The neuregulin, glial growth factor 2, diminishes autoimmune demyelination and enhances remyelination in a chronic relapsing model for multiple sclerosis

Glutamate excitotoxicity in a model of multiple sclerosis

Glutamate excitotoxicity mediated by the AMPA/kainate type of glutamate receptors damages not only neurons but also the myelin-producing cell of the central nervous system, the oligodendrocyte. In multiple sclerosis, myelin, oligodendrocytes and some axons are lost as a result of an inflammatory attack on the central nervous system. Because glutamate is released in large quantities by activated immune cells, we expected that during inflammation in MS, glutamate excitotoxicity might contribute to the lesion. We addressed this by using the AMPA/kainate antagonist NBQX to treat mice sensitized for experimental autoimmune encephalomyelitis, a demyelinating model that mimics many of the clinical and pathologic features of multiple sclerosis. Treatment resulted in substantial amelioration of disease, increased oligodendrocyte survival and reduced dephosphorylation of neurofilament H, an indicator of axonal damage. Despite the clinical differences, treatment with NBQX had no effect on lesion size and did not reduce the degree of central nervous system inflammation. In addition, NBQX did not alter the proliferative activity of antigen-primed T cells in vitro, further indicating a lack of effect on the immune system. Thus, glutamate excitotoxicity seems to be an important mechanism in autoimmune demyelination, and its prevention with AMPA/kainate antagonists may prove to be an effective therapy for multiple sclerosis.

Neuregulin and erbB receptor expression in normal and diseased human white matter

Human white matter from non-neurologic cases, multiple sclerosis (MS) and other neurologic diseases (OND, inflammatory and non-inflammatory), was subjected to immunocytochemistry and Western blotting for expression of the neuregulin, glial growth factor-2 (GGF2), and its receptors, erbB2, erbB3 and erbB4. GGF2 has previously been shown to have mitogenic effects upon oligodendrocytes in vitro and an enhancing effect upon remyelination in animals with autoimmune demyelination. In all types of human white matter examined, expression of the ligand GGF2 and its three receptors was consistently found on oligodendrocytes, with higher levels being seen in cases of MS. Expression was also seen, albeit at lower levels, on astrocytes and microglial cells, the latter most commonly in MS and OND. In human lymph node tissue, some lymphocytes were positive for erbB2, erbB3 and erbB4. Western blots confirmed the presence of all three receptors in normal, MS and OND white matter. GGF2 and erbB receptor expression did not correlate with areas of remyelination and reactivity occurred throughout the tissue, with some increase in intensity at the edge of MS lesions. Examination of precursor oligodendrocyte immunoreactivity (with anti-PDGF-Ralpha and NG2), revealed widespread expression throughout both normal and diseased white matter. The presence of GGF2 and its receptors on oligodendrocytes and lymphocytes render this cell type a candidate for functional signaling via this pathway, perhaps in relationship to myelinating activity.

Induction of myelin gene expression in Schwann cell cultures by an interleukin-6 receptor-interleukin-6 chimera

Expression of myelin basic protein (MBP) and Po gene products is induced during the final postnatal maturation of Schwann cells and reinduced during nerve regeneration. We show that a chimeric protein containing interleukin-6 fused to its soluble receptor (IL6RIL6 chimera) induces MBP and Po RNAs and proteins in cultures of dorsal root ganglia (DRG) from 14 day old mouse embryos. Activation of gp130 signaling by IL6RIL6 appears comparable to cyclic AMP elevating agents to induce the myelin gene products in DRG and in pure Schwann cell cultures.

Neuregulin in cardiac hypertrophy in rats with aortic stenosis. Differential expression of erbB2 and erbB4 receptors

BACKGROUND

Neuregulins are a family of peptide growth factors that promote cell growth and viability. The potential role of neuregulin-erbB signaling in hypertrophic growth and later failure in the adult heart in vivo is not known.

METHODS AND RESULTS

We used ribonuclease protection assays to quantify mRNA levels of neuregulin, erbB2, and erbB4 in left ventricular (LV) tissue and myocytes of normal rats and rats with aortic stenosis with pressure-overload hypertrophy 6 and 22 weeks after banding. At both stages of hypertrophy, Northern blot analyses of mRNA from LV myocytes showed upregulation of atrial natriuretic peptide, a molecular marker of hypertrophy (P<0.05). LV tissue neuregulin message levels were similar in animals with aortic stenosis compared with controls (P=NS) and were not detectable in myocytes. LV erbB2 and erbB4 message levels in LV tissue and myocytes were maintained during early compensatory hypertrophy in 6-week aortic stenosis animals compared with age-matched controls; in contrast, erbB2 and erbB4 message levels were depressed in 22-week aortic stenosis animals at the stage of early failure (both P<0.01 vs age-matched controls). Immunoblotting of erbB2 and erbB4 also showed normal protein levels in 6-week aortic stenosis animals compared with controls; however, erbB2 and erbB4 protein levels were depressed in 22-week aortic stenosis animals (48% decrease in erbB2, P<0.05, and 43% decrease in erbB4, P<0.01) relative to age-matched controls.

CONCLUSIONS

The neuregulin receptors erbB2 and erbB4 are downregulated at both the message and protein levels at the stage of early failure in animals with chronic hypertrophy secondary to aortic stenosis. These data suggest a role for disabled erbB receptor signaling in the transition from compensatory hypertrophy to failure.

GGF/neuregulin induces a phenotypic reversion of oligodendrocytes

We have previously shown that glial growth factor (GGF), a member of the neuregulin (NRG) family of growth factors, is a mitogen and survival factor for oligodendrocyte progenitors in cell culture and blocks their differentiation at the pro-oligodendrocyte stage (P. D. Canoll et al., 1996, Neuron 17, 229-243). We now show that GGF is able to induce differentiated oligodendrocytes to undergo a phenotypic reversion characterized by loss of MBP expression, reexpression of the intermediate filament protein nestin, reorganization of the actin cytoskeleton, and a dramatic reduction in the number of processes per cell. TUNEL analysis demonstrates that GGF is not cytotoxic for mature oligodendrocytes, but rather enhances their survival. GGF also induces the rapid activation of the PI 3-kinase and MAP kinase signaling pathways. These results further support a role for the NRGs in promoting the proliferation and survival of and inhibiting the differentiation of cells in the oligodendrocyte lineage and demonstrate that oligodendrocytes that differentiate in culture retain a substantial degree of phenotypic plasticity.