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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

Muscle architecture and forelimb fat at P8.(A) H&E stained cross sections of wildtype and Fbn2  forearms at P8 (left) and quantitation of percentages of myofibers with central nuclei (right). Quantitation was performed as in 1C and 1D. (B) Toluidine Blue stained cross sections of P8 wildtype and Fbn2  forearms showing accumulation of fat droplets (filled grey spheres) in the  forearm. Bars = 50 μm in (A) and (B). (C) Transmission electron microscopy of fat droplets in P8 Fbn2  forearm muscle. The micrograph was taken from a region containing fat droplets in the block shown in (B). Bar = 10 μm. (D) A comparable series of 3 μm thick sections of wildtype and Fbn2  forearms generated by micro-CT (sections numbered above each panel). Fat and bone appear white; fat is solid white, while bone includes grey space within the circular bone collar. Bars = 1 mm. (E) qPCR anaysis of fat specific markers in Fbn2 heterozygous and  mice compared to wildtype littermates.
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pgen.1005340.g002: Muscle architecture and forelimb fat at P8.(A) H&E stained cross sections of wildtype and Fbn2 forearms at P8 (left) and quantitation of percentages of myofibers with central nuclei (right). Quantitation was performed as in 1C and 1D. (B) Toluidine Blue stained cross sections of P8 wildtype and Fbn2 forearms showing accumulation of fat droplets (filled grey spheres) in the forearm. Bars = 50 μm in (A) and (B). (C) Transmission electron microscopy of fat droplets in P8 Fbn2 forearm muscle. The micrograph was taken from a region containing fat droplets in the block shown in (B). Bar = 10 μm. (D) A comparable series of 3 μm thick sections of wildtype and Fbn2 forearms generated by micro-CT (sections numbered above each panel). Fat and bone appear white; fat is solid white, while bone includes grey space within the circular bone collar. Bars = 1 mm. (E) qPCR anaysis of fat specific markers in Fbn2 heterozygous and mice compared to wildtype littermates.

Mentions: By P8, when contractures were apparently resolved, H&E staining of Fbn2 forearm cross sections showed that muscle architecture had improved. The number of myofibers with centrally located nuclei was no longer significantly greater than in wildtype (Fig 2A, right). However, toluidine blue staining on comparable cross sections showed increased fat deposition in the forearms of Fbn2 mice (Fig 2B). Transmission electron microscopy of fat droplets identified them as white adipocytes—cells containing large lipid droplets with eccentric flattened nuclei (Fig 2C). Skinned and strongly fixed P8 forearms were infiltrated with OsO4 to allow the visualization of both fat and bone as white matter by micro-computed tomography (μCT) (Fig 2D) (16). A series of digital sections demonstrated increased depositions of fat throughout most of the forearm muscle from the wrist to the elbow (Fig 2D). In wildtype forearms, fat was located at the periphery of muscles; in contrast, fat in Fbn2 forearms was found between muscle and bone and infiltrating muscle bundles (Fig 2D). Forearm muscle was studied in detail, in order to associate muscle abnormalities with contractures. However, whole body scans with μCT were performed using P5 littermates. Hindlimb muscles also showed reduced muscle mass and abnormal fat deposition (S1 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)

Muscle architecture and forelimb fat at P8.(A) H&E stained cross sections of wildtype and Fbn2  forearms at P8 (left) and quantitation of percentages of myofibers with central nuclei (right). Quantitation was performed as in 1C and 1D. (B) Toluidine Blue stained cross sections of P8 wildtype and Fbn2  forearms showing accumulation of fat droplets (filled grey spheres) in the  forearm. Bars = 50 μm in (A) and (B). (C) Transmission electron microscopy of fat droplets in P8 Fbn2  forearm muscle. The micrograph was taken from a region containing fat droplets in the block shown in (B). Bar = 10 μm. (D) A comparable series of 3 μm thick sections of wildtype and Fbn2  forearms generated by micro-CT (sections numbered above each panel). Fat and bone appear white; fat is solid white, while bone includes grey space within the circular bone collar. Bars = 1 mm. (E) qPCR anaysis of fat specific markers in Fbn2 heterozygous and  mice compared to wildtype littermates.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4482570&req=5

pgen.1005340.g002: Muscle architecture and forelimb fat at P8.(A) H&E stained cross sections of wildtype and Fbn2 forearms at P8 (left) and quantitation of percentages of myofibers with central nuclei (right). Quantitation was performed as in 1C and 1D. (B) Toluidine Blue stained cross sections of P8 wildtype and Fbn2 forearms showing accumulation of fat droplets (filled grey spheres) in the forearm. Bars = 50 μm in (A) and (B). (C) Transmission electron microscopy of fat droplets in P8 Fbn2 forearm muscle. The micrograph was taken from a region containing fat droplets in the block shown in (B). Bar = 10 μm. (D) A comparable series of 3 μm thick sections of wildtype and Fbn2 forearms generated by micro-CT (sections numbered above each panel). Fat and bone appear white; fat is solid white, while bone includes grey space within the circular bone collar. Bars = 1 mm. (E) qPCR anaysis of fat specific markers in Fbn2 heterozygous and mice compared to wildtype littermates.
Mentions: By P8, when contractures were apparently resolved, H&E staining of Fbn2 forearm cross sections showed that muscle architecture had improved. The number of myofibers with centrally located nuclei was no longer significantly greater than in wildtype (Fig 2A, right). However, toluidine blue staining on comparable cross sections showed increased fat deposition in the forearms of Fbn2 mice (Fig 2B). Transmission electron microscopy of fat droplets identified them as white adipocytes—cells containing large lipid droplets with eccentric flattened nuclei (Fig 2C). Skinned and strongly fixed P8 forearms were infiltrated with OsO4 to allow the visualization of both fat and bone as white matter by micro-computed tomography (μCT) (Fig 2D) (16). A series of digital sections demonstrated increased depositions of fat throughout most of the forearm muscle from the wrist to the elbow (Fig 2D). In wildtype forearms, fat was located at the periphery of muscles; in contrast, fat in Fbn2 forearms was found between muscle and bone and infiltrating muscle bundles (Fig 2D). Forearm muscle was studied in detail, in order to associate muscle abnormalities with contractures. However, whole body scans with μCT were performed using P5 littermates. Hindlimb muscles also showed reduced muscle mass and abnormal fat deposition (S1 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