Unregulated renal tubular CD44, hyaluronan, and osteopontin in kdkd mice with interstitial nephritis

Background. The hyaluronan (HA) receptor CD44 is upregulated on parenchymal cells in various inflammatory lesions and could play a role in immune injury. The purpose of the present study was to examine CD44 and its ligands HA and osteopontin (Opn) in a murine model of tubulointerstitial nephritis (TIN). Methods. The expression of CD44 was investigated by immunofluorescence staining and RNA analysis in kidneys of kdkd mice with autoimmune TIN. The CD44 expression was then correlated with the location of its ligands HA and Opn. Results. CD44 is expressed de novo by tubular epithelial cells (TEC) in areas of tubular injury in kdkd kidneys, but not in normal control kidneys. CD44 positive lymphocytes and macrophages also infiltrate the kidney in kdkd mice. RT-PCR and Southern blot analysis demonstrate that transcripts encoding standard and variant forms of CD44 are increased in kdkd mice with TIN. In parallel the CD44 ligand HA also accumulates in kdkd kidneys in the interstitial space, particularly in cortical areas of tubular injury. Furthermore, the expression of the chemotactic protein Opn is enhanced in kdkd kidney, predominantly in areas of tubular injury. Opn mRNA expression also increases markedly in kdkd kidneys compared with normal kidneys, and correlates with disease severity. Conclusions. Prominent CD44 expression by TEC in areas of tubulointerstitial lesions is a characteristic feature of kdkd mice. The de novo appearance of CD44 on injured TEC might allow interaction with the ligands HA and Opn in vivo. Interaction of CD44 with these ligands could participate in the tubulointerstitial inflammatory response in kdkd mice.