Genetic and Epigenomic Modifiers of Diabetic Neuropathy

Diabetic neuropathy (DN), the most common chronic and progressive complication of diabetes mellitus (DM), strongly affects patients’ quality of life. DN could be present as peripheral, autonomous or, clinically also relevant, uremic neuropathy. The etiopathogenesis of DN is multifactorial, and genetic components play a role both in its occurrence and clinical course. A number of gene polymorphisms in candidate genes have been assessed as susceptibility factors for DN, and most of them are linked to mechanisms such as reactive oxygen species production, neurovascular impairments and modified protein glycosylation, as well as immunomodulation and inflammation. Different epigenomic mechanisms such as DNA methylation, histone modifications and non-coding RNA action have been studied in DN, which also underline the importance of “metabolic memory” in DN appearance and progression. In this review, we summarize most of the relevant data in the field of genetics and epigenomics of DN, hoping they will become significant for diagnosis, therapy and prevention of DN.     

Pathogenic Hydrogel? A Novel-Entrapment Neuropathy Model Induced by Ultrasound-Guided Perineural Injections

Entrapment neuropathy (EN) is a prevalent and debilitative condition caused by a complex pathogenesis that involves a chronic compression–edema–ischemia cascade and perineural adhesion that results in excessive shear stress during motion. Despite decades of research, an easily accessible and surgery-free animal model mimicking the mixed etiology is currently lacking, thus limiting our understanding of the disease and the development of effective therapies. In this proof-of-concept study, we used ultrasound-guided perineural injection of a methoxy poly(ethylene glycol)-b-Poly(lactide-co-glycoilide) carboxylic acid (mPEG-PLGA-BOX) hydrogel near the rat’s sciatic nerve to induce EN, as confirmed sonographically, electrophysiologically, and histologically. The nerve that was injected with hydrogel appeared unevenly contoured and swollen proximally with slowed nerve conduction velocities across the injected segments, thus showing the compressive features of EN. Histology showed perineural cellular infiltration, deposition of irregular collagen fibers, and a possible early demyelination process, thus indicating the existence of adhesions. The novel method provides a surgery-free and cost-effective way to establish a small-animal model of EN that has mixed compression and adhesion features, thus facilitating the additional elucidation of the pathophysiology of EN and the search for promising treatments.     

Roles of Voltage-Gated Tetrodotoxin-Sensitive Sodium Channels NaV1.3 and NaV1.7 in Diabetes and Painful Diabetic Neuropathy

Diabetes mellitus (DM) is a common chronic medical problem worldwide; one of its complications is painful peripheral neuropathy, which can substantially erode quality of life and increase the cost of management. Despite its clinical importance, the pathogenesis of painful diabetic neuropathy (PDN) is complex and incompletely understood. Voltage-gated sodium channels (VGSCs) link many physiological processes to electrical activity by controlling action potentials in all types of excitable cells. Two isoforms of VGSCs, Na_V1.3 and Na_V1.7, which are encoded by the sodium voltage-gated channel alpha subunit 3 and 9 (Scn3A and Scn9A) genes, respectively, have been identified in both peripheral nociceptive neurons of dorsal root ganglion (DRG) and pancreatic islet cells. Recent advances in our understanding of tetrodotoxin-sensitive (TTX-S) sodium channels Na_V1.3 and Na_V1.7 lead to the rational doubt about the cause–effect relation between diabetes and painful neuropathy. In this review, we summarize the roles of Na_V1.3 and Na_V1.7 in islet cells and DRG neurons, discuss the link between DM and painful neuropathy, and present a model, which may provide a starting point for further studies aimed at identifying the mechanisms underlying diabetes and painful neuropathy.     

当归多糖对DPN大鼠TLR4/MyD88/NF-κB通路抑制影响

目的: 分析当归多糖对糖尿病神经病变（DPN）大鼠TLR4/MyD88/NF-κB通路抑制影响。方法: 选取SPF级Wistar雄性大鼠105只,随机选取15只作为正常组,剩余90只大鼠制备DPN模型,成功造模75只,随机分成5组,模型组、当归多糖低、中、高剂量组和阳性对照组,每组15只。模型组和正常组大鼠采用2 mL/100 g生理盐水灌胃,当归多糖低、中、高剂量组大鼠给予当归多糖药液灌胃,阳性对照组给予弥可保+二甲双胍溶液灌胃,每日给药体积均为2 mL/100 g。每天1次,连续灌胃10 d。给药3、10 d后检测大鼠机械缩足反应阈值（PWT）、热缩足反射潜伏期（PWL）,末次给药后检测大鼠空腹血糖、血清丙二醛（MDA）、超氧化物歧化酶（SOD）、过氧化氢酶（CAT）活性、谷胱甘肽过氧化物酶（GSH-Px）、白细胞介素-6（IL-6）、髓鞘碱性蛋白（MBP）、TNF-α及C反应蛋白（CRP）含量,检测大鼠运动神经传导速度（MNCV）、感觉神经传导速度（SNCV）,大鼠坐骨神经内核因子-κB（NF-κB） mRNA、髓样分子因子88（MyD88） mRNA及Toll样受体4（TLR4） mRNA表达。结果: 模型组及当归多糖低剂量组大鼠空腹血糖、MDA含量显著高于正常组,CAT、SOD及GSH-Px含量显著低于正常组,当归多糖中、高剂量组大鼠空腹血糖、MDA含量显著低于模型组、阳性对照组,CAT、SOD及GSH-Px含量显著高于模型组、阳性对照组,差异有统计学意义（P＜0.05）;模型组、当归多糖低剂量组大鼠血清IL-6、MBP、TNF-α及CRP含量均显著高于正常组,当归多糖中、高剂量组大鼠血清IL-6、MBP、TNF-α及CRP含量均显著低于模型组、阳性对照组,差异有统计学意义（P＜0.05）;模型组、当归多糖低剂量组大鼠NF-κB mRNA、MyD88 mRNA及TLR4 mRNA表达量均显著高于正常组,当归多糖中、高剂量组大鼠NF-κB mRNA、MyD88 mRNA及TLR4 mRNA表达量均显著低于模型组、阳性对照组,差异有统计学意义（P＜0.05）。结论: 当归多糖可显著改善DPN大鼠的周围神经损伤状态,促进神经传导的恢复,其机制可能与阻断TLR4/MyD88/NF-κB信号路径的转导,降低炎性因子水平,减轻神经的氧化应激损伤有关。     

Effects of Icariside II on Corpus Cavernosum and Major Pelvic Ganglion Neuropathy in Streptozotocin-Induced Diabetic Rats

Diabetic erectile dysfunction is associated with penile dorsal nerve bundle neuropathy in the corpus cavernosum and the mechanism is not well understood. We investigated the neuropathy changes in the corpus cavernosum of rats with streptozotocin-induced diabetes and the effects of Icariside II (ICA II) on improving neuropathy. Thirty-six 8-week-old Sprague-Dawley rats were randomly distributed into normal control group, diabetic group and ICA-II treated group. Diabetes was induced by a one-time intraperitoneal injection of streptozotocin (60 mg/kg). Three days later, the diabetic rats were randomly divided into 2 groups including a saline treated placebo group and an ICA II-treated group (5 mg/kg/day, by intragastric administration daily). Twelve weeks later, erectile function was measured by cavernous nerve electrostimulation with real time intracorporal pressure assessment. The penis was harvested for the histological examination (immunofluorescence and immunohistochemical staining) and transmission electron microscopy detecting. Diabetic animals exhibited a decreased density of dorsal nerve bundle in penis. The neurofilament of the dorsal nerve bundle was fragmented in the diabetic rats. There was a decreased expression of nNOS and NGF in the diabetic group. The ICA II group had higher density of dorsal nerve bundle, higher expression of NGF and nNOS in the penis. The pathological change of major pelvic nerve ganglion (including the microstructure by transmission electron microscope and the neurite outgrowth length of major pelvic nerve ganglion tissue cultured in vitro) was greatly attenuated in the ICA II-treated group (p < 0.01). ICA II treatment attenuates the diabetes-related impairment of corpus cavernosum and major pelvic ganglion neuropathy in rats with Streptozotocin-Induced Diabetes.     

Peptide–Peptide Co-Assembly: A Design Strategy for Functional Detection of C-peptide,A Biomarker of Diabetic Neuropathy

Diabetes-related neuropathy is a debilitating condition that may be averted if it can be detected early. One possible way this can be achieved at low cost is to utilise peptides to detect C-peptide, a biomarker of diabetic neuropathy. This depends on peptide-peptide co-assembly, which is currently in a nascent stage of intense study. Instead, we propose a bead-based triple-overlay combinatorial strategy that can preserve inter-residue information during the screening process for a suitable complementary peptide to co-assemble with C-peptide. The screening process commenced with a pentapeptide general library, which revealed histidine to be an essential residue. Further screening with seven tetrapeptide focused libraries led to a table of self-consistent peptide sequences that included tryptophan and lysine at high frequencies. Three complementary nonapeptides (9mer com-peptides), wpkkhfwgq (Trp-D), kwkkhfwgq (Lys-D), and KWKKHFWGQ (Lys-L) (as a negative control) were picked from this table for co-assembly studies with C-peptide. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) and circular dichroism (CD) spectroscopies were utilized to study inter-peptide interactions and changes in secondary structures respectively. ATR-FTIR studies showed that there is indeed inter-peptide interaction between C-peptide and the tryptophan residues of the 9mer com-peptides. CD studies of unaggregated and colloidal C-peptide with the 9mer com-peptides suggest that the extent of co-assembly of C-peptide with Trp-D is greatest, followed by Lys-D and Lys-L. These results are promising and indicate that the presented strategy is viable for designing and evaluating longer complementary peptides, as well as complementary peptides for co-assembly with other polypeptides of interest and importance. We discuss the possibility of designing complementary peptides to inhibit toxic amyloidosis with this approach.     

Distinctive Microbial Signatures and Gut-Brain Crosstalk in Pediatric Patients with Coeliac Disease and Type 1 Diabetes Mellitus

Coeliac disease (CD) and Type 1 diabetes mellitus (T1DM) are immune-mediated diseases. Emerging evidence suggests that dysbiosis in the gut microbiome plays a role in the pathogenesis of both diseases and may also be associated with the development of neuropathy. The primary goal in this cross-sectional pilot study was to identify whether there are distinct gut microbiota alterations in children with CD (n = 19), T1DM (n = 18) and both CD and T1DM (n = 9) compared to healthy controls (n = 12). Our second goal was to explore the relationship between neuropathy (corneal nerve fiber damage) and the gut microbiome composition. Microbiota composition was determined by 16S rRNA gene sequencing. Corneal confocal microscopy was used to determine nerve fiber damage. There was a significant difference in the overall microbial diversity between the four groups with healthy controls having a greater microbial diversity as compared to the patients. The abundance of pathogenic proteobacteria Shigella and E. coli were significantly higher in CD patients. Differential abundance analysis showed that several bacterial amplicon sequence variants (ASVs) distinguished CD from T1DM. The tissue transglutaminase antibody correlated significantly with a decrease in gut microbial diversity. Furthermore, the Bacteroidetes phylum, specifically the genus Parabacteroides was significantly correlated with corneal nerve fiber loss in the subjects with neuropathic damage belonging to the diseased groups. We conclude that disease-specific gut microbial features traceable down to the ASV level distinguish children with CD from T1DM and specific gut microbial signatures may be associated with small fiber neuropathy. Further research on the mechanisms linking altered microbial diversity with neuropathy are warranted.     

Stem Cell Therapy Enhances Motor Activity of Triceps Surae Muscle in Mice with Hereditary Peripheral Neuropathy

Impaired motor and sensory functions are the main features of Charcot–Marie–Tooth disease. Mesenchymal stem cell (MSCs) therapy is one of the possible treatments for this disease. It was assumed that MSCs therapy can improve the contractile properties of the triceps surae (TS) muscles in mice with hereditary peripheral neuropathy. Murine adipose-derived mesenchymal stromal cells (AD-MSCs) were obtained for transplantation into TS muscles of FVB-C-Tg(GFPU)5Nagy/J mice. Three months after AD-MSCs transplantation, animals were subjected to electrophysiological investigations. Parameters of TS muscle tension after intermittent high frequency electrical sciatic nerve stimulations were analyzed. It was found that force of TS muscle tension contraction in animals after AD-MSCs treatment was two-time higher than in untreated mice. Normalized values of force muscle contraction in different phases of electrical stimulation were 0.3 ± 0.01 vs. 0.18 ± 0.01 and 0.26 ± 0.03 vs. 0.13 ± 0.03 for treated and untreated animals, respectively. It is assumed that the two-fold increase in TS muscle strength was caused by stem cell therapy. Apparently, AD-MSCs therapy can promote nerve regeneration and partial restoration of muscle function, and thus can be a potential therapeutic agent for the treatment of peripheral neuropathies.     

Hypoglycemia,Vascular Disease and Cognitive Dysfunction in Diabetes: Insights from Text Mining-Based Reconstruction and Bioinformatics Analysis of the Gene Networks

Hypoglycemia has been recognized as a risk factor for diabetic vascular complications and cognitive decline, but the molecular mechanisms of the effect of hypoglycemia on target organs are not fully understood. In this work, gene networks of hypoglycemia and cardiovascular disease, diabetic retinopathy, diabetic nephropathy, diabetic neuropathy, cognitive decline, and Alzheimer’s disease were reconstructed using ANDSystem, a text-mining-based tool. The gene network of hypoglycemia included 141 genes and 2467 interactions. Enrichment analysis of Gene Ontology (GO) biological processes showed that the regulation of insulin secretion, glucose homeostasis, apoptosis, nitric oxide biosynthesis, and cell signaling are significantly enriched for hypoglycemia. Among the network hubs, INS, IL6, LEP, TNF, IL1B, EGFR, and FOS had the highest betweenness centrality, while GPR142, MBOAT4, SLC5A4, IGFBP6, PPY, G6PC1, SLC2A2, GYS2, GCGR, and AQP7 demonstrated the highest cross-talk specificity. Hypoglycemia-related genes were overrepresented in the gene networks of diabetic complications and comorbidity; moreover, 14 genes were mutual for all studied disorders. Eleven GO biological processes (glucose homeostasis, nitric oxide biosynthesis, smooth muscle cell proliferation, ERK1 and ERK2 cascade, etc.) were overrepresented in all reconstructed networks. The obtained results expand our understanding of the molecular mechanisms underlying the deteriorating effects of hypoglycemia in diabetes-associated vascular disease and cognitive dysfunction.     

A case of end-stage renal disease initially manifested with visual loss caused by uremic optic neuropathy

Uremic optic neuropathy (UON) is extremely rare, although sporadic cases have been reported. UON is sometimes regarded as a manifestation of uremic neuropathy. Here, we report a case of end-stage renal disease presenting as UON. A 22-year-old male was transferred to our nephrology department due to azotemia. Sudden deterioration of his vision occurred 3 days before his transfer. The patient's blood pressure was 150/90 mmHg, and he had no symptoms or signs of uremia, except for the visual disturbance. Blood tests showed an elevated serum creatinine of 6.0 mg/dL and serum BUN of 53.6 mg/dL. Both kidneys were decreased in size on ultrasound. His best-corrected vision was 20/62.5 in both the eyes. Ophthalmoscopy revealed hyperemia, swelling of both optic nerve heads, and blurred margins of both optic disks. These findings are compatible with UON. The patient's visual acuity and visual field improved following hemodialysis and corticosteroid treatment. The swelling of the patient's optic disks was also resolved. The patient is currently undergoing hemodialysis with the goal of vision restoration. Uremic optic neuropathy should be considered when patients with advanced chronic kidney disease complain of deterioration of their vision.