Neuronal plasticity in chronic pancreatitis is mediated via the neurturin/GFRα2 axis

The glial cell line-derived neurotrophic factor (GDNF) family member neurturin (NRTN) and its receptor GFR alpha 2 play a deciding role in the normal development of pancreatic parasympathetic innervation. In this study, we aimed at investigating the role of NRTN/GFR alpha 2 axis in pancreatic neuropathy in human chronic pancreatitis (CP). Expression of NRTN/GFR alpha 2 was compared between normal human pancreas (NP) and CP tissues via immunohistochemistry, immunoblotting, and quantitative RT-PCR and correlated to abdominal pain sensation. To elucidate the impact of NRTN in pancreatic neuroplasticity, neuronal phenotype and glial density were quantified via an in vitro neuroplasticity assay in dissociated newborn rat dorsal root ganglia (DRG) cultured 1) in CP tissue extracts depleted from NRTN, 2) in NP, 3) in untreated CP tissue extracts, and 4) CP extracts in which nerve growth factor, glial cell derived-neurotrophic factor, or TGF-beta(1) was depleted. NRTN and GFR alpha 2 were highly upregulated in CP, especially in intrapancreatic nerves and the extracellular matrix. CP tissue demonstrated increased amounts of mature multimeric NRTN and elevated levels of GFR alpha 2. The noticeable neurotrophic effect of CP tissue extracts on DRG neurons was diminished upon blockade of NRTN from these extracts. However, blockade of NRTN from CP extracts did not influence the density of DRG glia cells. In conclusion, the NRTN/GFR alpha 2 axis is activated during the course of CP and represents a major key player in the reactive neural alterations in CP. This is the first study to provide functional evidence for the contribution of neurotrophic factors to neuroplasticity in CP.