane receptors expressed both in neurons and in glial cells. Recent evidence has shown that glutamate uptake systems, particularly enriched in glia cells, trigger biochemical cascades in a similar fashion as receptors. A tight regulation of glutamate extracellular levels prevents neuronal overstimulation and cell death, and it is critically involved in glutamate turnover. Glial glutamate transporters are responsible of the majority of the brain glutamate uptake activity. Once internalized, this excitatory amino acid is rapidly metabolized to glutamine via the astrocyte-enriched enzyme glutamine synthetase. A coupling between glutamate uptake and glutamine synthesis and release has been commonly known as the glutamate/glutamine shuttle. Taking advantage of the established model of cultured Bergmann glia cells, in this contribution, we explored the gene expression regulation of glutamine synthetase. A time- and dose-dependent regulation of glutamine synthetase protein and activity levels was found. Moreover, glutamate exposure resulted in the transient shift of glutamine synthetase mRNA from the monosomal to the polysomal fraction. These results demonstrate a novel mode of glutamate-dependent glutamine synthetase regulation and strengthen the notion of an exquisite glia neuronal interaction in glutamatergic synapses.