Negative regulation of TREM2-mediated C9orf72 poly-GA clearance by the NLRP3 inflammasome.

Expansion of the hexanucleotide repeat GGGGCC in the C9orf72 gene is the most common genetic factor in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Poly-Gly-Ala (poly-GA), one form of dipeptide repeat proteins (DPRs) produced from GGGGCC repeats, tends to form neurotoxic protein aggregates. The C9orf72 GGGGCC repeats and microglial receptor TREM2 are both associated with risk for ALS/FTD. The role and regulation of TREM2 in C9orf72-ALS/FTD remain unclear. Here, we found that poly-GA proteins activate the microglial NLRP3 inflammasome to produce interleukin-1ß (IL-1ß), which promotes ADAM10-mediated TREM2 cleavage and inhibits phagocytosis of poly-GA. The inhibitor of the NLRP3 inflammasome, MCC950, reduces the TREM2 cleavage and poly-GA aggregates, resulting in the alleviation of motor deficits in poly-GA mice. Our study identifies a crosstalk between NLRP3 and TREM2 signaling, suggesting that targeting the NLRP3 inflammasome to sustain TREM2 is an approach to treat C9orf72-ALS/FTD.

Effects of Pretreatment of the Dorsal Meningovertebral Ligaments on the Incidence of Intraoperative Cerebrospinal Fluid Leakage: A Comparative Study.

Cerebrospinal fluid leakage can lead to postoperative refractory headaches and meningitis. Dural injury is the main cause of postoperative cerebrospinal fluid leakage. Previously, we performed a comprehensive anatomic study on the dorsal meningovertebral ligaments in the lumbosacral regions and concluded that these ligaments are an anatomic factor leading to dural laceration. However, no clinical study has examined the relationship between dorsal meningovertebral ligaments and the incidence of intraoperative cerebrospinal fluid leakage. The goal of this study was to investigate the effect of prophylactic intraoperative pretreatment of the meningovertebral ligaments on the incidence of cerebrospinal fluid leakage during surgery. [Orthopedics. 2023;46(1):e66-e71.].

UBQLN2-HSP70 axis reduces poly-Gly-Ala aggregates and alleviates behavioral defects in the C9ORF72 animal model.

Expansion of a hexanucleotide repeat GGGGCC (G4C2) in the intron of the C9ORF72 gene is the most common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) (C9-ALS/FTD). Transcripts carrying G4C2 repeat expansions generate neurotoxic dipeptide repeat (DPR) proteins, including poly-Gly-Ala (poly-GA), which tends to form protein aggregates. Here, we demonstrate that UBQLN2, another ALS/FTD risk factor, is recruited to reduce poly-GA aggregates and alleviate poly-GA-induced neurotoxicity. UBQLN2 could recognize HSP70 ubiquitination, which facilitates the UBQLN2-HSP70-GA complex formation and promotes poly-GA degradation. ALS/FTD-related UBQLN2 mutants fail to bind HSP70 and clear poly-GA aggregates. Disruption of the interaction between UBQLN2 and HSP70 inhibits poly-GA aggregation in C9-ALS/FTD iPSC-derived neurons. Finally, enhancing HSP70 by the chemical compound 17AAG at the adult stage mitigates behavioral defects in poly-GA animals. Our findings suggest a critical role of the UBQLN2-HSP70 axis in protein aggregate clearance in C9-ALS/FTD.

APC2CDH1 negatively regulates agrin signaling by promoting the ubiquitination and proteolytic degradation of DOK7.

Neuromuscular junctions (NMJs) are peripheral synapses between motoneurons and skeletal muscle fibers that are critical for the control of muscle contraction. Dysfunction of these synapses has been implicated in congenital myasthenic syndrome (CMS). In vertebrates, agrin-LRP4-MuSK signaling plays a critical role in acetylcholine receptor (AChR) clustering and NMJ formation. The adaptor protein DOK7 is the downstream substrate of MuSK and also a cytoplasmic activator of MuSK. The role of DOK7 in the promotion of AChR clustering and the mechanisms involved have been well studied; however, the negative regulation of DOK7 after MuSK activation remains unknown. Anaphase-promoting complex 2 (APC2), the core subunit of APC/C E3 ligase complex, was originally believed to regulate cell-cycle transitions. Here, we show that APC2 is enriched at post-synapse of NMJs in postmitotic myotubes. In response to agrin stimulation, APC2 negatively regulates AChR clustering by promoting the ubiquitination of DOK7 at lysine 243 for its proteolytic degradation, which relies on MuSK kinase activity and the phosphorylation of tyrosine 106 in DOK7. Thus, this study provides a mechanism whereby agrin signaling is negatively regulated as part of vertebrate NMJ homeostasis.

Loss of mitochondrial protein CHCHD10 in skeletal muscle causes neuromuscular junction impairment.

The neuromuscular junction (NMJ) is a synapse between motoneurons and skeletal muscles to control motor behavior. Acetylcholine receptors (AChRs) are restricted at the synaptic region for proper neurotransmission. Mutations in the mitochondrial CHCHD10 protein have been identified in multiple neuromuscular disorders; however, the physiological roles of CHCHD10 at NMJs remain elusive. Here, we report that CHCHD10 is highly expressed at the postsynapse of NMJs in skeletal muscles. Muscle conditional knockout CHCHD10 mice showed motor defects, abnormal neuromuscular transmission and NMJ structure. Mechanistically, we found that mitochondrial CHCHD10 is required for ATP production, which facilitates AChR expression and promotes agrin-induced AChR clustering. Importantly, ATP could effectively rescue the reduction of AChR clusters in the CHCHD10-ablated muscles. Our study elucidates a novel physiological role of CHCHD10 at the peripheral synapse. It suggests that mitochondria dysfunction contributes to neuromuscular pathogenesis.

Motoneuron Wnts regulate neuromuscular junction development.

The neuromuscular junction (NMJ) is a synapse between motoneurons and skeletal muscles to control motor behavior. Unlike extensively investigated postsynaptic differentiation, less is known about mechanisms of presynaptic assembly. Genetic evidence of Wnt in mammalian NMJ development was missing due to the existence of multiple Wnts and their receptors. We show when Wnt secretion is abolished from motoneurons by mutating the Wnt ligand secretion mediator (Wls) gene, mutant mice showed muscle weakness and neurotransmission impairment. NMJs were unstable with reduced synaptic junctional folds and fragmented AChR clusters. Nerve terminals were swollen; synaptic vesicles were fewer and mislocated. The presynaptic deficits occurred earlier than postsynaptic deficits. Intriguingly, these phenotypes were not observed when deleting Wls in muscles or Schwann cells. We identified Wnt7A and Wnt7B as major Wnts for nerve terminal development in rescue experiments. These observations demonstrate a necessary role of motoneuron Wnts in NMJ development, in particular presynaptic differentiation.

[Effectiveness of ISOBAR TTL semi-rigid dynamic stabilization system in treatment of lumbar degenerative disease].

OBJECTIVE: To investigate the short-term effectiveness of ISOBAR TTL semi-rigid dynamic stabilization system (ISOBAR TTL system) in treatment of lumbar degenerative disease. METHODS: Between June 2007 and May 2011, 38 cases of lumbar degenerative disease were treated, including 24 males and 14 females with an average age of 51.2 years (range, 21-67 years). The disease duration was 8 months to 10 years (mean, 4.7 years). In 38 cases, there were 4 cases of grade I spondylolisthesis, 11 cases of lumbar instability and lumbar disc protrusion, 21 cases of lumbar spinal stenosis and lumbar disc protrusion, and 2 cases of postoperative recurrence of lumbar disc protrusion. There were 22 cases of adjacent segment disc degeneration. All cases underwent posterior decompression and implantation of ISOBAR TTL system. The double-segment-fixed patients underwent interbody fusion. Visual analogue scale (VAS) and Japanese Orthopaedic Association (JOA) scores for low back pain were used to evaluate clinical outcomes. The range of motion (ROM) at the semi-rigid dynamic stabilization segment was also measured. RESULTS: The other cases achieved healing of incision by first intention, except 1 case of delayed healing. All the patients were followed up 8-53 months (mean, 27.8 months). After operation, ISOBAR TTL system showed reliable fixation, and no loosening, breakage, or kyphosis deformity occurred. No adjacent segment degeneration was observed. The ROM of the fixed segments was 0-1 degrees in 3 cases, 1-2 degrees in 4 cases, 2-3 degrees in 14 cases, 3-4 degrees in 15 cases, and > 4 degrees in 2 cases. At last follow-up, the VAS score was 1.93 +/- 2.43, and was significantly lower than preoperative score (8.20 +/- 1.78) (t = 7.761, P = 0.000). JOA score was 23.06 +/- 7.75, and was significantly higher than preoperative score (4.87 +/- 3.44) (t = 10.045, P = 0.000). According to Stauffer-Coventry evaluation standard, the results were excellent in 32 cases, good in 3 cases, fair in 2 cases, and poor in 1 case, with an excellent and good rate of 92.1%. CONCLUSION: Good short-term effectiveness can be achieved by surgical intervention with ISOBAR TTL system in treatment of lumbar degenerative disease.

[Finite element analysis of a new shape memory alloy cervical hook for atlantoaxial instability].

The mechanics of a new shape memory alloy cervical hook for atlantoaxial instability was analyzed with finite element method on the basis of a three-dimensional model reconstructed from the images of CT scanning of an adult cadaveric upper cervical at 1-mm interval. The stress and displacement of every nodule and element in the course of deformation of the internal fixation were tested, and the results showed that the cervical hook was strong enough against tensile stress, which concentrates in the middle of the device. The pull was 237.58 N at the loading point. With such mechanical performance, this cervical hook can be reliable for correction of atlantoaxial instability.