A Human-Specific Deletion in Mouse Cmah Increases Disease Severity in the mdx Model of Duchenne Muscular Dystrophy

Abstract

The evolution of humans included introduction of an inactivating deletion in the CMAH gene, which eliminated biosynthesis of N-glycolylneuraminic acid from all human cells. Here we show that this human-specific sialylation change contributes to the marked discrepancy in phenotype between the mdx mouse model for Duchenne muscular dystrophy (DMD) and the human disease. Despite lacking dystrophin protein in almost all muscle cells, mdx mice show slower development, relative to overall lifespan, or reduced severity of a number of clinically relevant disease phenotypes compared to DMD patients. This is especially true for loss of ambulation, cardiac and respiratory muscle weakness, and loss of lifespan, all major phenotypes contributing to DMD morbidity and mortality. All these phenotypes occur at an earlier age or to a greater degree in mdx mice bearing a human-like mutation in the mouse Cmah gene. Altered phenotypes correlate with changes in two mechanisms; reduced strength and expression of the dystrophin-associated glycoprotein complex and increased activation of complement. Activation of complement may be driven by the increased expression of anti-Neu5Gc antibodies in Cmah−/−mdx animals and ultimately by uptake of N-glycolylneuraminic acid, a foreign glycan in humans and Cmah-deficient mice, from dietary sources. Cmah-deficient mdx mice represent a new small animal model for DMD that better approximates the human glycome and its contributions to muscular dystrophy.

Peptide-Based Inhibition of NF-κB Rescues Diaphragm Muscle Contractile Dysfunction in a Murine Model of Duchenne Muscular Dystrophy

“…All contraction experiments were done at 37° C. Although this temperature deviates from previously established guidelines, it better reflects the physiological temperature for in vivo diaphragm contraction, and thus maximizes extrapolation of the data obtained to the physiological in vivo situation. Moreover, this temperature is inline with our own previous studies (2,25,26), and similar/ identical experiments have been done by other laboratories (27)(28)(29), indicating feasibility of bodytemperature experiments. The muscle was then stretched to the length where twitch contractions are optimal, and allowed to rest for 10 min.…”

Fetal Microchimeric Cells in a Fetus-Treats-Its-Mother Paradigm Do Not Contribute to Dystrophin Production in Serially ParousmdxFemales

“…The presence in mdx of a ubiquitous sugar residue, Neu5Gc, the synthesis of which has been lost in human cells, also reduces mdx muscle pathology. The introduction of this human-specific mutation in mdx animals results in a more severe phenotype that emulates better the human disease [42]. It is thus conceivable that the mdx muscle pathology may not be severe enough to facilitate engraftment of FMCs.…”

Altered expression of ganglioside GM3 molecular species and a potential regulatory role during myoblast differentiation

“…Taken together, these past and present findings indicate that the change of sialic acid species from Neu5Ac to Neu5Gc is crucial for myogenic differentiation in mice. Deletion of Cmah in mice increased the severity of muscular dystrophy (44,45), suggesting that this gene is a genetic modifier of muscle homeostasis. Taken together, our results suggest that myoblasts regulate their differentiation by changing the metabolism of sialic acids, ceramide, and, consequently, gangliosides.…”