Thymosin β4 Is Not Required for Embryonic Viability or Vascular Development

Rationale: Rossdeutsch et al describe a requirement for thymosin beta 4 (T beta 4) in vascular development. Impaired mural cell migration, differentiation, partial embryonic lethality, and hemorrhaging were observed after analysis of 2 lines of mice, one of which was germline null for T beta 4 and another in which T beta 4 was knocked down by endothelial-specific expression of T beta 4 short hairpin RNA. These data are in direct contrast to our published global and cardiac-specific T beta 4-knockout lines. Thus, the role of T beta 4 needs to be clarified to understand its importance in cardiovascular development. Objective: To investigate and clarify the role of T beta 4 in vascular smooth muscle cell development and vessel stability. Methods and Results: Examination of T beta 4 global knockouts did not demonstrate embryonic hemorrhaging, altered mural cell development, or lethality. Endothelial-specific knockouts also did not exhibit any embryonic lethality and were viable to adulthood. Conclusions: Analysis of our T beta 4 global and cardiac- and endothelial-specific knockout models demonstrated that T beta 4 is dispensable for embryonic viability and vascular development. (Circ Res. 2013;112:e25-e28.)