Background The roles of the neurotrophins NGF (Neurotrophic growth factor) and
BDNF (brain-derived neurotrophic factor) in neuronal growth and development
are already known. Meanwhile, the neurotrophin receptors TrkA (tropomyosin
related kinase A), TrkB, and p75 are important for determining the fate of
cells. In endometriosis, this complex system has not been fully elucidated
yet. The aim of this study was to evaluate the expression and location of
these neurotrophins and their receptors in peritoneal (PE) and deep
infiltrating endometriotic (DIE) tissues and to measure and compare the
density of nerve fibers in the disease subtypes. Methods PE lesions (n = 20)
and DIE lesions (n = 22) were immunostained and analyzed on serial slides with
anti-BDNF, −NGF, −TrkA, −TrkB, −p75,-protein gene product 9.5 (PGP9.5, intact
nerve fibers) and -tyrosine hydroxylase (TH, sympathetic nerve fibers)
antibodies. Result There was an equally high percentage (greater than 75 %) of
BDNF-positive immunostaining cells in both PE and DIE. TrkB (major BDNF
receptor) and p75 showed a higher percentage of immunostaining cells in DIE
compared to in PE in stroma only (p < 0.014, p < 0.027, respectively). Both
gland and stroma of DIE lesions had a lower percentage of NGF-positive
immunostaining cells compared to those in PE lesions (p < 0.01 and p < 0.01,
respectively), but there was no significant reduction in immunostaining of
TrkA in DIE lesions. There was no difference in the mean density of nerve
fibers stained with PGP9.5 between PE (26.27 ± 17.32) and DIE (28.19 ± 33.15,
p = 0.8). When we performed sub-group analysis, the density of nerves was
significantly higher in the bowel DIE (mean 57.33 ± 43.9) than in PE (mean
26.27 ± 17.32, p < 0.01) and non-bowel DIE (mean 14.6. ± 8.6 p < 0.002).
Conclusions While the neurotrophin BDNF is equally present in PE and DIE, its
receptors TrkB and p75 are more highly expressed in DIE and may have a
potential role in the pathophysiology of DIE, especially in promotion of cell
growth. BDNF has a stronger binding affinity than NGF to the p75 receptor,
likely inducing sympathetic nerve axonal pruning in DIE, resulting in the
lower nerve fiber density seen
