Lymphangiogenesis in renal inflammation and transplantation
Date
06/07/2013Author
Vass, David George
Metadata
Abstract
The lymphatic system plays an important role in both tissue homeostasis and
inflammation. During the surgical procedure there is complete disruption of
lymphatic drainage of the allograft kidney. The time course and nature of
lymphatic reconnection following transplantation is poorly understood. In
addition to the extra-renal lymphangiogenesis required for lymphatic
reconnection, some patients may develop de novo lymphatic vessels within
the renal parenchyma during acute rejection or chronic allograft damage. This
work sought to examine the time course and mechanism of
lymphangiogenesis and the role of macrophages in this process.
Injection of carbon black and Evan’s blue into the rat kidney resulted in rapid
transit to the draining hilar renal lymph node. Surgical disruption of the
lymphatic drainage of the kidney prevented trafficking of carbon black to the
renal lymph node at 24 hours. At day 6 there was macroscopic and
microscopic evidence of carbon black localisation in the renal lymph node
suggesting functional reconnection. Careful histological analysis of hilar renal
tissue indicated that the large lymphatic trunks were replaced by a network of
small proliferating lymphatic vessels.
Assessment of intra-renal lymphangiogenesis was undertaken in 2 distinct
experimental models of renal transplantation. In a murine model of acute
allograft rejection there was no evidence of increased lymphatic vessel
number at day 7. In a collaboration with Sheffield University, tissue from a rat
model of interstitial fibrosis and tubular atrophy was examined. The rat tissue
exhibited a prominent macrophage and T-cell infiltration at 12 months but
there was no difference in the number of perivascular lymphatic vessels. In
contrast, there were numerous lymphatic vessels evident in the interstitium
that were absent in control isograft tissue. Interestingly, the number of
lymphatic vessels correlated with the extent of fibrosis. Analysis of vascular
endothelial cell growth factor-C (VEGF-C) mRNA expression did not show any
increase in allografts.
The model of unilateral ureteric obstruction (UUO) was employed as a model
of rapidly progressive inflammatory fibrosis. UUO was associated with rapid
and prominent interstitial lymphangiogenesis. This was associated with a
marked increase in macrophage and T-lymphocyte infiltration and increased
whole kidney mRNA expression of VEGF-C. The role of macrophages in
lymphangiogenesis was explored by administration of macrophage depleting
liposomal clodronate. No effect upon lymphangiogenesis was found but
liposomal clodronate failed to deplete ED-1 positive macrophages in the
kidney. A macrophage isolation strategy was thus employed using the myeloid
CD11b marker cells and flow cytometric cell sorting and immunomagnetic
bead sorting. Although gene expression studies demonstrated increased ED1
mRNA expression by CD11b enriched cells, no difference in VEGF-C mRNA
expression between CD11b cells obtained from obstructed kidneys versus
cells from sham controls was evident. Lastly, despite extensive efforts,
immunostaining for VEGF-C was unsuccessful.
In summary, lymphangiogenesis can reconstitute the lymphatic drainage of
the kidney and is prominent in both chronic allograft injury and the acutely
obstructed kidney in the rat. Although VEGF-C is the likely driver of
lymphangiogenesis direct evidence of macrophage VEGF-C production was
not found.