NGF acts via p75 low-affinity neurotrophin receptor and calpain inhibition to reduce UV neurotoxicity

Small-molecule modulation of the p75 neurotrophin receptor inhibits a wide range of tau molecular pathologies and their sequelae in P301S tauopathy mice

In tauopathies, phosphorylation, acetylation, cleavage and other modifications of tau drive intracellular generation of diverse forms of toxic tau aggregates and associated seeding activity, which have been implicated in subsequent synaptic failure and neurodegeneration. Suppression of this wide range of pathogenic species, seeding and toxicity mechanisms, while preserving the physiological roles of tau, presents a key therapeutic goal. Identification and targeting of signaling networks that influence a broad spectrum of tau pathogenic mechanisms might prevent or reverse synaptic degeneration and modify disease outcomes. The p75 neurotrophin receptor (p75NTR) modulates such networks, including activation of multiple tau kinases, calpain and rhoA-cofilin activity. The orally bioavailable small-molecule p75NTR modulator, LM11A-31, was administered to tauP301S mice for 3 months starting at 6 months of age, when tau pathology was well established. LM11A-31 was found to reduce: excess activation of hippocampal cdk5 and JNK kinases and calpain; excess cofilin phosphorylation, tau phosphorylation, acetylation and cleavage; accumulation of multiple forms of insoluble tau aggregates and filaments; and, microglial activation. Hippocampal extracts from treated mice had substantially reduced tau seeding activity. LM11A-31 treatment also led to a reversal of pyramidal neuron dendritic spine loss, decreased loss of dendritic complexity and improvement in performance of hippocampal behaviors. These studies identify a therapeutically tractable upstream signaling module regulating a wide spectrum of basic mechanisms underlying tauopathies.

Adipose-derived Stem Cell Conditioned Media Extends Survival time of a mouse model of Amyotrophic Lateral Sclerosis

Adipose stromal cells (ASC) secrete various trophic factors that assist in the protection of neurons in a variety of neuronal death models. In this study, we tested the effects of human ASC conditional medium (ASC-CM) in human amyotrophic lateral sclerosis (ALS) transgenic mouse model expressing mutant superoxide dismutase (SOD1^G93A). Treating symptomatic SOD1^G93A mice with ASC-CM significantly increased post-onset survival time and lifespan. Moreover, SOD1^G93A mice given ASC-CM treatment showed high motor neuron counts, less activation of microglia and astrocytes at an early symptomatic stage in the spinal cords under immunohistochemical analysis. SOD1^G93A mice treated with ASC-CM for 7 days showed reduced levels of phosphorylated p38 (pp38) in the spinal cord, a mitogen-activated protein kinase that is involved in both inflammation and neuronal death. Additionally, the levels of α-II spectrin in spinal cords were also inhibited in SOD1^G93A mice treated with ASC-CM for 3 days. Interestingly, nerve growth factor (NGF), a neurotrophic factor found in ASC-CM, played a significant role in the protection of neurodegeneration inSOD1^G93A mouse. These results indicate that ASC-CM has the potential to develop into a novel and effective therapeutic treatment for ALS.

The biological functions and signaling mechanisms of the p75 neurotrophin receptor

The p75 neurotrophin receptor (p75(NTR)) regulates a wide range of cellular functions, including programmed cell death, axonal growth and degeneration, cell proliferation, myelination, and synaptic plasticity. The multiplicity of cellular functions governed by the receptor arises from the variety of ligands and co-receptors which associate with p75(NTR) and regulate its signaling. P75(NTR) promotes survival through interactions with Trk receptors, inhibits axonal regeneration via partnerships with Nogo receptor (Nogo-R) and Lingo-1, and promotes apoptosis through association with Sortilin. Signals downstream of these interactions are further modulated through regulated intramembrane proteolysis (RIP) of p75(NTR) and by interactions with numerous cytosolic partners. In this chapter, we discuss the intricate signaling mechanisms of p75(NTR), emphasizing how these signals are differentially regulated to mediate these diverse cellular functions.

Ultra violet-induced localized inflammatory hyperalgesia in awake rats and the role of sensory and sympathetic innervation of the skin

Exposure to mid range ultrat violet radiations (UVBs) has been shown to produce systemic inflammation and hyperalgesia in mice [Saadé, N.E., Nasr, I.W., Massaad, C.A., Safieh-Garabedian, B., Jabbur, S.J., Kanaan, S.A., 2000. Modulation of ultraviolet-induced hyperalgesia and cytokine upregulation by interleukins 10 and 13. Br. J. Pharmacol. 131, 1317-1324]. Our aim was to characterize a new rat model of localized exposure to UVB and to determine the role of skin innervation in the observed hyperalgesia and cytokine upregulation. In several groups of rats one hindpaw was exposed to UVB (250-350 mJ/cm(2)) and this was followed by the application, to the plantar area of the paw, of either Von Frey hairs or a few acetone drops to measure tactile and cold allodynia, respectively. Thermal hyperalgesia was assessed by the paw withdrawal latency and duration. Cytokine levels were determined, by ELISA, in processed samples of skin tissue isolated from the exposed and non-exposed paws. UVB induced a biphasic thermal hyperalgesia and cold and tactile allodynia with an early phase that peaked at 3-6h and disappeared at 24h and a late phase with a peak at 48 h and recovery at 72-h post-exposure. Tumor necrosis factor, interleukins 1 beta, 6, 8, 10 and NGF levels were significantly increased following the same biphasic temporal pattern. Chemical ablation of capsaicin sensitive afferents and guanethidine injection produced significant alteration of the hyperalgesia and allodynia. The increase in cytokine levels by UVB was also altered by both treatments. The present study describes a new animal model for localized UVB-induced inflammatory hyperalgesia and provides evidence about the involvement of neurogenic mechanisms in the observed hyperalgesia and upregulation of proinflammatory mediators.

Molecular and cellular immune mediators of neuroprotection

Our view of the immune privileged status of the brain has dramatically changed during the past two decades. Even though systemic immune stimuli have the ability to activate different populations of neurons, cells of monocytic lineage also have access to the neuronal tissue and populate it as microglia. Although such a phenomenon is limited in intact brains, it is greatly increased during neurodegenerative processes associated with innate immunity and the release of pro-inflammatory molecules by either resident microglia or those derived from the bone marrow stem cells. The role of these events is currently a matter of great debate and controversy, especially as it relates to brain protection, repair, or further injury. In recent years, accumulating data have supported the notion that when immune molecules are timely released by microglia, they limit neuronal injury in the presence of pathogens and toxic agents, help clear debris from degenerated cells, and restore the cerebral environment for repair. It has been shown that alteration of the natural innate immune response by microglia has direct consequences in exacerbating the damages following acute injury to neurons. This article presents and discusses these data, supporting a powerful neuroprotective role for microglia and their innate immune reactions in response to pathogens and central nervous system insults.

p35/Cyclin-dependent kinase 5 is required for protection against beta-amyloid-induced cell death but not tau phosphorylation by ceramide

Ceramide is a bioactive sphingolipid that can prevent calpain activation and beta-amyloid (A beta) neurotoxicity in cortical neurons. Recent evidence supports A beta induction of a calpain-dependent cleavage of the cyclin-dependent kinase 5 (cdk5) regulatory protein p35 that contributes to tau hyperphosphorylation and neuronal death. Using cortical neurons isolated from wild-type and p35 knockout mice, we investigated whether ceramide required p35/cdk5 to protect against A beta-induced cell death and tau phosphorylation. Ceramide inhibited A beta-induced calpain activation and cdk5 activity in wild-type neurons and protected against neuronal death and tau hyperphosphorylation. Interestingly, A beta also increased cdk5 activity in p35-/- neurons, suggesting that the alternate cdk5 regulatory protein, p39, might mediate this effect. In p35 null neurons, ceramide blocked A beta-induced calpain activation but did not inhibit cdk5 activity or cell death. However, ceramide blocked tau hyperphosphorylation potentially via inhibition of glycogen synthase kinase-3beta. These data suggest that ceramide can regulate A beta cell toxicity in a p35/cdk5-dependent manner.

Overexpression of selenoprotein H reduces Ht22 neuronal cell death after UVB irradiation by preventing superoxide formation

Selenoproteins have been shown to exhibit a variety of biological functions, including antioxidant functions, maintaining cellular redox balance, and heavy metal detoxification. UV irradiation-induced damage is partially mediated by increased oxygen radical production. The present study is designed to examine the antioxidative effects of human selenoprotein H (hSelH) after brief period of UVB irradiation on the murine hippocampal neuronal cell line Ht22. Ht22 cells were stably transfected with the hSelH gene or with MSCV empty vector and exposed to UVB irradiation with or without the presence of serum. The results showed that cell viability was significantly higher in hSelH-transfected cells compared to the MSCV vector-transfected cells after 24 h of recovery with or without the presence of serum in the media. Further studies revealed that while the number of superoxide anion (O2˙-) positive cells was increased following a 7 mJ/cm² of UVB irradiation and 5 h of recovery, overexpression of hSelH significantly reduced superoxide production. These results suggest that hSelH overexpression protects cells from UVB irradiation-induced cell death by reducing the O2˙- formation.

Nerve growth factor affects Ca2+ currents via the p75 receptor to enhance prolactin mRNA levels in GH3 rat pituitary cells

In clonal pituitary GH(3) cells, spontaneous action potentials drive the opening of Ca(v)1 (L-type) channels, leading to Ca(2+) transients that are coupled to prolactin gene transcription. Nerve growth factor (NGF) has been shown to stimulate prolactin synthesis by GH(3) cells, but the underlying mechanisms are unknown. Here we studied whether NGF influences prolactin gene expression and Ca(2+) currents. By using RT-PCR, NGF (50 ng ml(-1)) was found to augment prolactin mRNA levels by approximately 80% when applied to GH(3) cells for 3 days. A parallel change in the prolactin content was detected by Western blotting. Both NGF-induced responses were mimicked by an agonist (Bay K 8644) and prevented by a blocker (nimodipine) of L-type channels. In whole-cell patch-clamp experiments, NGF enhanced the L-type Ca(2+) current by approximately 2-fold within 60 min. This effect reversed quickly upon growth factor withdrawal, but was maintained for days in the continued presence of NGF. In addition, chronic treatment (>or= 24 h) with NGF amplified the T-type current, which flows through Ca(v)3 channels and is thought to support pacemaking activity. Thus, NGF probably increases the amount of Ca(2+) that enters per action potential and may also induce a late increase in spike frequency. MC192, a specific antibody for the p75 neurotrophin receptor, but not tyrosine kinase inhibitors (K252a and lavendustin A), blocked the effects of NGF on Ca(2+) currents. Overall, the results indicate that NGF activates the p75 receptor to cause a prolonged increase in Ca(2+) influx through L-type channels, which in turn up-regulates the prolactin mRNA.