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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

BMP signaling in wildtype and Fbn2  forearm muscle.(A) Phosphosmad 1/5/8 immunofluorescence signals (green dots) within DAPI blue-stained nuclei of Fbn2  muscle compared to wildtype at P1 and P8. (B)BMP mRNA expression levels in P0 Fbn2 heterozygous and  muscle compared to wildtype. (C) Absolute expression levels of Bmp mRNA in P0 wildtype forearm muscles. N = the number of animals analyzed. Error bars indicate mean ± SD. Bars = 50 μm.
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pgen.1005340.g005: BMP signaling in wildtype and Fbn2 forearm muscle.(A) Phosphosmad 1/5/8 immunofluorescence signals (green dots) within DAPI blue-stained nuclei of Fbn2 muscle compared to wildtype at P1 and P8. (B)BMP mRNA expression levels in P0 Fbn2 heterozygous and muscle compared to wildtype. (C) Absolute expression levels of Bmp mRNA in P0 wildtype forearm muscles. N = the number of animals analyzed. Error bars indicate mean ± SD. Bars = 50 μm.

Mentions: We therefore hypothesized that the increased numbers of muscle cells with centrally located nuclei in Fbn2 forearms were due to a delay in differentiation caused by activation of BMP signaling. To test this hypothesis, we analyzed cross sections of Fbn2 and wildtype forearms by immunofluorescence using antibodies against phospho-Smad (pSmad) 1/5/8 and pSmad 2/3, respective downstream mediators of BMP and TGFβ signaling. At early postnatal time points when contractures are severe, we detected abundant signals for pSmad 1/5/8 in Fbn2 , but not in wildtype, muscles (Fig 5A, upper panel). At P8, when contractures are resolved, pSmad 1/5/8 signals in Fbn2 forearm muscles were no longer detectable. In support of positive pSmad 1/5/8 staining, qPCR results for Id1, a BMP-responsive gene, showed a two-fold increase in P0 Fbn2 forearm extracts compared to wildtype (S5 Fig).


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)

BMP signaling in wildtype and Fbn2  forearm muscle.(A) Phosphosmad 1/5/8 immunofluorescence signals (green dots) within DAPI blue-stained nuclei of Fbn2  muscle compared to wildtype at P1 and P8. (B)BMP mRNA expression levels in P0 Fbn2 heterozygous and  muscle compared to wildtype. (C) Absolute expression levels of Bmp mRNA in P0 wildtype forearm muscles. N = the number of animals analyzed. Error bars indicate mean ± SD. Bars = 50 μm.
© Copyright Policy
Related In: Results  -  Collection

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

pgen.1005340.g005: BMP signaling in wildtype and Fbn2 forearm muscle.(A) Phosphosmad 1/5/8 immunofluorescence signals (green dots) within DAPI blue-stained nuclei of Fbn2 muscle compared to wildtype at P1 and P8. (B)BMP mRNA expression levels in P0 Fbn2 heterozygous and muscle compared to wildtype. (C) Absolute expression levels of Bmp mRNA in P0 wildtype forearm muscles. N = the number of animals analyzed. Error bars indicate mean ± SD. Bars = 50 μm.
Mentions: We therefore hypothesized that the increased numbers of muscle cells with centrally located nuclei in Fbn2 forearms were due to a delay in differentiation caused by activation of BMP signaling. To test this hypothesis, we analyzed cross sections of Fbn2 and wildtype forearms by immunofluorescence using antibodies against phospho-Smad (pSmad) 1/5/8 and pSmad 2/3, respective downstream mediators of BMP and TGFβ signaling. At early postnatal time points when contractures are severe, we detected abundant signals for pSmad 1/5/8 in Fbn2 , but not in wildtype, muscles (Fig 5A, upper panel). At P8, when contractures are resolved, pSmad 1/5/8 signals in Fbn2 forearm muscles were no longer detectable. In support of positive pSmad 1/5/8 staining, qPCR results for Id1, a BMP-responsive gene, showed a two-fold increase in P0 Fbn2 forearm extracts compared to wildtype (S5 Fig).

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