Glia
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The immune-mediated central nervous system (CNS) demyelinating disorder multiple sclerosis (MS) is the most common neurological disease in young adults. One important goal of MS research is to identify strategies that will preserve oligodendrocytes (OLs) in MS lesions. During active myelination and remyelination, OLs synthesize large quantities of membrane proteins in the endoplasmic reticulum (ER), which may result in ER stress. ⋯ Unexpectedly, OL-PERK(ko/ko) mice develop normally and show no myelination defects. Nevertheless, EAE is exacerbated in these mice, which is correlated with increased OL loss, demyelination, and axonal degeneration. These data indicate that although not needed for developmental myelination, PERK signaling provides protection to OLs against inflammatory demyelination and suggest that the ISR in OLs could be a valuable target for future MS therapeutics.
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Satellite glial cells (SGCs) surrounding primary sensory neurons are similar to astrocytes of the central nervous system in that they buffer the extracellular environment via potassium and calcium channels and express the intermediate filament glial fibrillary acidic protein (GFAP). Peripheral nerve injury induces a reactive state in SGCs that includes SGC proliferation, increased SGC/SGC coupling via gap junctions, decreased inward rectifying potassium channel 4.1 (Kir 4.1) expression and increased expression of GFAP and the common neurotrophin receptor, p75NTR. In contrast, neuronal p75NTR expression, normally detected in ∼80% of adult rat sensory neurons, decreases in response to peripheral axotomy. ⋯ We found that reducing neuronal p75NTR protein expression in uninjured sensory neurons by intrathecal subarachnoid infusion of p75NTR-selective anti-sense oligodeoxynucleotides for one week was sufficient to induce a "reactive-like" state in the perineuronal SGCs akin to that normally observed following peripheral nerve injury. This reactive state included significantly increased SGC p75NTR, GFAP and gap junction protein connexin-43 protein expression, increased numbers of SGCs surrounding individual sensory neurons and decreased SGC Kir 4.1 channel expression. Collectively, this supports the tenet that reductions in target-derived trophic support leading to, or as a consequence of, reduced neuronal p75NTR expression plays a critical role in switching the SGC to a reactive state.