Ivanovska, I. | bioRxiv Science

bioRxiv2022

Small, fat-filled lipid droplets remain spherical as they indent a nucleus, dilute the lamina, and cause rupture

The nucleus in many cell types is a stiff organelle, and yet fat-filled lipid droplets (FDs) in the cytoplasm can be seen to indent and displace the nucleus. FDs are phase-separated liquids with a poorly understood interfacial tension {gamma} that determines how FDs interact with other organelles. Here, micron-sized FDs remain spherical as they indent both the nucleus and peri-nuclear actomyosin, dilute Lamin-B1 locally independent of Lamin-A,C, and trigger rupture with locally persistent accumulation in the nucleus of cGAS, a cytosolic DNA sensor. FD-nucleus interactions initiate rapid mis-localization of the essential DNA repair factor KU80, and nuclear rupture associates with DNA damage and perturbed cell cycle. Similar results are evident in FD-laden cells after constricted 3D-migration, which is impeded by FDs. Spherical shapes of small FDs are consistent with a high {gamma} that we measure for FDs mechanically isolated from fresh adipose tissue as [~]40_mN/m - which is far higher than other liquid condensates, but typical of oils in water and sufficiently rigid to disrupt cell structures.

cell biology↗

bioRxiv2016

DNA damage in 3D constricted migration or after lamin-A depletion in 2D: shared mechanisms of repair factor mis-localization under nuclear stress

Cells that migrate through small, rigid pores and that have normal levels of the nuclear structure protein lamin-A exhibit an increase in DNA damage, which is also observed with lamin-A depletion in diseases such as cancer and with many lamin-A mutations. Here we show nuclear envelope rupture is a shared feature that increases in standard culture after lamin-A knockdown, which causes nuclear loss of multiple DNA repair factors and increased DNA damage. Some repair factors are merely mis-localized to cytoplasm whereas others are partially depleted unless rescued by lamin-A expression. Compared to standard cultures on rigid glass coverslips, the growth of lamin-A low cells on soft matrix relaxes cytoskeletal stress on the nucleus, suppresses the mis-localization of DNA repair factors, and minimizes DNA damage nearly to wildtype levels. Conversely, constricted migration of the lamin-A low cells causes abnormally high levels of DNA damage, consistent with sustained loss of repair factors. The findings add insight into why monogenic progeroid syndromes that often associate with increased DNA damage and predominantly impact cells in stiff tissues result from mutations only in lamin-A or DNA repair factors.

cell biology↗