Amyotrophic lateral sclerosis (ALS) is characterized by the degeneration of motoneurons in the cerebral cortex, brainstem and spinal cord. Neuroinflammation plays an important role in the pathogenesis of ALS and involves the activation of microglia and astrocytes. Intracellular inflammasome complexes are part of the innate immunity as they sense and execute host inflammatory responses. The best characterized component is the NLRP3 inflammasome comprised of the NLR protein NLRP3, the adaptor ASC and pro-caspase 1. The NLRP3 inflammasome is critical for the activation of caspase 1 and the processing and release of IL1β and IL18. In this study, we investigated the expression, activation and co-localization of the NLRP3 inflammasome in the spinal cord of male SOD1(G93A) mice carrying a mutant human superoxide dismutase 1 (SOD1) variant and regarded as an animal model for ALS as well as in post-mortem tissue of ALS patients. NLRP3 and its molecular components as well as IL1β were already detectable in SOD1 mice at a pre-symptomatic stage after 9 weeks and further increased in 14 week old animals. Spinal cord astrocytes were identified as the major cell type expressing NLRP3 components. In human ALS tissue, we also found increased NLRP3, ASC, IL18 and active caspase 1 levels compared to control patients. Our findings suggest that astroglial NLRP3 inflammasome complexes are critically involved in neuroinflammation in ALS.

Intracellular accumulations of mutant, misfolded proteins are major pathological hallmarks of amyotrophic lateral sclerosis (ALS) and related disorders. Recently, mutations in Sigma receptor 1 (SigR1) have been found to cause a form of ALS and frontotemporal lobar degeneration (FTLD). Our goal was to pinpoint alterations and modifications of SigR1 in ALS and to determine how these changes contribute to the pathogenesis of ALS. In the present study, we found that levels of the SigR1 protein were reduced in lumbar ALS patient spinal cord. SigR1 was abnormally accumulated in enlarged C-terminals and endoplasmic reticulum (ER) structures of alpha motor neurons. These accumulations co-localized with the 20s proteasome subunit. SigR1 accumulations were also observed in SOD1 transgenic mice, cultured ALS-8 patient's fibroblasts with the P56S-VAPB mutation and in neuronal cell culture models. Along with the accumulation of SigR1 and several other proteins involved in protein quality control, severe disturbances in the unfolded protein response and impairment of protein degradation pathways were detected in the above-mentioned cell culture systems. Furthermore, shRNA knockdown of SigR1 lead to deranged calcium signaling and caused abnormalities in ER and Golgi structures in cultured NSC-34 cells. Finally, pharmacological activation of SigR1 induced the clearance of mutant protein aggregates in these cells. Our results support the notion that SigR1 is abnormally modified and contributes to the pathogenesis of ALS.

Sex hormones, for example, estrogen and progesterone, are thought to affect and delay progression of multiple sclerosis (MS) in pregnant women. Although both steroid hormones are neuroprotective in the brain and elevated during pregnancy, only estrogen was tested in clinical trials. To evaluate the role of 17beta-estradiol (E) and progesterone (P) in prevention demyelination, young adult male mice were fed with cuprizone for a defined time interval and simultaneously treated with steroids by repeated injections into the neck region. The status of myelination was analyzed by magnetic resonance imaging and conventional histological staining. The individual application of E and P resulted only in a moderate prevention of demyelination in the corpus callosum (CC). The combined treatment with both steroid hormones counteracted the process of demyelination. Expression of the mature (PLP and MBP) and premature (PDGF-alpha-R) oligodendrocyte markers were significantly increased after hormone application in the affected CC. In addition, both hormones stimulated astrogliosis and the expression of IGF-1. Microglial invasion in demyelinated CC was pronounced and additionally localized in the midline of CC after hormone treatment. These data show that sex steroids can protect the brain from demyelination and stimulate remyelination. It appears that only the administration of both hormones is fully effective. The beneficial steroid effect requires interactions with oligodendrocytes possibly by preventing their degeneration or recruitment from precursor cells which are stimulated to remyelinated fibers. The positive hormonal influence on myelination in the CNS may be a future therapeutically strategy for the treatment of MS.

Stromal cell-derived factor-1 alpha (SDF-1a) or CXCL12 is an important cytokine with multiple functions in the brain during development and in adulthood. The inflammatory response initiated by spinal cord injury (SCI) involves the processing of interleukin-1beta (IL-1ß) and IL-18 mediated by caspase-1 which is under the control of an intracellular multiprotein complex termed inflammasome. Using an SCI rat model, we found improved functional long-term recovery which is paralleled by a reduction of apoptosis after intrathecal treatment with SDF-1a. An intriguing aspect is that SDF-1a changed the number of neuroinflammatory cells in the damaged area. We further examined the cellular localization and sequential expression of several inflammasomes during SCI at 6 h, 24 h, 3 days, and 7 days as well as the role of SDF-1a as a regulatory factor for inflammasomes. Using 14-week old male Wistar rats, spinal cord contusion was applied at the thoracic segment 9, and animals were subsequently treated with SDF-1a via intrathecal application through an osmotic pump. SCI temporally increased the expression of the inflammasomes NLRP3, ASC, the inflammatory marker tumor necrosis factor-a (TNF-a), interleukin-1ß (IL-1β) and IL-18. SDF-1a significantly reduced the levels of IL-18, IL-1b, TNF-a, NLRP3, ASC, and caspase-1. Immunofluorescence double-labeling demonstrated that microglia and neurons are major sources of the ASC and NLRP3 respectivley. Our data provide clear evidence that SCI stimulates a complex scenario of inflammasome activation at the injured site and that SDF-1a-mediated neuroprotection presumably depends on the attenuation of the inflammasome complex.