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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.


Expression of interleukin genes.Target gene expression was normalized to the stable housekeeping gene beta 2 microglobulin (B2M), and further normalized to plantaris tendons that were not subjected to synergist ablation. Values are mean±SD, N = 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.
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pone.0120044.g010: Expression of interleukin genes.Target gene expression was normalized to the stable housekeeping gene beta 2 microglobulin (B2M), and further normalized to plantaris tendons that were not subjected to synergist ablation. Values are mean±SD, N = 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.

Mentions: We next looked at the expression of genes involved in inflammation and immune cell recruitment. Interleukin genes were dramatically influenced both by time following overload and the inhibition of p38 MAPK. (Fig. 10). The pro-inflammatory interleukins, IL1b and IL6, were maximally expressed in both groups at 3 days and subsequently decreased in expression at the 7 and 28 day time points. The inhibition of p38 MAPK significantly decreased the expression of IL1b and IL6 at 3 and 7 days following synergist ablation. Expression of the anti-inflammatory interleukin, IL10, was elevated at 3 days in both groups but was significantly decreased with p38 MAPK inhibition, and its expression decreased through 28 days in both groups. Ly6c is a marker of neutrophils, and was downregulated compared to control tendons at all time points and appeared insensitive to p38 MAPK inhibition. While no effect was observed for neutrophil markers, inhibition of p38 MAPK and time following synergist ablation influenced the expression of several genes involved in macrophage recruitment and markers of macrophage phenotype (Fig. 11). CCL2, which plays an important role in macrophage recruitment, and the pan-macrophage marker, F4/80, were both expressed at their greatest at 3 days. Inhibition of p38 MAPK significantly reduced the expression of CCL2 and CD68 at 3 and 7 days, and increased the expression of F4/80 at 3 days. The M1 macrophage marker, CCR7 displayed little effect of time nor treatment, and the expression levels were generally similar to non-overloaded tendons. CD11b and CD68 are other markers of M1 macrophages, and both had the greatest level of expression at 3 days, and steadily decreased by 28 days. CD163 is a marker of M2 macrophages, and had the highest expression 3 days after overload and steadily declined thereafter in both vehicle and p38 MAPK inhibitor treated groups.


p38 MAPK signaling in postnatal tendon growth and remodeling.

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

Expression of interleukin genes.Target gene expression was normalized to the stable housekeeping gene beta 2 microglobulin (B2M), and further normalized to plantaris tendons that were not subjected to synergist ablation. Values are mean±SD, N = 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.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4359143&req=5

pone.0120044.g010: Expression of interleukin genes.Target gene expression was normalized to the stable housekeeping gene beta 2 microglobulin (B2M), and further normalized to plantaris tendons that were not subjected to synergist ablation. Values are mean±SD, N = 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.
Mentions: We next looked at the expression of genes involved in inflammation and immune cell recruitment. Interleukin genes were dramatically influenced both by time following overload and the inhibition of p38 MAPK. (Fig. 10). The pro-inflammatory interleukins, IL1b and IL6, were maximally expressed in both groups at 3 days and subsequently decreased in expression at the 7 and 28 day time points. The inhibition of p38 MAPK significantly decreased the expression of IL1b and IL6 at 3 and 7 days following synergist ablation. Expression of the anti-inflammatory interleukin, IL10, was elevated at 3 days in both groups but was significantly decreased with p38 MAPK inhibition, and its expression decreased through 28 days in both groups. Ly6c is a marker of neutrophils, and was downregulated compared to control tendons at all time points and appeared insensitive to p38 MAPK inhibition. While no effect was observed for neutrophil markers, inhibition of p38 MAPK and time following synergist ablation influenced the expression of several genes involved in macrophage recruitment and markers of macrophage phenotype (Fig. 11). CCL2, which plays an important role in macrophage recruitment, and the pan-macrophage marker, F4/80, were both expressed at their greatest at 3 days. Inhibition of p38 MAPK significantly reduced the expression of CCL2 and CD68 at 3 and 7 days, and increased the expression of F4/80 at 3 days. The M1 macrophage marker, CCR7 displayed little effect of time nor treatment, and the expression levels were generally similar to non-overloaded tendons. CD11b and CD68 are other markers of M1 macrophages, and both had the greatest level of expression at 3 days, and steadily decreased by 28 days. CD163 is a marker of M2 macrophages, and had the highest expression 3 days after overload and steadily declined thereafter in both vehicle and p38 MAPK inhibitor treated groups.

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.