Chimeric protein repair of laminin polymerization ameliorates muscular dystrophy phenotype
Karen K. McKee, … , Markus A. Rüegg, Peter D. Yurchenco
Karen K. McKee, … , Markus A. Rüegg, Peter D. Yurchenco
Published February 20, 2017
Citation Information: J Clin Invest. 2017;127(3):1075-1089. https://doi.org/10.1172/JCI90854.
View: Text | PDF
Research Article Muscle biology

Chimeric protein repair of laminin polymerization ameliorates muscular dystrophy phenotype

Abstract

Mutations in laminin α2-subunit (Lmα2, encoded by LAMA2) are linked to approximately 30% of congenital muscular dystrophy cases. Mice with a homozygous mutation in Lama2 (dy2J mice) express a nonpolymerizing form of laminin-211 (Lm211) and are a model for ambulatory-type Lmα2-deficient muscular dystrophy. Here, we developed transgenic dy2J mice with muscle-specific expression of αLNNd, a laminin/nidogen chimeric protein that provides a missing polymerization domain. Muscle-specific expression of αLNNd in dy2J mice resulted in strong amelioration of the dystrophic phenotype, manifested by the prevention of fibrosis and restoration of forelimb grip strength. αLNNd also restored myofiber shape, size, and numbers to control levels in dy2J mice. Laminin immunostaining and quantitation of tissue extractions revealed increased Lm211 expression in αLNNd-transgenic dy2J mice. In cultured myotubes, we determined that αLNNd expression increased myotube surface accumulation of polymerization-deficient recombinant laminins, with retention of collagen IV, reiterating the basement membrane (BM) changes observed in vivo. Laminin LN domain mutations linked to several of the Lmα2-deficient muscular dystrophies are predicted to compromise polymerization. The data herein support the hypothesis that engineered expression of αLNNd can overcome polymerization deficits to increase laminin, stabilize BM structure, and substantially ameliorate muscular dystrophy.

Authors

Karen K. McKee, Stephanie C. Crosson, Sarina Meinen, Judith R. Reinhard, Markus A. Rüegg, Peter D. Yurchenco

×

Figure 8

Model of laminin assembly in normal, dystrophic, and αLNNd-repaired muscle.

Options: View larger image (or click on image) Download as PowerPoint
Model of laminin assembly in normal, dystrophic, and αLNNd-repaired musc...
(A) Normally, Lm211 adhesion (LG domain–mediated) to sarcolemmal αDG and α7β1 integrin is coordinated with its polymerization. Assuming similarity with Schwann cell BM assembly, sulfated glycolipids (SGLs) might contribute to laminin adhesion in muscle as well. The heparan sulfate chains of perlecan and muscle agrin are thought to mediate bonds between laminin and nidogen and the collagen network. (B) In the dy2J (and some cases of human Lmα2) dystrophic state, Lm211 can still adhere to the sarcolemma but has lost its ability to polymerize. Findings of this study suggest that secreted laminin accumulates at reduced levels in the BM because of the loss of binding cooperativity with other architectural and receptor components. (C) In the Tg+dy2J mouse, αLNNd binds to the defective nonpolymerizing Lmα2, thereby enabling self-assembly. Endogenous nidogen-1 competes with αLNNd for binding to laminins, creating a mixture of polymerized and nonpolymerized laminins, the former favored for assembly into stable BM. While Lm411 polymerization is also enabled by αLNNd, the small increase is largely confined to capillaries adjacent to the myofibers in dy2J muscle.