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HSD2 in HgCl2-induced nephrotic syndrome in rats
1 The Water and Salt Research Center, University of Aarhus, Aarhus C, Denmark; Research Institute of Medical Sciences, Chonnam National University Medical School, Gwangju, Korea, Republic of
2 The Water and Salt Research Center, University of Aarhus, Aarhus C, Denmark; Institute of Anatomy, University of Aarhus, Aarhus C, Denmark
3 Research Institute of Medical Sciences, Chonnam National University Medical School, Gwangju, Korea, Republic of
4 Department of Anatomy, The Catholic University of Korea, Seoul, Korea, Republic of
5 Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
6 The Water and Salt Research Center, University of Aarhus, Aarhus C, Denmark; Institute of Clinical Medicine, Aarhus University Hospital, Aarhus N, Denmark
* To whom correspondence should be addressed. E-mail: sn{at}ana.au.dk.
Nephrotic syndrome is often accompanied by sodium retention and generalized edema.
We hypothesize that dysregulation of epithelial sodium channel (ENaC) and/or of
sodium (co)transporters may be responsible for the increased sodium retention
associated with HgCl2 induced nephropathy. In addition we examined the hypothesis
that the expression of type 2 11
-hydroxysteroid dehydrogenase (11
HSD2) is reduced
contributing to the enhanced mineralocorticoid activity. Membranous nephropathy was
induced in Brown Norway rats by repeated injections of HgCl2 (1 mg/kg, s.c.), while
the control group received only vehicle. After 13 days of treatment, the abundance of
ENaC subunits, sodium (co)transporters and 11
HSD2 in kidney was examined by
immunoblotting and immunohistochemistry. HgCl2 treatment induced marked
proteinuria, hypoalbuminemia, decreased urinary sodium excretion and ascites. The
protein abundance of
ENaC was increased in the cortex/outer stripe of outer medulla
(OSOM) and inner stripe of the outer medulla (ISOM). The protein abundances of
ENaC and
ENaC were decreased in the cortex/OSOM, while increased in the ISOM.
Immunoperoxidase microscopy demonstrated increased targeting of ENaC subunits to
the apical plasma membrane in the distal convoluted tubule (DCT2), connecting tubule,
and cortical and medullary collecting duct segments. Moreover, 11
HSD2 abundance
was decreased in cortex/OSOM and ISOM. The protein abundances of NHE3, NKCC2
and NCC were decreased. Moreover, the abundance of the
-1 subunit of the Na,K-ATPase
was decreased in the cortex/OSOM and ISOM, but remained unchanged in the
inner medulla. These results suggest that increased apical targeting of ENaC subunits
combined with diminished abundance of 11
HSD2 may contribute to sodium retention associated with HgCl2-induced nephrotic syndrome. The decreased abundance of NHE3,
NKCC2, NCC and Na,K-ATPase may play a compensatory role to promote sodium
excretion.
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