SAT-749 Defining The Role Of Androgens In Hernia Associated Skeletal Muscle Fibrosis

Introduction: Inguinal hernia is a highly prevalent condition occurring in 27% of adult men in their lifetime. The recurrence rate of hernia is 5-20%, resulting in a substantial cost burden in surgical repair procedures. Until recently, the mechanisms leading to the lower abdominal muscle (LAM) weakening characteristic of hernia were unknown. Our group developed the first mouse model of inguinal hernia through expression of the human aromatase enzyme in male mice (Arom(Hum)). Aromatase converts androgens to estrogens, and is expressed in the skeletal muscle in humans, but not mice. We found that locally formed estrogen from aromatase activity in LAM and decreased circulating testosterone levels are associated with muscle atrophy and fibrosis resulting in hernia. However, it is unclear how decreasing androgen levels might affect muscle fibrosis, and defining this potential mechanism could impact hernia treatment. We hypothesized that low androgen levels promote muscle fibroblast proliferation and fibrosis, and that androgen treatment would prevent hernia progression in Arom(Hum) mice. Methods: Arom (Hum) mice (3 weeks old) were treated with high-dose dihydrotestosterone (DHT) via injection for 7.5 weeks with hernia volume continuously recorded (n=5/group). Primary fibroblasts were isolated from LAM from WT and Arom(Hum) mice (n=5/genotype). Cells were treated for 24 hours with increasing doses (0.001, 0.01, 0.1, 1, 5, 10 and 100 nM) of R1881, a synthetic androgen, and compared to untreated cells by western blot. Results: Hernia volume was significantly decreased in Arom(Hum) mice treated with DHT compared to vehicle-treated mice, and volume remained consistently suppressed after DHT treatment (p < 0.005). In both primary fibroblast lines, R1881 treatment increased AR levels in a dose dependent manner, indicating that the treatment was effective. Preliminary data indicated that low doses of R1881 (0.001 and 0.01 nM) increased PCNA levels in LAM WT and LAM Arom(Hum) fibroblasts. Densitometry normalized to GAPDH showed 80% and 60% increases for 0.001 nM and 0.01 nM respectively in LAM WT fibroblasts, and 20% and 30% increases at these doses in LAM Arom(Hum) fibroblasts. Higher doses of R1881 decreased PCNA levels in LAM Arom(Hum) fibroblasts by 40% (10 nM) and 30% (100 nM), whereas a 25% decrease was detected in LAM WT fibroblasts at 100 nM. Conclusion: These data suggest that low androgen doses increase LAM fibroblast proliferation, which possibly contributes to hernia formation. Androgen treatment at higher doses can partially block the progression of hernia in vivo. However, it is unclear whether and how androgen deficiency in combination with excess estrogen affects fibroblast proliferation and hernia formation. Additional research is required to determine if androgen supplementation in sufficient doses is a potential therapeutic for inguinal hernia and other muscle weakness diseases.