CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 6, July 2012
AFRICA
e1
Cardiovascular Topics
p53 negatively regulates the osteogenic differentiation
of vascular smooth muscle cells in mice with chronic
kidney disease
KL LI, J CHEN, ZH LI, J ZHAN, L ZHAO, YN HE
Abstract
Aim:
To investigate the osteogenic differentiation of vascular
smooth muscle cells (VSMCs) in mice with chronic kidney
disease (CKD) and to evaluate the effects of p53 on the osteo-
genic differentiation of the VSMCs.
Methods:
Experimental models of CKD-associated vascular
calcification generated by five-sixth (5/6) nephrectomy (Nx)
and a high-phosphate (HP) diet were used in p53
+
/
+
and
p53–/– mice. Following 5/6 Nx, aortic calcification, mark-
ers of osteogenic differentiation, VSMCs and p53 protein in
aortic tissues were studied.
Results:
Aortic calcification was observed after eight weeks
following 5/6 Nx in mice of both genotypes, and expression
of the markers of osteogenic differentiation in the VSMCs
was increased. These changes were continuously observed up
to 12 weeks after 5/6 Nx, and particularly after 5/6 Nx + HP.
Compared with p53
+
/
+
mice, aortic calcification in p53–/–
mice was more severe (
p
<
0.001). Expression of the mark-
ers of osteogenic differentiation was noticeably increased
(
p
<
0.001), while expression of the marker of VSMCs had
decreased (
p
<
0.001). Statistical analysis demonstrated that
the markers of osteogenic differentiation were negatively
correlated with p53, and the marker of VSMCs was positively
correlated with p53 (
p
<
0.001).
Conclusion:
p53 has the potential to negatively regulate the
osteogenic differentiation of VSMCs in CKD mice.
Keywords:
chronic kidney disease, mouse, osteogenic differen-
tiation, P53, vascular smooth muscle cells
Submitted 1/3/11, accepted 22/11/11
Published online 1/12/11
Cardiovasc J Afr
2012;
23
: e1–e9
DOI: 10.5830/CVJA-2011-069
It is increasingly apparent that individuals with chronic kidney
disease (CKD) are more likely to die of cardiovascular disease
(CVD) than to develop kidney failure,
1,2
and CVD accounts for
approximately 50% of the premature deaths in dialysis patients.
3,4
Vascular calcification is more prevalent and more severe in
patients with stage V CKD (CKD-V),
5
and the extent of vascular
calcification has been identified as an independent risk factor for
cardiovascular death in patients on haemodialysis.
3
Calcification
can be found in atherosclerotic plaques and in the vascular
media, vascular smooth muscle cells (VSMCs) and elastic
laminae of large elastic and medium muscular arteries, as well
as in the cardiac valves.
1,6
Recent evidence indicates that vascular calcification is an
active, cell-mediated process. Osteoblast differentiation core-
binding factor
α
-1 (RUNX2) and several bone-associated
proteins, such as bone morphogenetic protein-2 (BMP-2) and
osterix (Osx), and alkaline phosphatase (ALP) are present in
histological sections of arteries as well as in uraemic serum
obtained from patients with CKD-V. This supports the theory
that VSMCs can dedifferentiate or transform into osteoblast-
like cells. The dedifferentiation of VSMCs via up-regulation
of core-binding factor a1 (Cbfa1) may be the first step in the
process of calcification of the arteries.
5,7,8
In addition, it is likely
that circulating inhibitors of calcification are also important, but
to date, the process is not clearly understood, particularly the
effect of cell cycle regulatory proteins (p53 for example) on the
osteogenic differentiation of VSMCs.
Activation of the tumour suppressor p53 induces cellular
programmes, including cell cycles, to shut down and undergo
apoptosis or senescence, which prevents the accumulation of
genetically altered cells.
9-11
Recent studies have found that p53
plays a critical role in bone organogenesis and homeostasis by
negatively regulating bone development and growth and by
suppressing bone neoplasia. Murine double-minute (Mdm2)-
mediated inhibition of p53 function is a prerequisite for
RUNX2 activation, osteoblast differentiation and proper skeletal
formation.
12
In atherosclerosis, p53 not only arrests growth and
promotes cell senescence and apoptosis, but also protect against
trans-differentiation of bone marrow stromal cells into VSMCs,
protects against apoptosis, and alters the mode of cell death
within the plaque.
In a previous study, we found that vascular calcification was
extensively present in patients with CKD-V on maintenance
haemodialysis, and it was accompanied by decreased expression
of p53 in VSMCs. This result indicates that inhibition of
expression p53 in VSMCs may be involved in the pathogenesis
Department of Nephrology, Research Institute of Surgery,
Daping Hospital, Third Military Medical University,
Chongqing, China
KL LI, MD
ZH LI, MD
J ZHAN, MD
YN HE, MD,
State Key Laboratory of Trauma, Burn and Combined
Injury, Research Institute of Surgery, Daping Hospital, Third
Military Medical University, Chongqing, China
J CHEN, MD
L ZHAO, MD
