Increased gene expression of growth associated protein-43 in skin of patients with early-stage peripheral neuropathies

• Age-dependent reduction in skin GAP-43 reactivity is disturbed in neuropathies.
• Cutaneous GAP-43 gene expression is increased in patients with recent neuropathies.
• GAP-43 may be a marker of recent peripheral neuropathies.

Growth associated protein-43 (GAP-43) is one of the neural proteins associated with nerve injury that is upregulated after nerve injury. To investigate whether GAP-43 quantification in skin biopsies would differentiate subtypes of peripheral neuropathies, we analyzed GAP-43 expression in skin from the lateral thigh and the distal leg. We prospectively enrolled 130 patients with peripheral neuropathies and compared data with healthy controls. Intraepidermal nerve fiber density (IENFD) was determined using antibodies against protein gene product 9.5 (PGP 9.5); anti-GAP-43 antibodies were applied to visualize regenerating nerve fibers. PGP 9.5 and GAP-43 gene expression was analyzed using qRT-PCR. Patients with neuropathies had a generalized reduction of IENFD and GAP-43 immunoreactive fibers compared to controls (p < 0.01). In contrast, cutaneous GAP-43 gene expression was increased in proximal skin in patients (p < 0.05), particularly when disease duration was short (< 3 years; p < 0.01). While fiber density for both markers decreased with age in healthy skin (p < 0.01), age-dependent reduction of skin innervation was absent in neuropathies. Diagnostic subgroups and neuropathic pain had no influence on skin innervation. We conclude that peripheral neuropathies lead to an initial increase in GAP-43 gene expression as a potential mechanism of regeneration, which is not sustained in neuropathies of long duration.