Nerve growth factor and its high-affinity receptor in chronic pancreatitis

Abstract

Objective: To study the mechanisms that are involved in nerve growth and contribute to pain generation in chronic pancreatitis (CP).

Summary background data: Chronic pancreatitis is a painful disease associated with characteristic nerve changes, including an increase in nerve number and diameter. The mechanisms that influence nerve growth are not known. Nerve growth factor (NGF) and its high-affinity tyrosine kinase receptor A (TrkA) are involved in neural development and survival and growth of central and peripheral nerves.

Methods: Nerve growth factor and TrkA were investigated by Northern blot analysis, in situ hybridization, and immunohistochemical staining in the pancreases of 24 patients with CP, and the findings were correlated with clinical parameters.

Results: By Northern blot analysis, NGF and TrkA mRNA expression were increased in 42% (13.1-fold) and 54% (5.5-fold) of the CP samples (p < 0.01), respectively. In situ hybridization revealed that in CP, enhanced NGF mRNA expression was present in metaplastic ductal cells, in degenerating acinar cells, and in acinar cells dedifferentiating into tubular structures. TrkA mRNA was intensely present in the perineurium. Further, enhanced NGF and TrkA mRNA signals were also present in intrapancreatic ganglia cells in CP samples. Immunohistochemistry confirmed the in situ hybridization findings. Analysis of the molecular findings with clinical parameters revealed a significant relation (p < 0.05) between NGF mRNA levels and pancreatic fibrosis (r = 0.64) and acinar cell damage (r = 0.74) and between TrkA mRNA and pain intensity (r = 0.84).

Conclusion: Activation of the NGF/TrkA pathway occurs in CP. It might influence neural morphologic changes and the pain syndrome in this disorder.

Figure 1. Northern blot analysis of NGF and TrkA mRNA expression in the normal pancreas (first 10 lanes) and in CP tissue samples (latter 12 lanes). In the normal controls, low NGF and TrkA mRNA levels were detectable and were often visible only on the original autoradiographs. In most CP samples, however, higher levels of NGF and TrkA mRNA were present. 7S RNA was used to assess equivalent RNA loading.

Figure 2. In situ hybridization of NGF (A, C, E, G) and TrkA (B, D, F, H) mRNA in the normal pancreas (A, B) and in CP (C through H). In the normal pancreas, NGF mRNA was weakly to moderately present in ductal cells and weakly present in some acinar cells (A). In CP samples, moderate to intense NGF mRNA expression was found in areas with ductal metaplasia (C), in acinar cells dedifferentiating into tubular structures (C), in degenerating acinar cells (E), and in the walls of arteries and veins (G). TrkA mRNA expression was absent in acinar cells and in ductal cells in the normal pancreas (B) and in areas with ductal metaplasia and acinar cells dedifferentiating into tubular structures (D) of CP samples. However, moderate TrkA mRNA expression was found in the perineurium of pancreatic nerves (F, H [arrows]) and moderate to strong expression was found in the wall of arteries (H) and veins in CP samples. (Original magnification: A, ×400; B through H, ×200)

Figure 3. Immunostaining of NGF (A), TrkA (B, C), and PGP9.5 (D) in the normal pancreas. A and B and C and D are consecutive tissue sections. NGF immunoreactivity was present in ductal cells but not in acinar cells (A). TrkA was absent in acinar and ductal cells (B, C) but was moderately present in arteries and veins (B) and in the perineurium of pancreatic nerves (C). The insert in panel C shows weak NGF immunostaining of this pancreatic nerve in a consecutive tissue section. PGP9.5 immunostaining (D) was used to identify all neural tissue. (Original magnification: A through D, ×200; inlay in C, ×400)

Figure 4. Immunostaining of NGF (A, D), TrkA (B, C, E), and PGP9.5 (F) in CP tissue samples. Moderate to intense NGF immunoreactivity was present in areas with ductal metaplasia, in degenerating acinar cells, and in acinar cells dedifferentiating into tubular structures (A). The inlay in panel A shows a magnification of NGF immunostaining in ductal cells. In contrast, areas with metaplastic ductal cells were devoid of TrkA immunoreactivity (B). Strong TrkA immunoreactivity was found in the perineurium of nerves (C, E [arrow]) and in the walls of blood vessels (E). PGP9.5 immunoreactivity (F) was present only in pancreatic nerves (right lower corner inlay shows a magnification of a pancreatic nerve) and was absent in blood vessels (inlay in the upper left corner shows a magnification of an artery and a vein). Panels D through F present a consecutive tissue section showing an enlarged pancreatic nerve surrounded by blood vessels. (Original magnification: A, B, D through F, ×200; C, inlays in A and F, ×400)