Sarm1 Gene Deficiency Attenuates Diabetic Peripheral Neuropathy in Mice

Programmed axon death: a promising target for treating retinal and optic nerve disorders

Programmed axon death is a druggable pathway of axon degeneration that has garnered considerable interest from pharmaceutical companies as a promising therapeutic target for various neurodegenerative disorders. In this review, we highlight mechanisms through which this pathway is activated in the retina and optic nerve, and discuss its potential significance for developing therapies for eye disorders and beyond. At the core of programmed axon death are two enzymes, NMNAT2 and SARM1, with pivotal roles in NAD metabolism. Extensive preclinical data in disease models consistently demonstrate remarkable, and in some instances, complete and enduring neuroprotection when this mechanism is targeted. Findings from animal studies are now being substantiated by genetic human data, propelling the field rapidly toward clinical translation. As we approach the clinical phase, the selection of suitable disorders for initial clinical trials targeting programmed axon death becomes crucial for their success. We delve into the multifaceted roles of programmed axon death and NAD metabolism in retinal and optic nerve disorders. We discuss the role of SARM1 beyond axon degeneration, including its potential involvement in neuronal soma death and photoreceptor degeneration. We also discuss genetic human data and environmental triggers of programmed axon death. Lastly, we touch upon potential therapeutic approaches targeting NMNATs and SARM1, as well as the nicotinamide trials for glaucoma. The extensive literature linking programmed axon death to eye disorders, along with the eye's suitability for drug delivery and visual assessments, makes retinal and optic nerve disorders strong contenders for early clinical trials targeting programmed axon death.

Roles of Sirt1 and its modulators in diabetic microangiopathy: A review

Diabetic vascular complications include diabetic macroangiopathy and diabetic microangiopathy. Diabetic microangiopathy is characterised by impaired microvascular endothelial function, basement membrane thickening, and microthrombosis, which may promote renal, ocular, cardiac, and peripheral system damage in diabetic patients. Therefore, new preventive and therapeutic strategies are urgently required. Sirt1, a member of the nicotinamide adenine dinucleotide-dependent histone deacetylase class III family, regulates different organ growth and development, oxidative stress, mitochondrial function, metabolism, inflammation, and aging. Sirt1 is downregulated in vascular injury and microangiopathy. Moreover, its expression and distribution in different organs correlate with age and play critical regulatory roles in oxidative stress and inflammation. This review introduces the background of diabetic microangiopathy and the main functions of Sirt1. Then, the relationship between Sirt1 and different diabetic microangiopathies and the regulatory roles mediated by different cells are described. Finally, we summarize the modulators that target Sirt1 to ameliorate diabetic microangiopathy as an essential preventive and therapeutic measure for diabetic microangiopathy. In conclusion, targeting Sirt1 may be a new therapeutic strategy for diabetic microangiopathy.

Serum SARM1 Levels and Diabetic Peripheral Neuropathy in Type 2 Diabetes: Correlation with Clinical Neuropathy Scales and Nerve Conduction Studies and Impact of COVID-19 vaccination

Patients with peripheral neuropathy with type 2 diabetes mellitus (T2DM) are more likely to have functional impairments. Recently, the gene for serum sterile alpha and toll/interleukin receptor motif-containing protein 1 (SARM1), which may contribute to the pathogenesis of Wallerian degeneration, was discovered in mice models of peripheral neuropathy. We set out to assess serum SARM1's activity as a potential biomarker for the early identification of diabetic peripheral neuropathy in T2DM patients while also examining the impact of the COVID-19 vaccine on SARM1 levels. We assessed the cross-sectional relationships between the SARM1 biomarker, clinical neuropathy scales, and nerve conduction parameters in 80 participants aged between 30 years and 60 years. The analysis was carried out after the patients were split into two groups since we discovered a significant increase in SARM1 levels following the second dose of the COVID-19 vaccination, where group A received one dose of the COVID-19 vaccine inoculation, and group B received two doses of the COVID-19 vaccine. SARM1 was correlated significantly (p < 0.05) with MNSIe and NSS in group A and showed a consistent positive correlation with the other neuropathy clinical scales in group A and group B without reaching statistical significance. Additionally, SARM1 was negatively correlated significantly (p < 0.05) with the median sensory amplitude in group A and showed a consistent negative correlation with the six other sensory and motor nerves' potential amplitude in group A and group B without reaching statistical significance. In conclusion, SARM1 showed a consistent correlation with clinical neuropathy scales and nerve conduction parameters after accounting for the influence of COVID-19 vaccination doses.

Targeting NAD Metabolism for the Therapy of Age-Related Neurodegenerative Diseases

As the aging population continues to grow rapidly, age-related diseases are becoming an increasing burden on the healthcare system and a major concern for the well-being of elderly individuals. While aging is an inevitable process for all humans, it can be slowed down and age-related diseases can be treated or alleviated. Nicotinamide adenine dinucleotide (NAD) is a critical coenzyme or cofactor that plays a central role in metabolism and is involved in various cellular processes including the maintenance of metabolic homeostasis, post-translational protein modifications, DNA repair, and immune responses. As individuals age, their NAD levels decline, and this decrease has been suggested to be a contributing factor to the development of numerous age-related diseases, such as cancer, diabetes, cardiovascular diseases, and neurodegenerative diseases. In pursuit of healthy aging, researchers have investigated approaches to boost or maintain NAD levels. Here, we provide an overview of NAD metabolism and the role of NAD in age-related diseases and summarize recent progress in the development of strategies that target NAD metabolism for the treatment of age-related diseases, particularly neurodegenerative diseases.

Integrating plasma metabolomics and gut microbiome to reveal the mechanisms of Huangqi Guizhi Wuwu Decoction intervene diabetic peripheral neuropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Huangqi Guizhi Wuwu Decoction (HGWD) is a classic traditional Chinese herbal formula from "Synopsis of Golden Chamber," which is used to treat blood stagnation and has been used for alleviating diabetic peripheral neuropathy (DPN) in the clinic. However, the mechanisms of HGWD intervention DPN are still to be discovered.

AIM OF THE STUDY

This study aims to explore the mechanism of HGWD intervention DPN by integrating plasma metabolomics and gut microbiome.

MATERIALS AND METHODS

BKS Cg-m+/+Leprdb/J (db/db) mice with DPN were at 16 weeks of age. The indices of DPN phenotypes in db/db mice, pathomorphology of the sciatic nerve, intraepithelial nerve fibers (IENF) of the foot pad, levels of blood lipids and oxidative stress, and inflammatory reaction were used to appraise the HGWD efficacy. Finally, the pharmacological mechanisms of HGWD intervening DPN were explored by metabolomics and 16S rRNA gene sequencing.

RESULTS

HGWD reversed DPN phenotypes in db/db mice, improved peripheral nerve structure, ameliorated the level of blood lipids and nerve growth factor in plasma, enhanced antioxidant capacity, and alleviated inflammatory responses. Plasma metabolomics disclosed that HGWD remarkably regulated the unusual levels of thirty-seven metabolites involved in sphingolipid metabolism, biosynthesis of unsaturated fatty acids, arachidonic acid metabolism, and amino acid biosynthesis pathways. The gut microbiome showed that nine bacteria were highly correlated with the efficacy of HGWD in DPN. Integrating analysis of microbiome and metabolomics demonstrated that the interaction of four bacteria with four metabolic pathways might be the significant mechanism of HGWD intervention in DPN.

CONCLUSIONS

The mediation of gut microbiota and plasma metabolism may be the potential mechanism of HGWD ameliorating DPN in db/db mice. The interaction of Lactobacillus, Alloprevotella, Bacteroides, and Desulfovibio with four metabolic pathways might be the critical mechanism for HGWD treating DPN.

Sarm1 knockout prevents type 1 diabetic bone disease in females independent of neuropathy

Patients with diabetes have a high risk of developing skeletal diseases accompanied by diabetic peripheral neuropathy (DPN). In this study, we isolated the role of DPN in skeletal disease with global and conditional knockout models of sterile-α and TIR-motif-containing protein-1 (Sarm1). SARM1, an NADase highly expressed in the nervous system, regulates axon degeneration upon a range of insults, including DPN. Global knockout of Sarm1 prevented DPN, but not skeletal disease, in male mice with type 1 diabetes (T1D). Female wild-type mice also developed diabetic bone disease but without DPN. Unexpectedly, global Sarm1 knockout completely protected female mice from T1D-associated bone suppression and skeletal fragility despite comparable muscle atrophy and hyperglycemia. Global Sarm1 knockout rescued bone health through sustained osteoblast function with abrogation of local oxidative stress responses. This was independent of the neural actions of SARM1, as beneficial effects on bone were lost with neural conditional Sarm1 knockout. This study demonstrates that the onset of skeletal disease occurs rapidly in both male and female mice with T1D completely independently of DPN. In addition, this reveals that clinical SARM1 inhibitors, currently being developed for treatment of neuropathy, may also have benefits for diabetic bone through actions outside of the nervous system.

A phase transition reduces the threshold for nicotinamide mononucleotide-based activation of SARM1, an NAD(P) hydrolase, to physiologically relevant levels

Axonal degeneration is a hallmark feature of neurodegenerative diseases. Activation of the NAD(P)ase sterile alpha and toll-interleukin receptor motif containing protein 1 (SARM1) is critical for this process. In resting neurons, SARM1 activity is inhibited, but upon damage, SARM1 is activated and catalyzes one of three NAD(P)+ dependent reactions: (1) NAD(P)+ hydrolysis to form ADP-ribose (ADPR[P]) and nicotinamide; (2) the formation of cyclic-ADPR (cADPR[P]); or (3) a base exchange reaction with nicotinic acid (NA) and NADP+ to form NA adenine dinucleotide phosphate. Production of these metabolites triggers axonal death. Two activation mechanisms have been proposed: (1) an increase in the nicotinamide mononucleotide (NMN) concentration, which leads to the allosteric activation of SARM1, and (2) a phase transition, which stabilizes the active conformation of the enzyme. However, neither of these mechanisms have been shown to occur at the same time. Using in vitro assay systems, we show that the liquid-to-solid phase transition lowers the NMN concentration required to activate the catalytic activity of SARM1 by up to 140-fold. These results unify the proposed activation mechanisms and show for the first time that a phase transition reduces the threshold for NMN-based SARM1 activation to physiologically relevant levels. These results further our understanding of SARM1 activation and will be important for the future development of therapeutics targeting SARM1.

Sildenafil Enhances the Therapeutic Effect of Islet Transplantation for Diabetic Peripheral Neuropathy via mTOR/S6K1 Pathway

Purpose

This study aimed to investigate the potential mechanism underlying the therapeutic effect of sildenafil in combination with islet transplantation for diabetic peripheral neuropathy.

Methods

A streptozotocin-induced diabetic mouse model was established to evaluate the effects of islet transplantation and sildenafil intervention. The mice were subjected to different interventions for 6 weeks, and histopathological staining and immunohistochemistry techniques were employed to examine the pathological changes and protein expressions of BDNF, MBP, and cleaved caspase-3 in the sciatic nerve tissue. Moreover, RSC96 cells were cocultured with islet cells and sildenafil under high glucose conditions to investigate the potential involvement of the mTOR/S6K1 pathway, BDNF, and MBP proteins. Western blotting was used to detect protein expression in each group.

Results

The results showed that islet transplantation can restore sciatic nerve injury in diabetic mice, and sildenafil can enhance the therapeutic effect of islet transplantation. In addition, the combination of sildenafil and islet cells significantly upregulated the expression levels of mTOR/S6K1, BDNF, and MBP in RSC96 cells under high glucose conditions.

Conclusions

Islet transplantation can reverse sciatic nerve injury in diabetic mice, and islet cells exhibit a protective effect on RSC96 cells under high glucose conditions via the activation of the mTOR/S6K1 pathway. Sildenafil enhances the therapeutic effect of islet transplantation, which may represent a potential treatment strategy for diabetic peripheral neuropathy.

Peripheral nervous system glia in support of metabolic tissue functions

The peripheral nervous system (PNS) relays information between organs and tissues and the brain and spine to maintain homeostasis, regulate tissue functions, and respond to interoceptive and exteroceptive signals. Glial cells perform support roles to maintain nerve function, plasticity, and survival. The glia of the central nervous system (CNS) are well characterized, but PNS glia (PNSG) populations, particularly tissue-specific subtypes, are underexplored. PNSG are found in large nerves (such as the sciatic), the ganglia, and the tissues themselves, and can crosstalk with a range of cell types in addition to neurons. PNSG are also subject to phenotypic changes in response to signals from their local tissue environment, including metabolic changes. These topics and the importance of PNSG in metabolically active tissues, such as adipose, muscle, heart, and lymphatic tissues, are outlined in this review.

Peripheral mechanisms of peripheral neuropathic pain

Peripheral neuropathic pain (PNP), neuropathic pain that arises from a damage or disease affecting the peripheral nervous system, is associated with an extremely large disease burden, and there is an increasing and urgent need for new therapies for treating this disorder. In this review we have highlighted therapeutic targets that may be translated into disease modifying therapies for PNP associated with peripheral neuropathy. We have also discussed how genetic studies and novel technologies, such as optogenetics, chemogenetics and single-cell RNA-sequencing, have been increasingly successful in revealing novel mechanisms underlying PNP. Additionally, consideration of the role of non-neuronal cells and communication between the skin and sensory afferents is presented to highlight the potential use of drug treatment that could be applied topically, bypassing drug side effects. We conclude by discussing the current difficulties to the development of effective new therapies and, most importantly, how we might improve the translation of targets for peripheral neuropathic pain identified from studies in animal models to the clinic.

New perspectives in diabetic neuropathy

Diabetes prevalence continues to climb with the aging population. Type 2 diabetes (T2D), which constitutes most cases, is metabolically acquired. Diabetic peripheral neuropathy (DPN), the most common microvascular complication, is length-dependent damage to peripheral nerves. DPN pathogenesis is complex, but, at its core, it can be viewed as a state of impaired metabolism and bioenergetics failure operating against the backdrop of long peripheral nerve axons supported by glia. This unique peripheral nerve anatomy and the injury consequent to T2D underpins the distal-to-proximal symptomatology of DPN. Earlier work focused on the impact of hyperglycemia on nerve damage and bioenergetics failure, but recent evidence additionally implicates contributions from obesity and dyslipidemia. This review will cover peripheral nerve anatomy, bioenergetics, and glia-axon interactions, building the framework for understanding how hyperglycemia and dyslipidemia induce bioenergetics failure in DPN. DPN and painful DPN still lack disease-modifying therapies, and research on novel mechanism-based approaches is also covered.

Emerging Nonpharmacologic Interventions to Treat Diabetic Peripheral Neuropathy

Significance: Diabetic peripheral neuropathy (DPN), a complication of metabolic syndrome, type I and type II diabetes, leads to sensory changes that include slow nerve conduction, nerve degeneration, loss of sensation, pain, and gate disturbances. These complications remain largely untreatable, although tight glycemic control can prevent neuropathy progression. Nonpharmacologic approaches remain the most impactful to date, but additional advances in treatment approaches are needed. Recent Advances: This review highlights several emerging interventions, including a focus on dietary interventions and physical activity, that continue to show promise for treating DPN. We provide an overview of our current understanding of how exercise can improve aspects of DPN. We also highlight new studies in which a ketogenic diet has been used as an intervention to prevent and reverse DPN. Critical Issues: Both exercise and consuming a ketogenic diet induce systemic and cellular changes that collectively improve complications associated with DPN. Both interventions may involve similar signaling pathways and benefits but also impact DPN through unique mechanisms. Future Directions: These lifestyle interventions are critically important as personalized medicine approaches will likely be needed to identify specific subsets of neuropathy symptoms and deficits in patients, and determine the most impactful treatment. Overall, these two interventions have the potential to provide meaningful relief for patients with DPN and provide new avenues to identify new therapeutic targets.

Netrin-3 Suppresses Diabetic Neuropathic Pain by Gating the Intra-epidermal Sprouting of Sensory Axons

Diabetic neuropathic pain (DNP) is the most common disabling complication of diabetes. Emerging evidence has linked the pathogenesis of DNP to the aberrant sprouting of sensory axons into the epidermal area; however, the underlying molecular events remain poorly understood. Here we found that an axon guidance molecule, Netrin-3 (Ntn-3), was expressed in the sensory neurons of mouse dorsal root ganglia (DRGs), and downregulation of Ntn-3 expression was highly correlated with the severity of DNP in a diabetic mouse model. Genetic ablation of Ntn-3 increased the intra-epidermal sprouting of sensory axons and worsened the DNP in diabetic mice. In contrast, the elevation of Ntn-3 levels in DRGs significantly inhibited the intra-epidermal axon sprouting and alleviated DNP in diabetic mice. In conclusion, our studies identified Ntn-3 as an important regulator of DNP pathogenesis by gating the aberrant sprouting of sensory axons, indicating that Ntn-3 is a potential druggable target for DNP treatment.

Abnormal intraepidermal nerve fiber density in disease: A scoping review

Background

Intraepidermal nerve fiber density (IENFD) has become an important biomarker for neuropathy diagnosis and research. The consequences of reduced IENFD can include sensory dysfunction, pain, and a significant decrease in quality of life. We examined the extent to which IENFD is being used as a tool in human and mouse models and compared the degree of fiber loss between diseases to gain a broader understanding of the existing data collected using this common technique.

Methods

We conducted a scoping review of publications that used IENFD as a biomarker in human and non-human research. PubMed was used to identify 1,004 initial articles that were then screened to select articles that met the criteria for inclusion. Criteria were chosen to standardize publications so they could be compared rigorously and included having a control group, measuring IENFD in a distal limb, and using protein gene product 9.5 (PGP9.5).

Results

We analyzed 397 articles and collected information related to publication year, the condition studied, and the percent IENFD loss. The analysis revealed that the use of IENFD as a tool has been increasing in both human and non-human research. We found that IENFD loss is prevalent in many diseases, and metabolic or diabetes-related diseases were the most studied conditions in humans and rodents. Our analysis identified 73 human diseases in which IENFD was affected, with 71 reporting IENFD loss and an overall average IENFD change of -47%. We identified 28 mouse and 21 rat conditions, with average IENFD changes of -31.6% and -34.7%, respectively. Additionally, we present data describing sub-analyses of IENFD loss according to disease characteristics in diabetes and chemotherapy treatments in humans and rodents.

Interpretation

Reduced IENFD occurs in a surprising number of human disease conditions. Abnormal IENFD contributes to important complications, including poor cutaneous vascularization, sensory dysfunction, and pain. Our analysis informs future rodent studies so they may better mirror human diseases impacted by reduced IENFD, highlights the breadth of diseases impacted by IENFD loss, and urges exploration of common mechanisms that lead to substantial IENFD loss as a complication in disease.

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.

Capsaicin receptor TRPV1 maintains quiescence of hepatic stellate cells in the liver via recruitment of SARM1

BACKGROUND & AIMS

Capsaicin receptor, also known as transient receptor potential vanilloid 1 (TRPV1), is involved in pain physiology and neurogenic inflammation. Herein, we discovered the presence of TRPV1 in hepatic stellate cells (HSCs) and aimed to delineate its function in this cell type and liver fibrosis.

METHODS

TRPV1 expression was examined in liver biopsies from patients with liver fibrosis using quantitative real-time PCR and immunostaining. Its contribution to liver fibrosis was examined in Trpv1^-/- mice, upon lentiviral delivery of the TRPV1 gene, and in human and mouse primary HSCs, using patch clamp, intracellular Ca²⁺ mobilization determination, FACS analyses and gain/loss of function experiments. Binding of sterile alpha and Toll/interleukin-1 receptor motif-containing protein 1 (SARM1) to TRPV1 was determined using mass spectrometry, co-immunoprecipitation, surface plasmon resonance, bioluminescence resonance energy transfer, and NanoBiT.

RESULTS

TRPV1 mRNA levels are significantly downregulated in patients with liver fibrosis and mouse models, showing a negative correlation with F stage and α-smooth muscle actin expression, a marker of HSC activation. TRPV1 expression and function decrease during HSC activation in fibrotic livers in vivo or during culture. Genetic and pharmacological inhibition of TRPV1 in quiescent HSCs leads to NF-κB activation and pro-inflammatory cytokine production. TRPV1 requires binding of its N-terminal ankyrin repeat domain to the TIR-His583 (Toll/interleukin-1 receptor) domain of SARM1 to prevent HSCs from pro-inflammatory activation. Trpv1^-/- mice display increased HSC activation and more severe liver fibrosis, whereas TRPV1 overexpression is antifibrotic in various disease models.

CONCLUSION

The antifibrotic properties of TRPV1 are attributed to the prevention of HSC activation via the recruitment of SARM1, which could be an attractive therapeutic strategy against liver fibrosis.

IMPACT AND IMPLICATIONS

We identified the neuronal channel protein TRPV1 as a gatekeeper of quiescence in hepatic stellate cells, a key driver of liver fibrogenesis and chronic liver disease. Physiologically expressed in healthy liver and consistently downregulated during liver fibrosis development, its therapeutic re-expression is expected to have few side effects, making it an attractive target diagnostic tool and drug candidate for industry and clinicians.

Bioinformatics and Next-Generation Data Analysis for Identification of Genes and Molecular Pathways Involved in Subjects with Diabetes and Obesity

Background and Objectives: A subject with diabetes and obesity is a class of the metabolic disorder. The current investigation aimed to elucidate the potential biomarker and prognostic targets in subjects with diabetes and obesity. Materials and Methods: The next-generation sequencing (NGS) data of GSE132831 was downloaded from Gene Expression Omnibus (GEO) database. Functional enrichment analysis of DEGs was conducted with ToppGene. The protein-protein interactions network, module analysis, target gene-miRNA regulatory network and target gene-TF regulatory network were constructed and analyzed. Furthermore, hub genes were validated by receiver operating characteristic (ROC) analysis. A total of 872 DEGs, including 439 up-regulated genes and 433 down-regulated genes were observed. Results: Second, functional enrichment analysis showed that these DEGs are mainly involved in the axon guidance, neutrophil degranulation, plasma membrane bounded cell projection organization and cell activation. The top ten hub genes (MYH9, FLNA, DCTN1, CLTC, ERBB2, TCF4, VIM, LRRK2, IFI16 and CAV1) could be utilized as potential diagnostic indicators for subjects with diabetes and obesity. The hub genes were validated in subjects with diabetes and obesity. Conclusion: This investigation found effective and reliable molecular biomarkers for diagnosis and prognosis by integrated bioinformatics analysis, suggesting new and key therapeutic targets for subjects with diabetes and obesity.

Lipid Nanoparticle Delivery of Chemically Modified NGFR100W mRNA Alleviates Peripheral Neuropathy

Messenger RNA (mRNA) carries genetic instructions to the cell machinery for the transient production of antigens or therapeutic proteins and shows enormous potential in vaccine development, cancer immunotherapy, protein replacement therapy, and genome engineering. Here, the synthesis of chemically modified nerve growth factor mutant (NGF^R100W ) mRNA through in vitro transcription is described. After the replacement of the original signal peptide sequence with the Ig Kappa leader sequence, codon-optimized NGF^R100W mRNA yielded high secretion of mature NGF^R100W , which promotes axon growth in PC12 cells. Using lipid nanoparticle (LNP)-delivery of N1-methylpseudouridine-modified mRNA in mice, NGF^R100W -mRNA-LNPs result in the successful expression of NGF^R100W protein, which significantly reduces nociceptive activity compared to that of NGF^WT . This indicates that NGF^R100W derived from exogenous mRNA elicited "painless" neuroprotective activity. Additionally, the therapeutic value of NGF^R100W mRNA is established in a paclitaxel-induced peripheral neuropathy model by demonstrating the rapid recovery of intraepidermal nerve fibers. The results show that in vitro-transcribed mRNA has significant flexibility in sequence design and fast in vivo functional validation of target proteins. Furthermore, the results highlight the therapeutic potential of mRNA as a supplement to beneficial proteins for preventing or reversing some chronic medical conditions, such as peripheral neuropathy.

NAD+ metabolism in peripheral neuropathic pain

Nicotinamide adenine dinucleotide (NAD⁺) is an omnipresent metabolite that participates in redox reactions. Multiple NAD⁺-consuming enzymes are implicated in numerous biological processes, including transcription, signaling, and cell survival. Multiple pieces of evidence have demonstrated that NAD⁺-consuming enzymes, including poly(ADP-ribose) polymerases (PARPs), sirtuins (SIRTs), and sterile alpha and TIR motif-containing 1 (SARM1), play major roles in peripheral neuropathic pain of various etiologies. These NAD⁺ consumers primarily participate in peripheral neuropathic pain via mechanisms such as mitochondrial dysfunction, oxidative stress, and inflammation. Furthermore, NAD⁺ synthase and nicotinamide phosphoribosyltransferase (NAMPT) have recently been found to contribute to the regulation of pain. Here, we review the evidence indicating the involvement of NAD⁺ metabolism in the pathological mechanisms of peripheral neuropathic pain. Advanced understanding of the molecular and cellular mechanisms associated with NAD⁺ in peripheral neuropathic pain will facilitate the development of novel treatment options for diverse types of peripheral neuropathic pain.

A SARM1-mitochondrial feedback loop drives neuropathogenesis in a Charcot-Marie-Tooth disease type 2A rat model

Charcot-Marie-Tooth disease type 2A (CMT2A) is an axonal neuropathy caused by mutations in the mitofusin 2 (MFN2) gene. MFN2 mutations result in profound mitochondrial abnormalities, but the mechanism underlying the axonal pathology is unknown. Sterile α and Toll/IL-1 receptor motif-containing 1 (SARM1), the central executioner of axon degeneration, can induce neuropathy and is activated by dysfunctional mitochondria. We tested the role of SARM1 in a rat model carrying a dominant CMT2A mutation (Mfn2H361Y) that exhibits progressive dying-back axonal degeneration, neuromuscular junction (NMJ) abnormalities, muscle atrophy, and mitochondrial abnormalities - all hallmarks of the human disease. We generated Sarm1-KO (Sarm1-/-) and Mfn2H361Y Sarm1 double-mutant rats and found that deletion of Sarm1 rescued axonal, synaptic, muscle, and functional phenotypes, demonstrating that SARM1 was responsible for much of the neuropathology in this model. Despite the presence of mutant MFN2 protein in these double-mutant rats, loss of SARM1 also dramatically suppressed many mitochondrial defects, including the number, size, and cristae density defects of synaptic mitochondria. This surprising finding indicates that dysfunctional mitochondria activated SARM1 and that activated SARM1 fed back on mitochondria to exacerbate the mitochondrial pathology. As such, this work identifies SARM1 inhibition as a therapeutic candidate for the treatment of CMT2A and other neurodegenerative diseases with prominent mitochondrial pathology.

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

Sexually dimorphic effects of SARM1 deletion on cardiac NAD+ metabolism and function

Nicotinamide adenine dinucleotide (NAD+) decline is repeatedly observed in heart disease and its risk factors. Although strategies promoting NAD+ synthesis to elevate NAD+ levels improve cardiac function, whether inhibition of NAD+ consumption can be therapeutic is less investigated. In this study, we examined the role of sterile-α and TIR motif containing 1 (SARM1) NAD+ hydrolase in mouse hearts, using global SARM1-knockout mice (KO). Cardiac function was assessed by echocardiography in male and female KO mice and wild-type (WT) controls. Hearts were collected for biochemical, histological, and molecular analyses. We found that the cardiac NAD+ pool was elevated in female KO mice, but only trended to increase in male KO mice. SARM1 deletion induced changes to a greater number of NAD+ metabolism transcripts in male mice than in female mice. Body weights, cardiac systolic and diastolic function, and geometry showed no changes in both male and female KO mice compared with WT counterparts. Male KO mice showed a small, but significant, elevation in cardiac collagen levels compared with WT counterparts, but no difference in collagen levels was detected in female mice. The increased collagen levels were associated with greater number of altered profibrotic and senescence-associated inflammatory genes in male KO mice, but not in female KO mice.NEW & NOTEWORTHY We examined the effects of SARM1 deletion on NAD+ pool, transcripts of NAD+ metabolism, and fibrotic pathway for the first time in mouse hearts. We observed the sexually dimorphic effects of SARM1 deletion. How these sex-dependent effects influence the outcomes of SARM1 deficiency in male and female mice in responses to cardiac stresses warrant further investigation. The elevation of cardiac NAD+ pool by SARM1 deletion provides evidence that targeting SARM1 may reverse disease-related NAD+ decline.

Multidisciplinary Progress in Obesity Research

Obesity is a chronic disease that endangers human health. In recent years, the phenomenon of obesity has become more and more common, and it has become a global epidemic. Obesity is closely associated with many adverse metabolic changes and diseases, such as insulin resistance, type 2 diabetes mellitus, coronary heart disease, nervous system diseases and some malignant tumors, which have caused a huge burden on the country's medical finance. In most countries of the world, the incidence of cancer caused by obesity is increasing year on year. Diabetes associated with obesity can lead to secondary neuropathy. How to treat obesity and its secondary diseases has become an urgent problem for patients, doctors and society. This article will summarize the multidisciplinary research on obesity and its complications.

Hesperidin Protects SH−SY5Y Neuronal Cells against High Glucose−Induced Apoptosis via Regulation of MAPK Signaling

Neurodegenerative diseases are associated with neuronal cell death through apoptosis. Apoptosis is tightly associated with the overproduction of reactive oxygen species (ROS), and high glucose levels contribute to higher oxidative stress in diabetic patients. Hesperidin, a natural active compound, has been reported to scavenge free radicals. Only a few studies have explored the protective effects of hesperidin against high glucose−induced apoptosis in SH−SY5Y neuronal cells. Glucose stimulated neuronal cells to generate excessive ROS and caused DNA damage. In addition, glucose triggered endoplasmic reticulum stress and upregulated cytoplasmic as well as mitochondrial calcium levels. Hesperidin inhibited glucose−induced ROS production and mitigated the associated DNA damage and endoplasmic reticulum stress. The downregulation of antiapoptotic protein Bcl−2 following glucose treatment was reversed by a hesperidin treatment. Furthermore, hesperidin repressed the glucose−induced Bcl−2−associated X protein, cleaved caspase−9, and cleaved caspase−3. Hesperidin also suppressed the glucose−induced phosphorylation of extracellular signal−regulated kinase and c−Jun N−terminal kinase. The current results confirmed that hesperidin could protect neuronal cells against glucose−induced ROS. Mechanistically, hesperidin was shown to promote cell viability via attenuation of the mitogen−activated protein kinase signaling pathway.

Natural variants of human SARM1 cause both intrinsic and dominant loss-of-function influencing axon survival

SARM1 is a central executioner of programmed axon death, and this role requires intrinsic NAD(P)ase or related enzyme activity. A complete absence of SARM1 robustly blocks axon degeneration in mice, but even a partial depletion confers meaningful protection. Since axon loss contributes substantially to the onset and progression of multiple neurodegenerative disorders, lower inherent SARM1 activity is expected to reduce disease susceptibility in some situations. We, therefore, investigated whether there are naturally occurring SARM1 alleles within the human population that encode SARM1 variants with loss-of-function. Out of the 18 natural SARM1 coding variants we selected as candidates, we found that 10 display loss-of-function in three complimentary assays: they fail to robustly deplete NAD in transfected HEK 293T cells; they lack constitutive and NMN-induced NADase activity; and they fail to promote axon degeneration in primary neuronal cultures. Two of these variants are also able to block axon degeneration in primary culture neurons in the presence of endogenous, wild-type SARM1, indicative of dominant loss-of-function. These results demonstrate that SARM1 loss-of-function variants occur naturally in the human population, and we propose that carriers of these alleles will have different degrees of reduced susceptibility to various neurological conditions.

Shared TIR enzymatic functions regulate cell death and immunity across the tree of life

In the 20th century, researchers studying animal and plant signaling pathways discovered a protein domain shared across diverse innate immune systems: the Toll/Interleukin-1/Resistance-gene (TIR) domain. The TIR domain is found in several protein architectures and was defined as an adaptor mediating protein-protein interactions in animal innate immunity and developmental signaling pathways. However, studies of nerve degeneration in animals, and subsequent breakthroughs in plant, bacterial and archaeal systems, revealed that TIR domains possess enzymatic activities. We provide a synthesis of TIR functions and the role of various related TIR enzymatic products in evolutionarily diverse immune systems. These studies may ultimately guide interventions that would span the tree of life, from treating human neurodegenerative disorders and bacterial infections, to preventing plant diseases.

The chemical biology of NAD+ regulation in axon degeneration

During axon degeneration, NAD⁺ levels are largely controlled by two enzymes: nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) and sterile alpha and toll interleukin motif containing protein 1 (SARM1). NMNAT2, which catalyzes the formation of NAD⁺ from NMN and ATP, is actively degraded leading to decreased NAD⁺ levels. SARM1 activity further decreases the concentration of NAD⁺ by catalyzing its hydrolysis to form nicotinamide and a mixture of ADPR and cADPR. Notably, SARM1 knockout mice show decreased neurodegeneration in animal models of axon degeneration, highlighting the therapeutic potential of targeting this novel NAD⁺ hydrolase. This review discusses recent advances in the SARM1 field, including SARM1 structure, regulation, and catalysis as well as the identification of the first SARM1 inhibitors.

Analgesic and neuroprotective effects of Baimai Ointment on diabetic peripheral neuropathy

ETHNOPHARMACOLOGY RELEVANCE

Baimai (BM) ointment, a traditional Tibetan medicine, has been widely used to treat "white vein" disease, paralysis, hemiplegia and claudication caused by trauma, because of its great effects on muscle stretching and collateral activation. As one of the most terrible complications in diabetes patients, diabetes peripheral neuropathy (DPN) is mainly manifested as abnormal pain or numbness in extremities. However, whether BM ointment is a potential drug for DPN treatment is unclear.

AIMS OF THE STUDY

The aim of this study was to investigate the therapeutic effects of BM on DPN in a high-fat diet/low-dose of streptozotocin induced type 2 diabetes rat model and explore underlying mechanisms.

METHODS

The chemical components of BM were determined by high performance liquid chromatography (HPLC), and the possible targets and related pathways candidates involved in the effects of BM on DPN were predicted using network pharmacology methods. Next, the effects of different doses (1.5, 3.0 and 6.0 g/kg) of BM on physiological changes, pain behaviors, motor nerve conduction velocity (MNCV) in DPN rats were assessed and compared with placebo- and mecobalamine (Meco)-treated DPN controls. Then, the effects of BM on the expression of pain associated genes as well as the phosphorylation of PI3K/AKT and MAPKs pathways in DRG of DPN rats were examined.

RESULTS

Through HPLC analysis, curcumin was identified as one of the primary contents of BM. The information from network pharmacology indicated a series of target candidates for BM including IL6, IL10, TNF, CCL2, CXCL12, EGF, VEGFA, BDNF, TGFβ1 and TNF, as well as PI3K-AKT and MAPK signaling pathways. Topical treatment of BM significantly improved the hypersensitivity of mechanical and thermal pain, MNCV and the morphological changes and demyelination of sciatic nerve fibers, without affecting the body weight, serum metabolism or blood glucose. The up-regulated levels of neuropeptides Cgrp, Sst, Sp and chemokines Ccl2 and Ccl3 along with the abnormal expression of p-P38, p-ERK and p-AKT in the DRG of DPN rats were alleviated by BM application.

CONCLUSION

BM ointment has great activities in relieving pain hypersensitivity, neuroprotecting peripheral nerves damage caused by DPN, which may be related to the inhibition of related neuropeptide (Cgrp, Sst, Sp) and chemokine (Ccl2, Ccl3) expression and the regulation of PI3K/AKT and MAPKs signaling pathways in DRG.

Distinct developmental and degenerative functions of SARM1 require NAD+ hydrolase activity

SARM1 is the founding member of the TIR-domain family of NAD⁺ hydrolases and the central executioner of pathological axon degeneration. SARM1-dependent degeneration requires NAD⁺ hydrolysis. Prior to the discovery that SARM1 is an enzyme, SARM1 was studied as a TIR-domain adaptor protein with non-degenerative signaling roles in innate immunity and invertebrate neurodevelopment, including at the Drosophila neuromuscular junction (NMJ). Here we explore whether the NADase activity of SARM1 also contributes to developmental signaling. We developed transgenic Drosophila lines that express SARM1 variants with normal, deficient, and enhanced NADase activity and tested their function in NMJ development. We find that NMJ overgrowth scales with the amount of NADase activity, suggesting an instructive role for NAD⁺ hydrolysis in this developmental signaling pathway. While degenerative and developmental SARM1 signaling share a requirement for NAD⁺ hydrolysis, we demonstrate that these signals use distinct upstream and downstream mechanisms. These results identify SARM1-dependent NAD⁺ hydrolysis as a heretofore unappreciated component of developmental signaling. SARM1 now joins sirtuins and Parps as enzymes that regulate signal transduction pathways via mechanisms that involve NAD⁺ cleavage, greatly expanding the potential scope of SARM1 TIR NADase functions.

SARM1 is the central executioner of axon loss, and inhibition of SARM1 is a therapeutic target for many devastating neurodegenerative disorders. SARM1 is the founding member of the TIR-domain family of NAD⁺ cleaving enzymes, destroying the essential metabolite NAD⁺ and inducing an energetic crisis in the axon. This was a surprising finding, as previously studied TIR-domain proteins were characterized as scaffolds that bind signaling proteins to coordinate signal transduction cascades. Indeed, before the discovery of the role of SARM1 in axon degeneration, SARM1 was studied as a regulator of intracellular signaling in immunity and neurodevelopment where it was assumed to act as a scaffold. Here we investigate whether the recently described SARM1 enzymatic activity also regulates such signal transduction pathways. Indeed, we show that a developmental signaling pathway scales with the amount of NADase activity, suggesting an instructive role for NAD⁺ cleavage. While degenerative and developmental SARM1 signaling share a requirement for NAD⁺ cleavage, they utilize distinct upstream and downstream mechanisms. With these findings, SARM1 now joins sirtuins and Parps as enzymes that regulate signal transduction pathways via mechanisms that involve NAD⁺ cleavage, greatly expanding the potential scope of SARM1 TIR NADase functions.

Current and Emerging Pharmacotherapeutic Interventions for the Treatment of Peripheral Nerve Disorders

Peripheral nerve disorders are caused by a range of different aetiologies. The range of causes include metabolic conditions such as diabetes, obesity and chronic kidney disease. Diabetic neuropathy may be associated with severe weakness and the loss of sensation, leading to gangrene and amputation in advanced cases. Recent studies have indicated a high prevalence of neuropathy in patients with chronic kidney disease, also known as uraemic neuropathy. Immune-mediated neuropathies including Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy may cause significant physical disability. As survival rates continue to improve in cancer, the prevalence of treatment complications, such as chemotherapy-induced peripheral neuropathy, has also increased in treated patients and survivors. Notably, peripheral neuropathy associated with these conditions may be chronic and long-lasting, drastically affecting the quality of life of affected individuals, and leading to a large socioeconomic burden. This review article explores some of the major emerging clinical and experimental therapeutic agents that have been investigated for the treatment of peripheral neuropathy due to metabolic, toxic and immune aetiologies.

NAD+ Precursors Repair Mitochondrial Function in Diabetes and Prevent Experimental Diabetic Neuropathy

Axon degeneration in diabetic peripheral neuropathy (DPN) is associated with impaired NAD+ metabolism. We tested whether the administration of NAD+ precursors, nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), prevents DPN in models of Type 1 and Type 2 diabetes. NMN was administered to streptozotocin (STZ)-induced diabetic rats and STZ-induced diabetic mice by intraperitoneal injection at 50 or 100 mg/kg on alternate days for 2 months. mice The were fed with a high fat diet (HFD) for 2 months with or without added NR at 150 or 300 mg/kg for 2 months. The administration of NMN to STZ-induced diabetic rats or mice or dietary addition of NR to HFD-fed mice improved sensory function, normalized sciatic and tail nerve conduction velocities, and prevented loss of intraepidermal nerve fibers in skin samples from the hind-paw. In adult dorsal root ganglion (DRG) neurons isolated from HFD-fed mice, there was a decrease in NAD+ levels and mitochondrial maximum reserve capacity. These impairments were normalized in isolated DRG neurons from NR-treated mice. The results indicate that the correction of NAD+ depletion in DRG may be sufficient to prevent DPN but does not significantly affect glucose tolerance, insulin levels, or insulin resistance.

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.

SARM1 Ablation Is Protective and Preserves Spatial Vision in an In Vivo Mouse Model of Retinal Ganglion Cell Degeneration

The challenge of developing gene therapies for genetic forms of blindness is heightened by the heterogeneity of these conditions. However, mechanistic commonalities indicate key pathways that may be targeted in a gene-independent approach. Mitochondrial dysfunction and axon degeneration are common features of many neurodegenerative conditions including retinal degenerations. Here we explore the neuroprotective effect afforded by the absence of sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1), a prodegenerative NADase, in a rotenone-induced mouse model of retinal ganglion cell loss and visual dysfunction. Sarm1 knockout mice retain visual function after rotenone insult, displaying preservation of photopic negative response following rotenone treatment in addition to significantly higher optokinetic response measurements than wild type mice following rotenone. Protection of spatial vision is sustained over time in both sexes and is accompanied by increased RGC survival and additionally preservation of axonal density in optic nerves of Sarm1^−/− mice insulted with rotenone. Primary fibroblasts extracted from Sarm1^−/− mice demonstrate an increased oxygen consumption rate relative to those from wild type mice, with significantly higher basal, maximal and spare respiratory capacity. Collectively, our data indicate that Sarm1 ablation increases mitochondrial bioenergetics and confers histological and functional protection in vivo in the mouse retina against mitochondrial dysfunction, a hallmark of many neurodegenerative conditions including a variety of ocular disorders.

Recent updates in the treatment of diabetic polyneuropathy

Distal symmetric diabetic peripheral polyneuropathy (DPN) is the most common form of neuropathy in the world, affecting 30 to 50% of diabetic individuals and resulting in significant morbidity and socioeconomic costs. This review summarizes updates in the diagnosis and management of DPN. Recently updated clinical criteria facilitate bedside diagnosis, and a number of new technologies are being explored for diagnostic confirmation in specific settings and for use as surrogate measures in clinical trials. Evolving literature indicates that distinct but overlapping mechanisms underlie neuropathy in type 1 versus type 2 diabetes, and there is a growing focus on the role of metabolic factors in the development and progression of DPN. Exercise-based lifestyle interventions have shown therapeutic promise. A variety of potential disease-modifying and symptomatic therapies are in development. Innovations in clinical trial design include the incorporation of detailed pain phenotyping and biomarkers for central sensitization.

[Swertiamarin alleviates diabetic peripheral neuropathy in rats by suppressing NOXS/ ROS/NLRP3 signal pathway]

OBJECTIVE

To observe the therapeutic effect of swertiamarin on diabetic peripheral neuropathy (DPN) in rats and explore the molecular mechanism in light of the NOXS/ROS/NLRP3 signal pathway.

OBJECTIVE

Thirty-two SD rats were randomly divided into control group, DPN model group (treated with saline), swertiamarin (5 mg/kg) treatment group and NOXS inhibitor (10 mL/kg DPI) treatment group. Rat models of DPN were established in the latter 3 groups by intraperitoneal injections of STZ, and the treatments were administered on days 1, 7 and 14 after modeling. Tactile hypersensitivity of the rats was evaluated 30 min after the treatment. The expressions of NOXS, ROS, NLRP3 and inflammatory factors in the spinal cord tissue were detected using ELISA, and the protein expressions of NOXS, ROS, and NLRP3 were also detected with Western blotting.

OBJECTIVE

Compared with those in the control group, the rats in DPN group showed significant hyperalgesia (P < 0.001), increased expressions of TNF-α (P < 0.001) and IL-6 (P < 0.001), decreased expressions of TGF-β (P < 0.001), and increased expressions of NOXS/ROS/NLRP3 signal pathway (P < 0.001). Compared with those in DPN model group, the rats with swertiamarin treatment showed improved hyperalgesia (P < 0.001), decreased expressions of TNF-α (P=0.03) and IL-6 (P=0.002), increased expressions of TGF-β (P=0.04), and decreased expressions of NOXS (P < 0.001), ROS (P < 0.001) and NLRP3 (P=0.002). Treatment with swertiamarin and the NOXS inhibitor produced similar effects on the expressions of the inflammatory factors in the rat models (P>0.05).

OBJECTIVE

DPN effectively relieves hyperalgesia in rat models of DPN by restoring the balance in the expressions of the inflammatory factors by suppressing NOXs/ROS/NLRP3 signaling pathway.

Tang Luo Ning, a Traditional Chinese Compound Prescription, Ameliorates Schwannopathy of Diabetic Peripheral Neuropathy Rats by Regulating Mitochondrial Dynamics In Vivo and In Vitro

Tang Luo Ning (TLN), a traditional Chinese compound prescription, has been used clinically to treat diabetic peripheral neuropathy (DPN) in China. However, the exact mechanisms remain unclear. The objective of this study is to unravel the effects of TLN on mitochondrial dynamics of DPN in streptozotocin-induced rat models and Schwann cells cultured in 150 mM glucose. Mitochondrial function was determined by Ca²⁺ and ATP levels of streptozotocin (STZ)-induced DPN rats and mitochondria structure, mitochondrial membrane potential (MMP), and mtDNA of high glucose incubated SCs. Mitochondrial dynamics protein including mitofusin 1 (Mfn1), mitofusin 2 (Mfn2), optic atrophy 1 (Opa1), and dynamin-related protein 1 (Drp1) were investigated using Western blot or immunofluorescence. Myelin basic protein (MBP), myelin protein zero (MPZ), and sex-determining region Y (SRY)-box 10 (Sox10) were measured to represent schwannopathy. Our results showed that TLN increased ATP levels (0.38 of model, 0.69 of HTLN, 0.61 of LTLN, P＜0.01; 0.52 of 150 mM glucose, 1.00 of 10% TLN, P＜0.01, 0.94 of 1% TLN, P＜0.05), MMP (0.56 of 150 mM glucose, P＜0.01, 0.75 of 10% TLN, P＜0.05, 0.83 of 1% TLN, P＜0.01), and mtDNA (0.32 of 150 mM glucose, 0.43 of 10% TLN, P＜0.01) while decreased Ca²⁺ (1.54 of model, 1.06 of HTLN, 0.96 of LTLN, P＜0.01) to improve mitochondrial function in vivo and in vitro. TLN helps maintain balance of mitochondrial dynamics: it reduces the mitochondria number (1.60 of 150 mM glucose, 1.10 of 10% TLN, P＜0.01) and increases the mitochondria coverage (0.51 of 150 mM glucose, 0.80 of 10% TLN, 0.87 of 1% TLN, P＜0.01), mitochondrial network size (0.51 of 150 mM glucose, 0.95 of 10% TLN, 0.94 of 1% TLN, P＜0.01), and branch length (0.63 of 150 mM glucose, P＜0.01, 0.73 of 10% TLN, P＜0.05, 0.78 of 1% TLN, P＜0.01). Further, mitochondrial dynamics–related Mfn1 (0.47 of model, 0.82 of HTLN, 0.77 of LTLN, P＜0.01; 0.42 of 150 mM glucose, 0.56 of 10% TLN, 0.57 of 1% TLN, P＜0.01), Mfn2 (0.40 of model, 0.84 of HTLN, 0.63 of LTLN, P＜0.01; 0.46 of 150 mM glucose, 1.40 of 10% TLN, 1.40 of 1% TLN, P＜0.01), and Opa1 (0.58 of model, 0.71 of HTLN, 0.90 of LTLN, P＜0.01; 0.69 of 150 mM glucose, 0.96 of 10% TLN, 0.98 of 1% TLN, P＜0.05) were increased, while Drp1 (1.39 of model, 0.96 of HTLN, 1.18 of LTLN, P＜0.01; 1.70 of 150 mM glucose, 1.20 of 10% TLN, 1.10 of 1% TLN, P＜0.05), phosphorylated Drp1 (2.61 of model, 1.44 of HTLN, P＜0.05; 2.80 of 150 mM glucose, 1.50 of 10% TLN, 1.30 of 1% TLN, P＜0.01), and Drp1 located in mitochondria (1.80 of 150 mM glucose, 1.00 of 10% TLN, P＜0.05) were decreased after treatment with TLN. Additionally, TLN improved schwannopathy by increasing MBP (0.50 of model, 1.05 of HTLN, 0.94 of HTLN, P＜0.01; 0.60 of 150 mM glucose, 0.78 of 10% TLN, P＜0.01, 0.72 of 1% TLN, P＜0.05), Sox101 (0.41 of model, 0.99 of LTLN, P＜0.01; 0.48 of 150 mM glucose, 0.65 of 10% TLN, P＜0.05, 0.69 of 1% TLN, P＜0.01), and MPZ (0.48 of model, 0.66 of HTLN, 0.55 of HTLN, P＜0.01; 0.60 of 150 mM glucose, 0.78 of 10% TLN, P＜0.01, 0.75 of 1% TLN, P＜0.05) expressions. In conclusion, our study indicated that TLN’s function on DPN may link to the improvement of the mitochondrial dynamics, which provides scientific evidence for the clinical application.

Pharmacological SARM1 inhibition protects axon structure and function in paclitaxel-induced peripheral neuropathy

Axonal degeneration is an early and ongoing event that causes disability and disease progression in many neurodegenerative disorders of the peripheral and central nervous systems. Chemotherapy-induced peripheral neuropathy (CIPN) is a major cause of morbidity and the main cause of dose reductions and discontinuations in cancer treatment. Preclinical evidence indicates that activation of the Wallerian-like degeneration pathway driven by sterile alpha and TIR motif containing 1 (SARM1) is responsible for axonopathy in CIPN. SARM1 is the central driver of an evolutionarily conserved programme of axonal degeneration downstream of chemical, inflammatory, mechanical or metabolic insults to the axon. SARM1 contains an intrinsic NADase enzymatic activity essential for its pro-degenerative functions, making it a compelling therapeutic target to treat neurodegeneration characterized by axonopathies of the peripheral and central nervous systems. Small molecule SARM1 inhibitors have the potential to prevent axonal degeneration in peripheral and central axonopathies and to provide a transformational disease-modifying treatment for these disorders.

Using a biochemical assay for SARM1 NADase we identified a novel series of potent and selective irreversible isothiazole inhibitors of SARM1 enzymatic activity that protected rodent and human axons in vitro. In sciatic nerve axotomy, we observed that these irreversible SARM1 inhibitors decreased a rise in nerve cADPR and plasma neurofilament light chain released from injured sciatic nerves in vivo. In a mouse paclitaxel model of CIPN we determined that Sarm1 knockout mice prevented loss of axonal function, assessed by sensory nerve action potential amplitudes of the tail nerve, in a gene-dosage-dependent manner. In that CIPN model, the irreversible SARM1 inhibitors prevented loss of intraepidermal nerve fibres induced by paclitaxel and provided partial protection of axonal function assessed by sensory nerve action potential amplitude and mechanical allodynia.

Vitamin A and Daucus carota root extract mitigate STZ-induced diabetic retinal degeneration in Wistar albino rats by modulating neurotransmission and downregulation of apoptotic pathways

The objective of our study was to explore the deleterious effects of diabetes on the visual functions of the retina and to address whether the administration of vitamin A and carrot root extract (CE) confer retinal protection in hyperglycemic rats via modulation of oxidative stress, biochemical alternations, and retinal neurotransmission. Fifty male Wistar albino rats weighing 180 ± 12.41 g were randomized into five groups (n = 10): controls, diabetic group (injected with 40 mg/kg dissolved in 0.1 sodium citrate buffer), diabetic group treated with vitamin A (2,500 IU/kg, low dose), diabetic group treated with vitamin (5,000 IU/kg, high dose), and diabetic groups administered CE (200 mg/kg/every other day). Our findings showed that, compared to controls, diabetic rats showed a significant decrease in their retinal thickness, increased apoptotic ganglion cells, and a noticeable degeneration of their synaptic layers. The inner retina displayed increased activity of neovascularization; however, the outer retina exhibited vacuolar degeneration of the photoreceptor cell layer. Our biochemical assessments showed reduced levels of CAT, SOD, and GST along with increased lipid peroxidation. Concurrently, cellular angiogenic and stress markers were significantly elevated associated with increased apoptotic activities as evidenced by increased expressions of annexin-V and PARP. Furthermore, the neurotransmitter content of the retina was altered in diabetic rats compared to controls and diabetic-treated groups. Paradoxically, vitamin A and CE supplementation attenuate these retinal insults in diabetic animals and normalized aforementioned assayed parameters; evidencing that both treatments exerted ameliorative impacts and restored visual functions by diminishing oxidative stress and neuronal degeneration. PRACTICAL APPLICATIONS: Diabetes is a complex disease that involves various physiological perturbations especially visual functions. In our study, we showed that vitamin A and carrot root extract (CE) confer remarkable protection against retinal degeneration in STZ-induced diabetic rats. Our findings showed that the chemical and phytochemical ingredients of the vitamin A and CE substantially attenuated the histopathological changes, oxidative stress, inflammatory reactions, and cellular death in diabetic rats. These favorable changes are attributable to the high content of retinoic acid, carotenoids, and phenolic compounds that effectively regulates the production of visual pigments, increases the antioxidant defense system, and diminishes the pro-inflammatory and apoptotic pathways. Thus, the nutritional values of vitamin A and CE represent promising therapeutic choices to mitigate the retinal-induced diabetic insults.

Metabolic stress drives sympathetic neuropathy within the liver

The nervous system instructs the body's metabolism, including that in the liver. However, the neural anatomy of the liver under either normal or metabolically stressed conditions remains to be unequivocally assessed. Here, we examined neural distributions in the mouse, nonhuman primate, and human livers with advanced 3D imaging. We observed that neural innervations within the liver are predominantly sympathetic, but not parasympathetic, inputs. Moreover, we discovered the profound and reversible loss of such sympathetic innervations during metabolic challenges. This hepatic sympathetic neuropathy was caused by TNFα derived from CD11b⁺ F4/80⁺ immune cells under high-fat-diet (HFD) condition. We further demonstrated that the Sarm1 deletion mitigated the hepatic sympathetic neuropathy and improved metabolic parameters in HFD-challenged mice. Mechanistically, the sympathetic neurotransmitter norepinephrine attenuated the immune-cell inflammation that would otherwise trigger the insulin insensitivity of hepatocytes. These results together reveal the previously unrecognized neuropathic event in the liver with metabolic relevance.

Identification of key pathways and genes in polycystic ovary syndrome via integrated bioinformatics analysis and prediction of small therapeutic molecules

To enhance understanding of polycystic ovary syndrome (PCOS) at the molecular level; this investigation intends to examine the genes and pathways associated with PCOS by using an integrated bioinformatics analysis. Based on the expression profiling by high throughput sequencing data GSE84958 derived from the Gene Expression Omnibus (GEO) database, the differentially expressed genes (DEGs) between PCOS samples and normal controls were identified. We performed a functional enrichment analysis. A protein-protein interaction (PPI) network, miRNA- target genes and TF - target gene networks, were constructed and visualized, with which the hub gene nodes were identified. Validation of hub genes was performed by using receiver operating characteristic (ROC) and RT-PCR. Small drug molecules were predicted by using molecular docking. A total of 739 DEGs were identified, of which 360 genes were up regulated and 379 genes were down regulated. GO enrichment analysis revealed that up regulated genes were mainly involved in peptide metabolic process, organelle envelope and RNA binding and the down regulated genes were significantly enriched in plasma membrane bounded cell projection organization, neuron projection and DNA-binding transcription factor activity, RNA polymerase II-specific. REACTOME pathway enrichment analysis revealed that the up regulated genes were mainly enriched in translation and respiratory electron transport and the down regulated genes were mainly enriched in generic transcription pathway and transmembrane transport of small molecules. The top 10 hub genes (SAA1, ADCY6, POLR2K, RPS15, RPS15A, CTNND1, ESR1, NEDD4L, KNTC1 and NGFR) were identified from PPI network, miRNA - target gene network and TF - target gene network. The modules analysis showed that genes in modules were mainly associated with the transport of respiratory electrons and signaling NGF, respectively. We find a series of crucial genes along with the pathways that were most closely related with PCOS initiation and advancement. Our investigations provide a more detailed molecular mechanism for the progression of PCOS, detail information on the potential biomarkers and therapeutic targets.

Trichostatin A increases BDNF protein expression by improving XBP-1s/ATF6/GRP78 axis in Schwann cells of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is the common complication of diabetes mellitus. Histone deacetylase (HDAC) inhibitor trichostatin A (TSA) is reported to ameliorate the peripheral nerves degeneration of DPN. However, the exact mechanism is still not well elucidated. Here, we first revealed that TSA promoted nerve conduction and brain derived neurotrophic factor (BDNF) expression in the sciatic nerves of diabetic mice. In line, TSA also reversed high glucose-reduced mature BDNF expression in vitro cultured rat Schwann cells (RSC96). Then unexpectedly, the downstream targets of TSA HDAC1 and HDAC5 were not involved in TSA-improved BDNF expression. Furthermore, unfolded protein response (UPR) chaperone GRP78 was revealed to be downregulated with high glucose stimulation in RSC96 cells, which was avoided with TSA treatment. Also, GRP78 upregulation mediated TSA-improved mature BDNF expression in high glucose-cultured RSC96 cells by binding with BDNF. As well, TSA treatment enhanced the binding of GRP78 with BDNF in RSC96 cells. Again, UPR-associated transcription factors XBP-1s and ATF6 were involved in TSA-increased GRP78 expression in high glucose-stimulated RSC96 cells. Finally, conditioned medium from high glucose-cultured RSC96 cells delayed neuron SH-SY5Y differentiation and that from TSA-treated high glucose-cultured RSC96 cells promoted SH-SY5Y cell differentiation. Taken together, our findings suggested that TSA increased BDNF expression to ameliorate DPN by improving XBP-1s/ATF6/GRP78 axis in Schwann cells.

Analysis of the effect of probucol-mecobalamin tablets combination on oxidative stress in patients with diabetic peripheral neuropathy

OBJECTIVE

This research aimed to observe the effect of probucol combined with mecobalamin tablets on oxidative stress in patients with diabetic peripheral neuropathy (DPN).

METHODS

In this prospective study, 104 patients with DPN who were treated in our hospital were included, from August 2018 to January 2020. They were divided into groups of combination (n = 52) and control (n = 52) by using a random number table. All patients took mecobalamin tablets after meals for 3 months (1 tablet/time, 3 times/d). On this basis, patients in the combination group took probucol for 3 months (4 tablets/time, 2 times/d). The observation indicators were the Toronto Clinical Scoring System (TCSS)(symptom, sensory, and reflex scores), nerve conduction velocity[sensory nerve conduction velocity (SNCV) and motor nerve conduction velocity(MNCV) of the common peroneal nerve and median nerve], oxidative stress indicators[superoxide dismutase(SOD), malondialdehyde(MDA), glutathione peroxidase(GSH-Px) and catalase(CAT)], clinical efficacy and adverse reactions.

RESULTS

There was no significant difference in the symptom scores, sensory scores, reflex scores, and total scores between the two groups before treatment (p > 0.05), while these four indicators of the combination group were significantly lower than that in the control group after treatment (p < 0.05). These four indicators of the two groups after treatment were significantly lower than before treatment (p < 0.05). There was no significant difference in the SNCV and NMCV of the common peroneal nerve and median nerve between the two groups before treatment (p > 0.05), while the indicators of the combination group were significantly higher than that of the control group (p < 0.05) after treatment, and these indicators of the two groups after treatment were significantly higher than that before treatment (p < 0.05). There was no significant difference in SOD, MDA, GSH-Px, and CAT between the two groups before treatment (p > 0.05). After treatment, the SOD, GSH-Px, and CAT in the combination group were significantly higher than that in the control group (p < 0.05), while the MDA in the combination group was significantly lower than that in the control group (p < 0.05). After treatment, the SOD, GSH-Px, and CAT in the two groups were significantly higher than that before treatment (p < 0.05), while the MDA was lower (p < 0.05). The clinical efficacy of the combination group was significantly better than that of the control group (94.23 % vs 78.85 %, p＜0.05) after treatment. There was no significant difference in the incidence of total adverse reactions between the two groups (3.85 % vs 5.77 %, p > 0.05).

CONCLUSION

The therapeutic effect of probucol combined with mecobalamin tablets for patients with DPN was significant, which could effectively improve the oxidative stress response of patients and was worthy of clinical promotion.

Sarm1 knockout protects against early but not late axonal degeneration in experimental allergic encephalomyelitis

Programmed axonal degeneration, also known as Wallerian degeneration, occurs in immune-mediated central nervous system (CNS) inflammatory disorders such as multiple sclerosis and the animal model experimental allergic encephalomyelitis (EAE). Sterile alpha and TIR domain containing protein 1 (SARM1) functions to promote programmed axonal degeneration. To test the hypothesis that loss of SARM1 will reduce axonal degeneration in immune-mediated CNS inflammatory disorders, the course and pathology of EAE was compared in Sarm1 knockout mice and wild type littermates. The clinical course of EAE was similar in Sarm1 knockout and wild type. Analysis of EAE in mice expressing neuronal yellow fluorescent protein (YFP) showed significantly less axonal degeneration in Sarm1 knockout mice compared to wild type littermates at 14 days post-induction of EAE. At 21 days post-induction, however, difference in axonal degeneration was not significant. At 42 days post-induction, Sarm1 knockout mice were indistinguishable from wild type with respect to markers of axonal injury, and were similar with respect to axonal density in the lumbar cords. There was no significant change in peripheral immune activation or CNS inflammatory cell infiltration associated with EAE in Sarm1 knockout mice. In conclusion, Sarm1 deletion delayed axonal degeneration early in the course of CNS inflammation, but did not confer long-term protection from axonal degeneration in an animal model of immune-mediated CNS inflammation.

The SARM1 axon degeneration pathway: control of the NAD+ metabolome regulates axon survival in health and disease

Axons are essential for nervous system function and axonal pathology is a common hallmark of many neurodegenerative diseases. Over a century and a half after the original description of Wallerian axon degeneration, advances over the past five years have heralded the emergence of a comprehensive, mechanistic model of an endogenous axon degenerative process that can be activated by both injury and disease. Axonal integrity is maintained by the opposing actions of the survival factors NMNAT2 and STMN2 and pro-degenerative molecules DLK and SARM1. The balance between axon survival and self-destruction is intimately tied to axonal NAD⁺ metabolism. These mechanistic insights may enable axon-protective therapies for a variety of human neurodegenerative diseases including peripheral neuropathy, traumatic brain injury and potentially ALS and Parkinson's.

Age-related NAD+ decline

Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite that is reported to decline in concentration in tissues of aged animals. Strategies to increase NAD+ availability have shown promise in treating many conditions in rodents, including age-related degeneration, which has in turn driven intense interest in the effects of supplements on human health. However, many aspects of NAD+ metabolism remain poorly understood, and human data are limited. Here, we discuss the state of the evidence for an age-related decline in NAD+, along with potential mechanistic explanations, including increased consumption or decreased synthesis of NAD+ and changes in the composition of cells or tissues with age. Key challenges for the field involve the development of better tools to resolve information on the NAD+ content of specific cells and subcellular compartments as well as determining the threshold levels at which NAD+ depletion triggers physiological consequences in different tissues. Understanding how NAD+ metabolism changes with age in humans may ultimately allow the design of more targeted strategies to maintain its availability, such as inhibition of key consumers in specific tissues or direct delivery of precursors to sites of deficiency. In the meantime, human clinical trials with oral supplements are poised to provide some of the first direct evidence as to whether increasing NAD+ availability can impact human physiology. Thus, it is an exciting time for NAD+ research, with much remaining to be learned in terms of both basic biology and potential therapeutic applications.

cADPR is a gene dosage-sensitive biomarker of SARM1 activity in healthy, compromised, and degenerating axons

SARM1 is the central executioner of pathological axon degeneration, promoting axonal demise in response to axotomy, traumatic brain injury, and neurotoxic chemotherapeutics that induce peripheral neuropathy. SARM1 is an injury-activated NAD⁺ cleavage enzyme, and this NADase activity is required for the pro-degenerative function of SARM1. At present, SARM1 function is assayed by either analysis of axonal loss, which is far downstream of SARM1 enzymatic activity, or via NAD⁺ levels, which are regulated by many competing pathways. Here we explored the utility of measuring cADPR, a product of SARM1-dependent cleavage of NAD⁺, as an in cell and in vivo biomarker of SARM1 enzymatic activity. We find that SARM1 is a major producer of cADPR in cultured dorsal root ganglion (DRG) neurons, sciatic nerve, and brain, demonstrating that SARM1 has basal activity in the absence of injury. Following injury, there is a dramatic SARM1-dependent increase in the levels of axonal cADPR that precedes morphological axon degeneration. In vivo, there is also a rapid and large injury-stimulated increase in cADPR in sciatic and optic nerves. The increase in cADPR after injury is proportional to SARM1 gene dosage, suggesting that SARM1 activity is the prime regulator of cADPR levels. The role of cADPR as an important calcium mobilizing agent prompted exploration of its functional contribution to axon degeneration. We used multiple bacterial and mammalian engineered enzymes to manipulate cADPR levels in neurons but found no changes in the time course of axonal degeneration, suggesting that cADPR is unlikely to be an important contributor to the degenerative mechanism. Using cADPR as a SARM1 biomarker, we find that SARM1 can be partially activated by a diverse array of mitochondrial toxins administered at doses that do not induce axon degeneration. Hence, the subcritical activation of SARM1 induced by mitochondrial dysfunction may contribute to the axonal vulnerability common to many neurodegenerative diseases. Finally, we assay levels of both nerve cADPR and plasma neurofilament light chain (NfL) following nerve injury in vivo, and demonstrate that both biomarkers are excellent readouts of SARM1 activity, with cADPR reporting the early molecular changes in the nerve and NfL reporting subsequent axonal breakdown. The identification and characterization of cADPR as a SARM1 biomarker will help identify neurodegenerative diseases in which SARM1 contributes to axonal loss and expedite target validation studies of SARM1-directed therapeutics.