BACKGROUND
The importance of the neuronal microenvironment has been recently highlighted in gut
region-specific diabetic enteric neuropathy. Regionally distinct thickening of endothelial
basement membrane (BM) of intestinal capillaries supplying the myenteric ganglia coincide
with neuronal damage in different intestinal segments. Accelerated synthesis of matrix
molecules and reduced degradation of matrix components may also contribute to the
imbalance of extracellular matrix dynamics resulting in BM thickening. Among the matrix
degrading proteinases, matrix metalloproteinase 9 (MMP9) and its tissue inhibitor
(TIMP1) are essential in regulating extracellular matrix remodelling.
AIM
To evaluate the intestinal segment-specific effects of diabetes and insulin replacement
on ganglionic BM thickness, MMP9 and TIMP1 expression.
METHODS
Ten weeks after the onset of hyperglycaemia gut segments were taken from the duodenum
and ileum of streptozotocin-induced diabetic, insulin-treated diabetic and sex- and
age-matched control rats. The thickness of BM surrounding myenteric ganglia was measured
by electron microscopic morphometry. Whole-mount preparations of myenteric plexus
were prepared from the different gut regions for MMP9/TIMP1 double-labelling fluorescent
immunohistochemistry. Post-embedding immunogold electron microscopy was applied on
ultrathin sections to evaluate the MMP9 and TIMP1 expression in myenteric ganglia
and their microenvironment from different gut segments and conditions. The MMP9 and
TIMP1 messenger ribonucleic acid (mRNA) level was measured by quantitative polymerase
chain reaction.
RESULTS
Ten weeks after the onset of hyperglycaemia, the ganglionic BM was significantly thickened
in the diabetic ileum, while it remained intact in the duodenum. The immediate insulin
treatment prevented the diabetes-related thickening of the BM surrounding the ileal
myenteric ganglia. Quantification of particle density showed an increasing tendency
for MMP9 and a decreasing tendency for TIMP1 from the proximal to the distal small
intestine under control conditions. In the diabetic ileum, the number of MMP9-indicating
gold particles decreased in myenteric ganglia, endothelial cells of capillaries and
intestinal smooth muscle cells, however, it remained unchanged in all duodenal compartments.
The MMP9/TIMP1 ratio was also decreased in ileal ganglia only. However, a marked segment-specific
induction was revealed in MMP9 and TIMP1 at the mRNA levels.
CONCLUSION
These findings support that the regional decrease in MMP9 expression in myenteric
ganglia and their microenvironment may contribute to extracellular matrix accumulation,
resulting in a region-specific thickening of ganglionic BM.
