Limits...
Abnormal Activation of BMP Signaling Causes Myopathy in Fbn2 Null Mice.

Sengle G, Carlberg V, Tufa SF, Charbonneau NL, Smaldone S, Carlson EJ, Ramirez F, Keene DR, Sakai LY - PLoS Genet. (2015)

Bottom Line: These new findings demonstrate that loss of fibrillin-2 results in phenotypes similar to those found in congenital muscular dystrophies and that FBN2 should be considered as a candidate gene for recessive congenital muscular dystrophy.In contrast to other reports that activated BMP signaling leads to muscle hypertrophy, our findings demonstrate the exquisite sensitivity of BMP signaling to the fibrillin-2 extracellular environment during early postnatal muscle development.New evidence presented here suggests that fibrillin-2 can sequester BMP complexes in a latent state.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, Oregon, United States of America; Shriners Hospital for Children, Portland, Oregon, United States of America.

ABSTRACT
Fibrillins are large extracellular macromolecules that polymerize to form the backbone structure of connective tissue microfibrils. Mutations in the gene for fibrillin-1 cause the Marfan syndrome, while mutations in the gene for fibrillin-2 cause Congenital Contractural Arachnodactyly. Both are autosomal dominant disorders, and both disorders affect musculoskeletal tissues. Here we show that Fbn2 mice (on a 129/Sv background) are born with reduced muscle mass, abnormal muscle histology, and signs of activated BMP signaling in skeletal muscle. A delay in Myosin Heavy Chain 8, a perinatal myosin, was found in Fbn2 forelimb muscle tissue, consistent with the notion that muscle defects underlie forelimb contractures in these mice. In addition, white fat accumulated in the forelimbs during the early postnatal period. Adult Fbn2 mice are already known to demonstrate persistent muscle weakness. Here we measured elevated creatine kinase levels in adult Fbn2 mice, indicating ongoing cycles of muscle injury. On a C57Bl/6 background, Fbn2 mice showed severe defects in musculature, leading to neonatal death from respiratory failure. These new findings demonstrate that loss of fibrillin-2 results in phenotypes similar to those found in congenital muscular dystrophies and that FBN2 should be considered as a candidate gene for recessive congenital muscular dystrophy. Both in vivo and in vitro evidence associated muscle abnormalities and accumulation of white fat in Fbn2 mice with abnormally activated BMP signaling. Genetic rescue of reduced muscle mass and accumulation of white fat in Fbn2 mice was accomplished by deleting a single allele of Bmp7. In contrast to other reports that activated BMP signaling leads to muscle hypertrophy, our findings demonstrate the exquisite sensitivity of BMP signaling to the fibrillin-2 extracellular environment during early postnatal muscle development. New evidence presented here suggests that fibrillin-2 can sequester BMP complexes in a latent state.

No MeSH data available.


Related in: MedlinePlus

Limb organ cultures of heterozygous and Fbn2  forearm muscles.(A) H & E sections of Fbn2  muscle cultured with or without Noggin (left) and quantitation of myofibers with central nuclei (right). (B) H & E sections of control forearms (Fbn2+/-) cultured with or without BMP-7 (left) and quantitation of myofibers with central nuclei (right). Sections from forelimbs were all taken from approximately the same plane in the forelimb. Five different sections from comparable areas in each forelimb were analyzed and counted. Error bars indicate mean ± SD, and asterisks indicate statistically significant differences (p < 0.05) between genotypes. Bars = 50 μm.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4482570&req=5

pgen.1005340.g006: Limb organ cultures of heterozygous and Fbn2 forearm muscles.(A) H & E sections of Fbn2 muscle cultured with or without Noggin (left) and quantitation of myofibers with central nuclei (right). (B) H & E sections of control forearms (Fbn2+/-) cultured with or without BMP-7 (left) and quantitation of myofibers with central nuclei (right). Sections from forelimbs were all taken from approximately the same plane in the forelimb. Five different sections from comparable areas in each forelimb were analyzed and counted. Error bars indicate mean ± SD, and asterisks indicate statistically significant differences (p < 0.05) between genotypes. Bars = 50 μm.

Mentions: To test the hypothesis that activated BMP signaling causes the muscle phenotype observed in Fbn2 forelimbs, we treated and wildtype forelimbs in organ culture with Noggin, a BMP inhibitor. Exogenous Noggin was titrated (200–800 ng/ml), and the number of myofibers with central nuclei was counted. Multiple fields from different H&E stained sections were counted, and the numbers were graphed as percentage of the total number of myofibers. Noggin treatment at 6 nM (200 ng/ml) for 2 days in organ culture was sufficient to significantly improve the muscle architecture, measured as the decrease of myofibers with central nuclei from 42 to 14% (p = 0,004; Fig 6A). In contrast, when control Fbn2+/- forelimbs were either treated with 6 nM (600 ng/ml) exogenous BMP-7 complex or were untreated for 2 days in organ culture, a significant increase of myofibers with central nuclei (from 20% in the untreated forelimb to almost 60% in the treated forelimb, p<0.001) was observed (Fig 6B).


Abnormal Activation of BMP Signaling Causes Myopathy in Fbn2 Null Mice.

Sengle G, Carlberg V, Tufa SF, Charbonneau NL, Smaldone S, Carlson EJ, Ramirez F, Keene DR, Sakai LY - PLoS Genet. (2015)

Limb organ cultures of heterozygous and Fbn2  forearm muscles.(A) H & E sections of Fbn2  muscle cultured with or without Noggin (left) and quantitation of myofibers with central nuclei (right). (B) H & E sections of control forearms (Fbn2+/-) cultured with or without BMP-7 (left) and quantitation of myofibers with central nuclei (right). Sections from forelimbs were all taken from approximately the same plane in the forelimb. Five different sections from comparable areas in each forelimb were analyzed and counted. Error bars indicate mean ± SD, and asterisks indicate statistically significant differences (p < 0.05) between genotypes. Bars = 50 μm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482570&req=5

pgen.1005340.g006: Limb organ cultures of heterozygous and Fbn2 forearm muscles.(A) H & E sections of Fbn2 muscle cultured with or without Noggin (left) and quantitation of myofibers with central nuclei (right). (B) H & E sections of control forearms (Fbn2+/-) cultured with or without BMP-7 (left) and quantitation of myofibers with central nuclei (right). Sections from forelimbs were all taken from approximately the same plane in the forelimb. Five different sections from comparable areas in each forelimb were analyzed and counted. Error bars indicate mean ± SD, and asterisks indicate statistically significant differences (p < 0.05) between genotypes. Bars = 50 μm.
Mentions: To test the hypothesis that activated BMP signaling causes the muscle phenotype observed in Fbn2 forelimbs, we treated and wildtype forelimbs in organ culture with Noggin, a BMP inhibitor. Exogenous Noggin was titrated (200–800 ng/ml), and the number of myofibers with central nuclei was counted. Multiple fields from different H&E stained sections were counted, and the numbers were graphed as percentage of the total number of myofibers. Noggin treatment at 6 nM (200 ng/ml) for 2 days in organ culture was sufficient to significantly improve the muscle architecture, measured as the decrease of myofibers with central nuclei from 42 to 14% (p = 0,004; Fig 6A). In contrast, when control Fbn2+/- forelimbs were either treated with 6 nM (600 ng/ml) exogenous BMP-7 complex or were untreated for 2 days in organ culture, a significant increase of myofibers with central nuclei (from 20% in the untreated forelimb to almost 60% in the treated forelimb, p<0.001) was observed (Fig 6B).

Bottom Line: These new findings demonstrate that loss of fibrillin-2 results in phenotypes similar to those found in congenital muscular dystrophies and that FBN2 should be considered as a candidate gene for recessive congenital muscular dystrophy.In contrast to other reports that activated BMP signaling leads to muscle hypertrophy, our findings demonstrate the exquisite sensitivity of BMP signaling to the fibrillin-2 extracellular environment during early postnatal muscle development.New evidence presented here suggests that fibrillin-2 can sequester BMP complexes in a latent state.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, Oregon, United States of America; Shriners Hospital for Children, Portland, Oregon, United States of America.

ABSTRACT
Fibrillins are large extracellular macromolecules that polymerize to form the backbone structure of connective tissue microfibrils. Mutations in the gene for fibrillin-1 cause the Marfan syndrome, while mutations in the gene for fibrillin-2 cause Congenital Contractural Arachnodactyly. Both are autosomal dominant disorders, and both disorders affect musculoskeletal tissues. Here we show that Fbn2 mice (on a 129/Sv background) are born with reduced muscle mass, abnormal muscle histology, and signs of activated BMP signaling in skeletal muscle. A delay in Myosin Heavy Chain 8, a perinatal myosin, was found in Fbn2 forelimb muscle tissue, consistent with the notion that muscle defects underlie forelimb contractures in these mice. In addition, white fat accumulated in the forelimbs during the early postnatal period. Adult Fbn2 mice are already known to demonstrate persistent muscle weakness. Here we measured elevated creatine kinase levels in adult Fbn2 mice, indicating ongoing cycles of muscle injury. On a C57Bl/6 background, Fbn2 mice showed severe defects in musculature, leading to neonatal death from respiratory failure. These new findings demonstrate that loss of fibrillin-2 results in phenotypes similar to those found in congenital muscular dystrophies and that FBN2 should be considered as a candidate gene for recessive congenital muscular dystrophy. Both in vivo and in vitro evidence associated muscle abnormalities and accumulation of white fat in Fbn2 mice with abnormally activated BMP signaling. Genetic rescue of reduced muscle mass and accumulation of white fat in Fbn2 mice was accomplished by deleting a single allele of Bmp7. In contrast to other reports that activated BMP signaling leads to muscle hypertrophy, our findings demonstrate the exquisite sensitivity of BMP signaling to the fibrillin-2 extracellular environment during early postnatal muscle development. New evidence presented here suggests that fibrillin-2 can sequester BMP complexes in a latent state.

No MeSH data available.


Related in: MedlinePlus