Inhibition of ALK5 signaling induces physeal dysplasia in rats
Related Experiment Video
Updated: Jul 16, 2026
A Rat Tibial Growth Plate Injury Model to Characterize Repair Mechanisms and Evaluate Growth Plate Regeneration Strategies
Published on: July 4, 2017
Kendall Frazier1, Roberta Thomas, Marshall Scicchitano
1GlaxoSmithKline-Safety Assessment, King of Prussia, PA 19406, USA. kendall.s.frazier@gsk.com
Abstract:
TGF-beta, and its type 1 (ALK5) receptor, are critical to the pathogenesis of fibrosis. In toxicologic studies of 4 or more days in 10-week-old Sprague-Dawley rats, using an ALK5 inhibitor (GW788388), expansion of hypertrophic and proliferation zones of femoral physes were noted. Subphyseal hyperostosis, chondrocyte hypertrophy/hyperplasia, and increased matrix were present. Physeal zones were laser microdissected from ALK5 inhibitor-treated and control rats sacrificed after 3 days of treatment. Transcripts for TGF-beta1, TGF-beta2, ALK5, IHH, VEGF, BMP-7, IGF-1, bFGF, and PTHrP were amplified by real-time PCR. IGF and IHH increased in all physis zones with treatment, but were most prominent in prehypertrophic zones. TGF-beta2, bFGF and BMP7 expression increased in proliferative, pre-and hypertrophic zones. PTHrP expression was elevated in proliferative zones but decreased in hypertrophic zones. VEGF expression was increased after treatment in pre- and hypertrophic zones. ALK5 expression was elevated in prehypertrophic zones. Zymography demonstrated gelatinolytic activity was reduced after treatment. Apoptotic markers (TUNEL and caspase-3) were decreased in hypertrophic zones. Proliferation assessed by Topoisomerase II and Ki67 was increased in multiple zones. Movat stains demonstrated that proteoglycan deposition was altered. Physeal changes occurred at doses well above those resulting in fibrosis. Interactions of factors is important in producing the physeal dysplasia phenotype.
Insights
An ALK5 inhibitor caused physeal dysplasia in rats, altering growth zones and gene expression. These bone changes occurred at higher doses than those causing fibrosis.
Area of Science:
- Bone biology and toxicology
- Connective tissue disorders
- Pharmacology
Background:
- Transforming growth factor-beta (TGF-beta) and its type 1 receptor (ALK5) are key in fibrosis development.
- Understanding the effects of ALK5 inhibition on skeletal tissues is crucial.
Purpose of the Study:
- To investigate the effects of an ALK5 inhibitor (GW788388) on femoral physeal development in Sprague-Dawley rats.
- To analyze gene expression changes and cellular alterations in response to ALK5 inhibition.
Main Methods:
- Toxicologic studies involving ALK5 inhibitor treatment in rats.
- Laser microdissection of physeal zones followed by real-time PCR for gene expression analysis.
- Zymography, TUNEL, caspase-3, Topoisomerase II, Ki67 staining, and Movat stains for cellular and matrix analysis.
Main Results:
- ALK5 inhibitor treatment led to femoral physeal expansion, subphyseal hyperostosis, and altered chondrocyte and matrix characteristics.
- Significant changes in gene expression, including increased IGF-1 and IHH in prehypertrophic zones, and altered TGF-beta2, bFGF, BMP7, PTHrP, and VEGF expression across zones.
- Reduced gelatinolytic activity, decreased apoptosis, increased proliferation, and altered proteoglycan deposition were observed.
- Physeal dysplasia occurred at doses exceeding those causing fibrosis.
Conclusions:
- ALK5 inhibition can induce a distinct physeal dysplasia phenotype in rats, separate from fibrotic effects.
- The observed skeletal changes are linked to alterations in growth factor signaling pathways (IGF, IHH, TGF-beta) and matrix remodeling.
- Interactions between various factors are critical in manifesting the physeal dysplasia phenotype.
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