Single-chain human Follicle-stimulating hormone promotes ovarian and testicular growth and improves pregnancy performance in mice.

Follicle-stimulating hormone (FSH) is a central regulator of folliculogenesis and reproductive function. To enhance its stability and pharmacological activity, we designed a single-chain (sc) gonadotropin containing two (LNN) specific N-glycosylation sites (Asn-X-Ser/Thr) in the linker, fusing the two subunits polypeptide chain sequences. This study evaluated the in vivo bioactivity of sc-hFSH LNN compared with the Standard hFSH NIBSC (hFSH NIBSC) reference preparation in ICR mice (an outbred Swiss strain that has been established and maintained in Vietnam). A total of 285 animals (21-day-old) were randomly assigned to three groups: (1) sc-hFSH LNN, (2) hFSH NIBSC, and (3) Control group receiving saline only. For each experimental condition, five animals per group were used. Depending on the experimental design, different concentrations (0.2, 1, 2.5, and 5 µg/mL) were administered. Experiment 1 tested a low-dose regimen, consisting of injecting five times a fifth of the total FSH dose (5 x 0.04 and 5 x 0.2 µg/mL) at 12-hour intervals. Experiment 2 used a single-dose injection (0.2 and 1 µg/mL). The control group received saline injections only. Mice were sacrificed 72 hours after treatment. Ovaries and uteri were collected and compared between the groups. Subsequent experiments were conducted using a single-dose injection protocol in 21-day-old female and male mice. Ovaries, uteri, testes, vas deferens, and blood samples were collected and compared between the groups. The mating experiment was performed in adult mice (8-week-old) with 24 males and 24 females. The results showed that a single-injection regimen produced a more potent stimulation than multiple split doses, and that a nonlinear dose-response was observed, with significant increases in ovarian and testicular weights measured only at 5 µg/mL compared to 1 µg/mL. In adult females, pre-mating treatment with sc-hFSH LNN and hFSH NIBSC resulted in the highest pregnancy rates and largest litter sizes compared to control, suggesting a superior ability to support follicular maturation and ovulation in vivo. These findings show that the engineered sc-hFSH LNN is biologically active, has the potential to improve reproductive outcomes, and may serve as a promising alternative to conventional heterologous FSH in both reproductive biology research and future biopharmaceutical applications.