Activation of the RAGE pathway: a general mechanism in the pathogenesis of polyneuropathies?

Binding of ligands to the receptor for advanced glycation end products (RAGE) results in activation of the transcription factor NF-kappaB and subsequent expression of NF-kappaB regulated cytokines and is a possible pathomechanism in diabetic and in vasculitic polyneuropathies (PNP). We wanted to investigate whether the newly discovered RAGE pathway also contributes to the pathogenesis of various other PNP.

The presence of the RAGE ligand Nepsilon-Carboxymethyllysine (CML), the receptor itself and NF-kappaBp65 was studied in sural nerve biopsies of patients with alcohol-associated PNP (n=5), PNP owing to vitamin B12 deficiency (n=5), chronic inflammatory demyelinating PNP (CIDP, n=10), Charcot-Marie-Tooth disease (CMT) I or II (n= 10), PNP caused by monoclonal gammopathy of unknown significance (MGUS) (n=5), idiopathic PNP (n=10) and five normal controls by immunohistochemistry. Biopsies of either ten patients with diabetic and vasculitic PNP served as positive controls.

CML, RAGE and NF-kappaBp65 were found in co-localization in epineurial vessels in PNP owing to vitamin B12 deficiency, diabetes and vasculitis and in the perineurium in diabetic PNP, vasculitic PNP and in some cases in CIDP and vitamin B12 deficiency. Only diabetic subjects demonstrated co-expression of the three antigens in endoneurial vessels. Increased CML, RAGE and NF-kappaBp65 expression was detected in endoneurial and epineurial mononuclear cells in CIDP and in vasculitic PNP. Additionally, RAGE expression in Schwann cells was significantly increased in diabetic PNP.

These data suggest that activation of the RAGE pathway might contribute to the pathogenesis of CIDP, PNP owing to vitamin B12 deficiency, diabetes and vasculitis, whereas it does not seem to be involved in the pathogenesis of PNP owing to alcohol, MGUS, CMT I or II and idiopathic PNP.