Induction of the inducible cyclooxygenase isoform COX-2 is likely to be an
important mechanism for increased prostaglandin production in renal inflamm
ation. We examined the effect of lipopolysaccharide (LPS) on regional renal
COX-2 expression in the rat. In the inner medulla, LPS injection (4 mg/kg
ip) induced a twofold and 2.5-fold increase in the levels of COX-2 mRNA and
COX-2 protein, respectively. In contrast, COX-2 expression in the renal co
rtex was not significantly altered. COX-2 promoter transgenic mice were cre
ated using the 2.7-kb flanking region of the rat COX-2 gene. In these anima
ls, LPS injection induced reporter gene expression predominately in the inn
er medulla. The LPS receptor CD14, usually regarded as a monocyte/macrophag
e specific marker, was found to be abundantly expressed in the inner medull
a and in dissected inner medullary collecting duct (IMCD) cells, suggesting
that it may mediate medullary COX-2 induction. CD14 was present only at lo
w levels in cortex and cortical segments, including glomeruli. Ln cultured
cells,it was abundant in mouse IMCD (mIMCD-K2) cells and renal medullary in
terstitial cells, but largely undetectable in mesangial cells and M1 cells,
a cell line derived from mouse cortical collecting ducts. In the mIMCD-K2
cell Line, LPS significantly induced COX-2 mRNA expression, with concomitan
t induction of CD14. LPS-stimulated COX-2 expression was reduced by the add
ition of an anti-CD14 monoclonal antibody to the culture medium. These resu
lts demonstrate that LPS selectively stimulates COX-2 expression in the ren
al inner medulla through a CD14-dependent mechanism.