Expression pattern of neuregulin-1 type III during the development of the peripheral nervous system

A Novel Form of Neuregulin 1 Type III Caused by N-Terminal Processing

Nrg1 (Neuregulin 1) type III, a susceptible gene of schizophrenia, exhibits a critical role in the central nervous system and is essential at each stage of Schwann's cell development. Nrg1 type III comprises double-pass transmembrane domains, with the N-terminal and C-terminal localizing inside the cells. The N-terminal transmembrane helix partially overlaps with the cysteine-rich domain (CRD). In this study, Nrg1 type III constructs with different tags were transformed into cultured cells to verify whether CRD destroyed the transmembrane helix formation. We took advantage of immunofluorescent and immunoprecipitation assays on whole cells and analyzed the N-terminal distribution. Astonishingly, we found that a novel form of Nrg1 type III, about 10% of Nrg1 type III, omitted the N-terminal transmembrane helix, with the N-terminal positioning outside the membrane. The results indicated that the novel single-pass transmembrane status was a minor form of Nrg1 type III caused by N-terminal processing, while the major form was a double-pass transmembrane status.

Type III NRG-1 plays a regulatory role in the regeneration process of nerves from the beginning of transplantation

The present study investigated the effect of type III Neuregulin-1 (NRG-1) on changes in the myelin sheath and the recovery of nerve function during the regeneration process following autologous nerve transplantation. Seventy-two Sprague-Dawley rats were divided into a Blank, Model and (antisense oligonucleotide, ASON) group. The Model and ASON groups of SD rats were subjected to autologous nerve transplantation, and the Blank group only had the sciatic nerve exposed. The Model and ASON groups were given local injections of 2 ml PBS buffer solution and 2 ml ASON of Type III NRG-1, respectively, the NRG-1 type III was inhibited by ASON. Changes in the sciatic nerve functional index (SFI) and conduction velocities were observed at different 6 time points. Regeneration of the myelin sheath was observed using transmission electron microscopy. Type III NRG-1 protein was detected using Western blotting and immunohistochemistry, and NRG-1 mRNA was detected using PCR. The SFI of the ASON group was lower than the Model group after transplantation. The conduction velocities of the ASON group on the 14th and 21st days after autologous nerve transplantation were lower than the Model group (P < 0.01). The protein and mRNA expression of type III NRG-1 in the ASON group was lower than the Model group at all 6 time points. The area of medullated nerve fibres was significantly different between the ASON group and the Model group on the 3rd day (P < 0.05), as was the number of medullated nerve fibres per unit area (P < 0.01). The diameter of axons was obviously different between the two groups (P < 0.01). Type III NRG-1 played an important regulatory role in the regeneration process of the nerve from the beginning of transplantation to the 28th day.

The Influence of Bisphenol A (BPA) on the Occurrence of Selected Active Substances in Neuregulin 1 (NRG1)-Positive Enteric Neurons in the Porcine Large Intestine

Bisphenol A (BPA) is a substance used in the manufacture of plastics which shows multidirectional adverse effects on living organisms. Since the main path of intoxication with BPA is via the gastrointestinal (GI) tract, the stomach and intestine are especially vulnerable to the impact of this substance. One of the main factors participating in the regulation of intestinal functions is the enteric nervous system (ENS), which is characterized by high neurochemical diversity. Neuregulin 1 (NRG1) is one of the lesser-known active substances in the ENS. During the present study (performed using the double immunofluorescence method), the co-localization of NRG1 with other neuronal substances in the ENS of the caecum and the ascending and descending colon has been investigated under physiological conditions and after the administration of BPA. The obtained results indicate that NRG1-positive neurons also contain substance P, vasoactive intestinal polypeptide, a neuronal isoform of nitric oxide synthase and galanin and the degree of each co-localization depend on the type of enteric plexus and the particular fragment of the intestine. Moreover, it has been shown that BPA generally increases the degree of co-localization of NRG1 with other substances.

The Endocrine Disruptor Bisphenol A (BPA) Affects the Enteric Neurons Immunoreactive to Neuregulin 1 (NRG1) in the Enteric Nervous System of the Porcine Large Intestine

The enteric nervous system (ENS), located in the wall of the gastrointestinal (GI) tract, is characterized by complex organization and a high degree of neurochemical diversity of neurons. One of the less known active neuronal substances found in the enteric neurons is neuregulin 1 (NRG1), a factor known to be involved in the assurance of normal development of the nervous system. During the study, made up using the double immunofluorescence technique, the presence of NRG1 in the ENS of the selected segment of porcine large intestine (caecum, ascending and descending colon) was observed in physiological conditions, as well as under the impact of low and high doses of bisphenol A (BPA) which is commonly used in the production of plastics. In control animals in all types of the enteric plexuses, the percentage of NRG1-positive neurons oscillated around 20% of all neurons. The administration of BPA caused an increase in the number of NRG1-positive neurons in all types of the enteric plexuses and in all segments of the large intestine studied. The most visible changes were noted in the inner submucous plexus of the ascending colon, where in animals treated with high doses of BPA, the percentage of NRG1-positive neurons amounted to above 45% of all neuronal cells. The mechanisms of observed changes are not entirely clear, but probably result from neurotoxic, neurodegenerative and/or proinflammatory activity of BPA and are protective and adaptive in nature.

Beagle sciatic nerve regeneration across a 30 mm defect bridged by chitosan/PGA artificial nerve grafts

Longitudinally oriented microstructures are essential for a nerve scaffold to promote the significant regeneration of injured peripheral axons across nerve gaps. In the current study, we present a novel nerve-guiding collagen-chitosan (CCH) scaffold that facilitated the repair of 30 mm-long sciatic nerve defects in beagles. The CCH scaffolds were observed with a scanning electron microscope. Eighteen beagles were equally divided into CCH group, autograft group and non-graft group. The posture and gait of each dog was recorded at 12 and 24 weeks after surgery. Electrophysiological tests, Fluoro-Gold retrograde tracing test, Histological assessment of gastrocnemius and immunofluorescent staining of nerve regeneration were performed. Our investigation of regenerated sciatic nerves indicated that a CCH scaffold strongly supported directed axon regeneration in a manner similar to that achieved by autologous nerve transplantation. In vivo animal experiments showed that the CCH scaffold achieved nerve regeneration and functional recovery equivalent to that achieved by an autograft but without requiring the exogenous delivery of regenerative agents or cell transplantation. We conclude that CCH nerve guides show great promise as a method for repairing peripheral nerve defects.

A histone deacetylase 3-dependent pathway delimits peripheral myelin growth and functional regeneration

Deficits in Schwann cell-mediated remyelination impair functional restoration after nerve damage, contributing to peripheral neuropathies. The mechanisms mediating block of remyelination remain elusive. Here, through small-molecule screening focusing on epigenetic modulators, we identified histone deacetylase 3 (HDAC3; a histone-modifying enzyme) as a potent inhibitor of peripheral myelinogenesis. Inhibition of HDAC3 enhanced myelin growth and regeneration and improved functional recovery after peripheral nerve injury in mice. HDAC3 antagonizes the myelinogenic neuregulin-PI3K-AKT signaling axis. Moreover, genome-wide profiling analyses revealed that HDAC3 represses promyelinating programs through epigenetic silencing while coordinating with p300 histone acetyltransferase to activate myelination-inhibitory programs that include the HIPPO signaling effector TEAD4 to inhibit myelin growth. Schwann cell-specific deletion of either Hdac3 or Tead4 in mice resulted in an elevation of myelin thickness in sciatic nerves. Thus, our findings identify the HDAC3-TEAD4 network as a dual-function switch of cell-intrinsic inhibitory machinery that counters myelinogenic signals and maintains peripheral myelin homeostasis, highlighting the therapeutic potential of transient HDAC3 inhibition for improving peripheral myelin repair.

Neuregulin-1 is essential for nerve plexus formation during cardiac maturation

The Neuregulin‐1 (Nrg1)/ErbB pathway plays multiple, critical roles in early cardiac and nervous system development and has been implicated in both heart and nerve repair processes. However, the early embryonic lethality of mouse Nrg1 mutants precludes an analysis of Nrg1's function in later cardiac development and homeostasis. In this study, we generated a novel nrg1 null allele targeting all known isoforms of nrg1 in zebrafish and examined cardiac structural and functional parameters throughout development. We found that zebrafish nrg1 mutants instead survived until young adult stages when they exhibited reduced survivorship. This coincided with structural and functional defects in the developing juvenile and young adult hearts, as demonstrated by reduced intracardiac myocardial density, cardiomyocyte cell number, swimming performance and dysregulated heartbeat. Interestingly, nrg1 mutant hearts were missing long axons on the ventricle surface by standard length (SL) 5 mm, which preceded juvenile and adult cardiac defects. Given that the autonomic nervous system normally exerts fine control of cardiac output through this nerve plexus, these data suggest that Nrg1 may play a critical role in establishing the cardiac nerve plexus such that inadequate innervation leads to deficits in cardiac maturation, function and survival.