Defects or deficiencies in nuclear
lamins cause pathology in many cell types, and recent studies have implicated nuclear membrane (NM)
ruptures as a cause of cell toxicity. We previously observed NM
ruptures and progressive cell death in the developing brain of
lamin B1-deficient mouse embryos. We also observed frequent NM
ruptures and DNA damage in nuclear
lamin-deficient fibroblasts. Factors modulating susceptibility to NM
ruptures remain unclear, but we noted low levels of LAP2β, a
chromatin-binding inner NM
protein, in fibroblasts with NM
ruptures. Here, we explored the apparent link between LAP2β and NM
ruptures in nuclear
lamin-deficient neurons and fibroblasts, and we tested whether manipulating LAP2β expression levels would alter NM
rupture frequency. In cortical plate neurons of
lamin B1-deficient embryos, we observed a strong correlation between low LAP2β levels and NM
ruptures. We also found low LAP2β levels and frequent NM
ruptures in neurons of cultured Lmnb1-/- neurospheres. Reducing LAP2β expression in Lmnb1-/- neurons with an
siRNA markedly increased the NM
rupture frequency (without affecting NM
rupture duration), whereas increased LAP2β expression eliminated NM
ruptures and reduced DNA damage. Consistent findings were observed in nuclear
lamin-deficient fibroblasts. Reduced LAP2β expression increased NM
ruptures, whereas increased LAP2β expression virtually abolished NM
ruptures. Increased LAP2β expression nearly abolished NM
ruptures in cells subjected to mechanical stress (an intervention that increases NM
ruptures). Our studies showed that increasing LAP2β expression bolsters NM integrity in nuclear
lamin-deficient cells and markedly reduces NM
rupture frequency.