Interleukin-1 beta released by gp120 drives neural death through tyrosine phosphorylation and trafficking of NMDA receptors

Interleukin-1 beta is a proinflammatory cytokine implicated under pathological conditions involving NMDA receptor activation, including the AIDS dementia complex (HAD). No information is available on the molecular mechanisms recruited by native interleukin-1 beta produced under this type of condition. Using a sandwich co-culture of primary hippocampal neurons and glia, we investigated whether native interleukin-1 beta released by HIV-gp120-activated glia (i) affects NMDAR functions and (ii) the relevance on neuronal spine density and survival, two specific traits of HAD. Increased phosphorylation of NR2B Tyr-1472 was observed after 24 h of exposure of neurons to 600 pM gp120. This effect occurred only when neurons were treated in the presence of glial cells and was abolished by the interleukin-1 receptor antagonist (IL-1ra). Gp120-induced phosphorylation of NR2B resulted in a sustained elevation of intracellular Ca2+ in neurons and in a significant increase of NR2B binding to PSD95. Increased intracellular Ca2+ was prevented by 10 mu M ifenprodil, that selectively inhibits receptors containing the NR2B, by interleukin-1ra and by Ca-pYEEIE, a Src family SH2 inhibitor peptide. These last two inhibitors, prevented also NR2B binding to PSD95. Finally, gp120 reduced by 35% of the total PSD95 positive spine density after 48 h of treatment and induced by 30% of the neuronal death. Again, both of these effects were blocked by Ca-pYEEIE. Altogether, our data show that gp120 releasing interleukin-1 beta from glia increases tyrosine phosphorylation of NMDAR. Thus, tyrosine phosphorylation may contribute to the sensitization of the receptor increasing its function and synaptic localization. Both of these effects are relevant for neurodegeneration

Characterization of molecular mechanisms underlying the axonal Charcot-Marie-Tooth neuropathy caused by MORC2 mutations

[EN] Mutations in MORC2 lead to an axonal form of Charcot-Marie-Tooth (CMT) neuropathy type 2Z. To date, 31 families have been described with mutations in MORC2, indicating that this gene is frequently involved in axonal CMT cases. While the genetic data clearly establish the causative role of MORC2 in CMT2Z, the impact of its mutations on neuronal biology and their phenotypic consequences in patients remains to be clarified. We show that the full-length form of MORC2 is highly expressed in both embryonic and adult human neural tissues and that Morc2 expression is dynamically regulated in both the developing and the maturing murine nervous system. To determine the effect of the most common MORC2 mutations, p.S87L and p.R252W, we used several in vitro cell culture paradigms. Both mutations induced transcriptional changes in patient-derived fibroblasts and when expressed in rodent sensory neurons. These changes were more pronounced and accompanied by abnormal axonal morphology, in neurons expressing the MORC2 p.S87L mutation, which is associated with a more severe clinical phenotype. These data provide insight into the neuronal specificity of the mutated MORC2-mediated phenotype and highlight the importance of neuronal cell models to study the pathophysiology of CMT2Z.Instituto de Salud Carlos III (ISCIII) - Subdireccion General de Evaluacion y Fomento de la Investigacion within the framework of the National R+D+I Plan (PI15/00187 to C. E. and PI16/00403 to T. S.), co-funded with FEDER funds; Ramon Areces Foundation (CIVP17A2810 to C. E.); Generalitat Valenciana (PROMETEO/2018/135 to C. E. and T. S.); AFM-Telethon (21500 to C. E. and R. C.); National Health and Medical Research Council of Australia Grant (APP1046680 to M. K.); Czech Health Research Council (AZV16-30206A to P. L.); Swedish StratNeuro program grant; Swedish Research Council (2015-02394 to R. C.). C. E. had a 'Miguel Servet' contract funded by the ISCIII and the Centro de Investigacion Principe Felipe (CPII14/00002). P. S. is the recipient of a FPU-PhD fellowship funded by the Spanish Ministry of Education, Culture and Sport [FPU15/00964]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Sancho, P.; Bartesaghi, L.; Miossec, O.; García-García, F.; Ramírez-Jiménez, L.; Siddell, A.; Ajkesson, E.... (2019). Characterization of molecular mechanisms underlying the axonal Charcot-Marie-Tooth neuropathy caused by MORC2 mutations. Human Molecular Genetics. 28(10):1629-1644. https://doi.org/10.1093/hmg/ddz00616291644281

Missense mutations in TENM4, a regulator of axon guidance and central myelination, cause essential tremor

Essential tremor (ET) is a common movement disorder with an estimated prevalence of 5% of the population aged over 65 years. In spite of intensive efforts, the genetic architecture of ET remains unknown. We used a combination of whole-exome sequencing and targeted resequencing in three ET families. In vitro and in vivo experiments in oligodendrocyte precursor cells and zebrafish were performed to test our findings. Whole-exome sequencing revealed a missense mutation in TENM4 segregating in an autosomal-dominant fashion in an ET family. Subsequent targeted resequencing of TENM4 led to the discovery of two novel missense mutations. Not only did these two mutations segregate with ET in two additional families, but we also observed significant over transmission of pathogenic TENM4 alleles across the three families. Consistent with a dominant mode of inheritance, in vitro analysis in oligodendrocyte precursor cells showed that mutant proteins mislocalize. Finally, expression of human mRNA harboring any of three patient mutations in zebrafish embryos induced defects in axon guidance, confirming a dominant-negative mode of action for these mutations. Our genetic and functional data, which is corroborated by the existence of a Tenm4 knockout mouse displaying an ET phenotype, implicates TENM4 in ET. Together with previous studies of TENM4 in model organisms, our studies intimate that processes regulating myelination in the central nervous system and axon guidance might be significant contributors to the genetic burden of this disorde

PRDM12 Is Required for Initiation of the Nociceptive Neuron Lineage during Neurogenesis

Summary: The sensation of pain is essential for the preservation of the functional integrity of the body. However, the key molecular regulators necessary for the initiation of the development of pain-sensing neurons have remained largely unknown. Here, we report that, in mice, inactivation of the transcriptional regulator PRDM12, which is essential for pain perception in humans, results in a complete absence of the nociceptive lineage, while proprioceptive and touch-sensitive neurons remain. Mechanistically, our data reveal that PRDM12 is required for initiation of neurogenesis and activation of a cascade of downstream pro-neuronal transcription factors, including NEUROD1, BRN3A, and ISL1, in the nociceptive lineage while it represses alternative fates other than nociceptors in progenitor cells. Our results thus demonstrate that PRDM12 is necessary for the generation of the entire lineage of pain-initiating neurons. : The sensation of pain, temperature, and itch by neurons of the nociceptive lineage is essential for animal survival. Bartesaghi et al. report that the transcriptional regulator PRDM12 is indispensable in neural crest cells (NCCs) for the initiation of the sensory neuronal differentiation program that generates the entire nociceptive lineage. Keywords: neurogenesis, pain, nociceptive neurons, Prdm12, neural crest cell

PLEKHG5 deficiency leads to an intermediate form of autosomal-recessive Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT) comprises a clinically and genetically heterogeneous group of peripheral neuropathies characterized by progressive distal muscle weakness and atrophy, foot deformities and distal sensory loss. Following the analysis of two consanguineous families affected by a medium to late-onset recessive form of intermediate CMT, we identified overlapping regions of homozygosity on chromosome 1p36 with a combined maximum LOD score of 5.4. Molecular investigation of the genes from this region allowed identification of two homozygous mutations in PLEKHG5 that produce premature stop codons and are predicted to result in functional null alleles. Analysis of Plekhg5 in the mouse revealed that this gene is expressed in neurons and glial cells of the peripheral nervous system, and that knockout mice display reduced nerve conduction velocities that are comparable with those of affected individuals from both families. Interestingly, a homozygous PLEKHG5 missense mutation was previously reported in a recessive form of severe childhood onset lower motor neuron disease (LMND) leading to loss of the ability to walk and need for respiratory assistance. Together, these observations indicate that different mutations in PLEKHG5 lead to clinically diverse outcomes (intermediate CMT or LMND) affecting the function of neurons and glial cell

Injured axons instruct schwann cells to build constricting actin spheres to accelerate axonal disintegration

After a peripheral nerve lesion, distal ends of injured axons disintegrate into small fragments that are subsequently cleared by Schwann cells and later by macrophages. Axonal debris clearing is an early step of the repair process that facilitates regeneration. We show here that Schwann cells promote distal cut axon disintegration for timely clearing. By combining cell-based and in vivo models of nerve lesion with mouse genetics, we show that this mechanism is induced by distal cut axons, which signal to Schwann cells through PlGF mediating the activation and upregulation of VEGFR1 in Schwann cells. In turn, VEGFR1 activates Pak1, leading to the formation of constricting actomyosin spheres along unfragmented distal cut axons to mediate their disintegration. Interestingly, oligodendrocytes can acquire a similar behavior as Schwann cells by enforced expression of VEGFR1. These results thus identify controllable molecular cues of a neuron-glia crosstalk essential for timely clearing of damaged axons

Long-term monitoring of oxygen saturation at altitude can be useful in predicting the subsequent development of moderate to severe Acute Mountain Sickness

The use of pulse oximetry (SpO2) to identify subjects susceptible to AMS is the subject of debate. To obtain more reliable data, we monitored SpO2 for 24 hours at altitude to investigate the ability to predict impending AMS. Methods The study was conducted during the climb from Alagna (1154m) to Capanna Regina Margherita (4559m) with an overnight stay in Capanna Gnifetti (3647m). Sixty-two subjects (11F) were recruited. Each subject was fitted with a 24-hr recording finger pulse oximeter. The subjects rode a cable car to 3275m and climbed to 3647m, where they spent the night. Results In the morning, 24 (4F) had a Lake Louise Questionnaire score (LLS) ≥3 (AMS+), and 15 (4F) exhibited moderate to severe disease (LLS ≥5 = AMS++). At Alagna, SpO2 did not differ between the AMS- and AMS+. At higher stations, all AMS+ exhibited a significantly lower SpO2 than did the AMS-: at 3275m, 85.4% vs 87.7%; resting at 3647m, 84.5% vs 86.4%. The ROC curve analysis resulted in a rather poor discrimination between the AMS– and all of the AMS+. With the cut-off LLS ≥5, the sensitivity was 86.67%, the specificity was 82.5%, the AUC was 0.88 (p <0.0001) for SpO2≤84% at 3647m. Conclusions We conclude that AMS+ exhibit a more severe and prolonged oxygen desaturation than do AMS- starting from the beginning of altitude exposure, but the predictive power of SpO2 is accurate only for AMS++