Nogo-A downregulation improves insulin secretion in mice

Nogo-A Mediated Endoplasmic Reticulum Stress During Myocardial Ischemic-Reperfusion Injury in Diabetic Rats

Among the three isoforms encoded by neurite outgrowth inhibitor proteins has been intensely investigated as a central nervous system inhibitor. Although neurite outgrowth inhibitor protein-A (Nogo-A) expression is increased in plasma of patients who have experienced a coronary heart disease, its role in heart disease is not well elucidated. In this study, we discovered a significant increase in Nogo-A expression in diabetic myocardial ischemia reperfusion (MI/R) injury conditions. Accelerated Nogo-A and MI/R injury in diabetic rats was attenuated by tauroursodeoxycholic acid treatment and knockdown of Nogo-A per se is sufficient to decrease endoplasmic reticulum (ER) stress as well as prevents cardiomyocyte apoptosis. We hypothesized that decreased Nogo-A levels might reducing diabetic MI/R injury. Nogo-A interacted with C/EBP homologous protein, suggesting a role for Nogo-A in ER stress during diabetic MI/R. In conclusion, Nogo-A mediated ER stress plays a major role in diabetic MI/R injury, and pathologically altered Nogo-A expression mediates diabetic MI/R injury, suggesting Nogo-A as a novel target for the treatment of diabetic MI/R injury in clinical settings.

Evaluating the effectiveness of anti-Nogo treatment in spinal cord injuries

As humans, we cannot regenerate axons within the central nervous system (CNS), therefore, making any damage to it permanent. This leads to the loss of sensory and motor function below the site of injury and can be crippling to a person’s health. Spontaneous recovery can occur from plastic changes, but it is minimal. The absence of regeneration is due to the inhibitory environment of the CNS as well as the inherent inability of CNS axons to form growth cones. Amongst many factors, one of the major inhibitory signals of the CNS environment is the myelin-associated Nogo pathway. Nogo-A, Nogo-B and Nogo-C (Nogo), stimulate the Nogo receptor, inhibiting neurite outgrowth by causing growth cones to collapse through activation of Rho Kinase (ROCK). Antibodies can be used to target this signalling pathway by binding to Nogo and thus promote the outgrowth of neuronal axons in the CNS. This use of anti-Nogo antibodies has been shown to upregulate CNS regeneration as well as drastically improve sensory and motor function in both rats and primates when coupled with adequate training. Here, we evaluate whether the experimental success of anti-Nogo at improving CNS regeneration can be carried over into the clinical setting to treat spinal cord injuries (SCI) and their symptoms successfully. Furthermore, we also discuss potential methods to improve the current treatment and any developmental obstacles.

Extracellular Pgk1 enhances neurite outgrowth of motoneurons through Nogo66/NgR-independent targeting of NogoA

NogoA inhibits neurite outgrowth of motoneurons (NOM) through interaction with its receptors, Nogo66/NgR. Inhibition of Nogo receptors rescues NOM, but not to the extent exhibited by NogoA-knockout mice, suggesting the presence of other pathways. We found that NogoA-overexpressing muscle cells reduced phosphoglycerate kinase 1 (Pgk1) secretion, resulting in inhibiting NOM. Apart from its glycolytic role and independent of the Nogo66 pathway, extracellular Pgk1 stimulated NOM by triggering a reduction of p-Cofilin-S3, a growth cone collapse marker, through decreasing a novel Rac1-GTP/p-Pak1-T423/p-P38-T180/p-MK2-T334/p-Limk1-S323/p-Cofilin-S3 molecular pathway. Not only did supplementary Pgk1 enhance NOM in defective cells, but injection of Pgk1 rescued denervation in muscle-specific NogoA-overexpression of zebrafish and an Amyotrophic Lateral Sclerosis mouse model, SOD1 G93A. Thus, Pgk1 secreted from muscle is detrimental to motoneuron neurite outgrowth and maintenance.

Novel protein signatures suggest progression to muscular invasiveness in bladder cancer

Patients with bladder cancer need frequent controls over long follow-up time due to high recurrence rate and risk of conversion to muscle invasive cancer with poor prognosis. We identified cancer-related molecular signatures in apparently healthy bladder in patients with subsequent muscular invasiveness during follow-up. Global proteomics of the normal tissue biopsies revealed specific proteome fingerprints in these patients prior to subsequent muscular invasiveness. In these presumed normal samples, we detected modulations of proteins previously associated with different cancer types. This study indicates that analyzing apparently healthy tissue of a cancer-invaded organ may suggest disease progression.

Clec16a, Nrdp1, and USP8 Form a Ubiquitin-Dependent Tripartite Complex That Regulates β-Cell Mitophagy

Mitophagy is a cellular quality-control pathway, which is essential for elimination of unhealthy mitochondria. While mitophagy is critical to pancreatic β-cell function, the posttranslational signals governing β-cell mitochondrial turnover are unknown. Here, we report that ubiquitination is essential for the assembly of a mitophagy regulatory complex, comprised of the E3 ligase Nrdp1, the deubiquitinase enzyme USP8, and Clec16a, a mediator of β-cell mitophagy with unclear function. We discover that the diabetes gene Clec16a encodes an E3 ligase, which promotes nondegradative ubiquitin conjugates to direct its mitophagy effectors and stabilize the Clec16a-Nrdp1-USP8 complex. Inhibition of the Clec16a pathway by the chemotherapeutic lenalidomide, a selective ubiquitin ligase inhibitor associated with new-onset diabetes, impairs β-cell mitophagy, oxygen consumption, and insulin secretion. Indeed, patients treated with lenalidomide develop compromised β-cell function. Moreover, the β-cell Clec16a-Nrdp1-USP8 mitophagy complex is destabilized and dysfunctional after lenalidomide treatment as well as after glucolipotoxic stress. Thus, the Clec16a-Nrdp1-USP8 complex relies on ubiquitin signals to promote mitophagy and maintain mitochondrial quality control necessary for optimal β-cell function.

Clinical implications of plasma Nogo-A levels in patients with coronary heart disease

INTRODUCTION

Nogo-A is an important neurite growth-regulatory protein in the adult and developing nervous system. Recently, increasing evidence has shown that Nogo-A plays important roles in cardiac development and may act as a potential indicator for heart failure. In addition, increased oxidative stress has been found in individuals with cardiovascular diseases. However, not much is known regarding the expression levels of Nogo-A and reactive oxygen species (ROS) in patients with coronary heart disease (CHD). Therefore, we sought to investigate the relationship between Nogo-A, ROS levels and CHD.

MATERIAL AND METHODS

The plasma Nogo-A and ROS concentrations of 122 acute coronary syndrome (ACS), 101 unstable angina pectoris (UAP), and 21 acute myocardial infarction (AMI) patients and 56 healthy controls were measured by enzyme-linked immunosorbent assay (ELISA). We further generated a receiver operating characteristic (ROC) curve to assess the diagnostic accuracy of Nogo-A and ROS in CHD.

RESULTS

The Nogo-A and ROS levels were significantly higher in patients with CHD than those in healthy controls. In addition, multivariate logistic regression analysis revealed that the level of Nogo-A (odds ratio (OR) = 1.624, 95% confidence interval: 1.125-2.293, p = 0.009) is a risk factor for prediction of CHD. Nogo-A has diagnostic value, with an optimal threshold of 5.466 ng/ml for maximized diagnostic performance (59% sensitivity and 78.6% specificity, area under curve, p < 0.05). However, ROS concentration is not a risk factor for prediction of CHD (OR = 0.999, 95% confidence interval: 0.997-1.001, p = 0.320).

CONCLUSIONS

Increased plasma Nogo-A level may be associated with CHD.

Effect of hyperglycaemia on muscarinic M3 receptor expression and secretory sensitivity to cholinergic receptor activation in islets

AIMS

Islets are innervated by parasympathetic nerves which release acetylcholine (ACh) to amplify glucose-induced insulin secretion, primarily via muscarinic M3 receptors (M3R). Here we investigate the consequence of chronic hyperglycaemia on islet M3R expression and secretory sensitivity of mouse islets to cholinergic receptor activation.

METHODS

The impact of hyperglycaemia was studied in (i) islets isolated from ob/ob mice, (ii) alginate-encapsulated mouse islets transplanted intraperitoneally into streptozotocin-induced diabetic mice and (iii) mouse and human islets maintained in vitro at 5.5 or 16 mmol/l glucose. Blood glucose levels were assessed by a commercial glucose meter, insulin content by RIA and M3R expression by qPCR and immunohistochemistry.

RESULTS

M3R mRNA expression was reduced in both ob/ob islets and islets maintained at 16 mmol/l glucose for 3 days (68 and 50% control, respectively). In all three models of hyperglycaemia the secretory sensitivity to the cholinergic receptor agonist, carbachol, was reduced by 60-70% compared to control islets. Treatment for 72 h with the irreversible PKC activator, PMA, or the PKC inhibitor, Gö6983, did not alter islet M3R mRNA expression nor did incubation with the PI3K-inhibitor, LY294002, although enhancement of glucose-induced insulin secretion by LY294002 was reduced in islets maintained at 16 mmol/l glucose, as was mRNA expression of the PI3K regulatory subunit, p85α.

CONCLUSIONS

Cholinergic regulation of insulin release is impaired in three experimental islet models of hyperglycaemia consistent with reduced expression of M3 receptors. Our data suggest that the receptor downregulation is a PKC- and PI3K-independent consequence of the hyperglycaemic environment, and they imply that M3 receptors could be potential targets in the treatment of type 2 diabetes.