Endogenous Nmnat2 Is an Essential Survival Factor for Maintenance of Healthy Axons

We conclude that endogenous Nmnat2 prevents spontaneous degeneration of healthy axons and propose that, when present, the more long-lived, functionally related WldS protein substitutes for Nmnat2 loss after axon injury. Endogenous Nmnat2 represents an exciting new therapeutic target for axonal disorders

Egr3 Dependent Sympathetic Target Tissue Innervation in the Absence of Neuron Death

Nerve Growth Factor (NGF) is a target tissue derived neurotrophin required for normal sympathetic neuron survival and target tissue innervation. NGF signaling regulates gene expression in sympathetic neurons, which in turn mediates critical aspects of neuron survival, axon extension and terminal axon branching during sympathetic nervous system (SNS) development. Egr3 is a transcription factor regulated by NGF signaling in sympathetic neurons that is essential for normal SNS development. Germline Egr3-deficient mice have physiologic dysautonomia characterized by apoptotic sympathetic neuron death and abnormal innervation to many target tissues. The extent to which sympathetic innervation abnormalities in the absence of Egr3 is caused by altered innervation or by neuron death during development is unknown. Using Bax-deficient mice to abrogate apoptotic sympathetic neuron death in vivo, we show that Egr3 has an essential role in target tissue innervation in the absence of neuron death. Sympathetic target tissue innervation is abnormal in many target tissues in the absence of neuron death, and like NGF, Egr3 also appears to effect target tissue innervation heterogeneously. In some tissues, such as heart, spleen, bowel, kidney, pineal gland and the eye, Egr3 is essential for normal innervation, whereas in other tissues such as lung, stomach, pancreas and liver, Egr3 appears to have little role in innervation. Moreover, in salivary glands and heart, two tissues where Egr3 has an essential role in sympathetic innervation, NGF and NT-3 are expressed normally in the absence of Egr3 indicating that abnormal target tissue innervation is not due to deregulation of these neurotrophins in target tissues. Taken together, these results clearly demonstrate a role for Egr3 in mediating sympathetic target tissue innervation that is independent of neuron survival or neurotrophin deregulation

WldS Reduces Paraquat-Induced Cytotoxicity via SIRT1 in Non-Neuronal Cells by Attenuating the Depletion of NAD

WldS is a fusion protein with NAD synthesis activity, and has been reported to protect axonal and synaptic compartments of neurons from various mechanical, genetic and chemical insults. However, whether WldS can protect non-neuronal cells against toxic chemicals is largely unknown. Here we found that WldS significantly reduced the cytotoxicity of bipyridylium herbicides paraquat and diquat in mouse embryonic fibroblasts, but had no effect on the cytotoxicity induced by chromium (VI), hydrogen peroxide, etoposide, tunicamycin or brefeldin A. WldS also slowed down the death of mice induced by intraperitoneal injection of paraquat. Further studies demonstrated that WldS markedly attenuated mitochondrial injury including disruption of mitochondrial membrane potential, structural damage and decline of ATP induced by paraquat. Disruption of the NAD synthesis activity of WldS by an H112A or F116S point mutation resulted in loss of its protective function against paraquat-induced cell death. Furthermore, WldS delayed the decrease of intracellular NAD levels induced by paraquat. Similarly, treatment with NAD or its precursor nicotinamide mononucleotide attenuated paraquat-induced cytotoxicity and decline of ATP and NAD levels. In addition, we showed that SIRT1 was required for both exogenous NAD and WldS-mediated cellular protection against paraquat. These findings suggest that NAD and SIRT1 mediate the protective function of WldS against the cytotoxicity induced by paraquat, which provides new clues for the mechanisms underlying the protective function of WldS in both neuronal and non-neuronal cells, and implies that attenuation of NAD depletion may be effective to alleviate paraquat poisoning

Building sensory receptors on the tongue

Neurotrophins, neurotrophin receptors and sensory neurons are required for the development of lingual sense organs. For example, neurotrophin 3 sustains lingual somatosensory neurons. In the traditional view, sensory axons will terminate where neurotrophin expression is most pronounced. Yet, lingual somatosensory axons characteristically terminate in each filiform papilla and in each somatosensory prominence within a cluster of cells expressing the p75 neurotrophin receptor (p75NTR), rather than terminating among the adjacent cells that secrete neurotrophin 3. The p75NTR on special specialized clusters of epithelial cells may promote axonal arborization in vivo since its over-expression by fibroblasts enhances neurite outgrowth from overlying somatosensory neurons in vitro . Two classical observations have implicated gustatory neurons in the development and maintenance of mammalian taste buds—the early arrival times of embryonic innervation and the loss of taste buds after their denervation in adults. In the modern era more than a dozen experimental studies have used early denervation or neurotrophin gene mutations to evaluate mammalian gustatory organ development. Necessary for taste organ development, brain-derived neurotrophic factor sustains developing gustatory neurons. The cardinal conclusion is readily summarized: taste buds in the palate and tongue are induced by innervation. Taste buds are unstable: the death and birth of taste receptor cells relentlessly remodels synaptic connections. As receptor cells turn over, the sensory code for taste quality is probably stabilized by selective synapse formation between each type of gustatory axon and its matching taste receptor cell. We anticipate important new discoveries of molecular interactions among the epithelium, the underlying mesenchyme and gustatory innervation that build the gustatory papillae, their specialized epithelial cells, and the resulting taste buds.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47466/1/11068_2005_Article_3332.pd

Endoplasmic reticulum stress in PLP-overexpressing transgenic rats: Gray matter oligodendrocytes are more vulnerable than white matter oligodendrocytes

Studies dealing with transport of proteins from the oligodendrocyte cell body it) the myelin sheath reveal the presence of different transport pathways. Proteolipid protein (PLP) is synthesized at the rough endoplasmic reticulum (ER) and then processed through the Golgi apparatus and transported to the myelin membranes, Myelin basic protein (MBP) on the other hand is synthesized locally at the ends of cell processes where its messenger RNA is translated Oil free ribosomes, Here we show that in rats that overexpress PLP. impairment of PLP transport front the cell body to the processes interferes with the translocation of other membrane proteins such as myelin- associated glycoprotein (MAG) and myelin oligodendrocyte glycoprotein (MOG), but not with peripherally translated MBP. In addition, it also impedes the transport of non-myelin proteins, for example the amyloid precursor protein (APP). At the ultrastructural level, the ER of these metabolically disturbed oligodendrocytes revealed extreme swelling of the cisternae, and immunohistochemistry revealed intense expression of the ER chaperone molecule BiP/GRP78 and ER folding enzyme protein disulfide isomerase (PDI). These features Suggest that these oligodendrocytes, which were found exclusively in gray matter areas of the spinal cord, started in unfolded protein response while suffering from ER stress. Some of these disturbed oligodendrocytes were seen to undergo programmed cell death. These results indicate that gray matter oligodendrocyte differ from white matter Oligodendrocytes in their capacity to stabilize metabolic disturbances by an unfolded protein response

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) protects cells against cold-shock-induced apoptosis by maintaining phosphorylation of protein kinase B (AKT)

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) blocks apoptosis and inhibits caspase-3 activation. We previously showed that serum starvation (removal of serum from tissue culture media), which takes several days to induce apoptosis, results in decreased levels of both AKT (protein kinase B) and phosphorylated AKT (pAKT) in cells not expressing LAT. In contrast in mouse neuroblastoma cells expressing LAT, AKT, and pAKT levels remained high. AKT is a serine/threonine protein kinase that promotes cell survival. To examine the effect of LAT on AKT-pAKT using a different and more rapid method of inducing apoptosis, a stable cell line expressing LAT was compared to non-LAT expressing cells as soon as 15 min following recovery from cold-shock-induced apoptosis. Expression of LAT appeared to inhibit dephosphorylation of pAKT. This protection correlated with blocking numerous pro-apoptotic events that are inhibited by pAKT. These results support the hypothesis that inhibiting dephosphorylation of pAKT may be one of the pathways by which LAT protects cells against apoptosis

Regional differences in cellular mechanisms of adipose tissue gain with overfeeding

Body fat distribution is an important predictor of the metabolic consequences of obesity, but the cellular mechanisms regulating regional fat accumulation are unknown. We assessed the changes in adipocyte size (photomicrographs) and number in response to overfeeding in upper- and lower-body s.c. fat depots of 28 healthy, normal weight adults (15 men) age 29 ± 2 y. We analyzed how these changes relate to regional fat gain (dual energy X-ray absorptiometry and computed tomography) and baseline preadipocyte proliferation, differentiation [peroxisome proliferator-activated receptor-γ2 (PPARγ2) and CCAAT/enhancer binding protein-α (C/EBPα) mRNA]), and apoptotic response to TNF-α. Fat mass increased by 1.9 ± 0.2 kg in the upper body and 1.6 ± 0.1 kg in the lower body. Average abdominal s.c. adipocyte size increased by 0.16 ± 0.06 μg lipid per cell and correlated with relative upper-body fat gain (r = 0.74, P < 0.0001). However, lower-body fat responded to overfeeding by fat-cell hyperplasia, with adipocyte number increasing by 2.6 ± 0.9 × 109 cells (P < 0.01). We found no depot-differences in preadipocyte replication or apoptosis that would explain lower-body adipocyte hyperplasia and abdominal s.c. adipocyte hypertrophy. However, baseline PPARγ2 and C/EBPα mRNA were higher in abdominal than femoral s.c. preadipocytes (P < 0.005 and P < 0.03, respectively), consistent with the ability of abdominal s.c. adipocytes to achieve a larger size. Inherent differences in preadipocyte cell dynamics may contribute to the distinct responses of different fat depots to overfeeding, and fat-cell number increases in certain depots in adults after only 8 wk of increased food intake