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Fig. 5 a Flow cytometric analysis of the liver nonparenchymal cells. VEGFR2
+
cells that are
CD45
-
, express endothelial-specific VE-cadherin. b Specific expression of VEGFR3 on
VEGFR2
+
VE-cadherin
+
CD45
-
LSECs, with a predominant fraction being CD34
-
Factor-
VIII
+
Prox-1
-
. c Forty-eight hours after partial hepatectomy, E-cadherin
+
P-H3
+
mitotic hepato-
cytes are localized adjacent to VE-cadherin
+
and VEGFR2
+
endothelial cells. Scale bars, 50 lm
(Adapted from [
65
])
deficient, VEGFR2
flox/flox
(VEGFR2
fl/fl
) mice [
68
]. Owing to the endothelial-cell
specific expression of VEGFR2 in the liver, in VEGFR2
fl/fl
mice only liver ECs,
but not non-endothelial cells, will manifest functional defects. As control, we used
mice with heterozygous deletion of the VEGFR2 gene (VEGFR2
fl/+
). Forty-eight
hours after partial hepatectomy, bromodeoxyuridine
+
hepatocyte proliferation
(BrdU
+
HNF4A
+
cell number) was decreased by 67 % in VEGFR2
fl/fl
mice
(Fig.
7
a, b). Despite the patency of the VE-cadherin
+
isolectin
+
perfused vessels at
this early phase, the regeneration of liver mass was attenuated in VEGFR2
fl/fl
mice
(Fig.
7
c). The result demonstrates that in the early phases (PH days 1-3) of liver
regeneration, targeting VEGFR2 primarily impairs the effect of endothelial-
derived angiocrine factors to induce hepatocyte regeneration, but not vascular
perfusion capacity.
However, in VEGFR2
fl/fl
mice at the later stages of liver regeneration (PH days
4-8), proliferative angiogenesis was also defective (Fig.
7
c), interfering with the
assembly of patent VE-cadherin
+
isolectin
+
vasculature (Fig.
7
d, e), thereby
diminishing restoration of the liver mass for at least 28 days. Furthermore, in
VEGFR2
fl/fl
mice, liver function after PH was abnormal, as manifested by elevated
plasma bilirubin levels. To confirm the endothelial-specific VEGFR2 function
in mediating liver regeneration, VEGFR2
loxP/loxP
mice were also crossed with
VE-cadherin-CreER
T2
mice to induce endothelial-selective deletion of VEGFR2.
Both the liver mass and formation of perfused vessels in the VE-cadherin-
CreER
T2
VEGFR2
fl/fl
mice were decreased after PH, which emphasizes the sig-
nificance of VEGFR2 in mediating liver regeneration. In fact, if the VEGF-A/
VEGFR2 pathway supports SEC-driven hepatic regeneration, then VEGF-A
should enhance liver regeneration. We compared the effect of VEGF-A
164
with
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