β4 Integrin and other Schwann cell markers in axonal neuropathy

Schwann cell gene expression is dynamically regulated after peripheral nerve injury and during regeneration. We hypothesized that the changes in protein expression described after rat peripheral nerve injury could be used to identify single Schwann cell-axon units in human axonal neuropathy. Therefore, we performed immunofluorescence staining on sections of injured rat sciatic nerves compared with sections of neuropathic human sural nerves. We chose the markers β4 integrin, P0 glycoprotein, and glial fibrillary acidic protein (GFAP) to characterize Schwann cells, and neurofilament- heavy (NF-H) to recognize axons. Normal rat or human myelin- forming units demonstrated a sharp ring of β4 staining at their outer surface, P0 staining in the myelin sheath, and NF-H staining in the axon. Acutely denervated rat units transited from broken rings of β4 and P0 staining, to diffuse β4 and absent P0 and NF-H staining. Chronically denervated rat Schwann cells re-expressed β4 more highly, but in a diffuse, non- polarized pattern. In contrast, regenerating units re-expressed β4, P0, and NF-H; β4 staining was polarized to the outer surface of Schwann cells. Finally, GFAP staining increased progressively after injury and decreased during regeneration in the distal nerve stump. In neuropathic human sural nerves, we identified units exhibiting each of these β4, P0, and NF-H staining patterns; the proportion of each pattern correlated best with the extent and chronicity of axonal injury. Thus, synchronous injury of rat sciatic nerve predicts patterns of Schwann cell marker expression in human axonal neuropathy. In addition, the unique changes in the polarity of β4 integrin expression, in combination with changes in P0 and NF-H expression, may distinguish normal from denervated or reinnervated myelin-forming Schwann cells in human sural nerve biopsies.