Extracellular matrix remodelling in human diabetic neuropathy

Deciphering the molecular landscape of human peripheral nerves: implications for diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is a prevalent complication of diabetes mellitus that is caused by metabolic toxicity to peripheral axons. We aimed to gain deep mechanistic insight into the disease process using bulk and spatial RNA sequencing on tibial and sural nerves recovered from lower leg amputations in a mostly diabetic population. First, our approach comparing mixed sensory and motor tibial and purely sensory sural nerves shows key pathway differences in affected nerves, with distinct immunological features observed in sural nerves. Second, spatial transcriptomics analysis of sural nerves reveals substantial shifts in endothelial and immune cell types associated with severe axonal loss. We also find clear evidence of neuronal gene transcript changes, like PRPH, in nerves with axonal loss suggesting perturbed RNA transport into distal sensory axons. This motivated further investigation into neuronal mRNA localization in peripheral nerve axons generating clear evidence of robust localization of mRNAs such as SCN9A and TRPV1 in human sensory axons. Our work gives new insight into the altered cellular and transcriptomic profiles in human nerves in DPN and highlights the importance of sensory axon mRNA transport as an unappreciated potential contributor to peripheral nerve degeneration.

Effect of Hesperidin on Sciatic Nerve Damage in STZ-Induced Diabetic Neuropathy: Modulation of TRPM2 Channel

Diabetic neuropathy (DNP) is a severe complication of diabetes mellitus. In this study, we examined the potential of hesperidin (HES) to attenuate DNP and the involvement of the TRPM2 channel in this process. The rats were given a single dose of 45 mg/kg of streptozotocin (STZ) intraperitoneally to induce diabetic neuropathic pain. On the third day, we confirmed the development of diabetes in the DNP and DNP + HES groups. The HES groups were treated with 100 mg/kg and intragastric gavage daily for 14 days. The results showed that treatment with HES in diabetic rats decreased STZ-induced hyperglycemia and thermal hyperalgesia. Furthermore, in the histopathological examination of the sciatic nerve, HES treatment reduced STZ-induced damage. The immunohistochemical analysis also determined that STZ-induced increased TRPM2 channel, type-4 collagen, and fibrinogen immunoactivity decreased with HES treatment. In addition, we investigated the TRPM2 channel activation in the sciatic nerve damage mechanism of DNP model rats created by STZ application using the ELISA method. We determined the regulatory effect of HES on increased ROS, and PARP1 and TRPM2 channel activation in the sciatic nerves of DNP model rats. These findings indicated that hesperidin treatment could attenuate diabetes-induced DNP by reducing TRPM2 channel activation.

Evaluation of the effects of sinapic acid and ellagic acid on sciatic nerve in experimental diabetic rats by immunohistochemical and stereological methods

In our study, we aimed to examine the effects of sinapic acid and ellagic acid on neuropathy caused by diabetes in peripheral nerves. Fifty-six adult Wistar Albino rats Control, Diabetes, Diabetes+Sinapic Acid, Diabetes+Ellagic Acid, Diabetes+Sinapic Acid+Ellagic Acid, Sinapic Acid, Ellagic Acid and as Sinapic Acid+Ellagic Acid, they were randomly divided into eight groups(n:7). A single dose of 50 mg/kg streptozotocin(STZ) was administered intraperitoneally to the groups to be diagnosed with diabetes. Diabetes was accepted as blood glucose value of 250 mg/dL and above. Streptozotocin was given to the diabetes groups, 20 mg/kg/day intragastric Sinapic acid to the Sinapic acid groups, 50 mg/kg/day intragastric Ellagic acid to the Ellagic acid groups for 28 days. At the end of the experiment, 0.5 cm of the right sciatic nerve was removed. It was fixed in 10% formaldehyde. After histological follow-up, it was embedded in paraffin, 5 µm thick sections were taken. Immunohistochemical staining with Fibrinogen alpha, Laminin β-1 and Collagen IV antibodies and stereological evaluation was performed by Physical Dissector Combination method. Collagen IV was used in control, diabetes and treatment groups showed similar immunostaining. Fibrinogen alpha was observed to be increased in the vessel wall in the diabetes group, while the uptake was minimal in the control and treatment groups. While Laminin β-1 was increased in the diabetes group compared to the control group, immunostaining was observed in the treatment groups similar to the control group. It was observed that the total nerve area diabetes group decreased significantly compared to the control group, and the treatment groups, except for D+EA group were similar to the control group, but there was no statistically significant difference. The axon numbers in the diabetes group decreased significantly compared to the control group, and the treatment groups were similar to the control group, and there was no statistically significant difference (P > 0.05). It was determined that Sinapic Acid and Ellagic acid had positive effects on the nervous tissue in diabetic neuropathy.

Collagen turnover is associated with cardiovascular autonomic and peripheral neuropathy in type 1 diabetes: novel pathophysiological mechanism?

BACKGROUND

Diabetic cardiovascular autonomic neuropathy (CAN) and distal symmetrical polyneuropathy (DSPN) are severe diabetic complications. Collagen type VI (COL6) and III (COL3) have been associated with nerve function. We investigated if markers of COL6 formation (PRO-C6) and COL3 degradation (C3M) were associated with neuropathy in people with type 1 diabetes (T1D).

METHODS

In a cross-sectional study including 300 people with T1D, serum and urine PRO-C6 and C3M were obtained. CAN was assessed by cardiovascular reflex tests: heart rate response to deep breathing (E/I ratio), to standing (30/15 ratio) and to the Valsalva maneuver (VM). Two or three pathological CARTs constituted CAN. DSPN was assessed by biothesiometry. Symmetrical vibration sensation threshold above 25 V constituted DSPN.

RESULTS

Participants were (mean (SD)) 55.7 (9.3) years, 51% were males, diabetes duration was 40.0 (8.9) years, HbA1c was 63 (11 mmol/mol, (median (IQR)) serum PRO-C6 was 7.8 (6.2;11.0) ng/ml and C3M 8.3 (7.1;10.0) ng/ml. CAN and DSPN were diagnosed in 34% and 43% of participants, respectively. In models adjusted for relevant confounders a doubling of serum PRO-C6, was significantly associated with odds ratio > 2 for CAN and > 1 for DSPN, respectively. Significance was retained after additional adjustments for eGFR only for CAN. Higher serum C3M was associated with presence of CAN, but not after adjustment for eGFR. C3M was not associated with DSPN. Urine PRO-C6 analyses indicated similar associations.

CONCLUSIONS

Results show previously undescribed associations between markers of collagen turnover and risk of CAN and to a lesser degree DSPN in T1D.

Effect of Surgical Release of Entrapped Peripheral Nerves in Sensorimotor Diabetic Neuropathy on Pain and Sensory Dysfunction-Study Protocol of a Prospective, Controlled Clinical Trial

BACKGROUND

Nerve entrapment has been hypothesized to contribute to the multicausal etiology of axonopathy in sensorimotor diabetic neuropathy. Targeted surgical decompression reduces external strain on the affected nerve and, therefore, may alleviate symptoms, including pain and sensory dysfunction. However, its therapeutic value in this cohort remains unclear.

AIM

Quantifying the treatment effect of targeted lower extremity nerve decompression in patients with preexisting painful sensorimotor diabetic neuropathy and nerve entrapment on pain intensity, sensory function, motor function, and neural signal conduction.

STUDY DESIGN

This prospective, controlled trial studies 40 patients suffering from bilateral therapy-refractory, painful (n = 20, visual analogue scale, VAS ≥ 5) or painless (n = 20, VAS = 0) sensorimotor diabetic neuropathy with clinical and/or radiologic signs of focal lower extremity nerve compression who underwent unilateral surgical nerve decompression of the common peroneal and the tibial nerve. Tissue biopsies will be analyzed to explore perineural tissue remodeling in correlation with intraoperatively measured nerve compression pressure. Effect size on symptoms including pain intensity, light touch threshold, static and moving two-point discrimination, target muscle force, and nerve conduction velocity will be quantified 3, 6, and 12 months postoperatively, and compared (1) to the preoperative values and (2) to the contralateral lower extremity that continues non-operative management.

CLINICAL SIGNIFICANCE

Targeted surgical release may alleviate mechanical strain on entrapped lower extremity nerves and thereby potentially improve pain and sensory dysfunction in a subset of patients suffering from diabetic neuropathy. This trial aims to shed light on these patients that potentially benefit from screening for lower extremity nerve entrapment, as typical symptoms of entrapment might be erroneously attributed to neuropathy only, thereby preventing adequate treatment.

Microvascular and macrovascular complications of type 2 diabetes mellitus: Exome wide association analyses

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a chronic, metabolic disorder in which concomitant insulin resistance and β-cell impairment lead to hyperglycemia, influenced by genetic and environmental factors. T2DM is associated with long-term complications that have contributed to the burden of morbidity and mortality worldwide. The objective of this manuscript is to conduct an Exome-Wide Association Study (EWAS) on T2DM Emirati individuals to improve our understanding on diabetes-related complications to improve early diagnostic methods and treatment strategies.

METHODS

This cross-sectional study recruited 310 Emirati participants that were stratified according to their medically diagnosed diabetes-related complications: diabetic retinopathy, diabetic neuropathy, diabetic nephropathy, and cardiovascular complications. The Illumina's Infinium Exome-24 array was used and 39,840 SNPs remained for analysis after quality control.

FINDINGS

The analysis revealed the associations of various genes with each complication category: 1) diabetic retinopathy was associated to SHANK3 gene in locus 22q13.33 (SNP rs9616915; p=5.18 x10^-4), ZSCAN5A gene in locus 19q13.43 (SNP rs7252603; p=7.55 x10^-4), and DCP1B gene in locus 12p13.33 (SNPs rs715146, rs1044950, rs113147414, rs34730825; p=7.62 x10^-4); 2) diabetic neuropathy was associated to ADH4 gene in locus 4q23 (SNP rs4148883; p=1.23 x10^-4), SLC11A1 gene in locus 2q35 (SNP rs17235409; p=1.85 x10^-4), and MATN4 gene in locus 20q13.12 (SNP rs2072788; p=2.68 x10^-4); 3) diabetic nephropathy was associated to PPP1R3A gene in locus 7q31.1 (SNP rs1799999; p=1.91 x10^-4), ZNF136 gene in locus 19p13.2 (SNP rs140861589; p=2.80 x10^-4), and HSPA12B gene in locus 20p13 (SNP rs6076550; p=2.86 x10^-4); and 4) cardiovascular complications was associated to PCNT gene in locus 21q22.3 (SNPs rs7279204, rs6518289, rs2839227, rs2839223; p=2.18 x10^-4,3.04 x10^-4,4.51 x10^-4,5.22 x10^-4 respectively), SEPT14 gene in locus 7p11.2 (SNP rs146350220; p=2.77 x10^-4), and WDR73 gene in locus 15q25.2 (SNP rs72750868; p=4.47 x10^-4).

INTERPRETATION

We have identified susceptibility loci associated with each category of T2DM-related complications in the Emirati population. Given that only 16% of the markers from the Illumina's Infinium Exome chip passed quality control assessment, this demonstrates that multiple variants were, either, monomorphic in the Arab population or were not genotyped due to the use of a Euro-centric EWAS array that limits the possibility of including targeted ethnic-specific SNPs. Our results suggest the alarming possibility that lack of representation in reference panels could inhibit discovery of functionally important loci associated to T2DM complications. Further effort must be conducted to improve the representation of diverse populations in genotyping and sequencing studies.

Implications of fibrotic extracellular matrix in diabetic retinopathy

Fibrosis is an accumulation of extracellular matrix (ECM) proteins and fibers in a disordered fashion, which compromises cell and tissue functions. High glucose-induced fibrosis, a major pathophysiological change of diabetic retinopathy (DR), severely affects vision by compromising the retinal vasculature and ultimately disrupting retinal tissue organization. The retina is a highly vascularized, stratified tissue with multiple cell types organized into distinct layers. Chronically high blood glucose stimulates certain retinal cells to increase production and assembly of ECM proteins resulting in excess ECM deposition primarily in the capillary walls on the basal side of the endothelium. This subendothelial fibrosis of the capillaries is the earliest histological change in the diabetic retina and has been linked to the vascular dysfunction that underlies DR. Proteins that are not normally abundant in the capillary basement membrane (BM) matrix, such as the ECM protein fibronectin, are assembled in significant quantities, disrupting the architecture of the BM and altering its properties. Cell culture models have identified multiple mechanisms through which elevated glucose can stimulate fibronectin matrix assembly, including intracellular signaling pathways, alternative splicing, and non-enzymatic glycation of the ECM. The fibrotic subendothelial matrix alters cell adhesion and supports further accumulation of other ECM proteins leading to disruption of endothelial cell-cell junctions. We review evidence supporting the notion that these molecular changes in the ECM contribute to the pathogenesis of DR, including vascular leakage, loss of endothelial cells and pericytes, changes in blood flow, and neovascularization. We propose that the accumulation of ECM, especially fibronectin matrix, first around the vasculature and later in extravascular locations, plays a critical role in DR and vision loss. Strategies for DR prevention and treatment should consider the ECM a potential therapeutic target.

Progressive multifocal fibrosing neuropathy: description of a novel disease

Entrapment peripheral neuropathies are clinically characterized by sensory impairment and motor deficits. They are usually caused by mechanical injuries, but they are also a frequent manifestation of metabolic diseases, toxic agent exposure, or systemic fibrotic disorders. Here we describe the clinical, radiological, and histopathological features of a novel progressive fibrotic disorder characterized by progressive multifocal fibrosing neuropathy. We identified two patients who presented with severe and progressive peripheral neuropathic symptoms sequentially affecting multiple sites. These patients presented with severe and progressive multifocal, sequentially additive peripheral neuropathic symptoms. Extensive nerve conduction and radiological studies showed the sequential development of multifocal motor and sensory peripheral neuropathy in the absence of any exposure to known infectious, inflammatory, or fibrotic triggers and the lack of family history of compression neuropathies. Extensive clinical and laboratory test evaluation failed to support the diagnosis of any primary inflammatory or genetic peripheral neuropathy and there was no evidence of any systemic fibrosing disorder including Systemic Sclerosis, lacking cutaneous fibrotic changes and cardiopulmonary abnormalities. The clinical course was progressive with sequential development of motor and sensory deficits of upper and lower extremities displaying proximal predominance. Histopathological study of tissues obtained during nerve release surgeries showed severe perineural fibrosis with marked accumulation of thick collagen bundles encroaching the peripheral nerves. There was no evidence of vasculitic, inflammatory, or vascular fibroproliferative lesions. We suggest that the clinical findings described here represent a previously undescribed fibrotic disorder affecting peripheral nerves, and we propose the descriptive term "Progressive Multifocal Fibrosing Neuropathy" to refer to this novel disorder. Despite the inherent limitations of this early description, we hope this is would contribute to the identification of additional cases.

Diabetes-related intestinal region-specific thickening of ganglionic basement membrane and regionally decreased matrix metalloproteinase 9 expression in myenteric ganglia

BACKGROUND

The importance of the neuronal microenvironment has been recently highlighted in gut region-specific diabetic enteric neuropathy. Regionally distinct thickening of endothelial basement membrane (BM) of intestinal capillaries supplying the myenteric ganglia coincide with neuronal damage in different intestinal segments. Accelerated synthesis of matrix molecules and reduced degradation of matrix components may also contribute to the imbalance of extracellular matrix dynamics resulting in BM thickening. Among the matrix degrading proteinases, matrix metalloproteinase 9 (MMP9) and its tissue inhibitor (TIMP1) are essential in regulating extracellular matrix remodelling.

AIM

To evaluate the intestinal segment-specific effects of diabetes and insulin replacement on ganglionic BM thickness, MMP9 and TIMP1 expression.

METHODS

Ten weeks after the onset of hyperglycaemia gut segments were taken from the duodenum and ileum of streptozotocin-induced diabetic, insulin-treated diabetic and sex- and age-matched control rats. The thickness of BM surrounding myenteric ganglia was measured by electron microscopic morphometry. Whole-mount preparations of myenteric plexus were prepared from the different gut regions for MMP9/TIMP1 double-labelling fluorescent immunohistochemistry. Post-embedding immunogold electron microscopy was applied on ultrathin sections to evaluate the MMP9 and TIMP1 expression in myenteric ganglia and their microenvironment from different gut segments and conditions. The MMP9 and TIMP1 messenger ribonucleic acid (mRNA) level was measured by quantitative polymerase chain reaction.

RESULTS

Ten weeks after the onset of hyperglycaemia, the ganglionic BM was significantly thickened in the diabetic ileum, while it remained intact in the duodenum. The immediate insulin treatment prevented the diabetes-related thickening of the BM surrounding the ileal myenteric ganglia. Quantification of particle density showed an increasing tendency for MMP9 and a decreasing tendency for TIMP1 from the proximal to the distal small intestine under control conditions. In the diabetic ileum, the number of MMP9-indicating gold particles decreased in myenteric ganglia, endothelial cells of capillaries and intestinal smooth muscle cells, however, it remained unchanged in all duodenal compartments. The MMP9/TIMP1 ratio was also decreased in ileal ganglia only. However, a marked segment-specific induction was revealed in MMP9 and TIMP1 at the mRNA levels.

CONCLUSION

These findings support that the regional decrease in MMP9 expression in myenteric ganglia and their microenvironment may contribute to extracellular matrix accumulation, resulting in a region-specific thickening of ganglionic BM.

Sensory neuron cultures derived from adult db/db mice as a simplified model to study type-2 diabetes-associated axonal regeneration defects

Diabetic neuropathy (DN) is an early common complication of diabetes mellitus (DM), leading to chronic pain, sensory loss and muscle atrophy. Owing to its multifactorial etiology, neuron in vitro cultures have been proposed as simplified systems for DN studies. However, the most used models currently available do not recreate the chronic and systemic damage suffered by peripheral neurons of type-2 DM (T2DM) individuals. Here, we cultured neurons derived from dorsal root ganglia from 6-month-old diabetic db/db-mice, and evaluated their morphology by the Sholl method as an easy-to-analyze readout of neuronal function. We showed that neurons obtained from diabetic mice exhibited neuritic regeneration defects in basal culture conditions, compared to neurons from non-diabetic mice. Next, we evaluated the morphological response to common neuritogenic factors, including nerve growth factor NGF and Laminin-1 (also called Laminin-111). Neurons derived from diabetic mice exhibited reduced regenerative responses to these factors compared to neurons from non-diabetic mice. Finally, we analyzed the neuronal response to a putative DN therapy based on the secretome of mesenchymal stem cells (MSC). Neurons from diabetic mice treated with the MSC secretome displayed a significant improvement in neuritic regeneration, but still reduced when compared to neurons derived from non-diabetic mice. This in vitro model recapitulates many alterations observed in sensory neurons of T2DM individuals, suggesting the possibility of studying neuronal functions without the need of adding additional toxic factors to culture plates. This model may be useful for evaluating intrinsic neuronal responses in a cell-autonomous manner, and as a throughput screening for the pre-evaluation of new therapies for DN.

Summary: Morphological characterization of a model for evaluating neuritic regeneration in vitro in dorsal root ganglion primary neurons derived from type-2 diabetic mice with an advanced stage of diabetic neuropathy.

Genome-wide profiling of DNA methylation and gene expression identifies candidate genes for human diabetic neuropathy

BACKGROUND

Diabetic peripheral neuropathy (DPN) is the most common complication of type 2 diabetes (T2D). Although the cellular and molecular mechanisms of DPN are poorly understood, we and others have shown that altered gene expression and DNA methylation are implicated in disease pathogenesis. However, how DNA methylation might functionally impact gene expression and contribute to nerve damage remains unclear. Here, we analyzed genome-wide transcriptomic and methylomic profiles of sural nerves from T2D patients with DPN.

RESULTS

Unbiased clustering of transcriptomics data separated samples into groups, which correlated with HbA1c levels. Accordingly, we found 998 differentially expressed genes (DEGs) and 929 differentially methylated genes (DMGs) between the groups with the highest and lowest HbA1c levels. Functional enrichment analysis revealed that DEGs and DMGs were enriched for pathways known to play a role in DPN, including those related to the immune system, extracellular matrix (ECM), and axon guidance. To understand the interaction between the transcriptome and methylome in DPN, we performed an integrated analysis of the overlapping genes between DEGs and DMGs. Integrated functional and network analysis identified genes and pathways modulating functions such as immune response, ECM regulation, and PI3K-Akt signaling.

CONCLUSION

These results suggest for the first time that DNA methylation is a mechanism regulating gene expression in DPN. Overall, DPN patients with high HbA1c have distinct alterations in sural nerve DNA methylome and transcriptome, suggesting that optimal glycemic control in DPN patients is an important factor in maintaining epigenetic homeostasis and nerve function.

Tenascin C in the Tumor-Nerve Microenvironment Enhances Perineural Invasion and Correlates With Locoregional Recurrence in Pancreatic Ductal Adenocarcinoma

OBJECTIVES

Perineural invasion is common in pancreatic ductal adenocarcinoma (PDAC) and worsens the postoperative prognosis. Tenascin C (TNC), an extracellular matrix glycoprotein, modulates tumor progression. We evaluated the functional roles of TNC, especially in perineural invasion of PDAC.

METHODS

We examined immunohistochemical TNC expression in 78 resected PDAC specimens. The relationships between TNC expression and clinicopathological features were retrospectively analyzed. Interactions between cancer cells and nerves with TNC supplementation were investigated using an in vitro coculture model with PDAC cell line and mouse dorsal root ganglion (DRG).

RESULTS

Tenascin C expression was predominant in perineural sites at the invasive tumor front. High perineural TNC expression in 30 patients (38%) was associated with perineural invasion, pathological T stage ≥3, and postoperative locoregional recurrence. High TNC expression was independently associated with postoperative, poor recurrence-free survival by multivariate analysis. In the in vitro coculture model, a TNC-rich matrix enhanced both PDAC cell colony extensions toward nerves and DRG axonal outgrowth toward cancer cell colonies, whereas TNC did not affect axonal outgrowth or cancer cell proliferation in separately cultured DRG and PDAC cells.

CONCLUSIONS

Strong perineural TNC expression indicated poor prognosis with locoregional recurrence. The neurotropism of TNC-induced PDAC suggests that TNC is a potential PDAC therapeutic target.

Matrix metalloproteinase 7 promoted Schwann cell migration and myelination after rat sciatic nerve injury

Schwann cells experience de-differentiation, proliferation, migration, re-differentiation and myelination, and participate in the repair and regeneration of injured peripheral nerves. Our previous sequencing analysis suggested that the gene expression level of matrix metalloproteinase 7 (MMP7), a Schwann cell-secreted proteolytic enzyme, was robustly elevated in rat sciatic nerve segments after nerve injury. However, the biological roles of MMP7 are poorly understood. Here, we exposed primary cultured Schwann cells with MMP7 recombinant protein and transfected siRNA against MMP7 into Schwann cells to examine the effect of exogenous and endogenous MMP7. Meanwhile, the effects of MMP7 in nerve regeneration after sciatic nerve crush in vivo were observed. Furthermore, RNA sequencing and bioinformatic analysis of Schwann cells were conducted to show the molecular mechanism behind the phenomenon. In vitro studies showed that MMP7 significantly elevated the migration rate of Schwann cells but did not affect the proliferation rate of Schwann cells. In vivo studies demonstrated that increased level of MMP7 contributed to Schwann cell migration and myelin sheaths formation after peripheral nerve injury. MMP7-mediated genetic changes were revealed by sequencing and bioinformatic analysis. Taken together, our current study demonstrated the promoting effect of MMP7 on Schwann cell migration and peripheral nerve regeneration, benefited the understanding of cellular and molecular mechanisms underlying peripheral nerve injury, and thus might facilitate the treatment of peripheral nerve regeneration in clinic.

Pathway crosstalk perturbation network modeling for identification of connectivity changes induced by diabetic neuropathy and pioglitazone

BACKGROUND

Aggregation of high-throughput biological data using pathway-based approaches is useful to associate molecular results to functional features related to the studied phenomenon. Biological pathways communicate with one another through the crosstalk phenomenon, forming large networks of interacting processes.

RESULTS

In this work, we present the pathway crosstalk perturbation network (PXPN) model, a novel model used to analyze and integrate pathway perturbation data based on graph theory. With this model, the changes in activity and communication between pathways observed in transitions between physiological states are represented as networks. The model presented here is agnostic to the type of biological data and pathway definition used and can be implemented to analyze any type of high-throughput perturbation experiments. We present a case study in which we use our proposed model to analyze a gene expression dataset derived from experiments in a BKS-db/db mouse model of type 2 diabetes mellitus-associated neuropathy (DN) and the effects of the drug pioglitazone in this condition. The networks generated describe the profile of pathway perturbation involved in the transitions between the healthy and the pathological state and the pharmacologically treated pathology. We identify changes in the connectivity of perturbed pathways associated to each biological transition, such as rewiring between extracellular matrix, neuronal system, and G-protein coupled receptor signaling pathways.

CONCLUSION

The PXPN model is a novel, flexible method used to integrate high-throughput data derived from perturbation experiments; it is agnostic to the type of data and enrichment function used, and it is applicable to a wide range of biological phenomena of interest.

Collagen VI in healthy and diseased nervous system

Collagen VI is a major extracellular matrix protein exerting a number of functions in different tissues, spanning from biomechanical to regulatory signals in the cell survival processes, and playing key roles in maintaining the stemness or determining the differentiation of several types of cells. In the last couple of years, emerging findings on collagen VI have led to increased interest in its role in the nervous system. The role of this protein in the peripheral nervous system was intensely studied and characterized in detail. Collagen VI acts as a regulator of Schwann cell differentiation and is required for preserving peripheral nerve myelination, function and structure, as well as for orchestrating nerve regeneration after injury. Although the role and distribution of collagen VI in the peripheral nervous system is now well established, the role of this distinctive extracellular matrix component in the central nervous system, along with its links to human neurological and neurodegenerative disorders, remains an open field of investigation. In this Review, we summarize and discuss a number of recent findings related to collagen VI in the central and peripheral nervous systems. We further link these findings to different aspects of the protein that are relevant to human diseases in these compartments in order to provide a comprehensive overview of the roles of this key matrix component in the nervous system.

Brain heparan sulphate proteoglycans are altered in developing foetus when exposed to in-utero hyperglycaemia

In-utero exposure of foetus to hyperglycaemic condition affects the growth and development of the organism. The brain is one of the first organs that start to develop during embryonic period and glycosaminoglycans (GAGs) and proteoglycans (PGs) are one of the key molecules involved in its development. But studies on the effect of hyperglycaemic conditions on brain GAGs/PGs are few and far between. We, therefore, looked into the changes in brain GAGs and PGs at various developmental stages of pre- and post-natal rats from non-diabetic and diabetic mothers as well as in adult rats induced with diabetes using a diabetogenic agent, Streptozotocin. Increased expression of GAGs especially that of heparan sulphate class in various developmental stages were observed in the brain as a result of in-utero hyperglycaemic condition but not in that of adult rats. Changes in disaccharides of heparan sulphate (HS) were observed in various developmental stages. Furthermore, various HSPGs namely, syndecans-1 and -3 and glypican-1 were overexpressed in offspring from diabetic mother. However, in adult diabetic rats, only glypican-1 was overexpressed. The offsprings from diabetic mothers became hyperphagic at the end of 8 weeks after birth which can have implications in the long run. Our results highlight the likely impact of the in-utero exposure of foetus to hyperglycaemic condition on brain GAGs/PGs compared to diabetic adult rats.

Sodium-dependent Vitamin C transporter 2 deficiency impairs myelination and remyelination after injury: Roles of collagen and demethylation

Peripheral nerve myelination involves rapid production of tightly bound lipid layers requiring cholesterol biosynthesis and myelin protein expression, but also a collagen-containing extracellular matrix providing mechanical stability. In previous studies, we showed a function of ascorbic acid in peripheral nerve myelination and extracellular matrix formation in adult mice. Here, we sought the mechanism of action of ascorbic acid in peripheral nerve myelination using different paradigms of myelination in vivo and in vitro. We found impaired myelination and reduced collagen expression in Sodium-dependent Vitamin C Transporter 2 heterozygous mice (SVCT2^+/- ) during peripheral nerve development and after peripheral nerve injury. In dorsal root ganglion (DRG) explant cultures, hypo-myelination could be rescued by precoating with different collagen types. The activity of the ascorbic acid-dependent demethylating Ten-eleven-translocation (Tet) enzymes was reduced in ascorbic acid deprived and SVCT2^+/- DRG cultures. Further, in ascorbic acid-deprived DRG cultures, methylation of a CpG island in the collagen alpha1 (IV) and alpha2 (IV) bidirectional promoter region was increased compared to wild-type and ascorbic acid treated controls. Taken together, these results provide further evidence for the function of ascorbic acid in myelination and extracellular matrix formation in peripheral nerves and suggest a putative molecular mechanism of ascorbic acid function in Tet-dependent demethylation of collagen promoters.

Serum prolidase enzyme activity and oxidative stress levels in patients with diabetic neuropathy

Previous studies have suggested that prolidase and nitric oxide (NO) regulate many processes, such as collagen synthesis and matrix remodeling. Oxidative stress plays an important role in the development of microvascular complications in diabetic patients. Data on serum prolidase activity in patients with diabetes mellitus or diabetic neuropathy (DN) are limited and conflicting. The aim of this study was to measure serum prolidase activity, NO, total antioxidant status (TAS), and malondialdehyde (MDA) levels in patients with DN. Forty-five patients with DN and 40 healthy controls were enrolled. Serum prolidase activity, TAS, MDA, and NO levels were determined. Serum MDA and NO levels were significantly higher in DN patients than controls (p = 0.002, p = 0.001, respectively), while prolidase activity and TAS levels were lower (p = 0.003, p = 0.001, respectively). Prolidase activity was negatively correlated with NO and MDA (r = -0.911, p < 0.001; r = -0.905, p < 0.001, respectively), while positively correlated with TAS (r = 0.981, p < 0.001) in DN patients. The current study is the first showing the decreased serum prolidase enzyme activity. Our results suggest that decreased collagen turnover may occur in DN patients, who have increased oxidative stress and increased NO levels. Decreased prolidase activity seems to be associated with increased NO levels and oxidative stress along with decreased antioxidant levels in DN. Therefore, decreased prolidase activity may play a role in pathogenesis of DN. Prospective clinical studies are necessary to confirm these findings.

Morphometric analysis of connective tissue sheaths of sural nerve in diabetic and nondiabetic patients

One of the most common complications of diabetes mellitus is diabetic neuropathy. It may be provoked by metabolic and/or vascular factors, and depending on duration of disease, various layers of nerve may be affected. Our aim was to investigate influence of diabetes on the epineurial, perineurial, and endoneurial connective tissue sheaths. The study included 15 samples of sural nerve divided into three groups: diabetic group, peripheral vascular disease group, and control group. After morphological analysis, morphometric parameters were determined for each case using ImageJ software. Compared to the control group, the diabetic cases had significantly higher perineurial index (P < 0.05) and endoneurial connective tissue percentage (P < 0.01). The diabetic group showed significantly higher epineurial area (P < 0.01), as well as percentage of endoneurial connective tissue (P < 0.01), in relation to the peripheral vascular disease group. It is obvious that hyperglycemia and ischemia present in diabetes lead to substantial changes in connective tissue sheaths of nerve, particularly in peri- and endoneurium. Perineurial thickening and significant endoneurial fibrosis may impair the balance of endoneurial homeostasis and regenerative ability of the nerve fibers. Future investigations should focus on studying the components of extracellular matrix of connective tissue sheaths in diabetic nerves.

Altered tibial nerve biomechanics in patients with diabetes mellitus

INTRODUCTION

Hyperglycemia associated with diabetes mellitus (DM) has adverse impacts on peripheral nerve connective tissue structure, and there is preliminary evidence that nerve biomechanics may be altered.

METHODS

Ultrasound imaging was utilized to quantify the magnitude and timing of tibial nerve excursion during ankle dorsiflexion in patients with DM and matched healthy controls.

RESULTS

Tibial nerve longitudinal excursion at the ankle and knee was reduced, and timing was delayed at the ankle in the DM group. Severity of neuropathy was correlated with larger reductions in longitudinal excursion. Nerve cross-sectional area was increased at the ankle in the DM group.

CONCLUSIONS

Larger tibial nerve size within the tarsal tunnel in patients with DM may restrict longitudinal excursion, which was most evident with more severe neuropathy. It is hypothesized that these alterations may be related to painful symptoms during functional activities that utilize similar physiological motions through various biomechanical and physiological mechanisms.

Characterization of Endoneurial Fibroblast-like Cells from Human and Rat Peripheral Nerves

Endoneurial fibroblast-like cells (EFLCs) are one of the cell populations present in the peripheral nervous system. The role and immunophenotypic characteristics of EFLCs are not well known and led us to perform a histological and cytological study of EFLCs in normal human and rat peripheral nerves. We found that all EFLCs express CD34, neural/glial antigen 2 (NG2), and prolyl-4-hydrolase-beta. In addition, half of the EFLCs in normal peripheral nerves express platelet-derived growth factor receptor-β (PDGFR-β) and some also express the intermediate filament nestin in vivo (at a lower level than Schwann cells, which express high levels of nestin). Using cell cultures of purified EFLCs, we characterized subpopulations of EFLCs expressing PDGFR-β alone or PDGFR-β and nestin. Experimental nerve lesions in rat resulted in an increase in nestin-positive EFLCs, which returned to normal levels after 8 days. This suggests that some EFLCs could have a different proliferative and/or regenerative potential than others, and these EFLCs may play a role in the initial phase of nerve repair. These "activated" EFLCs share some immunophenotypic similarities with pericytes and Interstitial cells of Cajal, which have progenitor cell potentials. This raises the questions as to whether a proportion of EFLCs have a possible role as endoneurial progenitor cells.

Pathology of human diabetic neuropathy

Pathologic study of a disease provides insights into the precise mechanisms and targets of damage and may provide insights into new therapies. The main targets in diabetic neuropathy are myelinated and unmyelinated fibers as dysfunction and damage to them explains the symptoms of painful neuropathy and the major end points of foot ulceration and amputation as well as mortality. Demyelination and axonal degeneration are established hallmarks of the pathology of human diabetic neuropathy and were derived from pioneering light and electronmicroscopic studies of sural nerve biopsies in the late 1960s and early 1970s. Additional abnormalities, which are relevant to the pathogenesis of human diabetic neuropathy, include pathology of the microvessels and extracellular space. Intraepidermal and sudomotor nerve quantification in skin biopsies provides a minimally invasive means for the detection of early nerve damage. Studies of muscle biopsies are limited and show significant alterations in the expression of neurotrophins, but limited changes in muscle fiber size and capillary density.

Collagen VI regulates peripheral nerve myelination and function

Collagen VI is an extracellular matrix protein with broad distribution in several tissues. Although Col6a1 is expressed by Schwann cells, the role of collagen VI in the peripheral nervous system (PNS) is yet unknown. Here we show that Schwann cells, but not axons, contribute to collagen VI deposition in peripheral nerves. By using Col6a1-null mice, in which collagen VI deposition is compromised, we demonstrate that lack of collagen VI leads to increased myelin thickness (P<0.001) along with 60-130% up-regulation in myelin-associated proteins and disorganized C fibers in the PNS. The hypermyelination of PNS in Col6a1(-/-) mice is supported by alterations of signaling pathways involved in myelination, including increase of P-FAK, P-AKT, P-ERK1, P-ERK2, and P-p38 (4.15, 1.67, 2.47, 3.34, and 2.60-fold, respectively) and reduction of vimentin (0.49-fold), P-JNK (0.74-fold), and P-c-Jun (0.50-fold). Pathologically, Col6a1(-/-) mice display an impairment of nerve conduction velocity and motor coordination (P<0.05), as well as a delayed response to acute pain stimuli (P<0.001), indicating that lack of collagen VI causes functional defects of peripheral nerves. Altogether, these results indicate that collagen VI is a critical component of PNS contributing to the structural integrity and proper function of peripheral nerves.

The pattern of tibial nerve excursion with active ankle dorsiflexion is different in older people with diabetes mellitus

BACKGROUND

The peripheral nervous system has an inherent capability to tolerate the gliding (excursion), stretching (increased strain), and compression associated with limb motions necessary for functional activities. The biomechanical properties during joint movements are well studied but the influence of other factors such as limb pre-positioning, age and the effects of diabetes mellitus are not well established for the lower extremity. The purposes of this pilot study were to compare the impact of two different hip positions on lower extremity nerve biomechanics during an active ankle dorsiflexion motion in healthy individuals and to determine whether nerve biomechanics are altered in older individuals with diabetes mellitus.

METHODS

Ultrasound imaging was used to quantify longitudinal motion of the tibial nerve and transverse plane motion of the tibial and common fibular nerves in the popliteal fossa during active ankle movements.

FINDINGS

In healthy individuals, ankle dorsiflexion created mean tibial nerve movement of 2.18 mm distally, 1.36 mm medially and 3.98 mm superficially. When the hip was in a flexed position there was a mean three-fold reduction in distal movement. In people with diabetes mellitus there was significantly less distal movement of the tibial nerve in the neutral hip position and less superficial movement of the nerve in both hip positions compared to healthy individuals.

INTERPRETATION

We have documented reductions in tibial nerve excursion due to limb pre-positioning thought to pre-load the nervous system using a non-invasive methodology. Thus, lower limb pre-positioning impacts nerve biomechanics during ankle motions common in functional activities. Additionally, our findings indicate that nerve biomechanics have the potential to be altered in older individuals with diabetes mellitus compared to younger healthy individuals.

[Update on diabetic macroangiopathy]

Current findings from the literature on the multifactorial genesis of macroangiopathy of diabetes mellitus (DM) were compiled using the PubMed database. The primary aim was to find an explanation for the morphological, immunohistochemical and molecular characteristics of this form of atherosclerosis. The roles of advanced glycation end products (AGE), defective signal transduction and imbalance of matrix metalloproteinases in the increased progression of atherosclerosis in coronary and cerebral arteries as well as peripheral vascular disease are discussed. The restricted formation of collateral arteries (arteriogenesis) in diabetic patients with postischemic lesions is also a focus of attention. The increased level of prothrombotic factors and the role of diabetic neuropathy in DM are also taken into account. Therapeutic influences of AGE-RAGE (receptor of AGE) interactions on the vascular wall and the effects of endothelial progenitor cells in the repair of diabetic vascular lesions are additionally highlighted.

Morphometric analysis of human sciatic nerve perineurial collagen type IV content

OBJECTIVES

Aging is the process which unavoidably alters structure and function of the basal membranes in humans. Though, collagen type IV presents the most prominent component of the basal membranes, we estimated its presence in the perineurium of the human sciatic nerve samples during the aging process.

MATERIALS AND METHODS

Material was 12 sciatic nerve samples, obtained from cadavers whose age ranged from 36 to 84 years. Cadavers were classified into three age groups: first which age ranged from 35 to 54 years, second which age ranged from 55 to 74 years and third which included cases older than 75 years. Tissue slices were further stained by labeled streptavidin-biotin method with collagen type IV monoclonal antibody and analyzed with light microscope under 100× lens magnification with oil immersion. Digital images of sciatic nerve perineurium were further processed and analyzed with ImageJ software.

RESULTS

Our results showed that there is statistically significant increase of perineurial area, perimeter, collagen type IV area, and collagen type IV area per perineurial perimeter unit in the third age group. These parameters also increased in the second age group, but this increase was not significant. Multiple regression analysis showed that beside fascicular size, age more significantly predict perineurial collagen type IV content.

CONCLUSIONS

Results of morphometric and statistical analysis pointed to the conclusion that there is significant increase of sciatic nerve perineurial thickness during the aging process. This increase might represent the consequence of perineurial collagen type IV deposition with aging.

Regeneration of the perineurium after microsurgical resection examined with immunolabeling for tenascin-C and alpha smooth muscle actin

The regenerative process of the perineurium and nerve function were examined using an in vivo model of perineurium resection in the rat sciatic nerve. Our hypothesis is that the regenerative process of the perineurium can be demonstrated by immunolabeling for tenascin-C and alpha smooth muscle actin after microsurgical resection of the perineurium in vivo. A total of 38 Lewis rats were used. Eight-week-old animals were assigned to one of two groups: the epi-perineurium removal group or the sham group. Under operative microscopy, the sciatic nerve was dissected from surrounding tissues at the thigh level from the ischial tuberosity to the fossa poplitea. The epi-perineurium was carefully removed by cutting circumferentially and stripping distally for 15 mm. For CatWalk® dynamic gait analysis, only right sciatic nerves underwent surgery; the left sciatic nerves were left intact. For pathological and electrophysiological tests, both the right and left sciatic nerves underwent surgery. Analysis of data was performed at each time interval with a two-group t-test. P<0.05 was considered statistically significant. After resection of a 15-mm section of the epi-perineurium, immediate endoneurial swelling occurred in the outer portion and spread into the central portion. Although demyelination and axonal degeneration were found in the swollen area, remyelination and recovery of electrophysiological function were seen after regeneration of the perineurium. An immunohistological and electron microscopic study revealed that the perineurium regenerated via fusion of the residual interfascicular perineurium and endoneurial fibroblast-like cells of mesenchymal origin. CatWalk gait analysis showed not only motor paresis but also neuropathic pain during the early phases of this model.