Regenerative phenotype in mice with a point mutation in transforming growth factor β type I receptor ( TGFBR1 )

Abstract

Regeneration of peripheral differentiated tissue in mammals is rare, and regulators of this process are largely unknown. We carried out a forward genetic screen in mice using N -ethyl- N -nitrosourea mutagenesis to identify genetic mutations that affect regenerative healing in vivo. More than 400 pedigrees were screened for closure of a through-and-through punch wound in the mouse ear. This led to the identification of a single pedigree with a heritable, fast, and regenerative wound-healing phenotype. Within 5 wk after ear-punch, a threefold decrease in the diameter of the wound was observed in the mutant mice compared with the wild-type mice. At 22 wk, new cartilage, hair follicles, and sebaceous glands were observed in the newly generated tissue. This trait was mapped to a point mutation in a receptor for TGF-β, TGFBR1 . Mouse embryonic fibroblasts from the affected mice had increased expression of a subset of TGF-β target genes, suggesting that the mutation caused partial activation of the receptor. Further, bone marrow stromal cells from the mutant mice more readily differentiated to chondrogenic precursors, providing a plausible explanation for the enhanced development of cartilage islands in the regenerated ears. This mutant mouse strain provides a unique model to further explore regeneration in mammals and, in particular, the role of TGFBR1 in chondrogenesis and regenerative wound healing.

The Role of TGFβ Signaling in Wound Epithelialization

“…3) identified a single point mutation in a TGFbR1. 63 This mutation resulted in enhanced TGFb signaling and a super-healer phenotype that epithelialized and healed faster with newly generated tissue rather than fibrosis. 63 In addition, embryonic fibroblasts from these mice had increased expression of a subset of TGFb target genes, confirming that the mutation, indeed, caused activation of the receptor and the TGFb signaling pathway.…”

“…63 This mutation resulted in enhanced TGFb signaling and a super-healer phenotype that epithelialized and healed faster with newly generated tissue rather than fibrosis. 63 In addition, embryonic fibroblasts from these mice had increased expression of a subset of TGFb target genes, confirming that the mutation, indeed, caused activation of the receptor and the TGFb signaling pathway. 63 In contrast to these results, abrogation of TGFb1 signaling in TGFb1/ Rag2 double knockout mice resulted in improved closure of ear holes in comparison to wild-type or Rag2…”

“…60,61 Expansion of work with MRL mice showed alterations in the Smad signaling pathway, which might contribute to the observed regenerative phenotype by reduction of the pro-inflammatory responses and overall enhanced TGFb signaling. 62 A more recent study by Liu J et al 63 further explored the underlying molecular mechanisms of regeneration in mammals by inducing mutations in mice and screening for regenerative wound healing phenotypes in the same ear hole punch model. Prospective genetic screens of obtained regenerative phenotypes (Fig.…”

Transforming Growth Factor Beta Signaling in Cutaneous Wound Healing: Lessons Learned from Animal Studies

“…Intriguingly, a recent study has discovered a regenerative phenotype in mice with a point mutation in ALK5. 69 These mice display accelerated closure of ear punch wounds reminiscent of the perfect wound-healing response observed in ear punch wounds created in MRL/MpJ mice. 70 A preliminary study showed a small but significant acceleration in cutaneous (dorsal skin) wound closure in the ALK5 mutant mice, but the healing architecture and histological appearance did not markedly differ between ALK5 mutant and WT mice.…”

“…70 A preliminary study showed a small but significant acceleration in cutaneous (dorsal skin) wound closure in the ALK5 mutant mice, but the healing architecture and histological appearance did not markedly differ between ALK5 mutant and WT mice. 69 Further studies using these mice in incisional and excisional wound-healing models are needed to fully appreciate their potential for investigating TGF-b signaling dynamics in wound healing.…”