Although knowledge of the functions of neurotrophins has advanced rapidly in recent years, studies concerning the involvement of neurotrophins in glial-neuronal interactions rarely extend further than their roles in supporting the survival and differentiation of neuronal cells. In this study endogenous brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) were identified in Schwann cell͞dorsal root ganglia neuronal cocultures and shown to modulate the myelination program of the peripheral nervous system. The differential expression of BDNF and NT3 were examined and compared with the expression profiles of myelin proteins in the cocultures throughout the myelination process. BDNF levels correlated with active myelin formation, whereas NT3 expression was initially high and then down regulated throughout the proliferation and premyelination periods. Addition of exogenous BDNF enhanced myelination, whereas the removal of the endogenous BDNF by using the BDNF receptor TrkB-Fc fusion protein inhibited the formation of mature myelin internodes. Interestingly, exogenous NT3 significantly inhibited myelination, whereas the removal of the endogenous NT3 by using the NT3 receptor TrkC-Fc fusion protein resulted in an enhancement similar to that obtained with the addition of BDNF. In addition, in vivo studies were performed during the development of the mouse sciatic nerve. Subcutaneous injections of BDNF resulted in an enhancement of myelin formation in the sciatic nerve, whereas the removal of the endogenous BDNF dramatically inhibited myelination. Injections of NT3 inhibited myelin formation, and the removal of the endogenous NT3 enhanced myelination. These results demonstrate that BDNF and NT3 possess different modulatory roles in the myelination program of the peripheral nervous system and that their mechanisms of action are specific and highly regulated. T he myelin sheath is a unique component of the nervous system that functions to maximize the efficiency and velocity of action potentials transmitted through nerve cell axons. The composition of myelin differs in the peripheral and central nervous systems principally in the nature of the proteins that are embedded in the lipid bilayers of the multiple myelin wraps. The proteins in peripheral myelin have received considerable attention because alterations in genes encoding these proteins are responsible for the demyelinating peripheral neuropathies, especially the Charcot-Marie-Tooth diseases (1). The formation of peripheral myelin is a complex, dynamic process involving two different cell types, the myelin forming glia (Schwann cells) and the neurons, that involve a series of neuronal-glial interactions controlling the various stages of myelination (2-4). Much has been learned about the interactions that define the three major phases of Schwann cell growth and differentiation in myelination. These include the proliferation and migration of Schwann cells on axons in the proliferative stage, the elongation and ensheathment of the axon by the Schwann cell in...

Neurotrophins (NTs) play an important role in the modulation of synaptic transmission and in morphological changes in synaptic structures. Although there is agreement that brain-derived neurotrophic factor (BDNF) is sorted to large dense-core vesicles (LDCVs) and released via the regulated secretory pathway, there has been some dispute regarding the mode of secretion of nerve growth factor (NGF) and neurotrophin-3 (NT-3), two structurally related members of the NT family. In this study, we examined the subcellular localization and release characteristics of NGF, BDNF, and NT-3 in adenovirus-infected primary cortical neurons. We found that all members of the NT family colocalized with markers for the endoplasmic reticulum and Golgi within cell bodies and in a punctate manner with a marker for LDCVs within processes. Moreover, their release was triggered by depolarization, indicating that NGF, BDNF, and NT-3 are released via the regulated secretory pathway. When neurons were coinfected with two separate adenoviruses coding for NGF or BDNF, both NTs showed almost complete vesicular colocalization within single cells, suggesting that different NTs might be packaged into shared vesicles. We also examined whether the two splice variants of NGF, the short and long precursors, differ in their release characteristics. We found that neurons infected with viruses coding for either splice variant released NGF in a regulated way. Overall, our study supports the notion that all members of the NT family undergo activity-dependent regulated release from neurons, enabling them to act as "synaptotrophins" on electrically active neurons.

Inflammatory response and renal fibrosis are the hallmarks of chronic kidney disease (CKD). However, the specific mechanism of aldosterone-induced renal injury in the progress of CKD requires elucidation. Emerging evidence has demonstrated that absent in melanoma 2 (AIM2)-mediated inflammasome activation and endoplasmic reticulum stress (ERS) play a pivotal role in the renal fibrosis. Here, we investigated whether overexpression or deficiency of AIM2 affects ERS and fibrosis in aldosterone-infused renal injury. Interestingly, we found that AIM2 was markedly expressed in the diseased proximal tubules from human and experimental chronic kidney disease. Mechanically, overactivation of AIM2 aggravated aldosterone-induced ERS and fibrotic changes in vitro while knockdown of AIM2 blunted these effects in vivo and vitro. By contrast, AIM2 deficiency ameliorated renal structure and function deterioration, decreased proteinuria levels and lower systolic blood pressure in vivo; silencing of AIM2 blocked inflammasome-mediated signaling pathway, relieved ERS and fibrotic changes in vivo. Furthermore, mineralocorticoid receptor antagonist eplerenone and ERS inhibitor tauroursodeoxycholic acid (TUDCA) had nephroprotective effects on the basis of AIM2 overactivation in vitro while they failed to produce a more remarkable reno-protective effect on the treatment of AIM2 silence in vitro. Notably, the combination of TUDCA with AIM2 knockdown significantly reduced proteinuria levels in vivo. Additionally, immunofluorescence assay identified that apoptosis-associated speck-like protein (ASC) recruitment and Gasdermin-D (GSDMD) cleavage respectively occurred in the glomeruli and tubules in vivo. These findings establish a crucial role for AIM2 inflammasome in aldosterone-induced renal injury, which may provide a novel therapeutic target for the pathogenesis of CKD.