This study aimed to investigate time-dependent gene expression
of injured human anterior cruciate ligament (ACL), and to evaluate
the histological changes of the ACL remnant in terms of cellular
Injured human ACL tissues were harvested from 105 patients undergoing
primary ACL reconstruction and divided into four phases based on
the period from injury to surgery. Phase I was < three weeks,
phase II was three to eight weeks, phase III was eight to 20 weeks,
and phase IV was ≥ 21 weeks. Gene expressions of these tissues were
analysed in each phase by quantitative real-time polymerase chain
reaction using selected markers (collagen types 1 and 3, biglycan,
decorin, α-smooth muscle actin, IL-6, TGF-β1, MMP-1, MMP-2 and TIMP-1).
Immunohistochemical staining was also performed using primary antibodies
against CD68, CD55, Stat3 and phosphorylated-Stat3 (P-Stat3).
Expression of IL-6 was mainly seen in phases I, II and III, collagen
type 1 in phase II, MMP-1, 2 in phase III, and decorin, TGF-β1 and α-smooth
muscle actin in phase IV. Histologically, degradation and scar formation
were seen in the ACL remnant after phase III. The numbers of CD55
and P-Stat3 positive cells were elevated from phase II to phase
Elevated cell numbers including P-Stat3 positive cells were not
related to collagens but to MMPs’ expressions.