Generation of mice for evaluating endogenous p16Ink4a protein expression

Abstract

The cyclin-dependent kinase inhibitor p16Ink4a plays a central role in cellular senescence in vitro. Although previous studies suggested cellular senescence is integrated in the systemic mechanisms of organismal aging, the localization and the dynamics of p16Ink4a in tissues remain poorly understood, which hinders uncovering the role of p16Ink4a under the in vivo context. One of the reasons is due to the lack of reliable reagents; as we also demonstrate here that commonly used antibodies raised against human p16INK4A barely recognize its murine ortholog. Here we generated a mouse model, in which the endogenous p16Ink4a is HA-tagged at its N-terminus, to explore the protein expression of p16Ink4a at the organismal level. p16Ink4a was induced at the protein level along the course of senescence in primary embryonic fibroblasts derived from the mice, consistently to its transcriptional level. Remarkably, however, p16Ink4a was not detected in the tissues of the mice exposed to pro-senescence conditions including genotoxic stress and activation of oncogenic signaling pathways, indicating that there is only subtle p16Ink4a proteins induced. These results in our mouse model highlight the need for caution in evaluating p16Ink4a protein expression in vivo.