The BAF A12T mutation associated with premature aging impedes lamin A/C recruitment to sites of nuclear rupture, contributing to nuclear envelope fragility

Abstract

The premature aging disorder Nestor Guillermo Progeria Syndrome (NGPS) is caused by a homozygous Alanine to Threonine mutation at position 12 (A12T) in Barrier-to-Autointegration Factor (BAF). BAF is a small essential protein binding to DNA and to various proteins, thereby playing a role in various cellular processes including transcription regulation and nuclear envelope reformation after mitosis. More recently, BAF was identified as an important factor for nuclear envelope repair upon rupture in interphase. However, the mechanism by which the BAF A12T mutation causes NGPS has remained unclear. To investigate the effects of this mutation on nuclear envelope integrity, we used NGPS-derived patient cells and engineered an isogenic cell line by reversing the BAF A12T homozygous mutation using CRISPR/Cas9. Using a combination of cellular models, structural data and in vitro assays, we identified that the A12T mutation reduces the binding affinity of BAF to lamin A/C by tenfold. As a result, BAF A12T is unable to recruit lamin A/C to sites of nuclear envelope rupture. This leads to the persistence of lamina gaps at sites of ruptures that could contribute to nuclear fragility in NGPS patients. Overexpression of wild-type BAF in a NGPS context rescues lamin A/C recruitment to sites of nuclear rupture, which could explain why the heterozygous A12T mutation does not cause premature ageing.