Spontaneous neural activity promotes axon growth in many types of developing neurons, including motoneurons. In motoneurons from a mouse model of spinal muscular atrophy (SMA), defects in axonal growth and presynaptic function correlate with a reduced frequency of spontaneous Ca(2+) transients in axons which are mediated by N-type Ca(2+) channels. To characterize the mechanisms that initiate spontaneous Ca(2+) transients, we investigated the role of voltage-gated sodium channels (VGSCs). We found that low concentrations of the VGSC inhibitors tetrodotoxin (TTX) and saxitoxin (STX) reduce the rate of axon growth in cultured embryonic mouse motoneurons without affecting their survival. STX was 5- to 10-fold more potent than TTX and Ca(2+) imaging confirmed that low concentrations of STX strongly reduce the frequency of spontaneous Ca(2+) transients in somatic and axonal regions. These findings suggest that the Na(V)1.9, a VGSC that opens at low thresholds, could act upstream of spontaneous Ca(2+) transients. qPCR from cultured and laser-microdissected spinal cord motoneurons revealed abundant expression of Na(V)1.9. Na(V)1.9 protein is preferentially localized in axons and growth cones. Suppression of Na(V)1.9 expression reduced axon elongation. Motoneurons from Na(V)1.9(-/-) mice showed the reduced axon growth in combination with reduced spontaneous Ca(2+) transients in the soma and axon terminals. Thus, Na(V)1.9 function appears to be essential for activity-dependent axon growth, acting upstream of spontaneous Ca(2+) elevation through voltage-gated calcium channels (VGCCs). Na(V)1.9 activation could therefore serve as a target for modulating axonal regeneration in motoneuron diseases such as SMA in which presynaptic activity of VGCCs is reduced.

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disease affecting lower motor neurons. SMA is caused by mutations in the Survival Motor Neuron 1 (SMN1) gene, which result in reduced levels of functional SMN protein. Biochemical studies have linked the ubiquitously expressed SMN protein to the assembly of pre-mRNA processing U snRNPs, raising the possibility that aberrant splicing is a major defect in SMA. Accordingly, several transcripts affected upon SMN deficiency have been reported. A second function for SMN in axonal mRNA transport has also been proposed that may likewise contribute to the SMA phenotype. The underlying etiology of SMA, however, is still not fully understood. Here, we have used a combination of genomics and live Ca(2+) imaging to investigate the consequences of SMN deficiency in a zebrafish model of SMA. In a transcriptome analyses of SMN-deficient zebrafish, we identified neurexin2a (nrxn2a) as strongly down-regulated and displaying changes in alternative splicing patterns. Importantly, the knock-down of two distinct nrxn2a isoforms phenocopies SMN-deficient fish and results in a significant reduction of motor axon excitability. Interestingly, we observed altered expression and splicing of Nrxn2 also in motor neurons from the Smn(-/-);SMN2(+/+) mouse model of SMA, suggesting conservation of nrxn2 regulation by SMN in mammals. We propose that SMN deficiency affects splicing and abundance of nrxn2a. This may explain the pre-synaptic defects at neuromuscular endplates in SMA pathophysiology.

Dichlorvos (DDVP) and monocrotophos (MC) are systemic insecticides and known to produce cholinergic and non-cholinergic effects. Individual toxic effects of these chemicals are known but their combined effects have not been studied. We studied the effect of concomitant exposure to DDVP and MC on selected biochemical variables suggestive of liver damage, changes in whole brain biogenic amines levels, acetylcholinesterase (AchE) and monoamine oxidase (MAO) activities in rats. Female rats were exposed to DDVP (2.5 mg/kg subcutaneously) and MC (1.8 mg/kg oral) either individually or in combination for 4 weeks. We observed significant decrease in more pronounced depletion in norepinephrine (NE) and dopamine (DA) levels during co-exposure to DDVP and MC. Brain AChE activity increased and activity of MAO showed significant depletion on co-exposure to DDVP and MC. Brain glutathione (GSH) and oxidized glutathione (GSSG) ratio decreased significantly during exposure to DDVP or MC while co-exposure to these toxicants led to a more pronounced depletion of GSH: GSSG ratio. Serum aspartate amino transferase (AST) and alkaline phosphatase (ALP) activities increased significantly on exposure to MC suggesting liver injury, while DDVP alone had no effect on these variables. There were no effects of DDVP and MC exposure on haematological biochemical variables except for depletion in serum glucose level after MC exposure which was more pronounced DDVP + MC during co-exposure. It can be concluded that only moderate synergistic effects occur between MC and DDVP during co-exposure. A more detailed study with variable doses, prolonged exposure and alterations in different brain regions is recommended.

Palmitoylation has been recently identified as an important post-translational rheostat for controlling protein function in eukaryotes. However, the molecular machinery underlying palmitoylation remains unclear in the neglected tropical parasite, Leishmania donovani. Herein, we have identified a catalog of 20 novel palmitoyl acyltransferases (PATs) and characterized the promastigote-specific PAT (LdPAT4) containing the canonical Asp-His-His-Cys (DHHC) domain. Immunofluorescence analysis using in-house generated LdPAT4-specific antibody demonstrated distinct expression of LdPAT4 in the flagellar pocket of promastigotes. Using metabolic labeling-coupled click chemistry method, the functionality of this recombinant enzyme could be authenticated in E. coli strain expressing LdPAT4-DHHC domain. This was evident by the cellular uptake of palmitic acid analogs, which could be successfully inhibited by 2-BMP, a PAT-specific inhibitor. Using CSS-Palm based in-silico proteomic analysis, we could predict up to 23 palmitoylated sites per protein in the promastigotes, and further identify distinctive palmitoylated protein clusters involved in microtubule assembly, flagella motility and vesicular trafficking. To highlight, proteins such as Flagellar Member proteins (FLAM1, FLAM5), Intraflagellar Transport proteins (IFT88), and flagellar motor assembly proteins including the Dynein family were found to be enriched. Furthermore, analysis of global palmitoylation in promastigotes using Acyl-biotin exchange purification identified a set of S-palmitoylated proteins overlapping with the in-silico proteomics data. The attenuation of palmitoylation using 2-BMP demonstrated several phenotypic alterations in the promastigotes including distorted morphology, reduced motility (flagellar loss or slow flagellar beating), and inefficient invasion of promastigotes to host macrophages. These analyses confirm the essential role of palmitoylation in promastigotes. In summary, the findings suggest that LdPAT4 acts as a functional acyltransferase that can regulate palmitoylation of proteins involved in parasite motility and invasion, thus, can serve as a potential target for designing chemotherapeutics in Visceral Leishmaniasis.

Abrin is a plant glycoprotein toxin from the seeds of Abrus precatorius, sharing similarity in structure and properties with ricin. Abrin is highly toxic, with an estimated human fatal dose of 0.1-1 µg/kg, causing death after accidental or intentional poisoning. It is a potent biological toxin warfare agent. There is no chemical antidote available against the abrin. The elucidation of molecular mechanism of abrin-induced cell death is important for development of therapy. Intrinsic pathway-mediated apoptosis has been well established in abrin-induced cell death. However, the detailed mechanism especially extrinsic receptor-mediated pathway remains uncharacterized. To assess whether some of the apoptosis known to occur after abrin exposure might be mediated by Fas/Fas ligand (Fas L) interactions, we analyzed effect of abrin on Fas pathway in Jurkat cells. Here, we report that activation of the Fas pathway is involved in abrin-induced apoptosis. Following treatment of abrin, Fas L was induced, which stimulated the Fas pathway by cross-linking Fas receptor (Fas R). Apoptosis was mediated by cleavage of the Fas R proximal caspase-8 and the downstream caspase-3, resulting in activation of the prototype caspase substrate poly-(ADP-ribose) polymerase and caspase-activated DNase. Blocking Fas L/Fas R interaction by using Fas inhibitor reduced abrin-induced apoptosis, further confirms involvement of Fas pathway. Activation of components of Fas pathway and caspases upon abrin treatment was also found in splenocytes in mice. Our findings offer new perspective for understanding the fundamental mechanism in abrin-induced apoptotic mechanism and may have implication in developing novel therapeutic strategies in the management for abrin-induced complications.