Genetic modulation of CD44 expression by intragraft fibroblasts

This study investigated the genetic composition and the functional implication of CD44 species expressed by intragraft fibroblasts. An LEW-to-F344 heart transplant model of chronic rejection was used. Intragraft fibroblasts recovered from the chronically rejecting allografts displayed a 4.5-fold increase in expression of CD44 mRNA when compared with that of the fibroblasts isolated from non-rejecting heart allografts (P < 0.01). The intragraft fibroblasts preferentially expressed CD44 variant isoforms containing v1 exon transcript. Automated nucleotide sequence analysis revealed that the majority (90.12%) of the CD44 v1 isoforms expressed by the rejecting graft fibroblasts were encoded by a mutated CD44 mRNA, which contained two point mutations and a codon deletion in the v1 coding region. Histochemistry demonstrated a massive deposition of extracellular HA in the rejecting heart allografts. Hyaluronic acid (HA) was able to promote in vitro fibroblast adhesion, migration in a CD44-dependent manner, and survival in a serum-free culture condition. The study concludes that up-regulation of CD44 v1 isoforms expressed by the intragraft fibroblasts is associated with an increase in the deposition of extracellular HA, the principal ligand for CD44, in the allografts, suggesting that CD44-HA interaction plays an important role in regulating fibroblast recruitment and growth in allografts developing chronic rejection.