Wnt and Extraocular Muscle Sparing in Amyotrophic Lateral Sclerosis

• PURPOSE: The extraocular muscles (EOM) and their motor neurons are spared in amyotrophic lateral sclerosis (ALS). In limb muscle axon retraction from the neuromuscular junctions occurs early in the disease. Wnts, a conserved family of secreted signaling molecules, play a critical role in neuromuscular junction formation. This is the first study to examine Wnt signaling for its potential involvement in maintenance of normal morphology in EOMs in ALS.METHODS: EOM and limb muscle axons, neuromuscular junctions, and myofibers from control, aging, and ALS patients and the SOD1G93A mouse model of ALS were quantified for their expression of Wnt1, Wnt3a, Wnt5a, Wnt7a, and beta-catenin.RESULTS: All four Wnt isoforms were expressed in most axon profiles in all human EOMs. Significantly fewer were positive for Wnt1, Wnt3a, and Wnt7a in the human limb muscles. Similar differential patterns in Wnt myofiber expression was also seen, except for Wnt7a, where expression was elevated. In the SOD1G93A mouse, all 4 Wnt isoforms were significantly decreased in the neuromuscular junctions at the terminal stage compared to age matched controls. Beta-catenin was activated in a subset of myofibers in EOM and limb muscle in all patients.CONCLUSIONS: The differences in Wnt expression in EOM and limb muscle, particularly at the neuromuscular junction level, suggest that they play a role in the pathophysiology of ALS. Collectively, the data support a role for Wnt signaling in the preservation of the EOM in ALS and their dysregulation and the subsequent development of pathology in the ALS limb muscles.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Oftalmologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Ophthalmology (hsv//eng)

Nyckelord

extraocular muscles

Wnt

neuromuscular junctions

amyotrophic lateral sclerosis

beta-catenin

skeletal muscle

SOD1(G93A) mice

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