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Genetic analysis of the role of proteolysis in the activation of latent myostatin.

Lee SJ - PLoS ONE (2008)

Bottom Line: We previously showed that this latent complex can be activated in vitro by cleavage of the propeptide with members of the bone morphogenetic protein-1/tolloid (BMP-1/TLD) family of metalloproteases.Furthermore, I show that a loss-of-function mutation in Tll2, which encodes one member of this protease family, has a small, but significant, effect on muscle mass, implying that its function is likely redundant with those of other family members.These findings provide genetic support for the hypothesis that proteolytic cleavage of the propeptide by BMP-1/TLD proteases plays a critical role in the activation of latent myostatin in vivo and suggest that targeting the activities of these proteases may be an effective therapeutic strategy for enhancing muscle growth in clinical settings of muscle loss and degeneration.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. sjlee@jhmi.edu

ABSTRACT
Myostatin is a secreted protein that normally acts to limit skeletal muscle growth. As a result, there is considerable interest in developing agents capable of blocking myostatin activity, as such agents could have widespread applications for the treatment of muscle degenerative and wasting conditions. Myostatin normally exists in an inactive state in which the mature C-terminal portion of the molecule is bound non-covalently to its N-terminal propeptide. We previously showed that this latent complex can be activated in vitro by cleavage of the propeptide with members of the bone morphogenetic protein-1/tolloid (BMP-1/TLD) family of metalloproteases. Here, I show that mice engineered to carry a germline point mutation rendering the propeptide protease-resistant exhibit increases in muscle mass approaching those seen in mice completely lacking myostatin. Mice homozygous for the point mutation have increased muscling even though their circulating levels of myostatin protein are dramatically increased, consistent with an inability of myostatin to be activated from its latent state. Furthermore, I show that a loss-of-function mutation in Tll2, which encodes one member of this protease family, has a small, but significant, effect on muscle mass, implying that its function is likely redundant with those of other family members. These findings provide genetic support for the hypothesis that proteolytic cleavage of the propeptide by BMP-1/TLD proteases plays a critical role in the activation of latent myostatin in vivo and suggest that targeting the activities of these proteases may be an effective therapeutic strategy for enhancing muscle growth in clinical settings of muscle loss and degeneration.

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Related in: MedlinePlus

Analysis of muscles of mutant mice.(a) Muscle weight increases in MstnD76A/D76A mice. Numbers represent percent increases relative to wild type mice and were calculated from the data shown in Table 1. Muscles analyzed were: pectoralis (red), triceps (gray), quadriceps (blue), and gastrocnemius (green). (b) Distribution of fiber diameters. Gray bars represent muscle fibers from wild type mice, and red bars represent muscle fibers from Mstn−/− and MstnD76A/D76A.
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pone-0001628-g002: Analysis of muscles of mutant mice.(a) Muscle weight increases in MstnD76A/D76A mice. Numbers represent percent increases relative to wild type mice and were calculated from the data shown in Table 1. Muscles analyzed were: pectoralis (red), triceps (gray), quadriceps (blue), and gastrocnemius (green). (b) Distribution of fiber diameters. Gray bars represent muscle fibers from wild type mice, and red bars represent muscle fibers from Mstn−/− and MstnD76A/D76A.

Mentions: As shown in Table 1 and Figure 2a, mice homozygous for the LoxP allele but wild type at aspartate 76 had muscle weights that were comparable to those of wild type mice. In contrast, mice carrying the D76A point mutation exhibited significant increases in muscle mass in all four skeletal muscles that were examined as well as in both males and females. Moreover, the effect of the point mutation was dose-dependent, with mice heterozygous for the mutation exhibiting increases of 14–19% and mice homozygous for the mutation exhibiting increases of 60–99% compared to wild type mice. This overall pattern was qualitatively similar to that observed in mice heterozygous or homozygous for a Mstn allele; however, the effect of the point mutation was slightly reduced in magnitude compared to that of the allele.


Genetic analysis of the role of proteolysis in the activation of latent myostatin.

Lee SJ - PLoS ONE (2008)

Analysis of muscles of mutant mice.(a) Muscle weight increases in MstnD76A/D76A mice. Numbers represent percent increases relative to wild type mice and were calculated from the data shown in Table 1. Muscles analyzed were: pectoralis (red), triceps (gray), quadriceps (blue), and gastrocnemius (green). (b) Distribution of fiber diameters. Gray bars represent muscle fibers from wild type mice, and red bars represent muscle fibers from Mstn−/− and MstnD76A/D76A.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2237902&req=5

pone-0001628-g002: Analysis of muscles of mutant mice.(a) Muscle weight increases in MstnD76A/D76A mice. Numbers represent percent increases relative to wild type mice and were calculated from the data shown in Table 1. Muscles analyzed were: pectoralis (red), triceps (gray), quadriceps (blue), and gastrocnemius (green). (b) Distribution of fiber diameters. Gray bars represent muscle fibers from wild type mice, and red bars represent muscle fibers from Mstn−/− and MstnD76A/D76A.
Mentions: As shown in Table 1 and Figure 2a, mice homozygous for the LoxP allele but wild type at aspartate 76 had muscle weights that were comparable to those of wild type mice. In contrast, mice carrying the D76A point mutation exhibited significant increases in muscle mass in all four skeletal muscles that were examined as well as in both males and females. Moreover, the effect of the point mutation was dose-dependent, with mice heterozygous for the mutation exhibiting increases of 14–19% and mice homozygous for the mutation exhibiting increases of 60–99% compared to wild type mice. This overall pattern was qualitatively similar to that observed in mice heterozygous or homozygous for a Mstn allele; however, the effect of the point mutation was slightly reduced in magnitude compared to that of the allele.

Bottom Line: We previously showed that this latent complex can be activated in vitro by cleavage of the propeptide with members of the bone morphogenetic protein-1/tolloid (BMP-1/TLD) family of metalloproteases.Furthermore, I show that a loss-of-function mutation in Tll2, which encodes one member of this protease family, has a small, but significant, effect on muscle mass, implying that its function is likely redundant with those of other family members.These findings provide genetic support for the hypothesis that proteolytic cleavage of the propeptide by BMP-1/TLD proteases plays a critical role in the activation of latent myostatin in vivo and suggest that targeting the activities of these proteases may be an effective therapeutic strategy for enhancing muscle growth in clinical settings of muscle loss and degeneration.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. sjlee@jhmi.edu

ABSTRACT
Myostatin is a secreted protein that normally acts to limit skeletal muscle growth. As a result, there is considerable interest in developing agents capable of blocking myostatin activity, as such agents could have widespread applications for the treatment of muscle degenerative and wasting conditions. Myostatin normally exists in an inactive state in which the mature C-terminal portion of the molecule is bound non-covalently to its N-terminal propeptide. We previously showed that this latent complex can be activated in vitro by cleavage of the propeptide with members of the bone morphogenetic protein-1/tolloid (BMP-1/TLD) family of metalloproteases. Here, I show that mice engineered to carry a germline point mutation rendering the propeptide protease-resistant exhibit increases in muscle mass approaching those seen in mice completely lacking myostatin. Mice homozygous for the point mutation have increased muscling even though their circulating levels of myostatin protein are dramatically increased, consistent with an inability of myostatin to be activated from its latent state. Furthermore, I show that a loss-of-function mutation in Tll2, which encodes one member of this protease family, has a small, but significant, effect on muscle mass, implying that its function is likely redundant with those of other family members. These findings provide genetic support for the hypothesis that proteolytic cleavage of the propeptide by BMP-1/TLD proteases plays a critical role in the activation of latent myostatin in vivo and suggest that targeting the activities of these proteases may be an effective therapeutic strategy for enhancing muscle growth in clinical settings of muscle loss and degeneration.

Show MeSH
Related in: MedlinePlus