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MeCP2 Affects Skeletal Muscle Growth and Morphology through Non Cell-Autonomous Mechanisms.

Conti V, Gandaglia A, Galli F, Tirone M, Bellini E, Campana L, Kilstrup-Nielsen C, Rovere-Querini P, Brunelli S, Landsberger N - PLoS ONE (2015)

Bottom Line: Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects.Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain.Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.

View Article: PubMed Central - PubMed

Affiliation: Division of Regenerative Medicine, Stem Cells and Gene Therapy, San Raffaele Scientific Institute, Milan, Italy.

ABSTRACT
Rett syndrome (RTT) is an autism spectrum disorder mainly caused by mutations in the X-linked MECP2 gene and affecting roughly 1 out of 10.000 born girls. Symptoms range in severity and include stereotypical movement, lack of spoken language, seizures, ataxia and severe intellectual disability. Notably, muscle tone is generally abnormal in RTT girls and women and the Mecp2- mouse model constitutively reflects this disease feature. We hypothesized that MeCP2 in muscle might physiologically contribute to its development and/or homeostasis, and conversely its defects in RTT might alter the tissue integrity or function. We show here that a disorganized architecture, with hypotrophic fibres and tissue fibrosis, characterizes skeletal muscles retrieved from Mecp2- mice. Alterations of the IGF-1/Akt/mTOR pathway accompany the muscle phenotype. A conditional mouse model selectively depleted of Mecp2 in skeletal muscles is characterized by healthy muscles that are morphologically and molecularly indistinguishable from those of wild-type mice raising the possibility that hypotonia in RTT is mainly, if not exclusively, mediated by non-cell autonomous effects. Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects. Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain. Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.

No MeSH data available.


Related in: MedlinePlus

Mecp2-/y muscles exhibit deregulated protein synthesis signalling pathways.(A) qPCR evaluation of IGF-1 (n = 8) and IGF-R (n = 3) mRNA expression in WT and Mecp2-/y gastrocnemius. All data points were calculated in triplicate, normalized to GAPDH and represented as gene expression relative to WT expression. Significance is calculated with t test (**** P value: <0.0001 for IGF-1; ns, P value: 0.7437 for IGF-R). Data are represented as mean ± s.e.m. (B) ELISA assay quantifying IGF-1 protein levels on WT and Mecp2-/y plasma and triceps (n = 6). All data points were calculated in duplicate. Significance is calculated with t test (*, P value: 0.0313 and **, P value: 0.0096). Data are represented as mean ± s.e.m. (C) Representative WB (left) and summary graph (right) of total rpS6 and phosphorylated rpS6 protein levels in WT and Mecp2-/y triceps lysates (n = 6). GAPDH was included as loading control. Significance is calculated with t test (*, P value: 0.0225; ns, P value: 0.1924). Data are represented as mean ± s.e.m. (D) qPCR evaluation of BDNF mRNA expression in WT and Mecp2-/y Gast. All data points were calculated in triplicate, normalized to GAPDH and represented relative to the WT expression (n = 5). Significance is calculated with t test (*, P value: 0.0425).
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pone.0130183.g002: Mecp2-/y muscles exhibit deregulated protein synthesis signalling pathways.(A) qPCR evaluation of IGF-1 (n = 8) and IGF-R (n = 3) mRNA expression in WT and Mecp2-/y gastrocnemius. All data points were calculated in triplicate, normalized to GAPDH and represented as gene expression relative to WT expression. Significance is calculated with t test (**** P value: <0.0001 for IGF-1; ns, P value: 0.7437 for IGF-R). Data are represented as mean ± s.e.m. (B) ELISA assay quantifying IGF-1 protein levels on WT and Mecp2-/y plasma and triceps (n = 6). All data points were calculated in duplicate. Significance is calculated with t test (*, P value: 0.0313 and **, P value: 0.0096). Data are represented as mean ± s.e.m. (C) Representative WB (left) and summary graph (right) of total rpS6 and phosphorylated rpS6 protein levels in WT and Mecp2-/y triceps lysates (n = 6). GAPDH was included as loading control. Significance is calculated with t test (*, P value: 0.0225; ns, P value: 0.1924). Data are represented as mean ± s.e.m. (D) qPCR evaluation of BDNF mRNA expression in WT and Mecp2-/y Gast. All data points were calculated in triplicate, normalized to GAPDH and represented relative to the WT expression (n = 5). Significance is calculated with t test (*, P value: 0.0425).

Mentions: The deregulation of signaling pathways involved in myofiber maintenance and homeostasis and in the balance between protein synthesis and degradation could underlie muscle hypotrophy. Insulin-like Growth Factor 1 (IGF1) in particular has been suggested as a therapeutic agent for RTT [12–15] and clinical trials are ongoing in patients; further, MeCP2 affects protein synthesis and the AKT/mTOR pathway in brain [16]. Accordingly, we demonstrate that IGF1 mRNA expression is down regulated in Mecp2- muscles retrieved from 6 weeks old mice (Fig 2A, P<0.0001) while the levels of the IGF1-receptor are unaffected (Fig 2A). IGF-1 protein expression is significantly reduced in Mecp2-/y mice, both in the blood and in the muscle (Fig 2B, P = 0.0313, P = 0.0096, respectively). The expression of phosphorylated ribosomal protein S6 (P-rpS6), involved in protein synthesis and down-regulated in brains of MeCP2 defective mice and in human neurons derived from iPS cells [16,17], is also lower in MeCP2 deficient muscles with respect to wild-type controls (Fig 2C).


MeCP2 Affects Skeletal Muscle Growth and Morphology through Non Cell-Autonomous Mechanisms.

Conti V, Gandaglia A, Galli F, Tirone M, Bellini E, Campana L, Kilstrup-Nielsen C, Rovere-Querini P, Brunelli S, Landsberger N - PLoS ONE (2015)

Mecp2-/y muscles exhibit deregulated protein synthesis signalling pathways.(A) qPCR evaluation of IGF-1 (n = 8) and IGF-R (n = 3) mRNA expression in WT and Mecp2-/y gastrocnemius. All data points were calculated in triplicate, normalized to GAPDH and represented as gene expression relative to WT expression. Significance is calculated with t test (**** P value: <0.0001 for IGF-1; ns, P value: 0.7437 for IGF-R). Data are represented as mean ± s.e.m. (B) ELISA assay quantifying IGF-1 protein levels on WT and Mecp2-/y plasma and triceps (n = 6). All data points were calculated in duplicate. Significance is calculated with t test (*, P value: 0.0313 and **, P value: 0.0096). Data are represented as mean ± s.e.m. (C) Representative WB (left) and summary graph (right) of total rpS6 and phosphorylated rpS6 protein levels in WT and Mecp2-/y triceps lysates (n = 6). GAPDH was included as loading control. Significance is calculated with t test (*, P value: 0.0225; ns, P value: 0.1924). Data are represented as mean ± s.e.m. (D) qPCR evaluation of BDNF mRNA expression in WT and Mecp2-/y Gast. All data points were calculated in triplicate, normalized to GAPDH and represented relative to the WT expression (n = 5). Significance is calculated with t test (*, P value: 0.0425).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4476581&req=5

pone.0130183.g002: Mecp2-/y muscles exhibit deregulated protein synthesis signalling pathways.(A) qPCR evaluation of IGF-1 (n = 8) and IGF-R (n = 3) mRNA expression in WT and Mecp2-/y gastrocnemius. All data points were calculated in triplicate, normalized to GAPDH and represented as gene expression relative to WT expression. Significance is calculated with t test (**** P value: <0.0001 for IGF-1; ns, P value: 0.7437 for IGF-R). Data are represented as mean ± s.e.m. (B) ELISA assay quantifying IGF-1 protein levels on WT and Mecp2-/y plasma and triceps (n = 6). All data points were calculated in duplicate. Significance is calculated with t test (*, P value: 0.0313 and **, P value: 0.0096). Data are represented as mean ± s.e.m. (C) Representative WB (left) and summary graph (right) of total rpS6 and phosphorylated rpS6 protein levels in WT and Mecp2-/y triceps lysates (n = 6). GAPDH was included as loading control. Significance is calculated with t test (*, P value: 0.0225; ns, P value: 0.1924). Data are represented as mean ± s.e.m. (D) qPCR evaluation of BDNF mRNA expression in WT and Mecp2-/y Gast. All data points were calculated in triplicate, normalized to GAPDH and represented relative to the WT expression (n = 5). Significance is calculated with t test (*, P value: 0.0425).
Mentions: The deregulation of signaling pathways involved in myofiber maintenance and homeostasis and in the balance between protein synthesis and degradation could underlie muscle hypotrophy. Insulin-like Growth Factor 1 (IGF1) in particular has been suggested as a therapeutic agent for RTT [12–15] and clinical trials are ongoing in patients; further, MeCP2 affects protein synthesis and the AKT/mTOR pathway in brain [16]. Accordingly, we demonstrate that IGF1 mRNA expression is down regulated in Mecp2- muscles retrieved from 6 weeks old mice (Fig 2A, P<0.0001) while the levels of the IGF1-receptor are unaffected (Fig 2A). IGF-1 protein expression is significantly reduced in Mecp2-/y mice, both in the blood and in the muscle (Fig 2B, P = 0.0313, P = 0.0096, respectively). The expression of phosphorylated ribosomal protein S6 (P-rpS6), involved in protein synthesis and down-regulated in brains of MeCP2 defective mice and in human neurons derived from iPS cells [16,17], is also lower in MeCP2 deficient muscles with respect to wild-type controls (Fig 2C).

Bottom Line: Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects.Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain.Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.

View Article: PubMed Central - PubMed

Affiliation: Division of Regenerative Medicine, Stem Cells and Gene Therapy, San Raffaele Scientific Institute, Milan, Italy.

ABSTRACT
Rett syndrome (RTT) is an autism spectrum disorder mainly caused by mutations in the X-linked MECP2 gene and affecting roughly 1 out of 10.000 born girls. Symptoms range in severity and include stereotypical movement, lack of spoken language, seizures, ataxia and severe intellectual disability. Notably, muscle tone is generally abnormal in RTT girls and women and the Mecp2- mouse model constitutively reflects this disease feature. We hypothesized that MeCP2 in muscle might physiologically contribute to its development and/or homeostasis, and conversely its defects in RTT might alter the tissue integrity or function. We show here that a disorganized architecture, with hypotrophic fibres and tissue fibrosis, characterizes skeletal muscles retrieved from Mecp2- mice. Alterations of the IGF-1/Akt/mTOR pathway accompany the muscle phenotype. A conditional mouse model selectively depleted of Mecp2 in skeletal muscles is characterized by healthy muscles that are morphologically and molecularly indistinguishable from those of wild-type mice raising the possibility that hypotonia in RTT is mainly, if not exclusively, mediated by non-cell autonomous effects. Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects. Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain. Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.

No MeSH data available.


Related in: MedlinePlus