A preliminary examination of short-term tacrolimus treatment for a CRISPR/Cas9-generated rat model with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a X-linked progressive genetic muscle disorder. A clinical report showed significant improvements of motor function in patients with dystrophinopathy who received heart transplantation with immunosuppressant tacrolimus (TCL) treatment. This preliminary animal study aimed to clarify whether TCL administration can suppress muscle inflammation and improve muscle strength in a CRISPR/Cas9-generated DMD rat model. Eleven-week-old male DMD rats were treated with either TCL (0.5 mg/kg, twice daily, p.o.) or vehicle for 14 days. After the medication, forelimb grip strengths were measured and systemic inflammation was analyzed by whole blood counts and splenic flow cytometry (CD45, CD3, CD4, CD8, and CD11b). Histopathological changes in the tibialis anterior, soleus, and extensor digitorum longus muscles were evaluated. No significant differences were observed in body weight or grip strength between the TCL-treated and vehicle groups. Furthermore, TCL treatment did not significantly alter the proportions of splenic T-cell subsets or myeloid cells. Histopathological analysis revealed persistent myofiber necrosis, inflammatory infiltration, and fibrosis in both groups, without significant improvements in the TCL group. These findings indicate that a short-term TCL administration for DMD rats is insufficient to yield functional or pathological improvements. Although this preliminary study did not demonstrate therapeutic efficacy, our results provide a baseline knowledge of immunosuppressant for future investigations to optimize dosage, timing, and intervention duration using animal DMD model.