SARM1 deficiency up-regulates XAF1, promotes neuronal apoptosis, and accelerates prion disease

SARM1 deletion inhibits astrogliosis and BBB damage through Jagged-1/Notch-1/NF-κB signaling to improve neurological function after ischemic stroke

Reactive astrogliosis is a critical process in the development of ischemic stroke. However, the precise mechanism by which reactive astrogliosis changes the pathogenesis of ischemic stroke remains elusive. Sterile alpha and TIR motif-containing 1 protein (SARM1) plays a key role in axonal degeneration and is involved in different cell death programs that regulate neuronal survival. The present study investigated the role of SARM1 in regulating reactive astrogliosis and neurological function after stroke in whole-body SARM1 knockout (SARM1-/-) mice. SARM1-/- mice showed significantly smaller infarction, slighter apoptosis, and fewer neurological function deficits 1-7 days after ischemic injury. Immunohistochemistry, western blot, and real-time PCR analyses revealed that compared with the wild-type (WT) mice, SARM1-/- mice exhibited reduced astrocytic proliferation, increased anti-inflammatory astrocytes, decreased glial scar formation in the infarct zone on day 7 after ischemic injury. SARM1 deletion also suppressed cerebral microvascular damage and blood-brain barrier (BBB) injury in ischemic brains. Mechanistically, SARM1 deletion inhibited the stroke-triggered activation of NF-κB signaling and decreased the expression of Jagged-1 and NICD in astrocytes. Overall, these findings provide the first line of evidence for a causative role of SARM1 protein in ischemia-induced reactive astrogliosis and ischemic neurovascular damage.

Mechanisms underlying targeted mitochondrial therapy for programmed cardiac cell death

Heart diseases are common clinical diseases, such as cardiac fibrosis, heart failure, hypertension and arrhythmia. Globally, the incidence rate and mortality of heart diseases are increasing by years. The main mechanism of heart disease is related to the cellular state. Mitochondrion is the organ of cellular energy supply, participating in various signal transduction pathways and playing a vital role in the occurrence and development of heart disease. This review summarizes the cell death patterns and molecular mechanisms associated with heart disease and mitochondrial dysfunction.

SARM regulates cell apoptosis and inflammation during Toxoplasma gondii infection through a multistep mechanism

BACKGROUND

The sterile alpha and HEAT/Armadillo motif (SARM) is the fifth Toll-like receptor (TLR) adaptor protein containing the Toll/interleukin-1 receptor (TIR) domain, which is highly enriched in the brain. Toxoplasma gondii (T. gondii) is an obligate intracellular parasitic protozoan that causes zoonotic toxoplasmosis, resulting in threats to human health, such as brain damage. Previous studies have shown that SARM plays crucial roles in cell death and triggers specific transcription programs of innate immunity in response to cell stress, viral, and bacterial infections. However, whether SARM is involved in T. gondii infection remains unclear.

METHODS

In this report, quantitative real-time polymerase chain reaction (qPCR), western blot, flow cytometry, ethynyldeoxyuridine (EdU) assay, and enzyme-linked immunosorbent assay (ELISA) were used to explore the relationship between SARM and T. gondii.

RESULTS

Here, we showed that T. gondii infection increased the expression of SARM in vitro and in vivo. SARM induced cell apoptosis during T. gondii infection, activating the mitochondrial apoptotic pathway, the endoplasmic reticulum stress (ER) pathway, and the mitogen-activated protein kinase (MAPK) signaling pathway, and prompting the production of reactive oxygen species (ROS). Furthermore, SARM participated in the regulation of the inflammatory response through the nod-like receptor pyrin domain 3 (NLRP3) inflammasome signaling pathway during T. gondii in vitro infection.

CONCLUSIONS

These results elucidate the relationship between SARM and T. gondii infection, suggesting that SARM may represent a potential target for T. gondii control.

Irisin regulates oxidative stress and mitochondrial dysfunction through the UCP2-AMPK pathway in prion diseases

Prion diseases are a group of fatal neurodegenerative disorders characterized by the abnormal folding of cellular prion proteins into pathogenic forms. The development of these diseases is intricately linked to oxidative stress and mitochondrial dysfunction. Irisin, an endogenous myokine, has demonstrated considerable neuroprotective potential due to its antioxidative properties. However, the protective effects of irisin against prion diseases have yet to be clarified. Our findings indicate that treatment with exogenous irisin can mitigate the apoptosis induced by PrP106-126. Additionally, irisin significantly reduces oxidative stress and alleviates the mitochondrial dysfunction triggered by PrP106-126. Furthermore, irisin treatment targets uncoupling protein 2 (UCP2) and activates the AMPK-Nrf2 pathway, substantially improving oxidative stress and mitochondrial dysfunction in N2a cells induced by PrP106-126. These results suggest that irisin represents a novel and promising therapeutic approach for treating prion diseases.

SARM1 in the pathogenesis of immune-related disease

Background

Sterile alpha and toll interleukin receptor motif-containing protein 1 (SARM1) are primarily expressed in the mammalian nervous system, with their presence in neurons being associated with mitochondrial aggregation. SARM1 functions as a mediator of cell death and morphological changes, while also regulating Waller degeneration in nerve fibers and influencing glial cell formation.

Purpose

Recent reports demonstrate SARM1 serves as a connector in the Toll-like receptor (TLR) pathway and plays a role in regulating inflammation during periods of stress such as infection, trauma, and hypoxia. These findings offer new insights into pathogenesis research and the prevention and treatment of neurodegenerative diseases and pathogen infections.

Methods

This review synthesizes recent findings on the immune-related mechanisms of SARM1, emphasizing its roles in inflammation and its functional impact on the nervous system and other bodily systems.

Conclusions

Understanding the multifaceted roles of SARM1 in immune regulation and neuronal health provides novel insights into its involvement in disease pathogenesis. These insights hold promise for advancing research into the prevention and treatment of neurodegenerative diseases and pathogen-induced conditions.

Sarm1 Controls the MYD88-Mediated Inflammatory Responses in Inflammatory Bowel Disease via the Regulation of TRAF3 Recruitment

BACKGROUND

Sterile alpha and TIR motif-containing 1 (Sarm1) is known as a negative regulator of inflammatory responses. However, its role in inflammatory bowel disease (IBD) is still unclear.

OBJECTIVE

This study aimed to explore the function of Sarm1 in IBD and its underlying mechanisms. Sarm1 and tumor necrosis factor (TNF) receptor associated factor 3 (TRAF3) knockout (KO) micewere established.

METHODS

The colitis was induced using dextran sulfate sodium (DSS). Bone marrow-derived macrophages (BMDMs) were isolated and stimulated with lipopolysaccharides (LPS) or cytidine phosphate guanosine(CpG). Inflammatory cytokines were measured viaELISA. qPCR and Western blotting were used to determine the levels of the mRNA and protein expression, respectively.

RESULTS

It was demonstrated that reduced expression of Sarm1 was correlated with the severity of IBD in ulcerative colitis patients, and also with the reduction of pro-inflammatory cytokines in the mouse model induced by DSS. It was further observed that Sarm1 KO enhanced the induction of pro-inflammatory cytokines in both animal and in vitro cell models. Sarm1 deficiency in macrophages increased the severity of colitis in the mouse model induced by DSS. Moreover, Sarm1 regulatedTRAF3 recruitment to myeloid differentiation primary response protein 88 (MyD88), which in turn controlled the MYD88-mediated inflammatory responses.

CONCLUSIONS

In summary, our data suggest that Sarm1 controls the MYD88-mediated inflammatory responses in IBD via its regulation of TRAF3 recruitment.

Longitudinal microbiome investigation throughout prion disease course reveals pre- and symptomatic compositional perturbations linked to short-chain fatty acid metabolism and cognitive impairment in mice

Commensal intestinal bacteria shape our microbiome and have decisive roles in preserving host metabolic and immune homeostasis. They conspicuously impact disease development and progression, including amyloid-beta (Aβ) and alpha (α)-synuclein pathology in neurodegenerative diseases, conveying the importance of the brain-gut-microbiome axis in such conditions. However, little is known about the longitudinal microbiome landscape and its potential clinical implications in other protein misfolding disorders, such as prion disease. We investigated the microbiome architecture throughout prion disease course in mice. Fecal specimens were assessed by 16S ribosomal RNA sequencing. We report a temporal microbiome signature in prion disease and uncovered alterations in Lachnospiraceae, Ruminococcaceae, Desulfovibrionaceae, and Muribaculaceae family members in this disease. Moreover, we determined the enrichment of Bilophila, a microorganism connected to cognitive impairment, long before the clinical manifestation of disease symptoms. Based on temporal microbial abundances, several associated metabolic pathways and resulting metabolites, including short-chain fatty acids, were linked to the disease. We propose that neuroinflammatory processes relate to perturbations of the intestinal microbiome and metabolic state by an interorgan brain-gut crosstalk. Furthermore, we describe biomarkers possibly suitable for early disease diagnostics and anti-prion therapy monitoring. While our study is confined to prion disease, our discoveries might be of equivalent relevance in other proteinopathies and central nervous system pathologies.

SARM1 promotes the neuroinflammation and demyelination through IGFBP2/NF-κB pathway in experimental autoimmune encephalomyelitis mice

AIM

Multiple sclerosis (MS) is an autoimmune disease, and its typical characteristics are neuroinflammation and the demyelination of neurons in the central nervous system (CNS). Sterile alpha and TIR motif containing 1 (SARM1) is an essential factor mediating axonal degeneration and SARM1 deletion reduces the neuroinflammation in spinal cord injury. This study aimed to explore the roles of SARM1 and its underlying mechanisms in MS.

METHODS

Experimental autoimmune encephalomyelitis (EAE, a model of MS) model was established. Immunostaining, western blot, electron microscope, and HE staining were used to examine the pathological manifestations such as inflammation, demyelination, and neuronal death in SARM1^f/f EAE mice and SARM1^Nestin -CKO EAE mice. In addition, RNA-seq, real-time PCR and double-immunostaining were used to examine the underlying mechanism of SARM1 in EAE mice.

RESULTS

SARM1 was upregulated in neurons of the spinal cords of EAE mice. SARM1 knockout in CNS ameliorated EAE with less neuroinflammation, demyelination, and dead neurons. Mechanically, SARM1 knockout resulted in the reduction of insulin-like growth factor (IGF)-binding protein 2 (IGFBP2) in neurons of EAE mice, which might inhibit the neuroinflammation through inhibiting NF-κB signaling. Finally, activation of NF-κB partially aggravated the neuroinflammation and demyelination deficits of SARM1^Nestin -CKO EAE mice.

CONCLUSIONS

These results identified the unknown role of SARM1 in the promotion of neuroinflammation and demyelination and revealed a novel drug target pathway of SARM1/IGFBP2/NF-κB for MS.

SARM1 detection in myelinating glia: sarm1/Sarm1 is dispensable for PNS and CNS myelination in zebrafish and mice

Since SARM1 mutations have been identified in human neurological disease, SARM1 inhibition has become an attractive therapeutic strategy to preserve axons in a variety of disorders of the peripheral (PNS) and central nervous system (CNS). While SARM1 has been extensively studied in neurons, it remains unknown whether SARM1 is present and functional in myelinating glia? This is an important question to address. Firstly, to identify whether SARM1 dysfunction in other cell types in the nervous system may contribute to neuropathology in SARM1 dependent diseases? Secondly, to ascertain whether therapies altering SARM1 function may have unintended deleterious impacts on PNS or CNS myelination? Surprisingly, we find that oligodendrocytes express sarm1 mRNA in the zebrafish spinal cord and that SARM1 protein is readily detectable in rodent oligodendrocytes in vitro and in vivo. Furthermore, activation of endogenous SARM1 in cultured oligodendrocytes induces rapid cell death. In contrast, in peripheral glia, SARM1 protein is not detectable in Schwann cells and satellite glia in vivo and sarm1/Sarm1 mRNA is detected at very low levels in Schwann cells, in vivo, in zebrafish and mouse. Application of specific SARM1 activators to cultured mouse Schwann cells does not induce cell death and nicotinamide adenine dinucleotide (NAD) levels remain unaltered suggesting Schwann cells likely contain no functionally relevant levels of SARM1. Finally, we address the question of whether SARM1 is required for myelination or myelin maintenance. In the zebrafish and mouse PNS and CNS, we show that SARM1 is not required for initiation of myelination and myelin sheath maintenance is unaffected in the adult mouse nervous system. Thus, strategies to inhibit SARM1 function to treat neurological disease are unlikely to perturb myelination in humans.

Liver-Targeted Delivery of Small Interfering RNA of C-C Chemokine Receptor 2 with Tetrahedral Framework Nucleic Acid Attenuates Liver Cirrhosis

Liver cirrhosis is the end stage of chronic liver diseases without approved clinical drugs. In this study, a new strategy that uses a C-C chemokine receptor 2 (CCR2) small interfering RNA silencing (siCcr2)-based therapy by loading multivalent siCcr2 with tetrahedron framework DNA nanostructure (tFNA) vehicle (tFNA-siCcr2) was established to attenuate liver fibrosis. tFNA-siCcr2 was successfully synthesized without changing the physiochemical properties of tFNA. Compared to the naked siCcr2 molecule, the tFNA-siCcr2 complex altered the accumulation from the kidney to the liver after the intraperitoneal injection. The tFNA-siCcr2 complex also prolonged hepatic retention and mainly colocalized within macrophages and endothelial cells. tFNA-siCcr2 efficiently silenced CCR2 and significantly ameliorated liver fibrosis in prevention and treatment interventions. Single-cell RNA sequencing followed by experimental validation suggested that tFNA-siCcr2 can restore the immune cell landscape and construct an antifibrotic niche by inhibiting profibrotic macrophage and neutrophil accumulation in the murine fibrotic liver. Molecularly, the tFNA-siCcr2 complex reduced inflammatory mediator production by inactivating the NF-κB signaling pathway. In conclusion, the tFNA-based liver-targeted tFNA-siCcr2 delivery complex efficiently ameliorated liver fibrosis by restoring the immune cell landscape and constructing an antifibrotic niche, which makes the tFNA-siCcr2 complex a potential therapeutic candidate for the clinical treatment of liver cirrhosis.

SARM1 participates in axonal degeneration and mitochondrial dysfunction in prion disease

Prion disease represents a group of fatal neurogenerative diseases in humans and animals that are associated with energy loss, axonal degeneration, and mitochondrial dysfunction. Axonal degeneration is an early hallmark of neurodegeneration and is triggered by SARM1. We found that depletion or dysfunctional mutation of SARM1 protected against NAD⁺ loss, axonal degeneration, and mitochondrial functional disorder induced by the neurotoxic peptide PrP^106-126. NAD⁺ supplementation rescued prion-triggered axonal degeneration and mitochondrial dysfunction and SARM1 overexpression suppressed this protective effect. NAD⁺ supplementation in PrP^106-126-incubated N2a cells, SARM1 depletion, and SARM1 dysfunctional mutation each blocked neuronal apoptosis and increased cell survival. Our results indicate that the axonal degeneration and mitochondrial dysfunction triggered by PrP^106-126 are partially dependent on SARM1 NADase activity. This pathway has potential as a therapeutic target in the early stages of prion disease.

Longitudinal and simultaneous profiling of 11 modes of cell death in mouse retina post-optic nerve injury

Retinal ganglion cell (RGC) death is a critical pathological trigger leading to irreversible visual impairment and blindness after optic nerve (ON) injury. Yet, there is still no effective clinical treatment to rescue RGC death after ON injury. Understanding the involvement of different modes of cell death post-ON injury could facilitate the development of targeting treatments against RGC death. Herein we aimed to characterize the regulation of 11 modes of cell death simultaneously and longitudinally in mouse retina post-ON injury. The number of RGCs gradually decreased from Day 3-14 in mice post-ON injury. Increase in the apoptosis (cleaved caspase-3), autolysis (cleaved cathespin B) and pyroptosis (cleaved caspase-1) marker expression in the retina began at Day 3 post-ON injury. Meanwhile, the markers for autophagy (Atg7 and Becn1) and phagocytosis (Mfge8 and Mertk) were downregulated from Day 1 to Day 5. Additionally, the expression of ferroptosis marker (4-hydroxynonenal) was upregulated from Day 7 to Day 14 post-ON injury following the early reduction of Gpx4. Yet, the reduction of parthanatos, sarmoptosis, and mitochondrial permeable transition could be related to autophagy and apoptosis. The markers for necroptosis did not show significant changes post-ON injury. In summary, this study revealed that the activation of apoptosis, autolysis, pyroptosis and ferroptosis, together with the early downregulation of autophagy and phagocytosis, are the major modes of cell death involved in the RGC death post-ON injury. Simultaneously targeting multiple modes of cell death at different time courses could be a potential treatment approach against RGC death for traumatic optic neuropathy.

SARM1 deletion in parvalbumin neurons is associated with autism-like behaviors in mice

Autism spectrum disorder (ASD), a group of neurodevelopmental disorder diseases, is characterized by social deficits, communication difficulties, and repetitive behaviors. Sterile alpha and TIR motif-containing 1 protein (SARM1) is known as an autism-associated protein and is enriched in brain tissue. Moreover, SARM1 knockdown mice exhibit autism-like behaviors. However, its specific mechanism in ASD pathogenesis remains unclear. Here we generated parvalbumin-positive interneurons (PVI)-specific conditional SARM1 knockout (SARM1^PV-CKO) mice. SARM1^PV-CKO male mice showed autism-like behaviors, such as mild social interaction deficits and repetitive behaviors. Moreover, we found that the expression level of parvalbumin was reduced in SARM1^PV-CKO male mice, together with upregulated apoptosis-related proteins and more cleaved-caspase-3-positive PVIs, suggesting that knocking out SARM1 may cause a reduction in the number of PVIs due to apoptosis. Furthermore, the expression of c-fos was shown to increase in SARM1^PV-CKO male mice, in combination with upregulation of excitatory postsynaptic proteins such as PSD-95 or neuroligin-1, indicating enhanced excitatory synaptic input in mutant mice. This notion was further supported by the partial rescue of autism-like behavior deficits by the administration of GABA receptor agonists in SARM1^PV-CKO male mice. In conclusion, our findings suggest that SARM1 deficiency in PVIs may be involved in the pathogenesis of ASD.

Sarm1 is Essential for Anesthesia-Induced Neuroinflammation and Cognitive Impairment in Aged Mice

Postoperative cognitive dysfunction (POCD) is a common phenomenon among elderly patients with unclear etiology. Sterile alpha and TIR motif-containing 1 (Sarm1) plays important roles in neuroinflammation and cognitive function, and activates Calpain which has been shown to promote POCD through TrkB cleavage. This study aims to test the hypothesis that Sarm1 is involved in POCD through regulating Calpain activity. Wild type and Sarm1 knock out mice were exposed to isoflurane. Mouse cognitive function was determined by Morris water maze test. Neuroinflammation was determined by Iba1 and GFAP protein levels and mRNA expression of proinflammatory cytokines. Calpain activation was determined by αII-spectrin degradation and TrkB cleavage. Mitogen-activated protein kinase (MAPK) signaling was determined by c-Jun N-terminal kinase and cJun phosphorylation both in vivo and in vitro by Western blot and immunofluorescence staining. We found that Sarm1 deletion suppressed isoflurane induced cognitive impairment and neuroinflammation. Deletion of Sarm1 inhibited isoflurane induced αII-spectrin degradation and TrkB cleavage, which indicates suppression of Calpain activation. Finally, deletion of Sarm1 suppressed isoflurane induced MAPK signaling both in vivo and in vitro. Our findings suggest that isoflurane anesthesia induced cognitive impairment is prevented by Sarm1 deletion in mice, making Sarm1 a potent therapeutic target for treating or preventing POCD.

Lack of the immune adaptor molecule SARM1 accelerates disease in prion infected mice and is associated with increased mitochondrial respiration and decreased expression of NRF2

Prion diseases are a group of fatal, transmissible neurodegenerative diseases of mammals. In the brain, axonal loss and neuronal death are prominent in prion infection, but the mechanisms remain poorly understood. Sterile alpha and heat/Armadillo motif 1 (SARM1) is a protein expressed in neurons of the brain that plays a critical role in axonal degeneration. Following damage to axons, it acquires an NADase activity that helps to regulate mitochondrial health by breaking down NAD⁺, a molecule critical for mitochondrial respiration. SARM1 has been proposed to have a protective effect in prion disease, and we hypothesized that it its role in regulating mitochondrial energetics may be involved. We therefore analyzed mitochondrial respiration in SARM1 knockout mice (SARM1^KO) and wild-type mice inoculated either with prions or normal brain homogenate. Pathologically, disease was similar in both strains of mice, suggesting that SARM1 mediated axonal degradation is not the sole mechanism of axonal loss during prion disease. However, mitochondrial respiration was significantly increased and disease incubation time accelerated in prion infected SARM1^KO mice when compared to wild-type mice. Increased levels of mitochondrial complexes II and IV and decreased levels of NRF2, a potent regulator of reactive oxygen species, were also apparent in the brains of SARM1^KO mice when compared to wild-type mice. Our data suggest that SARM1 slows prion disease progression, likely by regulating mitochondrial respiration, which may help to mitigate oxidative stress via NRF2.

SARM1 can be a potential therapeutic target for spinal cord injury

Injury to the spinal cord is devastating. Studies have implicated Wallerian degeneration as the main cause of axonal destruction in the wake of spinal cord injury. Therefore, the suppression of Wallerian degeneration could be beneficial for spinal cord injury treatment. Sterile alpha and armadillo motif-containing protein 1 (SARM1) is a key modulator of Wallerian degeneration, and its impediment can improve spinal cord injury to a significant degree. In this report, we analyze the various signaling domains of SARM1, the recent findings on Wallerian degeneration and its relation to axonal insults, as well as its connection to SARM1, the mitogen-activated protein kinase (MAPK) signaling, and the survival factor, nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2). We then elaborate on the possible role of SARM1 in spinal cord injury and explicate how its obstruction could potentially alleviate the injury.

An integrative bioinformatics analysis for identifying hub genes associated with infection of lung samples in patients infected with SARS-CoV-2

Background

At the end of 2019, the world witnessed the emergence and ravages of a viral infection induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Also known as the coronavirus disease 2019 (COVID-19), it has been identified as a public health emergency of international concern (PHEIC) by the World Health Organization (WHO) because of its severity.

Methods

The gene data of 51 samples were extracted from the GSE150316 and GSE147507 data set and then processed by means of the programming language R, through which the differentially expressed genes (DEGs) that meet the standards were screened. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed on the selected DEGs to understand the functions and approaches of DEGs. The online tool STRING was employed to construct a protein–protein interaction (PPI) network of DEGs and, in turn, to identify hub genes.

Results

A total of 52 intersection genes were obtained through DEG identification. Through the GO analysis, we realized that the biological processes (BPs) that have the deepest impact on the human body after SARS-CoV-2 infection are various immune responses. By using STRING to construct a PPI network, 10 hub genes were identified, including IFIH1, DDX58, ISG15, EGR1, OASL, SAMD9, SAMD9L, XAF1, IFITM1, and TNFSF10.

Conclusion

The results of this study will hopefully provide guidance for future studies on the pathophysiological mechanism of SARS-CoV-2 infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40001-021-00609-4.

CRISPR/Cas9-mediated SARM1 knockout and epitope-tagged mice reveal that SARM1 does not regulate nuclear transcription, but is expressed in macrophages

SARM1 is a toll/interleukin-1 receptor -domain containing protein, with roles proposed in both innate immunity and neuronal degeneration. Murine SARM1 has been reported to regulate the transcription of chemokines in both neurons and macrophages; however, the extent to which SARM1 contributes to transcription regulation remains to be fully understood. Here, we identify differential gene expression in bone-marrow-derived macrophages (BMDMs) from C57BL/6 congenic 129 ES cell-derived Sarm1^-/- mice compared with wild type (WT). However, we found that passenger genes, which are derived from the 129 donor strain of mice that flank the Sarm1 locus, confound interpretation of the results, since many of the identified differentially regulated genes come from this region. To re-examine the transcriptional role of SARM1 in the absence of passenger genes, here we generated three Sarm1^-/- mice using CRISPR/Cas9. Treatment of neurons from these mice with vincristine, a chemotherapeutic drug causing axonal degeneration, confirmed SARM1's function in that process; however, these mice also showed that lack of SARM1 has no impact on transcription of genes previously shown to be affected such as chemokines. To gain further insight into SARM1 function, we generated an epitope-tagged SARM1 mouse. In these mice, we observed high SARM1 protein expression in the brain and brainstem and lower but detectable levels in macrophages. Overall, the generation of these SARM1 knockout and epitope-tagged mice has clarified that SARM1 is expressed in mouse macrophages yet has no general role in macrophage transcriptional regulation and has provided important new models to further explore SARM1 function.

Calcineurin Activation by Prion Protein Induces Neurotoxicity via Mitochondrial Reactive Oxygen Species

Prion diseases are caused by PrPsc accumulation in the brain, which triggers dysfunctional mitochondrial injury and reactive oxygen species (ROS) generation in neurons. Recent studies on prion diseases suggest that endoplasmic reticulum (ER) stress induced by misfolding proteins such as misfolded prion protein results in activation of calcineurin. Calcineurin is a calcium-related protein phosphatase of type 2B that exists in copious quantities in the brain and acts as a critical nodal component in the control of cellular functions. To investigate the relationship between calcineurin and intracellular ROS, we assessed the alteration of CaN and ROS induced by prion peptide (PrP) 106-126. Human prion peptide increased mitochondrial ROS by activating calcineurin, and the inhibition of calcineurin activity protected mitochondrial function and neuronal apoptosis in neuronal cells. These results suggest that calcineurin plays a pivotal role in neuronal apoptosis by mediating mitochondrial injury and ROS in prion diseases.

Loss of PIKfyve drives the spongiform degeneration in prion diseases

Brain‐matter vacuolation is a defining trait of all prion diseases, yet its cause is unknown. Here, we report that prion infection and prion‐mimetic antibodies deplete the phosphoinositide kinase PIKfyve—which controls endolysosomal maturation—from mouse brains, cultured cells, organotypic brain slices, and brains of Creutzfeldt‐Jakob disease victims. We found that PIKfyve is acylated by the acyltransferases zDHHC9 and zDHHC21, whose juxtavesicular topology is disturbed by prion infection, resulting in PIKfyve deacylation and rapid degradation, as well as endolysosomal hypertrophy and activation of TFEB‐dependent lysosomal enzymes. A protracted unfolded protein response (UPR), typical of prion diseases, also induced PIKfyve deacylation and degradation. Conversely, UPR antagonists restored PIKfyve levels in prion‐infected cells. Overexpression of zDHHC9 and zDHHC21, administration of the antiprion polythiophene LIN5044, or supplementation with the PIKfyve reaction product PI(3,5)P₂ suppressed prion‐induced vacuolation and restored lysosomal homeostasis. Thus, PIKfyve emerges as a central mediator of vacuolation and neurotoxicity in prion diseases.

Transcription Factor-Binding Site Identification and Enrichment Analysis

Transcription factors orchestrate complex regulatory networks of gene expression. A better understanding of the common transcription factors, and their shared interactions, among a set of coregulated or differentially expressed genes can provide powerful insights into the key pathways governing such expression patterns. Critically, such information must also be considered in the context of the frequency in which a transcription factor is present in a properly selected background, and in the context of existing evidence of gene and transcription factor interaction. Given the vast amount of publicly available gene expression data that can be further scrutinized by the user-friendly analysis tools described here, many useful insights are assuredly to be revealed. The proceeding methods for application of the analysis tool CiiiDER for transcription factor-binding site identification, enrichment analysis, and coregulatory factor identification should be applicable to any dataset comparing differential gene expression in response to various stimuli and gene coexpression datasets. These methods should assist the researcher in identifying the most relevant regulators within a gene set, and refining the list of targets for future study to those which may share biologically important regulatory networks.

Passenger Mutations Confound Phenotypes of SARM1-Deficient Mice

The Toll/IL-1R-domain-containing adaptor protein SARM1 is expressed primarily in the brain, where it mediates axonal degeneration. Roles for SARM1 in TLR signaling, viral infection, inflammasome activation, and chemokine and Xaf1 expression have also been described. Much of the evidence for SARM1 function relies on SARM1-deficient mice generated in 129 ESCs and backcrossed to B6. The Sarm1 gene lies in a gene-rich region encompassing Xaf1 and chemokine loci, which remain 129 in sequence. We therefore generated additional knockout strains on the B6 background, confirming the role of SARM1 in axonal degeneration and WNV infection, but not in VSV or LACV infection, or in chemokine or Xaf1 expression. Sequence variation in proapoptotic Xaf1 between B6 and 129 results in coding changes and distinct splice variants, which may account for phenotypes previously attributed to SARM1. Reevaluation of phenotypes in these strains will be critical for understanding the function of SARM1.

The antidiabetic drug troglitazone protects against PrP (106‑126)‑induced neurotoxicity via the PPARγ‑autophagy pathway in neuronal cells

Prion diseases, which involve the alteration of cellular prion protein into a misfolded isoform, disrupt the central nervous systems of humans and animals alike. Prior research has suggested that peroxisome proliferator-activator receptor (PPAR)γ and autophagy provide some protection against neurodegeneration. PPARs are critical to lipid metabolism regulation and autophagy is one of the main cellular mechanisms by which cell function and homeostasis is maintained. The present study examined the effect of troglitazone, a PPARγ agonist, on autophagy flux in a prion peptide (PrP) (106–126)-mediated neurodegeneration model. Western blot analysis confirmed that treatment with troglitazone increased LC3-II and p62 protein expression, whereas an excessive increase in autophagosomes was verified by transmission electron microscopy. Troglitazone weakened PrP (106–126)-mediated neurotoxicity via PPARγ activation and autophagy flux inhibition. A PPARγ antagonist blocked PPARγ activation as well as the neuroprotective effects induced by troglitazone treatment, indicating that PPARγ deactivation impaired troglitazone-mediated protective effects. In conclusion, the present study demonstrated that troglitazone protected primary neuronal cells against PrP (106–126)-induced neuronal cell death by inhibiting autophagic flux and activating PPARγ signals. These results suggested that troglitazone may be a useful therapeutic agent for the treatment of neurodegenerative disorders and prion diseases.

Neuroinflammation in Prion Disease

Neuroinflammation, typically manifest as microglial activation and astrogliosis accompanied by transcriptomic alterations, represents a common hallmark of various neurodegenerative conditions including prion diseases. Microglia play an overall neuroprotective role in prion disease, whereas reactive astrocytes with aberrant phenotypes propagate prions and contribute to prion-induced neurodegeneration. The existence of heterogeneous subpopulations and dual functions of microglia and astrocytes in prion disease make them potential targets for therapeutic intervention. A variety of neuroinflammation-related molecules are involved in prion pathogenesis. Therapeutics targeting neuroinflammation represents a novel approach to combat prion disease. Deciphering neuroinflammation in prion disease will deepen our understanding of pathogenesis of other neurodegenerative disorders.

SARM1 promotes neuroinflammation and inhibits neural regeneration after spinal cord injury through NF-κB signaling

Axonal degeneration is a common pathological feature in many acute and chronic neurological diseases such as spinal cord injury (SCI). SARM1 (sterile alpha and TIR motif-containing 1), the fifth TLR (Toll-like receptor) adaptor, has diverse functions in the immune and nervous systems, and recently has been identified as a key mediator of Wallerian degeneration (WD). However, the detailed functions of SARM1 after SCI still remain unclear.

Methods: Modified Allen's method was used to establish a contusion model of SCI in mice. Furthermore, to address the function of SARM1 after SCI, conditional knockout (CKO) mice in the central nervous system (CNS), SARM1^Nestin-CKO mice, and SARM1^GFAP-CKO mice were successfully generated by Nestin-Cre and GFAP-Cre transgenic mice crossed with SARM1^flox/flox mice, respectively. Immunostaining, Hematoxylin-Eosin (HE) staining, Nissl staining and behavioral test assays such as footprint and Basso Mouse Scale (BMS) scoring were used to examine the roles of SARM1 pathway in SCI based on these conditional knockout mice. Drugs such as FK866, an inhibitor of SARM1, and apoptozole, an inhibitor of heat shock protein 70 (HSP70), were used to further explore the molecular mechanism of SARM1 in neural regeneration after SCI.

Results: We found that SARM1 was upregulated in neurons and astrocytes at early stage after SCI. SARM1^Nestin-CKO and SARM1^GFAP-CKO mice displayed normal development of the spinal cords and motor function. Interestingly, conditional deletion of SARM1 in neurons and astrocytes promoted the functional recovery of behavior performance after SCI. Mechanistically, conditional deletion of SARM1 in neurons and astrocytes promoted neuronal regeneration at intermediate phase after SCI, and reduced neuroinflammation at SCI early phase through downregulation of NF-κB signaling after SCI, which may be due to upregulation of HSP70. Finally, FK866, an inhibitor of SARM1, reduced the neuroinflammation and promoted the neuronal regeneration after SCI.

Conclusion: Our results indicate that SARM1-mediated prodegenerative pathway and neuroinflammation promotes the pathological progress of SCI and anti-SARM1 therapeutics are viable and promising approaches for preserving neuronal function after SCI.

Programmed axon degeneration: from mouse to mechanism to medicine

Wallerian degeneration is a widespread mechanism of programmed axon degeneration. In the three decades since the discovery of the Wallerian degeneration slow (Wld^S) mouse, research has generated extensive knowledge of the molecular mechanisms underlying Wallerian degeneration, demonstrated its involvement in non-injury disorders and found multiple ways to block it. Recent developments have included: the detection of NMNAT2 mutations that implicate Wallerian degeneration in rare human diseases; the capacity for lifelong rescue of a lethal condition related to Wallerian degeneration in mice; the discovery of 'druggable' enzymes, including SARM1 and MYCBP2 (also known as PHR1), in Wallerian pathways; and the elucidation of protein structures to drive further understanding of the underlying mechanisms and drug development. Additionally, new data have indicated the potential of these advances to alleviate a number of common disorders, including chemotherapy-induced and diabetic peripheral neuropathies, traumatic brain injury, and amyotrophic lateral sclerosis.

Prion disease is accelerated in mice lacking stress-induced heat shock protein 70 (HSP70)

Prion diseases are a group of incurable neurodegenerative disorders that affect humans and animals via infection with proteinaceous particles called prions. Prions are composed of PrP^Sc, a misfolded version of the cellular prion protein (PrP^C). During disease progression, PrP^Sc replicates by interacting with PrP^C and inducing its conversion to PrP^Sc As PrP^Sc accumulates, cellular stress mechanisms are activated to maintain cellular proteostasis, including increased protein chaperone levels. However, the exact roles of several of these chaperones remain unclear. Here, using various methodologies to monitor prion replication (i.e. protein misfolding cyclic amplification and cellular and animal infectivity bioassays), we studied the potential role of the molecular chaperone heat shock protein 70 (HSP70) in prion replication in vitro and in vivo Our results indicated that pharmacological induction of the heat shock response in cells chronically infected with prions significantly decreased PrP^Sc accumulation. We also found that HSP70 alters prion replication in vitro More importantly, prion infection of mice lacking the genes encoding stress-induced HSP70 exhibited accelerated prion disease progression compared with WT mice. In parallel with HSP70 being known to respond to endogenous and exogenous stressors such as heat, infection, toxicants, and ischemia, our results indicate that HSP70 may also play an important role in suppressing or delaying prion disease progression, opening opportunities for therapeutic intervention.