Diabetes-induced myelin abnormalities are associated with an altered lipid pattern: protective effects of LXR activation

Glial cell alterations in diabetes-induced neurodegeneration

Type 2 diabetes mellitus is a global epidemic that due to its increasing prevalence worldwide will likely become the most common debilitating health condition. Even if diabetes is primarily a metabolic disorder, it is now well established that key aspects of the pathogenesis of diabetes are associated with nervous system alterations, including deleterious chronic inflammation of neural tissues, referred here as neuroinflammation, along with different detrimental glial cell responses to stress conditions and neurodegenerative features. Moreover, diabetes resembles accelerated aging, further increasing the risk of developing age-linked neurodegenerative disorders. As such, the most common and disabling diabetic comorbidities, namely diabetic retinopathy, peripheral neuropathy, and cognitive decline, are intimately associated with neurodegeneration. As described in aging and other neurological disorders, glial cell alterations such as microglial, astrocyte, and Müller cell increased reactivity and dysfunctionality, myelin loss and Schwann cell alterations have been broadly described in diabetes in both human and animal models, where they are key contributors to chronic noxious inflammation of neural tissues within the PNS and CNS. In this review, we aim to describe in-depth the common and unique aspects underlying glial cell changes observed across the three main diabetic complications, with the goal of uncovering shared glial cells alterations and common pathological mechanisms that will enable the discovery of potential targets to limit neuroinflammation and prevent neurodegeneration in all three diabetic complications. Diabetes and its complications are already a public health concern due to its rapidly increasing incidence, and thus its health and economic impact. Hence, understanding the key role that glial cells play in the pathogenesis underlying peripheral neuropathy, retinopathy, and cognitive decline in diabetes will provide us with novel therapeutic approaches to tackle diabetic-associated neurodegeneration.

Metabolomics Analysis of DRG and Serum in the CCI Model of Mice

Neuropathic pain (NP) is a chronic and intractable disease that is widely present in the general population. It causes painful behavior and even mood changes such as anxiety and depression by altering the metabolism of substances. However, there have been limited metabolomics studies conducted in relation to neuropathic pain. Therefore, in this study, the effects of NP on metabolites in serum and the dorsal root ganglion (DRG) were investigated using a non-targeted metabolomics approach detected by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) to uncover differential metabolites and affected metabolic pathways associated with NP. Sixty mice were divided into the following two groups: a chronic constriction injury (CCI) of the sciatic nerve group and a sham group (n = 30, each). After 7 days of CCI modeling, the metabolite profiles of serum and the DRG were analyzed using GC/LC-MS for both the CCI and sham groups of mice. Multivariate analysis revealed differential metabolites and altered metabolic pathways between the CCI and sham groups. In the CCI group, our findings provided insights into the complex phospholipid, amino acid and acylcarnitine metabolic perturbations of DRG metabolism. In addition, phospholipid metabolic disorders and impaired glucose metabolism were observed in the serum. Moreover, the metabolic differences in the DRG and serum were correlated with each other. The results from this untargeted metabolomics study provide a perspective on the metabolic impact of NP on serum and the DRG.

The effects of voluntary exercise on histological and stereological changes of sciatic nerve, nitric oxide levels, and peripheral neuropathy caused by high-fat diet-induced type 2 diabetes in male rats

This research was conducted to investigate the possible beneficial impacts of voluntary exercise on sciatic tissue, nitric oxide levels, stereological changes, and peripheral neuropathy caused by "high-fat-diet (HFD)"-induced "type 2 diabetes mellitus (T2DM)" in male rats. Rats were put into four experimental groups at random: "healthy control (C), voluntary exercise (VE), diabetic (D), and diabetic rats treated by voluntary exercise (VED)"; each group contain eight animals. Animals in VE and VED groups performed "voluntary exercise (VE)" for ten weeks. Animals in D and VED groups became diabetic after receiving a HFD for four weeks and an intraperitoneal injection (IP) of "streptozotocin (STZ)" (35 mg/kg). In order to evaluate mechanical and thermal algesia, hot plate, tail withdrawal, and von Frey tests were carried out. At the end of this study, serum NOx levels were assessed, and histological and stereological analyses were conducted. Mechanical nociceptive thresholds indicated considerable reduction (p < 0.001) which was followed by a remarkable enhance (p < 0.001) in thermal nociceptive threshold of D group. Tissue changes were also seen in sciatic nerve of D group. Voluntary exercise modified thermal and mechanical sensitivity in diabetic rats. It also improved the damaged sciatic nerve in diabetic animals.

Therapeutic potential of endoplasmic reticulum stress inhibitors in the treatment of diabetic peripheral neuropathy

Endoplasmic stress response, the unfolded protein response (UPR), is a homeostatic signaling pathway comprising transmembrane sensors that get activated upon alterations in ER luminal environment. Studies suggest a relation between activated UPR pathways and several disease states such as Parkinson, Alzheimer, inflammatory bowel disease, tumor growth, and metabolic syndrome. Diabetic peripheral neuropathy (DPN), a common microvascular complication of diabetes-related chronic hyperglycemia, causes chronic pain, loss of sensation, foot ulcers, amputations, allodynia, hyperalgesia, paresthesia, and spontaneous pain. Factors like disrupted calcium signaling, dyslipidemia, hyperglycemia, inflammation, insulin signaling, and oxidative stress disturb the UPR sensor levels manifesting as DPN. We discuss new effective therapeutic alternatives for DPN that can be developed by targeting UPR pathways like synthetic ER stress inhibitors like 4-PhenylButyric acid (4-PBA), Sephin 1, Salubrinal and natural ER stress inhibitors like Tauroursodeoxycholic acid (TUDCA), Cordycepin, Proanthocyanidins, Crocin, Purple Rice extract and cyanidin and Caffeic Acid Phenethyl Ester (CAPE).

Diabetic complications and prospective immunotherapy

The incidence of Diabetes Mellitus is increasing globally. Individuals who have been burdened with diabetes for many years often develop complications as a result of hyperglycemia. More and more research is being conducted highlighting inflammation as an important factor in disease progression. In all kinds of diabetes, hyperglycemia leads to activation of alternative glucose metabolic pathways, resulting in problematic by-products including reactive oxygen species and advanced glycation end products. This review takes a look into the pathogenesis of three specific diabetic complications; retinopathy, nephropathy and neuropathy as well as their current treatment options. By considering recent research papers investigating the effects of immunotherapy on relevant conditions in animal models, multiple strategies are suggested for future treatment and prevention of diabetic complications with an emphasis on molecular targets associated with the inflammation.

The circ_0002538/miR-138-5p/plasmolipin axis regulates Schwann cell migration and myelination in diabetic peripheral neuropathy

Circular RNAs (circRNAs) play a vital role in diabetic peripheral neuropathy. However, their expression and function in Schwann cells in individuals with diabetic peripheral neuropathy remain poorly understood. Here, we performed protein profiling and circRNA sequencing of sural nerves in patients with diabetic peripheral neuropathy and controls. Protein profiling revealed 265 differentially expressed proteins in the diabetic peripheral neuropathy group. Gene Ontology indicated that differentially expressed proteins were mainly enriched in myelination and mitochondrial oxidative phosphorylation. A real-time polymerase chain reaction assay performed to validate the circRNA sequencing results yielded 11 differentially expressed circRNAs. circ_0002538 was markedly downregulated in patients with diabetic peripheral neuropathy. Further in vitro experiments showed that overexpression of circ_0002538 promoted the migration of Schwann cells by upregulating plasmolipin (PLLP) expression. Moreover, overexpression of circ_0002538 in the sciatic nerve in a streptozotocin-induced mouse model of diabetic peripheral neuropathy alleviated demyelination and improved sciatic nerve function. The results of a mechanistic experiment showed that circ_0002538 promotes PLLP expression by sponging miR-138-5p, while a lack of circ_0002538 led to a PLLP deficiency that further suppressed Schwann cell migration. These findings suggest that the circ_0002538/miR-138-5p/PLLP axis can promote the migration of Schwann cells in diabetic peripheral neuropathy patients, improving myelin sheath structure and nerve function. Thus, this axis is a potential target for therapeutic treatment of diabetic peripheral neuropathy.

Integration of MRI and somatosensory evoked potentials facilitate diagnosis of spinal cord compression

This study aimed to integrate magnetic resonance imaging (MRI) and related somatosensory evoked potential (SSEP) features to assist in the diagnosis of spinal cord compression (SCC). MRI scans were graded from 0 to 3 according to the changes in the subarachnoid space and scan signals to confirm differences in SCC levels. The amplitude, latency, and time-frequency analysis (TFA) power of preoperative SSEP features were extracted and the changes were used as standard judgments to detect neurological function changes. Then the patient distribution was quantified according to the SSEP feature changes under the same and different MRI compression grades. Significant differences were found in the amplitude and TFA power between MRI grades. We estimated three degrees of amplitude anomalies and power loss under each MRI grade and found the presence or absence of power loss occurs after abnormal changes in amplitude only. For SCC, few integrated approach combines the advantages of both MRI and evoked potentials. However, integrating the amplitude and TFA power changes of SSEP features with MRI grading can help in the diagnosis and speculate progression of SCC.

Changes in phrenic nerve compound muscle action potential in streptozotocin-induced diabetic rats

PURPOSE

To evaluate the phrenic nerve compound muscle action potential (CMAP) in rats after diabetes mellitus (DM) induction.

METHODS

Twenty DM animals (intravenous streptozotocin, 45 mg.kg^-1) and 25 controls underwent CMAP analysis before and 30, 60 and 90 days after DM induction.

RESULTS

Amplitude (mV) progressively declined in DM group after 30 (Mean difference (MD): -0.915, 95 % Confidence interval (CI) -1.580 to -0.250, p < 0.01), 60 (MD: -1.122, 95 % CI -1.664 to -0.581, p < 0.001) and 90 days (MD: -2.226, 95 % CI -3.059 to -1.393, p < 0.001); as well as the area (mV.ms) after 30 (MD: -3.19, 95 % CI -5.94 to -0.44, p < 0.05), 60 (MD: -3.94, 95 % CI -6.24 to -1.64, p < 0.001) and 90 days (MD: -8.64, 95 % CI -12.08 to -5.21, p < 0.001). Transient differences were observed in latency and duration at 60 days.

CONCLUSIONS

The progressive changes in phrenic nerve CMAP observed during DM suggest a decrement in axonal function rather than substantial demyelination.

Activation of 20-HETE Synthase Triggers Oxidative Injury and Peripheral Nerve Damage in Type 2 Diabetic Mice

Diabetic Peripheral Neuropathy (DPN), highly prevalent among patients with diabetes, is characterized by peripheral nerve dysfunction. Reactive Oxygen Species (ROS) overproduction has been suggested to orchestrate diabetic complications including DPN. Untargeted antioxidant therapy has exhibited limited efficacy, highlighting a critical need to explore ROS sources altered in a cell-specific manner in DPN. Cytochromes P450 (CYP) enzymes are prominent sources of ROS. Particularly, the 20-HETE synthase, CYP4A, is reported to mediate diabetes-induced renal, retinal, and cardiovascular injuries. This work investigates the role of CYP4A/20-HETE in DPN and their mechanisms of action. Non-obese type 2 Diabetic mice (MKR) were used and treated with a CYP4A-inhibitor (HET0016) or AMPK-activator (Metformin). Peripheral nerves of MKR mice reflect increased CYP4A and 20-HETE levels, concurrent with altered myelin proteins and sensorimotor deficits. This was associated with increased ROS production and altered Beclin-1 and LC3 protein levels, indicative of disrupted autophagic responses in tandem with AMPK inactivation. AMPK activation via Metformin restored nerve integrity, reduced ROS production, and regulated autophagy. Interestingly, similar outcomes were revealed upon HET0016 treatment whereby ROS production, autophagic responses, and AMPK signaling were normalized in diabetic mice. Altogether, the results highlight hyperglycemia-mediated oxidative injury in DPN through a novel CYP4A/20-HETE/AMPK pathological axis. PERSPECTIVE: To our knowledge, this is the first study to highlight the role of CYPs/20-HETE-induced oxidative injury in the pathogenesis of diabetic peripheral neuropathy. Targeting the identified pathological axis CYP4A/20-HETE/AMPK may be of clinical potential in predicting and alleviating peripheral nerve injury in patients with Type 2 Diabetes Mellitus.

Cilostazol Ameliorates Peripheral Neuropathic Pain in Streptozotocin-Induced Type I Diabetic Rats

Background: Cilostazol is an antiplatelet agent with vasodilating, endothelial function restoration, and anti-inflammatory effects. This study aims to investigate the efficacy of oral cilostazol for preventing the development of diabetic peripheral neuropathy (DPN).

Materials and Methods: Ninety adult male Sprague-Dawley rats were divided into five groups: 1) naïve (control); 2) diabetic (DM); 3) DM receiving 10 mg/kg cilostazol (cilo-10); 4) DM receiving 30 mg/kg cilostazol (cilo-30); and 5) DM receiving 100 mg/kg cilostazol (cilo-100). Hindpaw responses to thermal and mechanical stimuli were measured. Activation of microglia and astrocytes in the spinal dorsal horn (SDH) and expression of NaVs in the dorsal root ganglia (DRG) were examined with Western blots and immunofluorescence.

Results: DM rats displayed decreased withdrawal thresholds to mechanical stimuli (mechanical allodynia) and blunted responses to thermal stimuli. In addition, the expression of microglia increased, but astrocytes were reduced in the SDH. Upregulation of Nav −1.1, 1.2, −1.3, −1.6, and −1.7 and downregulation of Nav-1.8 were observed in the DRG. The DM rats receiving cilostazol all returned DM-induced decrease in withdrawal threshold to mechanical stimuli and attenuated neuropathic pain. Additionally, all cilostazol treatments suppressed the level of activated microglial cells and ameliorated the DM-induced decline in astrocyte expression levels in the SDH. However, only the rats treated with cilo-100 demonstrated significant improvements to the aberrant NaV expression in the DRG.

Conclusion: Oral cilostazol can blunt the responses of mechanical allodynia and has the potential to treat diabetic neuropathy by attenuating NaV and glial cell dysregulation.

Proteome-wide systems genetics identifies UFMylation as a regulator of skeletal muscle function

Improving muscle function has great potential to improve the quality of life. To identify novel regulators of skeletal muscle metabolism and function, we performed a proteomic analysis of gastrocnemius muscle from 73 genetically distinct inbred mouse strains, and integrated the data with previously acquired genomics and >300 molecular/phenotypic traits via quantitative trait loci mapping and correlation network analysis. These data identified thousands of associations between protein abundance and phenotypes and can be accessed online (https://muscle.coffeeprot.com/) to identify regulators of muscle function. We used this resource to prioritize targets for a functional genomic screen in human bioengineered skeletal muscle. This identified several negative regulators of muscle function including UFC1, an E2 ligase for protein UFMylation. We show UFMylation is up-regulated in a mouse model of amyotrophic lateral sclerosis, a disease that involves muscle atrophy. Furthermore, in vivo knockdown of UFMylation increased contraction force, implicating its role as a negative regulator of skeletal muscle function.

Neuron-specific biomarkers predict hypo- and hyperalgesia in individuals with diabetic peripheral neuropathy

AIMS/HYPOTHESIS

The individual risk of progression of diabetic peripheral neuropathy is difficult to predict for each individual. Mutations in proteins that are responsible for the process of myelination are known to cause neurodegeneration and display alteration in experimental models of diabetic neuropathy. In a prospective observational human pilot study, we investigated myelin-specific circulating mRNA targets, which have been identified in vitro, for their capacity in the diagnosis and prediction of diabetic neuropathy. The most promising candidate was tested against the recently established biomarker of neural damage, neurofilament light chain protein.

METHODS

Schwann cells were cultured under high-glucose conditions and mRNAs of various myelin-specific genes were screened intra- and extracellularly. Ninety-two participants with type 2 diabetes and 30 control participants were enrolled and evaluated for peripheral neuropathy using neuropathy deficit scores, neuropathy symptom scores and nerve conduction studies as well as quantitative sensory testing at baseline and after 12/24 months of a follow-up period. Magnetic resonance neurography of the sciatic nerve was performed in 37 individuals. Neurofilament light chain protein and four myelin-specific mRNA transcripts derived from in vitro screenings were measured in the serum of all participants. The results were tested for associations with specific neuropathic deficits, fractional anisotropy and the progression of neuropathic deficits at baseline and after 12 and 24 months.

RESULTS

In neuronal Schwann cells and human nerve sections, myelin protein zero was identified as the strongest candidate for a biomarker study. Circulating mRNA of myelin protein zero was decreased significantly in participants with diabetic neuropathy (p < 0.001), whereas neurofilament light chain protein showed increased levels in participants with diabetic neuropathy (p < 0.05). Both variables were linked to altered electrophysiology, fractional anisotropy and quantitative sensory testing. In a receiver-operating characteristic curve analysis myelin protein zero improved the diagnostic performance significantly in combination with a standard model (diabetes duration, age, BMI, HbA_1c) from an AUC of 0.681 to 0.836 for the detection of diabetic peripheral neuropathy. A follow-up study revealed that increased neurofilament light chain was associated with the development of a hyperalgesic phenotype (p < 0.05), whereas decreased myelin protein zero predicted hypoalgesia (p < 0.001) and progressive loss of nerve function 24 months in advance (HR of 6.519).

CONCLUSIONS/INTERPRETATION

This study introduces a dynamic and non-invasive assessment strategy for the underlying pathogenesis of diabetic peripheral neuropathy. The diagnosis of axonal degeneration, associated with hyperalgesia, and demyelination, linked to hypoalgesia, could benefit from the usage of neurofilament light chain protein and circulating mRNA of myelin protein zero as potential biomarkers.

3D culture platform of human iPSCs-derived nociceptors for peripheral nerve modelling and tissue innervation

Functional humanized in vitro nerve models are coveted as an alternative to animal models due to their ease of access, lower cost, clinical relevance and no need for recurrent animal sacrifice. To this end, we developed a sensory nerve model using induced pluripotent stem cells (iPSCs)-derived nociceptors that are electrically active and exhibit a functional response to noxious stimuli. The differentiated neurons were co-cultured with primary Schwann cells on an aligned microfibrous scaffold to produce biomimetic peripheral nerve tissue. Compared to glass coverslips, our scaffold enhances tissue development and stabilization. Using this model, we demonstrate that myelin damage can be induced from hyperglycemia exposure (glucose at 45 mM) and mitigated by epalrestat (1µM) supplementation. Through fibrin embedding of the platform, we were able to create 3D anisotropic myelinated tissue, reaching over 6.5 mm in length. Finally, as a proof-of-concept, we incorporated pancreatic pseudoislets and endometrial organoids into our nerve platform, to demonstrate the potential in generating nociceptor innervation models. In summary, we propose here an improved tool for neurobiology research with potential applications in pathology modelling, drug screening and target tissue innervation.

Effects of paroxetine treatment and its withdrawal on neurosteroidogenesis

Selective serotonin reuptake inhibitors (SSRI) show high efficacy in treating depression, however during treatment side effects, like for instance sexual dysfunction, may appear, decreasing compliance. In some cases, this condition will last after drug discontinuation, leading to the so-called post-SSRI sexual dysfunction (PSSD). The etiology of PSSD is still unknown, however a role for neuroactive steroids may be hypothesized. Indeed, these molecules are key physiological regulators of the nervous system, and their alteration has been associated with several neuropathological conditions, including depression. Additionally, neuroactive steroids are also involved in the control of sexual function. Interestingly, sexual dysfunction induced by SSRI treatment has been also observed in animal models. On this basis, we have here evaluated whether a subchronic treatment with paroxetine for two weeks and/or its withdrawal (i.e., a month) may affect the levels of neuroactive steroids in brain areas (i.e., hippocampus, hypothalamus, and cerebral cortex) and/or in plasma and cerebrospinal fluid of male rats. Data obtained indicate that the SSRI treatment alters neuroactive steroid levels and the expression of key enzymes of the steroidogenesis in a brain tissue- and time-dependent manner. Indeed, these observations with the finding that plasma levels of neuroactive steroids are not affected suggest that the effect of paroxetine treatment is directly on neurosteroidogenesis. In particular, a negative impact on the expression of steroidogenic enzymes was observed at the withdrawal. Therefore, it is possible to hypothesize that altered neurosteroidogenesis may also occur in PSSD and consequently it may represent a possible pharmacological target for this disorder.

Peripheral neurovascular link: an overview of interactions and in vitro models

Nerves and blood vessels (BVs) establish extensive arborized networks to innervate tissues and deliver oxygen/metabolic support. Developmental cues direct the formation of these intricate and often overlapping patterns, which reflect close interactions within the peripheral neurovascular system. Besides the mutual dependence to survive and function, nerves and BVs share several receptors and ligands, as well as principles of differentiation, growth and pathfinding. Neurovascular (NV) interactions are maintained in adult life and are essential for certain regenerative mechanisms, such as wound healing. In pathological situations (e.g., type 2 diabetes mellitus), the NV system can be severely perturbed and become dysfunctional. Unwanted neural growth and vascularization are also associated with the progression of some pathologies, such as cancer and endometriosis. In this review, we describe the fundamental NV interactions in development, highlighting the similarities between both networks and wiring mechanisms. We also describe the NV contribution to regenerative processes and potential pathological dysfunctions. Finally, we provide an overview of current in vitro models used to replicate and investigate the NV ecosystem, addressing present limitations and future perspectives.

Lipoprotein-Induced Increases in Cholesterol and 7-Ketocholesterol Result in Opposite Molecular-Scale Biophysical Effects on Membrane Structure

Under hypercholesterolemic conditions, exposure of cells to lipoproteins results in a subtle membrane increase in the levels of cholesterol and 7-ketocholesterol, as compared to normal conditions. The effect of these physiologically relevant concentration increases on multicomponent bilayer membranes was investigated using coarse-grained molecular dynamics simulations. Significant changes in the structural and dynamic properties of the bilayer membranes resulted from these subtle increases in sterol levels, with both sterol species inducing decreases in the lateral area and inhibiting lateral diffusion to varying extents. Cholesterol and 7-ketocholesterol, however, exhibited opposite effects on lipid packing and orientation. The results from this study indicate that the subtle increases in membrane sterol levels induced by exposure to lipoproteins result in molecular-scale biophysical perturbation of membrane structure.

Simulations of Diabetic and Non-Diabetic Peripheral Nerve Myelin Lipid Bilayers

The multilayered myelin sheath is a critical component of both central and peripheral nervous systems, forming a protective barrier against axonal damage and facilitating the movement of nervous impulses. It is primarily composed of cholesterol (CHL1), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), sphingomyelin (SM), and galactosylceramide (GalCer) lipids. For rat sciatic nerve myelin (part of the peripheral nervous system, PNS), it has been found that cholesterol and unsaturated fatty acid contents are significantly lower in diabetic than in non-diabetic conditions. In this study, lipid compositions from experimental data are used to create four model rat sciatic nerve myelin lipid bilayers: PI-containing (non-diabetic and diabetic) and PS-containing (non-diabetic and diabetic), which were then simulated using the all-atom CHARMM36 force field. Simulation results of diabetic membranes indicate less rigid, more laterally expansive, and thinner bilayers as well as potentially reduced interactions between GalCer on opposing myelin leaflets, supporting a direct role of the cholesterol content decrease in instigating myelin deterioration and diabetic peripheral neuropathy. Compared to PI-lipids, PS-lipids were found to cause higher inter-lipid spacing and decreased order within membranes as a result of their smaller headgroup size and higher inter-lipid hydrogen bonding potential, which allow them to more frequently reside deeper in the membrane plane and produce pushing effects on other lipids. GalCer deuterium order parameters and non-diabetic headgroup-to-headgroup bilayer thicknesses were compared to experimental data, exhibiting close alignment, supporting the future usage of these models to study the PNS myelin sheath.

Evolving concepts on the role of dyslipidemia, bioenergetics, and inflammation in the pathogenesis and treatment of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most widespread and disabling neurological conditions, accounting for half of all neuropathy cases worldwide. Despite its high prevalence, no approved disease modifying therapies exist. There is now a growing body of evidence that DPN secondary to type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) represents different disease processes, with T2DM DPN best understood within the context of metabolic syndrome rather than hyperglycemia. In this review, we highlight currently understood mechanisms of DPN, along with their corresponding potential therapeutic targets. We frame this discussion within a practical overview of how the field evolved from initial human observations to murine pathomechanistic and therapeutic models into ongoing and human clinical trials, with particular emphasis on T2DM DPN and metabolic syndrome.

The Effects of Insulin on Immortalized Rat Schwann Cells, IFRS1

Schwann cells play an important role in peripheral nerve function, and their dysfunction has been implicated in the pathogenesis of diabetic neuropathy and other demyelinating diseases. The physiological functions of insulin in Schwann cells remain unclear and therefore define the aim of this study. By using immortalized adult Fischer rat Schwann cells (IFRS1), we investigated the mechanism of the stimulating effects of insulin on the cell proliferation and expression of myelin proteins (myelin protein zero (MPZ) and myelin basic protein (MBP). The application of insulin to IFRS1 cells increased the proliferative activity and induced phosphorylation of Akt and ERK, but not P38-MAPK. The proliferative potential of insulin-stimulated IFRS1 was significantly suppressed by the addition of LY294002, a PI3 kinase inhibitor. The insulin-stimulated increase in MPZ expression was significantly suppressed by the addition of PD98059, a MEK inhibitor. Furthermore, insulin-increased MBP expression was significantly suppressed by the addition of LY294002. These findings suggest that both PI3-K/Akt and ERK/MEK pathways are involved in insulin-induced cell growth and upregulation of MPZ and MBP in IFRS1 Schwann cells.

Lipidomic analysis of cancer cells cultivated at acidic pH reveals phospholipid fatty acids remodelling associated with transcriptional reprogramming

Cancer cells need to modulate the biosynthesis of membrane lipids and fatty acids to adapt themselves to an accelerated rate of cell division and survive into an extracellular environment characterised by a low pH. To gain insight this crucial survival process, we investigated the lipid composition of Mel 501 melanoma cells cultured at either physiological or acidic pH and observed the remodelling of phospholipids towards longer and more unsaturated acyl chains at low pH. This modification was related to changes in gene expression profile, as we observed an up-regulation of genes involved in acyl chain desaturation, elongation and transfer to phospholipids. PC3 prostate and MCF7 breast cancer cells adapted at acidic pH also demonstrated phospholipid fatty acid remodelling related to gene expression changes. Overall findings clearly indicate that low extracellular pH impresses a specific lipid signature to cells, associated with transcriptional reprogramming.

Protective effect of cerium oxide nanoparticles on cisplatin and oxaliplatin primary toxicities in male albino rats

Cisplatin and oxaliplatin are widely used anticancer drugs. Their use is restricted by their dose-limiting side effects: nephrotoxicity and neurotoxicity, respectively. Cerium oxide nanoparticles (CONPs) are promising antioxidant and anti-inflammatory agent. To test the possible ameliorative impact of CONPs on the toxic effect of cisplatin and oxaliplatin in male albino rats. Forty eight rats were divided into 6 groups: control group, CONPs group, cisplatin group, cisplatin and CONPs group, oxaliplatin group, and oxaliplatin and CONPs group. After 4 weeks, serum urea and creatinine, renal tissue level of interleukin 10 (IL10), and total antioxidant (TAO) were measured in control, CONPs, and cisplatin groups. The other kidney was used for histopathological and immunohistochemical studies. The right sciatic nerves and the lumbar spinal cord of rats from control, CONPs, and oxaliplatin groups were used for immunohistochemical evaluations of nitrotyrosine, myelin basic protein (MBP), and glial fibrillary acidic protein (GFAP). Cisplatin significantly increased serum urea and creatinine levels, significantly decreased the kidney level of IL10 and TAO with marked tubular necrosis, hemorrhage and renal damage. Also, it decreased IL10 immunohistochemical expression. CONPs significantly decreased the serum urea and creatinine level and increased IL10 and TAO with lower renal damage and strong IL10 expression compared with cisplatin group. Oxaliplatin significantly decreased MBP immunoreactivity and increased nitrotyrosine immunoreactivity. In the lumbar spinal cord, GFAP immunoreactivity was significantly increased. CONPs significantly increased MBP and decreased nitrotyrosine immunoreactivity. GFAP immunoreactivity was significantly decreased. CONPs ameliorated cisplatin and oxaliplatin primary toxicities through anti-inflammatory and antioxidant characteristics.

Physiopathological Role of Neuroactive Steroids in the Peripheral Nervous System

Peripheral neuropathy (PN) refers to many conditions involving damage to the peripheral nervous system (PNS). Usually, PN causes weakness, numbness and pain and is the result of traumatic injuries, infections, metabolic problems, inherited causes, or exposure to chemicals. Despite the high prevalence of PN, available treatments are still unsatisfactory. Neuroactive steroids (i.e., steroid hormones synthesized by peripheral glands as well as steroids directly synthesized in the nervous system) represent important physiological regulators of PNS functionality. Data obtained so far and here discussed, indeed show that in several experimental models of PN the levels of neuroactive steroids are affected by the pathology and that treatment with these molecules is able to exert protective effects on several PN features, including neuropathic pain. Of note, the observations that neuroactive steroid levels are sexually dimorphic not only in physiological status but also in PN, associated with the finding that PN show sex dimorphic manifestations, may suggest the possibility of a sex specific therapy based on neuroactive steroids.

A three-dimensional biomimetic peripheral nerve model for drug testing and disease modelling

In vitro peripheral nerve models provide valuable tools to study neurobiology questions and assess drug performance, in a regenerative or pathology context. To this end, we have developed a representative model of the peripheral nerve that displays three-dimensional (3D) neural anisotropy and myelination, which we showcase here as a simple and low-cost platform for drug screening. The model is composed of three main parts, including rat primary Schwann cells (SCs) seeded onto an electrospun scaffold to create bands of Büngner (BoB), primed PC12 cells as neuronal cell population, and a fibrin hydrogel to provide three-dimensionality. We also validated the use of primed PC12 as a neuron population by comparing it to rat dorsal root ganglions (DRGs) neurons. In both models we could obtain well aligned neurites and mature myelin segments. In short term cultures (7 days), we found that the addition of exogenous SCs enhanced neurite length and neurite growth area, compared to scaffolds with a laminin coating only. Addition of fibrin also lead to increased outgrowth of DRG and primed PC12 neurites, compared to 2D cultures. Moreover, neurite outgrowth in fibrin cultures was simultaneously multiplanar and anisotropic, suggesting that the SC-seeded scaffold can direct not only the growth of adjacent neurites, but also those growing above it. These results highlight the feasibility of the combination of a SC pre-seeded scaffold with a fibrin hydrogel, to direct and improve neurite growth in 3D. To demonstrate the model potential, we tested our platform at an immature (7 days in vitro) and mature state (28 days in vitro) of development. At the immature stage we could inhibit neurite growth through protein blocking (via antibody binding) and show suramin (200 μM) neurotoxicity on cells. At the mature stage, when myelin is compact, we exposed cells to hyperglycemic conditions (45 mM glucose) to mimic diabetic conditions and showed that myelin deforms consequently. Moreover, we demonstrated that by supplementing cultures with epalrestat (1 μM), myelin deformation can be partly prevented. In sum, we developed a biomimetic nerve platform using an affordable and accessible cell line as neuronal population, which displays similar results to primary neurons, but does not require recurrent animal sacrifice. This platform holds great promise as it can be used to conveniently and inexpensively perform drug screenings on peripheral nerve-like tissue, in a normal or pathological state.

Selective LXR agonist DMHCA corrects retinal and bone marrow dysfunction in type 2 diabetes

In diabetic dyslipidemia, cholesterol accumulates in the plasma membrane, decreasing fluidity and thereby suppressing the ability of cells to transduce ligand-activated signaling pathways. Liver X receptors (LXRs) make up the main cellular mechanism by which intracellular cholesterol is regulated and play important roles in inflammation and disease pathogenesis. N, N-dimethyl-3β-hydroxy-cholenamide (DMHCA), a selective LXR agonist, specifically activates the cholesterol efflux arm of the LXR pathway without stimulating triglyceride synthesis. In this study, we use a multisystem approach to understand the effects and molecular mechanisms of DMHCA treatment in type 2 diabetic (db/db) mice and human circulating angiogenic cells (CACs), which are hematopoietic progenitor cells with vascular reparative capacity. We found that DMHCA is sufficient to correct retinal and BM dysfunction in diabetes, thereby restoring retinal structure, function, and cholesterol homeostasis; rejuvenating membrane fluidity in CACs; hampering systemic inflammation; and correcting BM pathology. Using single-cell RNA sequencing on lineage-sca1+c-Kit+ (LSK) hematopoietic stem cells (HSCs) from untreated and DMHCA-treated diabetic mice, we provide potentially novel insights into hematopoiesis and reveal DMHCA's mechanism of action in correcting diabetic HSCs by reducing myeloidosis and increasing CACs and erythrocyte progenitors. Taken together, these findings demonstrate the beneficial effects of DMHCA treatment on diabetes-induced retinal and BM pathology.

Understanding Human Cerebral Malaria through a Blood Transcriptomic Signature: Evidences for Erythrocyte Alteration, Immune/Inflammatory Dysregulation, and Brain Dysfunction

Background

Cerebral malaria (CM), a reversible encephalopathy affecting young children, is a medical emergency requiring rapid clinical assessment and treatment. However, understanding of the genes/proteins and the biological pathways involved in the disease outcome is still limited.

Methods

We have performed a whole transcriptomic analysis of blood samples from Malian children with CM or uncomplicated malaria (UM). Hierarchical clustering and pathway, network, and upstream regulator analyses were performed to explore differentially expressed genes (DEGs). We validated gene expression for 8 genes using real-time quantitative PCR (RT-qPCR). Plasma levels were measured for IP-10/CXCL10 and IL-18.

Results

A blood RNA signature including 538 DEGs (∣FC | ≥2.0, adjusted P value ≤ 0.01) allowed to discriminate between CM and UM. Ingenuity Pathway Analysis (IPA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed novel genes and biological pathways related to immune/inflammatory responses, erythrocyte alteration, and neurodegenerative disorders. Gene expressions of CXCL10, IL12RB2, IL18BP, IL2RA, AXIN2, and NET were significantly lower in CM whereas ARG1 and SLC6A9 were higher in CM compared to UM. Plasma protein levels of IP-10/CXCL10 were significantly lower in CM than in UM while levels of IL-18 were higher. Interestingly, among children with CM, those who died from a complication of malaria tended to have higher concentrations of IP-10/CXCL10 and IFN-γ than those who recovered.

Conclusions

This study identified some new factors and mechanisms that play crucial roles in CM and characterized their respective biological pathways as well as some upstream regulators.

Palanisamy UD, Ahmad B, Abdul Kadir K. The Effects of Tocotrienol-Rich Vitamin E (Tocovid) on Diabetic Neuropathy: A Phase II Randomized Controlled Trial

Chronic hyperglycemia increases oxidative stress, activates inflammatory pathways and reduces nerve growth factor (NGF) among diabetic patients, which contribute to development of diabetic peripheral neuropathy (DPN). Tocotrienol-Rich Vitamin E (Tocovid) possesses potent antioxidant and anti-inflammatory properties which are postulated to target these pathogeneses in order to ameliorate DPN. This study aims to evaluate the effects of Tocovid on nerve conduction parameters and serum biomarkers among diabetic patients. This multicenter, prospective, randomized, double-blind, placebo-controlled clinical trial was conducted on 80 eligible participants. The intervention group (n = 39) was randomly allocated to receive 200 mg of Tocovid twice a day, and the control group (n = 41) received placebo twice a day. At the end of eight weeks, the nerve conduction parameters, as assessed by nerve conduction study, as well as serum biomarkers (NGF, malondialdehyde, vascular cell adhesion molecule 1, tumor necrosis factor receptor 1 and thromboxane B2) were compared between the two groups. Compared to placebo, Tocovid significantly improves the nerve conduction velocities of all nerves (+1.25 m/s, interquartile range [IQR] 3.35, p < 0.001, median nerve; +1.60 m/s, IQR 1.80, p < 0.001, sural nerve; +0.75 m/s, IQR 2.25, p < 0.001, tibial nerve). Meanwhile, the levels of serum NGF were significantly higher in the Tocovid group as compared to placebo at eight weeks post-intervention. Participants receiving Tocovid illustrated highly significant improvement in terms of nerve conduction velocities for all nerves tested after eight weeks of supplementation. In addition, Tocovid supplementation elevated the levels of serum NGF, in which its increase is postulated to reflect enhanced neuronal functions. This novel finding suggests that Tocovid could be a disease-modifying agent targeting serum NGF to improve nerve conduction velocities.

Enhanced axonal neuregulin-1 type-III signaling ameliorates neurophysiology and hypomyelination in a Charcot-Marie-Tooth type 1B mouse model

Charcot-Marie-Tooth (CMT) neuropathies are a group of genetic disorders that affect the peripheral nervous system with heterogeneous pathogenesis and no available treatment. Axonal neuregulin 1 type III (Nrg1TIII) drives peripheral nerve myelination by activating downstream signaling pathways such as PI3K/Akt and MAPK/Erk that converge on master transcriptional regulators of myelin genes, such as Krox20. We reasoned that modulating Nrg1TIII activity may constitute a general therapeutic strategy to treat CMTs that are characterized by reduced levels of myelination. Here we show that genetic overexpression of Nrg1TIII ameliorates neurophysiological and morphological parameters in a mouse model of demyelinating CMT1B, without exacerbating the toxic gain-of-function that underlies the neuropathy. Intriguingly, the mechanism appears not to be related to Krox20 or myelin gene upregulation, but rather to a beneficial rebalancing in the stoichiometry of myelin lipids and proteins. Finally, we provide proof of principle that stimulating Nrg1TIII signaling, by pharmacological suppression of the Nrg1TIII inhibitor tumor necrosis factor-alpha-converting enzyme (TACE/ADAM17), also ameliorates the neuropathy. Thus, modulation of Nrg1TIII by TACE/ADAM17 inhibition may represent a general treatment for hypomyelinating neuropathies.

Targeting the NADPH Oxidase-4 and Liver X Receptor Pathway Preserves Schwann Cell Integrity in Diabetic Mice

Diabetes triggers peripheral nerve alterations at a structural and functional level, collectively referred to as diabetic peripheral neuropathy (DPN). This work highlights the role of the liver X receptor (LXR) signaling pathway and the cross talk with the reactive oxygen species (ROS)-producing enzyme NADPH oxidase-4 (Nox4) in the pathogenesis of DPN. Using type 1 diabetic (T1DM) mouse models together with cultured Schwann cells (SCs) and skin biopsies from patients with type 2 diabetes (T2DM), we revealed the implication of LXR and Nox4 in the pathophysiology of DPN. T1DM animals exhibit neurophysiological defects and sensorimotor abnormalities paralleled by defective peripheral myelin gene expression. These alterations were concomitant with a significant reduction in LXR expression and increase in Nox4 expression and activity in SCs and peripheral nerves, which were further verified in skin biopsies of patients with T2DM. Moreover, targeted activation of LXR or specific inhibition of Nox4 in vivo and in vitro to attenuate diabetes-induced ROS production in SCs and peripheral nerves reverses functional alteration of the peripheral nerves and restores the homeostatic profiles of MPZ and PMP22. Taken together, our findings are the first to identify novel, key mediators in the pathogenesis of DPN and suggest that targeting LXR/Nox4 axis is a promising therapeutic approach.

Sodium nitrate preconditioning prevents progression of the neuropathic pain in streptozotocin-induced diabetes Wistar rats

Purpose

The purpose of the study was to evaluate the possible protective effects of low dose sodium nitrate preconditioning on the peripheral neuropathy in streptozotocin (STZ)-induced diabetic model.

Methods

Male Wistar rats were randomly divided into five groups: control (no intervention), control treated sodium nitrate (100 mg/L in drinking water), diabetic (no intervention), diabetic treated NPH insulin (2-4 U), and diabetic treated sodium nitrate (100 mg/L in drinking water). Diabetes was induced by intraperitoneal injection of STZ (60 mg/kg). All interventions were done for 60 days immediately following diabetes confirmation. Thermal and mechanical algesia thresholds were measured by means of hot-plate test, von Frey test, and tail-withdrawal test before the diabetic induction and after diabetes confirmation. At the end of the experiment, serum NOx level and serum insulin level were assessed. Blood glucose concentration and body weight have recorded at the base and duration of the experiment.

Results

Both hypoalgesia, hyperalgesia along with allodynia developed in diabetic rats. Significant alterations including, decrease in tail withdrawal latency (30th day), decreased mechanical threshold (60th day), and an increase in hot plate latency (61st day) were displayed in diabetic rats compared to control rats. Nitrate and insulin preconditioning produced protective effects against diabetes-induced peripheral neuropathy. Data analysis also showed a significant increase in glucose level as well as a considerable reduction in serum insulin and body weight of diabetic rats, which restored by both insulin and nitrate preconditioning.

Conclusion

Sodium nitrate preconditioning produces a protective effect in diabetic neuropathy, which may be mediated by its antihyperglycemic effects and increased serum insulin level.

Disrupting insulin signaling in Schwann cells impairs myelination and induces a sensory neuropathy

Although diabetic mice have been studied for decades, little is known about the cell type specific contributions to diabetic neuropathy (DN). Schwann cells (SCs) myelinate and provide trophic support to peripheral nervous system axons. Altered SC metabolism leads to myelin defects, which can be seen both in inherited and DNs. How SC metabolism is altered in DN is not fully understood, but it is clear that insulin resistance underlies impaired lipid metabolism in many cell types throughout the body via the phosphoinositide 3-kinase/protein kinase b (PKB)/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway. Here, we created an insulin resistant SC by deleting both insulin receptor (INSR) and insulin-like growth factor receptor 1 (IGF1R), to determine the role of this signaling pathway in development and response to injury in order to understand SC defects in DN. We found that myelin is thinner throughout development and adulthood in INSR/IGF1R Schwann cell specific knock out mice. The nerves of these mutant mice had reduced expression of key genes that mediate fatty acid and cholesterol synthesis due to reduced mTOR-sterol regulatory element-binding protein signaling. In adulthood, these mice show sensory neuropathy phenotypes reminiscent of diabetic mice. Altogether, these data suggest that SCs may play an important role in DN and targeting their metabolism could lead to new therapies for DN.

Negative impact of gestational diabetes mellitus on progress of pelvic floor muscle electromyography activity: Cohort study

BACKGROUND AND OBJECTIVE

Pelvic floor muscles are involved in postural stability, in maintenance intra-abdominal pressure, and on mechanical support for pelvic organ. Gestational Diabetes Mellitus' (GDM) pregnancies complicated by fetal macrosomia, large placenta and polyhydramnios contribute for abrupt and intense increase in maternal intra-abdominal pressure. Our objective was analyze the impact of GDM on pelvic floor muscle (PFM) electromyography (EMG) activity progress from 24-30 to 36-38 weeks of gestation. We conducted a prospective cohort study. PFM EMG was performed in nulliparous or primiparous women with one previous elective cesarean delivery and with or not GDM diagnosed by the American Diabetes Association criteria. A careful explanation of the muscle anatomy and functionality of the PFM was given before EMG assessment. The outcome measures were PFM recruitment and progress from 24-30 to 36-38 weeks of gestation analyzed by the normalized root mean square (RMS) during rest-activity, fast and hold pelvic floor muscle contraction.

RESULTS

Fifty-two pregnant women were assigned to 2 groups: the GDM (n = 26) and normoglycemic (NG) (n = 26). The demographic and obstetric data showed homogeneity between the groups. PFM activity progress was decreased in rest-activity (P = 0.042) and hold contraction (P = 0.044) at 36-38 weeks of gestation in the GDM group relative to that in the NG group.

CONCLUSION

GDM group showed a progressive decrease in EMG-PFM activity during rest-activity and hold contractions from 24-30 to 36-38 weeks of gestation.

New insights into the mechanisms of diabetic complications: role of lipids and lipid metabolism

Diabetes adversely affects multiple organs, including the kidney, eye and nerve, leading to diabetic kidney disease, diabetic retinopathy and diabetic neuropathy, respectively. In both type 1 and type 2 diabetes, tissue damage is organ specific and is secondary to a combination of multiple metabolic insults. Hyperglycaemia, dyslipidaemia and hypertension combine with the duration and type of diabetes to define the distinct pathophysiology underlying diabetic kidney disease, diabetic retinopathy and diabetic neuropathy. Only recently have the commonalities and differences in the metabolic basis of these tissue-specific complications, particularly those involving local and systemic lipids, been systematically examined. This review focuses on recent progress made using preclinical models and human-based approaches towards understanding how bioenergetics and metabolomic profiles contribute to diabetic kidney disease, diabetic retinopathy and diabetic neuropathy. This new understanding of the biology of complication-prone tissues highlights the need for organ-specific interventions in the treatment of diabetic complications.

Liver X Receptors and Their Implications in the Physiology and Pathology of the Peripheral Nervous System

Recent research in the last decade has sought to explore the role and therapeutic potential of Liver X Receptors (LXRs) in the physiology and pathologies of the Peripheral Nervous System. LXRs have been shown to be important in maintaining the redox homeostasis in peripheral nerves for proper myelination, and they regulate ER stress in sensory neurons. Furthermore, LXR stimulation has a positive impact on abrogating the effects of diabetic peripheral neuropathy and obesity-induced allodynia in the Peripheral Nervous System (PNS). This review details these findings and addresses certain important questions that are yet to be answered. The potential roles of LXRs in different cells of the PNS are speculated based on existing knowledge. The review also aims to provide important perspectives for further research in elucidating the role of LXRs and assessing the potential of LXR based therapies to combat pathologies of the Peripheral Nervous System.

Fluoxetine Attenuated Anxiety-Like Behaviors in Streptozotocin-Induced Diabetic Mice by Mitigating the Inflammation

Patients with diabetes mellitus (DM) showed an increased risk of anxiety. High anxiety levels are also shown to increase stress of diabetic patients, which may contribute to poor clinical outcomes. The mechanisms underlying the development of anxiety disorders in diabetic patients remain unknown. As a result, there are no available treatments yet. Here, we tested the hypothesis that glial cells in the hippocampal area of DM mice might be responsible for their anxiety-like behaviors. Furthermore, we postulated that treatment with antidepressant, fluoxetine, could reduce anxiety behaviors and prevent the dysregulation of glial cells (oligodendrocyte and astrocyte) in DM mice. Diabetic mice were administered a single injection of streptozotocin (STZ), followed by treatment with fluoxetine. Mice were then tested on Y maze, open field, dark and light transition, and elevated plus maze tests to measure the status of anxiety and cognition. After completing these behavioral tests, mice were sacrificed and western blot was used to detect the oligodendrocyte and astrocyte maker proteins in hippocampal tissues. Emphasis was directed towards adult oligodendrocyte precursor cells (OPCs) and their marker protein to measure their proliferation and differentiation. We found that fluoxetine could effectively mitigate the level of anxiety and attenuate the cognitive dysfunction in diabetic mice. Meanwhile, fluoxetine inhibited astrocyte activation in mice exposed to STZ, prevented the loss of myelin basic protein (MBP), and affected the function of OPCs in these diabetic mice. The results suggested that the changes of these glial cells in the brains of diabetic mice might be related to the high anxiety levels and cognitive deficit in DM mice. Fluoxetine could ameliorate the high anxiety level and prevent cognitive deficit via inhibiting astrocyte activation and repairing the oligodendrocyte damage.

Peripheral nerve pathology in sickle cell disease mice

INTRODUCTION

Many patients with sickle cell disease (SCD) suffer from chronic pain, which is often described as neuropathic in nature. Although vascular and inflammatory pathology undoubtedly contribute to the SCD pain experience, the nociceptive signals that ultimately drive symptoms are detected and transmitted by peripheral sensory neurons. To date, no systematic histological examination of peripheral nerves has been completed in patients or mouse models of SCD to diagnose disease-related neuropathy.

OBJECTIVES

In this brief report, we compared peripheral nerve morphology in tissues obtained from Berkeley transgenic SCD mice and control animals.

METHODS

Sciatic nerves were visualized using light and transmission electron microscopy. Myelin basic protein expression was assessed through Western blot. Blood-nerve barrier permeability was measured using Evan's blue plasma extravasation.

RESULTS

Peripheral fibers from SCD mice have thinner myelin sheaths than control mice and widespread myelin instability as evidenced by myelin sheath infolding and unwrapping. Deficits are also observed in nonmyelinating Schwann cell structures; Remak bundles from SCD nerves contain fewer C fibers, some of which are not fully ensheathed by the corresponding Schwann cell. Increased blood-nerve barrier permeability and expression of myelin basic protein are noted in SCD tissue.

CONCLUSIONS

These data are the first to characterize Berkeley SCD mice as a naturally occurring model of peripheral neuropathy. Widespread myelin instability is observed in nerves from SCD mice. This pathology may be explained by increased permeability of the blood-nerve barrier and, thus, increased access to circulating demyelinating agents at the level of primary sensory afferents.

Epigenetic suppression of liver X receptor β in anterior cingulate cortex by HDAC5 drives CFA-induced chronic inflammatory pain

Background

Liver X receptors (LXRs), including LXRα and LXRβ, are key regulators of transcriptional programs for both cholesterol homeostasis and inflammation in the brain. Here, the modes of action of LXRs and the epigenetic mechanisms regulating LXRβ expression in anterior cingulate cortex (ACC) of chronic inflammatory pain (CIP) are investigated.

Methods

The deficit of LXR isoform and analgesic effect of LXR activation by GW3965 were evaluated using the mouse model of CIP induced by hindpaw injection of complete Freund’s adjuvant (CFA). The mechanisms involved in GW-mediated analgesic effects were analyzed with immunohistochemical methods, ELISA, co-immunoprecipitation (Co-IP), Western blot, and electrophysiological recording. The epigenetic regulation of LXRβ expression was investigated by chromatin immunoprecipitation, quantitative real-time PCR, and sequencing.

Results

We revealed that CFA insult led to LXRβ reduction in ACC, which was associated with upregulated expression of histone deacetylase 5 (HDAC5), and knockdown of LXRβ by shRNA led to thermal hyperalgesia. Co-IP showed that LXRβ interacted with NF-κB p65 physically. LXRβ activation by GW3965 exerted analgesic effects by inhibiting the nuclear translocation of NF-κB, reducing the phosphorylation of mitogen-activated protein kinases (MAPKs) in ACC, and decreasing the promoted input-output and enhanced mEPSC frequency in ACC neurons after CFA exposure. In vitro experiments confirmed that HDAC5 triggered histone deacetylation on the promoter region of Lxrβ, resulting in downregulation of Lxrβ transcription.

Conclusion

These findings highlight an epigenetic mechanism underlying LXRβ deficits linked to CIP, and LXRβ activation may represent a potential novel target for the treatment of CIP with an alteration in inflammation responses and synaptic transmission in ACC.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1507-3) contains supplementary material, which is available to authorized users.

Microarray analyses of lncRNAs and mRNAs expression profiling associated with diabetic peripheral neuropathy in rats

Diabetic peripheral neuropathy (DPN) is considered to be the most frequent neuropathic complication of diabetes, and severely affects the quality of life of patients. Long noncoding RNAs (lncRNAs) participate in various pathophysiological processes and associate with many diseases. However, the exact impact of lncRNAs on DPN remains obscure. To discover a potential connection, a microarray study was conducted to analyze the expression profiling of lncRNAs and messenger RNAs (mRNAs) in dorsal root ganglia (DRG) from streptozotocin-induced diabetic rats with DPN. As a result, 983 lncRNAs and 1357 mRNAs were aberrantly expressed compared with control samples. Using bioinformatics analyses, we identified 558 Gene Ontology terms and 94 Kyoto Encyclopedia of Genes and Genomes pathways to be significantly enriched. Additionally, the signal-net analysis indicated that integrin receptors, including Itgb3, Itgb1, Itgb8, and Itga6, might be important players in network regulation. Furthermore, the lncRNA-mRNA network analysis showed dynamic interactions between the dysregulated lncRNAs and mRNAs. This is the first study to present an overview of lncRNA and mRNA expressions in DRG tissues from DPN rats. Our results indicate that these differentially expressed lncRNAs may have crucial roles in pathological processes of DPN by regulating their coexpressed mRNAs. The data may provide novel targets for future studies, which should focus on validating their roles in the progression of DPN.

Activation of liver x receptors prevents the spinal LTP induced by skin/muscle retraction in the thigh via SIRT1/NF-Κb pathway

It has been reported that skin/muscle incision and retraction (SMIR) in the thigh, produces mechanical allodynia in the hind paw, far from the site of incision/retraction. The mechanical allodynia lasts about 22 days, indicating chronic post-operative pain develops. The precise mechanisms, however, are largely unclear. In the current study, we further found that SMIR surgery induced LTP of c-fiber evoked field potentials that lasted at least 4 h. The mRNA and protein level of tumor necrosis factor-alpha (TNFα) and acetylated nuclear factor-kappaB p65 (ac-NF-κB p65) in the lumbar spinal dorsal horn was gradually increased during LTP development, while pretreatment with either TNFα neutralization antibody or NF-κB inhibitor PDTC completely prevented the induction of LTP. Moreover, the expression of Silent information regulator 1 (SIRT1) in the lumbar spinal dorsal horn was decreased and activation of SIRT1 by SRT1720 also prevented the induction of LTP. Importantly, the spinal expression of Liver X receptors (LXRs) was increased, both at mRNA and protein level following SMIR. Application of LXRs agonist T0901317 to the spinal dorsal horn prevented LTP induction following SMIR. Mechanistically, T0901317 enhanced the expression of SIRT1 and decreased the expression of ac-NF-κB p65 and TNFα. Spinal application of SIRT1 antagonist EX-527, 30 min before T0901317 administration, completely blocked the inhibiting effect of T0901317 on LTP, and on expression of ac-NF-κB p65 and TNFα. These results indicated that activation of LXRs prevented SMIR-induced LTP by inhibiting NF-κB/TNFα pathway via increasing SIRT1 expression.

Expression of LRP1 and CHOP genes associated with peripheral neuropathy in type 2 diabetes mellitus: Correlations with nerve conduction studies

AIM

Diabetic peripheral neuropathy (DPN) is a frequent and debilitating complication of diabetes mellitus. The low-density lipoprotein receptor-related protein-1 (LRP-1) is a multifunctional cell surface receptor playing critical roles in lipoprotein metabolism and several cell signaling processes. C/EBP homologous protein (CHOP) is a main conduit to endoplasmic reticulum stress-induced apoptosis. We aimed to investigate LRP1 and CHOP gene expression in peripheral blood cells of type 2 diabetes mellitus (T2DM) subjects to clarify its possible relation to DPN pathogenesis.

METHOD

The study included 20 non-complicated T2DM subjects, 20 subjects with DPN and 20 healthy controls. Quantitative real time PCR was used to study gene expression.

RESULTS

There was a significant reduction in LRP1 mRNA expression and a significant increase in CHOP mRNA expression in subjects with DPN compared to non-complicated group and healthy controls. Both LRP1 and CHOP expression levels were inversely correlated, and both showed significant correlation with HbA1c, hyperlipidemia, hs-CRP, and different electrophysiological parameters. Receiver operating characteristics (ROC) analysis suggested that both LRP1 and CHOP mRNA expression and hs-CRP levels had great potential advantages to predict the progression of DPN.

CONCLUSION

LRP1 and CHOP might be involved in DPN pathogenesis and progression, thus providing opportunities for early detection and treatment.

Conserved Transcriptional Signatures in Human and Murine Diabetic Peripheral Neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most common complications of diabetes. In this study, we employed a systems biology approach to identify DPN-related transcriptional pathways conserved across human and various murine models. Eight microarray datasets on peripheral nerve samples from murine models of type 1 (streptozotocin-treated) and type 2 (db/db and ob/ob) diabetes of various ages and human subjects with non-progressive and progressive DPN were collected. Differentially expressed genes (DEGs) were identified between non-diabetic and diabetic samples in murine models, and non-progressive and progressive human samples using a unified analysis pipeline. A transcriptional network for each DEG set was constructed based on literature-derived gene-gene interaction information. Seven pairwise human-vs-murine comparisons using a network-comparison program resulted in shared sub-networks including 46 to 396 genes, which were further merged into a single network of 688 genes. Pathway and centrality analyses revealed highly connected genes and pathways including LXR/RXR activation, adipogenesis, glucocorticoid receptor signalling, and multiple cytokine and chemokine pathways. Our systems biology approach identified highly conserved pathways across human and murine models that are likely to play a role in DPN pathogenesis and provide new possible mechanism-based targets for DPN therapy.

Transplantation of human mobilized mononuclear cells improved diabetic neuropathy

Rodent stem cells demonstrated regenerative effects in diabetic neuropathy via improvement in nerve perfusion. As a pre-clinical step, we explored if human mobilized mononuclear cells (hMNC) would have the same effects in rats. hMNC were injected into Rt. hind-limb muscles of streptozotocin-induced diabetic nude rats, and the grafts were monitored using with MRI. After 4 weeks, the effects were compared with those in the vehicle-injected Lt. hind limbs. Nerve conduction, muscle perfusion and gene expression of sciatic nerves were assessed. Induction of diabetes decreased nerve function and expression of Mpz and Met in the sciatic nerves, which are related with myelination. hMNC injection significantly improved the amplitude of compound muscle action potentials along with muscle perfusion and sciatic nerve Mpz expression. On MRI, hypointense signals were observed for 4 weeks at the graft site, but their correlation with the presence of hMNC was detectable for only 1 week. To evaluate paracrine effects of hMNC, IMS32 cells were tested with hepatocyte growth factor (HGF), which had been reported as a myelination-related factor from stem cells. We could observe that HGF enhanced Mpz expression in the IMS32 cells. Because hMNC secreted HGF, IMS32 cells were co-cultured with hMNC, and the expression of Mpz increased along with morphologic maturation. The hMNC-induced Mpz expression was abrogated by treatment of anti-HGF. These results suggest that hMNC could improve diabetic neuropathy, possibly through enhancement of myelination as well as perfusion. According to in vitro studies, HGF was involved in the hMNC-induced myelination activity, at least in part.

Neuroactive Steroids and Sex-Dimorphic Nervous Damage Induced by Diabetes Mellitus

Diabetes mellitus is a metabolic disease where improper glycaemic control may induce severe complications in different organs. In this review, we will discuss alterations occurring in peripheral and central nervous system of patients with type 1 (i.e., insulin dependent diabetes mellitus,) or type 2 diabetes (i.e., non-insulin dependent diabetes mellitus), as well as related experimental models. A particular focus will be on the role exerted by neuroactive steroids (i.e., important regulators of nervous functions) in the nervous damage induced by diabetes. Indeed, the nervous levels of these molecules are affected by the pathology and, in agreement, their neuroprotective effects have been reported. Interestingly, the sex is another important variable. As discussed, nervous diabetic complications show sex dimorphic features in term of incidence, functional outcomes and neuroactive steroid levels. Therefore, these features represent an interesting background for possible sex-oriented therapies with neuroactive steroids aimed to counteract nervous damage observed in diabetic pathology.

Insulin-induced upregulation of lipoprotein lipase in Schwann cells during diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the major complications associated with diabetes. It is characterized by the degeneration of the myelin sheath around axons, referred to as demyelination. Such demyelinations are often caused by reduced lipid component of the myelin sheath. Since, lipoprotein lipase (LPL) provides the lipid for myelin sheath by hydrolysing the triglyceride rich lipoproteins, and also helps in the uptake of lipids by the Schwann cells (SCs) for its utilization, LPL is considered as the important factor in the regeneration of myelin sheath during diabetic neuropathy. Earlier reports from our laboratory have provided the insights of insulin and its receptor in SCs during diabetic neuropathy. In order to evaluate the long term effect of insulin on lipid metabolism during diabetic neuropathy, in this study, we analyzed the expression of LPL in SCs under normal, high glucose and insulin treated conditions. A decrease in the expression of LPL was observed in SCs of high glucose condition and it was reversed upon insulin treatment. Histochemical observations of sciatic nerve of insulin treated neuropathy subjects showed the improved nerve morphology, signifying the importance of insulin in restoring the pathophysiology of diabetic neuropathy.

Diabetes induces mitochondrial dysfunction and alters cholesterol homeostasis and neurosteroidogenesis in the rat cerebral cortex

The nervous system synthesizes and metabolizes steroids (i.e., neurosteroidogenesis). Recent observations indicate that neurosteroidogenesis is affected by different nervous pathologies. Among these, long-term type 1 diabetes, together with other functional and biochemical changes, has been shown to alter neuroactive steroid levels in the nervous system. Using an experimental model of type 1 diabetes (i.e., streptozotocin injection) we here show that the levels of these molecules are already decreased in the rat cerebral cortex after one month of the initiation of the pathology. Moreover, decreased levels of free cholesterol, together with alterations in the expression of molecules involved in cholesterol biosynthesis, bioavailability, trafficking and metabolism were detected in the rat cerebral cortex after one month of diabetes. Furthermore, mitochondrial functionality was also affected in the cerebral cortex and consequently may also contribute to the decrease in neuroactive steroid levels. Altogether, these results indicate that neurosteroidogenesis is an early target for the effect of type 1 diabetes in the cerebral cortex.

Neuroactive steroids and diabetic complications in the nervous system

Important complications of diabetes mellitus in the nervous system are represented by diabetic peripheral neuropathy and diabetic encephalopathy. In this context, an important link is represented by neuroactive steroids (i.e., steroids coming from peripheral glands and affecting nervous functionality as well as directly synthesized in the nervous system). Indeed, diabetes does not only affect the reproductive axis and consequently the levels of sex steroid hormones, but also those of neuroactive steroids. Indeed, as will be here summarized, the levels of these neuromodulators present in the central and peripheral nervous system are affected by the pathology in a sex-dimorphic way. In addition, some of these neuroactive steroids, such as the metabolites of progesterone or testosterone, as well as pharmacological tools able to increase their levels have been demonstrated, in experimental models, to be promising protective agents against diabetic peripheral neuropathy and diabetic encephalopathy.

HDAC3 is a molecular brake of the metabolic switch supporting white adipose tissue browning

White adipose tissue (WAT) can undergo a phenotypic switch, known as browning, in response to environmental stimuli such as cold. Post-translational modifications of histones have been shown to regulate cellular energy metabolism, but their role in white adipose tissue physiology remains incompletely understood. Here we show that histone deacetylase 3 (HDAC3) regulates WAT metabolism and function. Selective ablation of Hdac3 in fat switches the metabolic signature of WAT by activating a futile cycle of de novo fatty acid synthesis and β-oxidation that potentiates WAT oxidative capacity and ultimately supports browning. Specific ablation of Hdac3 in adipose tissue increases acetylation of enhancers in Pparg and Ucp1 genes, and of putative regulatory regions of the Ppara gene. Our results unveil HDAC3 as a regulator of WAT physiology, which acts as a molecular brake that inhibits fatty acid metabolism and WAT browning.Histone deacetylases, such as HDAC3, have been shown to alter cellular metabolism in various tissues. Here the authors show that HDAC3 regulates WAT metabolism by activating a futile cycle of fatty acid synthesis and oxidation, which supports WAT browning.

Improvement of spatial learning and memory, cortical gyrification patterns and brain oxidative stress markers in diabetic rats treated with Ficus deltoidea leaf extract and vitexin

Despite the fact that Ficus deltoidea and vitexin played important roles in controlling hyperglycemia, an effective mitigation strategy dealing with cognitive deficit observed in diabetes, little is known about its neuroprotective effects. The study is aimed to determine changes in behavioral, gyrification patterns and brain oxidative stress markers in streptozotocin (STZ)-induced diabetic rats following F. deltoidea and vitexin treatments. Diabetic rats were treated orally with metformin, methanolic extract of F. deltoidea leaves and vitexin for eight weeks. Morris water maze (MWM) test was performed to evaluate learning and memory functions. The patterns of cortical gyrification were subsequently visualized using micro-computed tomography (micro-CT). Quantification of brain oxidative stress biomarkers, insulin, amylin as well as serum testosterone were measured using a spectrophotometer. The brain fatty acid composition was determined using gas chromatography (GC). Biochemical variation in brain was estimated using Fourier transform infrared (FT-IR) spectroscopy. Results showed that oral administration of F. deltoidea extract and vitexin to diabetic rats attenuated learning and memory impairment, along with several clusters of improved gyrification. Both treatments also caused a significant increase in the superoxide dismutase (SOD) and glutathione peroxidase (GPx) values, as well as a significant reduction of TBARS. Strikingly, improvement of cortical gyrification, spatial learning and memory are supported by serum testosterone levels, fatty acid composition of brain and FT-IR spectra.

Proteomic approach to detect changes in hippocampal protein levels in an animal model of type 2 diabetes

In our previous study, we demonstrated that type 2 diabetes affects blood-brain barrier integrity and ultrastructural morphology in Zucker diabetic fatty (ZDF) rats at 40 weeks of age. In the present study, we investigated the possible candidates for diabetes-related proteins in the hippocampus of ZDF rats and their control littermates (Zucker lean control, ZLC), by using two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF). Approximately 2756 protein spots were detected by 2D-DIGE, and an increase or decrease of more than 1.4-fold was observed for 13 proteins in the hippocampal homogenates of ZDF rats relative to those of ZLC rats. Among these proteins, we found four proteins whose levels were significantly lower in the hippocampi of ZDF rats than in those of ZLC rats: glial fibrillary acidic protein (GFAP), apolipoprotein A-I preprotein (apoAI-P), myelin basic protein (MBP), and rCG39881, isoform CRA_a. Among these proteins, apoAI-P protein levels were decreased most prominently in ZDF rats than in ZLC rats, based on Western blot analysis. In addition, immunohistochemical and Western blot studies demonstrated that MBP, not GFAP, immunoreactivity and protein levels were significantly decreased in the hippocampus of ZDF rats compared to ZLC rats. In addition, ultrastructural analysis showed that ZDF rats showed myelin degeneration and disarrangement in the hippocampal tissue. These results suggest that chronic type 2 diabetes affects hippocampal function via reduction of MBP and apoAI-P levels as well as disarrangement of myelin.