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p38 MAPK signaling in postnatal tendon growth and remodeling.

Schwartz AJ, Sarver DC, Sugg KB, Dzierzawski JT, Gumucio JP, Mendias CL - PLoS ONE (2015)

Bottom Line: By 28 days after overload, tendon mass had increased by 30% compared to non-overloaded samples, and cross-sectional area (CSA) increased by around 50%, with most of the change occurring in the neotendon.Inhibition of p38 MAPK resulted in a profound decrease in IL6 expression, and had a modest effect on the expression of other ECM and cell proliferation genes, but had a negligible impact on overall tendon growth.The combined results from this study provided novel insights into tendon mechanobiology, and suggest that p38 MAPK signaling does not appear to be necessary for tendon growth in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, University of Michigan Medical School, Ann Arbor, Michigan, United States of America; Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

ABSTRACT
Tendon is a dynamic tissue whose structure and function is influenced by mechanical loading, but little is known about the fundamental mechanisms that regulate tendon growth and remodeling in vivo. Data from cultured tendon fibroblasts indicated that the p38 MAPK pathway plays an important role in tendon fibroblast proliferation and collagen synthesis in vitro. To gain greater insight into the mechanisms of tendon growth, and explore the role of p38 MAPK signaling in this process, we tested the hypotheses that inducing plantaris tendon growth through the ablation of the synergist Achilles tendon would result in rapid expansion of a neotendon matrix surrounding the original tendon, and that treatment with the p38 MAPK inhibitor SB203580 would prevent this growth. Rats were treated with vehicle or SB203580, and subjected to synergist ablation by bilateral tenectomy of the Achilles tendon. Changes in histological and biochemical properties of plantaris tendons were analyzed 3, 7, or 28 days after overload, and comparisons were made to non-overloaded animals. By 28 days after overload, tendon mass had increased by 30% compared to non-overloaded samples, and cross-sectional area (CSA) increased by around 50%, with most of the change occurring in the neotendon. The expansion in CSA initially occurred through the synthesis of a hyaluronic acid rich matrix that was progressively replaced with mature collagen. Pericytes were present in areas of active tendon growth, but never in the original tendon ECM. Inhibition of p38 MAPK resulted in a profound decrease in IL6 expression, and had a modest effect on the expression of other ECM and cell proliferation genes, but had a negligible impact on overall tendon growth. The combined results from this study provided novel insights into tendon mechanobiology, and suggest that p38 MAPK signaling does not appear to be necessary for tendon growth in vivo.

No MeSH data available.


Hydroxyproline content of overloaded tendons.Values are mean±SD. N, 4 to 8 tendons for each group. Differences between groups were tested using a two-way ANOVA (α = 0.05) followed by Newman-Keuls post hoc sorting: a, different (P<0.05) from 3D vehicle; b, different (P<0.05) from 3D p38 MAPK inhibitor; c, different (P<0.05) from 7D vehicle; d, different (P<0.05) from 7D p38 MAPK inhibitor; e, different (P<0.05) from 28D vehicle. For reference, horizontal dashed line indicates the hydroxyproline content of plantaris tendons that were not subjected to synergist ablation.
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pone.0120044.g005: Hydroxyproline content of overloaded tendons.Values are mean±SD. N, 4 to 8 tendons for each group. Differences between groups were tested using a two-way ANOVA (α = 0.05) followed by Newman-Keuls post hoc sorting: a, different (P<0.05) from 3D vehicle; b, different (P<0.05) from 3D p38 MAPK inhibitor; c, different (P<0.05) from 7D vehicle; d, different (P<0.05) from 7D p38 MAPK inhibitor; e, different (P<0.05) from 28D vehicle. For reference, horizontal dashed line indicates the hydroxyproline content of plantaris tendons that were not subjected to synergist ablation.

Mentions: After measuring changes in mass and cell density, we next sought to assess changes in collagen content of tendons (Fig. 4A-B). We used picrosirius red staining to identify fibrillar collagens, and similar to what was observed in hematoxylin and eosin stains, p38 MAPK inhibition did not have an effect on gross tendon morphology, so representative images from vehicle treated tendons are shown at each time point. Dense staining of collagen was observed in the original tendon at all time points after overload, and other than differences in cell density, the general features of the collagen was similar to non-overloaded tendons. In the neotendon, however, collagen was present in small pockets 3 days after overload, and gradually increased until nearly the entire neotendon was filled with collagen (Fig. 4B). To perform quantitative measurements of collagen content, we measured levels of the fibrillar collagen marker hydroxyproline. As shown in Fig. 5, the hydroxyproline content of overloaded tendons was approximately 60–200% greater than non-overloaded tendons. With the exception of an increase in hydroxyproline that was observed in the vehicle treated tendons 28 days after overload compared to both 3 day groups and the 7 day control group, there was no effect of time or treatment on hydroxyproline content of tendons (Fig. 5).


p38 MAPK signaling in postnatal tendon growth and remodeling.

Schwartz AJ, Sarver DC, Sugg KB, Dzierzawski JT, Gumucio JP, Mendias CL - PLoS ONE (2015)

Hydroxyproline content of overloaded tendons.Values are mean±SD. N, 4 to 8 tendons for each group. Differences between groups were tested using a two-way ANOVA (α = 0.05) followed by Newman-Keuls post hoc sorting: a, different (P<0.05) from 3D vehicle; b, different (P<0.05) from 3D p38 MAPK inhibitor; c, different (P<0.05) from 7D vehicle; d, different (P<0.05) from 7D p38 MAPK inhibitor; e, different (P<0.05) from 28D vehicle. For reference, horizontal dashed line indicates the hydroxyproline content of plantaris tendons that were not subjected to synergist ablation.
© Copyright Policy
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC4359143&req=5

pone.0120044.g005: Hydroxyproline content of overloaded tendons.Values are mean±SD. N, 4 to 8 tendons for each group. Differences between groups were tested using a two-way ANOVA (α = 0.05) followed by Newman-Keuls post hoc sorting: a, different (P<0.05) from 3D vehicle; b, different (P<0.05) from 3D p38 MAPK inhibitor; c, different (P<0.05) from 7D vehicle; d, different (P<0.05) from 7D p38 MAPK inhibitor; e, different (P<0.05) from 28D vehicle. For reference, horizontal dashed line indicates the hydroxyproline content of plantaris tendons that were not subjected to synergist ablation.
Mentions: After measuring changes in mass and cell density, we next sought to assess changes in collagen content of tendons (Fig. 4A-B). We used picrosirius red staining to identify fibrillar collagens, and similar to what was observed in hematoxylin and eosin stains, p38 MAPK inhibition did not have an effect on gross tendon morphology, so representative images from vehicle treated tendons are shown at each time point. Dense staining of collagen was observed in the original tendon at all time points after overload, and other than differences in cell density, the general features of the collagen was similar to non-overloaded tendons. In the neotendon, however, collagen was present in small pockets 3 days after overload, and gradually increased until nearly the entire neotendon was filled with collagen (Fig. 4B). To perform quantitative measurements of collagen content, we measured levels of the fibrillar collagen marker hydroxyproline. As shown in Fig. 5, the hydroxyproline content of overloaded tendons was approximately 60–200% greater than non-overloaded tendons. With the exception of an increase in hydroxyproline that was observed in the vehicle treated tendons 28 days after overload compared to both 3 day groups and the 7 day control group, there was no effect of time or treatment on hydroxyproline content of tendons (Fig. 5).

Bottom Line: By 28 days after overload, tendon mass had increased by 30% compared to non-overloaded samples, and cross-sectional area (CSA) increased by around 50%, with most of the change occurring in the neotendon.Inhibition of p38 MAPK resulted in a profound decrease in IL6 expression, and had a modest effect on the expression of other ECM and cell proliferation genes, but had a negligible impact on overall tendon growth.The combined results from this study provided novel insights into tendon mechanobiology, and suggest that p38 MAPK signaling does not appear to be necessary for tendon growth in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Orthopaedic Surgery, University of Michigan Medical School, Ann Arbor, Michigan, United States of America; Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

ABSTRACT
Tendon is a dynamic tissue whose structure and function is influenced by mechanical loading, but little is known about the fundamental mechanisms that regulate tendon growth and remodeling in vivo. Data from cultured tendon fibroblasts indicated that the p38 MAPK pathway plays an important role in tendon fibroblast proliferation and collagen synthesis in vitro. To gain greater insight into the mechanisms of tendon growth, and explore the role of p38 MAPK signaling in this process, we tested the hypotheses that inducing plantaris tendon growth through the ablation of the synergist Achilles tendon would result in rapid expansion of a neotendon matrix surrounding the original tendon, and that treatment with the p38 MAPK inhibitor SB203580 would prevent this growth. Rats were treated with vehicle or SB203580, and subjected to synergist ablation by bilateral tenectomy of the Achilles tendon. Changes in histological and biochemical properties of plantaris tendons were analyzed 3, 7, or 28 days after overload, and comparisons were made to non-overloaded animals. By 28 days after overload, tendon mass had increased by 30% compared to non-overloaded samples, and cross-sectional area (CSA) increased by around 50%, with most of the change occurring in the neotendon. The expansion in CSA initially occurred through the synthesis of a hyaluronic acid rich matrix that was progressively replaced with mature collagen. Pericytes were present in areas of active tendon growth, but never in the original tendon ECM. Inhibition of p38 MAPK resulted in a profound decrease in IL6 expression, and had a modest effect on the expression of other ECM and cell proliferation genes, but had a negligible impact on overall tendon growth. The combined results from this study provided novel insights into tendon mechanobiology, and suggest that p38 MAPK signaling does not appear to be necessary for tendon growth in vivo.

No MeSH data available.