Amyotrophic lateral sclerosis (ALS) is a fatal degenerative motor neuron disorder of which the progression is influenced by several disease-modifying factors. Here, we investigated ELP3, a subunit of the elongator complex that modifies tRNA wobble uridines, as one of such ALS disease modifiers. ELP3 attenuated the axonopathy of a mutant SOD1, as well as of a mutant C9orf72 ALS zebrafish model. Furthermore, the expression of ELP3 in the SOD1^G93A mouse extended the survival and attenuated the denervation in this model. Depletion of ELP3 in vitro reduced the modified tRNA wobble uridine mcm⁵s²U and increased abundance of insoluble mutant SOD1, which was reverted by exogenous ELP3 expression. Interestingly, the expression of ELP3 in the motor cortex of ALS patients was reduced and correlated with mcm⁵s²U levels. Our results demonstrate that ELP3 is a modifier of ALS and suggest a link between tRNA modification and neurodegeneration.

Striatal-enriched protein tyrosine phosphatase (STEP) is highly expressed in striatal projection neurons, the neuronal population most affected in Huntington's disease. Here, we examined STEP expression and phosphorylation, which regulates its activity, in N-terminal exon-1 and full-length mutant huntingtin mouse models. R6/1 mice displayed reduced STEP protein levels in the striatum and cortex, whereas its phosphorylation was increased in the striatum, cortex, and hippocampus. The early increase in striatal STEP phosphorylation levels correlated with a deregulation of the protein kinase A pathway, and decreased calcineurin activity at later stages further contributes to an enhancement of STEP phosphorylation and inactivation. Accordingly, we detected an accumulation of phosphorylated ERK2 and p38, two targets of STEP, in R6/1 mice striatum at advanced stages of the disease. Activation of STEP participates in excitotoxic-induced cell death. Because Huntington's disease mouse models develop resistance to excitotoxicity, we analyzed whether decreased STEP activity was involved in this process. After intrastriatal quinolinic acid (QUIN) injection, we detected higher phosphorylated STEP levels in R6/1 than in wild-type mice, suggesting that STEP inactivation could mediate neuroprotection in R6/1 striatum. In agreement, intrastriatal injection of TAT–STEP increased QUIN-induced cell death. R6/2, Tet/HD94, and Hdh^Q7/Q111mice striatum also displayed decreased STEP protein and increased phosphorylation levels. In Tet/HD94 mice striatum, mutant huntingtin transgene shutdown reestablished STEP expression. In conclusion, the STEP pathway is severely downregulated in the presence of mutant huntingtin and may participate in compensatory mechanisms activated by striatal neurons that lead to resistance to excitotoxicity.

Huntington’s disease (HD) is a polyglutamine disorder caused by a CAG expansion in the Huntingtin (HTT) gene exon 1. This expansion encodes a mutant protein whose abnormal function is traditionally associated with HD pathogenesis; however, recent evidence has also linked HD pathogenesis to RNA stable hairpins formed by the mutant HTT expansion. Here, we have shown that a locked nucleic acid–modified antisense oligonucleotide complementary to the CAG repeat (LNA-CTG) preferentially binds to mutant HTT without affecting HTT mRNA or protein levels. LNA-CTGs produced rapid and sustained improvement of motor deficits in an R6/2 mouse HD model that was paralleled by persistent binding of LNA-CTG to the expanded HTT exon 1 transgene. Motor improvement was accompanied by a pronounced recovery in the levels of several striatal neuronal markers severely impaired in R6/2 mice. Furthermore, in R6/2 mice, LNA-CTG blocked several pathogenic mechanisms caused by expanded CAG RNA, including small RNA toxicity and decreased Rn45s expression levels. These results suggest that LNA-CTGs promote neuroprotection by blocking the detrimental activity of CAG repeats within HTT mRNA. The present data emphasize the relevance of expanded CAG RNA to HD pathogenesis, indicate that inhibition of HTT expression is not required to reverse motor deficits, and further suggest a therapeutic potential for LNA-CTG in polyglutamine disorders.

Amyotrophic lateral sclerosis (ALS) is characterized by the selective death of motor neurons in the motor cortex, brainstem and spinal cord. It is a neurodegenerative disorder with high genetic and phenotypic variability. In most patients, the cause of the disease is unknown. Until now, no treatment strategy has been discovered with the exception of riluzole which has a moderate effect on the disease process. While developing a new causal therapy targeting a specific disease-causing gene can have a huge effect on the disease process, only a limited number of ALS patients will benefit from such a therapy. Alternatively, pathogenic processes that are common in ALS patients with different etiology can also be targeted. The effect of such a modifying treatment will be smaller, but the target population will be larger as more ALS patients could benefit. In this review, we summarize the evidence for the involvement of different biological processes in the pathogenesis of ALS and will discuss how strategies influencing these processes can be translated into new therapeutic approaches. In order to further improve this translational step, there is an urgent need for a better understanding of the underlying mechanism(s), for new ALS animal models and for rigorous protocols to perform preclinical studies.

Liver X receptors (LXRs) exert key functions in lipid homeostasis and in control of inflammation. In this study we have explored the impact of LXR activation on the macrophage response to the endogenous inflammatory cytokine IFN-γ. Transcriptional profiling studies demonstrate that ∼38% of the IFN-γ–induced transcriptional response is repressed by LXR activation in macrophages. LXRs also mediated inhibitory effects on selected IFN-γ–induced genes in primary microglia and in a model of IFN-γ–induced neuroinflammation in vivo. LXR activation resulted in reduced STAT1 recruitment to the promoters tested in this study without affecting STAT1 phosphorylation. A closer look into the mechanism revealed that SUMOylation of LXRs, but not the presence of nuclear receptor corepressor 1, was required for repression of the NO synthase 2 promoter. We have also analyzed whether IFN-γ signaling exerts reciprocal effects on LXR targets. Treatment with IFN-γ inhibited, in a STAT1-dependent manner, the LXR-dependent upregulation of selective targets, including ATP-binding cassette A1 (ABCA1) and sterol response element binding protein 1c. Downregulation of ABCA1 expression correlated with decreased cholesterol efflux to apolipoprotein A1 in macrophages stimulated with IFN-γ. The inhibitory effects of IFN-γ on LXR signaling did not involve reduced binding of LXR/retinoid X receptor heterodimers to target gene promoters. However, overexpression of the coactivator CREB-binding protein/p300 reduced the inhibitory actions of IFN-γ on the Abca1 promoter, suggesting that competition for CREB-binding protein may contribute to STAT1-dependent downregulation of LXR targets. The results from this study suggest an important level of bidirectional negative cross-talk between IFN-γ/STAT1 and LXRs with implications both in the control of IFN-γ–mediated immune responses and in the regulation of lipid metabolism.

The ephrin receptor A4 (EphA4) is one of the receptors in the ephrin system that plays a pivotal role in a variety of cell-cell interactions, mostly studied during development. In addition, EphA4 has been found to play a role in cancer biology as well as in the pathogenesis of several neurological disorders such as stroke, spinal cord injury, multiple sclerosis, amyotrophic lateral sclerosis (ALS), and Alzheimer's disease. Pharmacological blocking of EphA4 has been suggested to be a therapeutic strategy for these disorders. Therefore, the aim of our study was to generate potent and selective Nanobodies against the ligand-binding domain of the human EphA4 receptor. We identified two Nanobodies, Nb 39 and Nb 53, that bind EphA4 with affinities in the nanomolar range. These Nanobodies were most selective for EphA4, with residual binding to EphA7 only. Using Alphascreen technology, we found that both Nanobodies displaced all known EphA4-binding ephrins from the receptor. Furthermore, Nb 39 and Nb 53 inhibited ephrin-induced phosphorylation of the EphA4 protein in a cell-based assay. Finally, in a cortical neuron primary culture, both Nanobodies were able to inhibit endogenous EphA4-mediated growth-cone collapse induced by ephrin-B3. Our results demonstrate the potential of Nanobodies to target the ligand-binding domain of EphA4. These Nanobodies may deserve further evaluation as potential therapeutics in disorders in which EphA4-mediated signaling plays a role.