Neuregulin‐1 promotes remyelination and fosters a pro‐regenerative inflammatory response in focal demyelinating lesions of the spinal cord

Abstract

Oligodendroglial cell death and demyelination are hallmarks of neurotrauma and multiple sclerosis that cause axonal damage and functional impairments. Remyelination remains a challenge as the ability of endogenous precursor cells for oligodendrocyte replacement is hindered in the unfavorable milieu of demyelinating conditions. Here, in a rat model of lysolecithin lysophosphatidyl-choline (LPC)-induced focal demyelination, we report that Neuregulin-1 (Nrg-1), an important factor for oligodendrocytes and myelination, is dysregulated in demyelinating lesions and its bio-availability can promote oligodendrogenesis and remyelination. We delivered recombinant human Nrg-1β1 (rhNrg-1β1) intraspinally in the vicinity of LPC demyelinating lesion in a sustained manner using poly lactic-co-glycolic acid microcarriers. Availability of Nrg-1 promoted generation and maturation of new oligodendrocytes, and accelerated endogenous remyelination by both oligodendrocyte and Schwann cell populations in demyelinating foci. Importantly, Nrg-1 enhanced myelin thickness in newly remyelinated spinal cord axons. Our complementary in vitro studies also provided direct evidence that Nrg-1 significantly promotes maturation of new oligodendrocytes and facilitates their transition to a myelinating phenotype. Nrg-1 therapy remarkably attenuated the upregulated expression chondroitin sulfate proteoglycans (CSPGs) specific glycosaminoglycans in the extracellular matrix of demyelinating foci and promoted interleukin-10 (IL-10) production by immune cells. CSPGs and IL-10 are known to negatively and positively regulate remyelination, respectively. We found that Nrg-1 effects are mediated through ErbB2 and ErbB4 receptor activation. Our work provides novel evidence that dysregulated levels of Nrg-1 in demyelinating lesions of the spinal cord pose a challenge to endogenous remyelination, and appear to be an underlying cause of myelin thinning in newly remyelinated axons.

LAR and PTPσ receptors are negative regulators of oligodendrogenesis and oligodendrocyte integrity in spinal cord injury

“…Primary OPCs cultures were isolated from the cerebral cortex and spinal cord of postnatal day 1–3 (P1–3) rats as we described previously (Kataria et al, ). Briefly, cerebral cortices or spinal cord tissue were dissected out and enzymatically dissociated in a solution containing papain (0.9 mg/ml; Worthington Biochemical, New Jersey, United States), l ‐cysteine (0.2 mg/ml; Sigma‐Aldrich, Oakville, ON, Canada), Ethylenediaminetetraacetic acid (EDTA) (0.2 mg/ml; Sigma‐Aldrich, Oakville, ON, Canada) diluted in Hanks’ Balanced Salt solution (HBSS) (Invitrogen, LifeTechnologies Inc, ON, Canada) for 45 min, at 37°C.…”

“…Fractal dimension (FD) analysis was performed to evaluate morphological complexity of oligodendrocytes as we described earlier (Kataria et al, ). In this analysis, a numerical value close to 1 represents cells with low morphological complexity (essentially bipolar cells), whereas an FD value near 2 identifies those with high complexity (highly branched cells or with a bi‐dimensional planar structure).…”

“…The dorsal root ganglia (DRGs) were isolated from P1–3 SD rats as we described previously (Kataria et al, ). The ganglia were digested with collagenase (0.06 μg/ml) for 1 hr at 37°C followed by additional digestion with trypsin/EDTA (0.125%/0.05%, Sigma‐Aldrich, Oakville, ON, Canada) for 15 min.…”

“…For assessment of myelination, oligodendrocyte/DRG co‐cultures were co‐immunolabeled for myelin basic protein (anti‐MBP, rabbit) and NF200 (anti‐NF200, mouse) and were imaged from 5–7 different fields (20× objective) across the tissue culture well for each condition under the same microscopy settings as we described previously (Kataria et al, ). The extent of myelination was quantified by measuring the length of MBP‐positive sheath surrounding the NF200 positive fibers with ImageJ (NIH) software.…”

“…To examine the proliferation kinetics and fate of the mitotically active cells in the injured spinal cord after treatments, all rats received daily subcutaneous injection of BrdU (IP, 50 mg/kg) starting immediately following injury for up to 14 days post‐injury as we described previously (Gauthier et al, ; Karimi‐Abdolrezaee et al, ; Kataria et al, ).…”