Effects of sequential injections of hepatocyte growth factor and insulin-like growth factor-I on adult rabbit extraocular muscle

Effects of myostatin gene knockout on porcine extraocular muscles

Myostatin (MSTN), a negative regulator of skeletal muscle mass, is not well known in extraocular muscles (EOMs). EOMs are specialized skeletal muscles. Hence, in this study, the effect of MSTN on the superior rectus (SR) and superior oblique (SO) of 2-month-old MSTN knockout (MSTN-/-) and wild-type (WT) pigs of the same genotype was investigated. SR (P < 0.01) and SO (P < 0.001) fiber cross-sectional areas of MSTN-/- pigs were significantly larger than those of WT pigs. Compared with WT pigs, MSTN-/- SO displayed a decrease in type I fibers (WT: 27.24%, MSTN-/-: 10.32%, P < 0.001). Type IIb fibers were higher in MSTN-/- pigs than in WT pigs (WT: 30.38%, MSTN-/-: 62.24%, P < 0.001). The trend in SR was the same as that in SO, although the trend in SO was greater than that in SR. The expression of myogenic differentiation factor (MyoD) and myogenic (MyoG) showed a significant increase in MSTN-/- SO (about 2.5-fold and 2-fold, respectively at the gene expression level, about 1.5-fold at the protein level) compared with WT pigs. MSTN plays an important role in the development of EOMs and regulates the muscle fiber type by modulating the gene expression of MyoD and MyoG in pigs.

Eye alignment changes caused by sustained GDNF treatment of an extraocular muscle in infant non-human primates

The ability of sustained treatment of a single extraocular muscle with glial cell line-derived neurotrophic factor (GDNF) to produce a strabismus in infant non-human primates was tested. Six infant non-human primates received a pellet containing GDNF, releasing 2 µg/day for 90 days, on one medial rectus muscle. Eye alignment was assessed up to 6 months. Five of the six animals showed a slow decrease in eye misalignment from the significant exotropia present at birth, ending with approximately 10° of exotropia. Controls became orthotropic. Misalignment averaged 8° three months after treatment ended. After sustained GDNF treatment, few changes were seen in mean myofiber cross-sectional areas compared to age-matched naïve controls. Neuromuscular junction number was unaltered in the medial rectus muscles, but were significantly reduced in the untreated lateral recti. Neuromuscular junctions on slow fibers became multiply innervated after this sustained GDNF treatment. Pitx2-positive cells significantly decreased in treated and contralateral medial rectus muscles. Our study suggests that balanced GDNF signaling plays a role in normal development and maintenance of orthotropia. Sustained GDNF treatment of one medial rectus muscle resulted in a measurable misalignment largely maintained 3 months after treatment ended. Structural changes suggest mechanisms for producing an imbalance in muscle function.

Flavonoids Sophoranone Promotes Differentiation of C2C12 and Extraocular Muscle Satellite Cells

INTRODUCTION

Paralytic strabismus involves a functional loss of extraocular muscles resulting from muscular or neuronal disorders. Currently, only a limited number of drugs are available for functional repair of extraocular muscles. Here, we investigated the effects of a novel drug, flavonoids sophoranone, on the differentiation of extraocular muscles as assessed in bothin vivo and in vitro models.

MATERIALS AND METHODS

The effect of flavonoids sophoranone on C2C12 cells was examinedin vitro as evaluated with use of apoptosis, reactive oxygen species (ROS), and cell viability assays. Then, both in vivo and in vitro effects of this drug were examined on the differentiation of C2C12 and satellite cells within extraocular muscles in rabbits. For these latter experiments, RT-PCR and Western blot assays were used to determine expression levels of markers for myogenic differentiation.

RESULTS

With use of flavonoids sophoranone concentrations ranging from 0 to 10 μM, no effects were observed upon cell apoptosis, ROS, and cell cycle in C2C12 cells. Based on MTT assay results, flavonoids sophoranone was shown to increase C2C12 cell proliferation. Moreover, flavonoids sophoranone promoted the differentiation of C2C12 and satellite cells within extraocular muscles in rabbits, which were verified as based on cell morphology and expression levels of mRNA and protein markers of myogenic differentiation. Finally, flavonoids sophoranone treatment also increased gene expressions of Myh3, Myog, and MCK.

CONCLUSION

The capacity for flavonoids sophoranone to upgrade the differentiation of both C2C12 and satellite cells within extraocular muscles in rabbits at concentrations producing no adverse effects suggest that this drug may provide a safe and effective means to promote repair of damaged extraocular muscles.