Figure 2. S100a4 haploinsufficiency promotes regenerative, mechanically superior tendon healing.

(A) S100a4^GFP/+ haploinsufficient and wild type (WT) littermates underwent transection and repair of the FDL tendon, and tendons were harvested at D14 post-surgery. (B) S100a4 mRNA expression was reduced by 50% in S100a4^GFP/+ tendon repairs, relative to WT (n = 3 per group). (C) A substantial reduction in S100a4 protein expression was observed in S100a4^GFP/+ tendon repairs, relative to WT. Tendon ends are outlined in blue and bridging scar tissue outlined in black (n = 3–4 per group). (D–G) At D14, MTP Flexion Angle was significantly increased in S100a4^GFP/+ repairs (D), and Gliding Resistance was significantly decreased in S100a4^GFP/+ repairs (E). Max load at failure was significantly improved in S100a4^GFP/+ repairs (F), while no change in Stiffness was observed between genotypes (G) (n = 7–10 per group). (*) indicates p<0.05, (**) indicates p<0.01 between genotypes, n = 7–10 for (D–G) (un-paired t-test).

Figure 2—figure supplement 1. S100a4 haploinsufficiency does not alter gliding function or mechanical properties of un-injured tendons.

No changes in (A) MTP Flexion Angle, (B) Gliding Resistance, (C) Max load at failure, or (D) Stiffness were observed between WT and S100a4^GFP/+ un-injured contralateral control FDL tendons. n = 11–13, (un-paired t-test).

Figure 2—figure supplement 2. S100a4^GFP/+mice permit tracing of S100a4 haploinsufficient cells.

To determine if S100a4 haploinsufficiency altered the S100a4⁺ population during healing, fluorescent imaging of uninjured and D14 repairs from S100a4^GFP/+ and S100a4^+/+ (WT) mice were analyzed. No GFP expression was observed in S100a4^+/+ WT mice either at baseline or at D14 post-surgery. In contrast, knock-down of S100a4 does not alter the S100a4^GFP+ resident tendon cell population, or the expansion of the S100a4^GFP+ population at D14 post-surgery. Orange insets identify high-power magnification images.