Gaussian curvature dilutes the nuclear lamina, favoring nuclear rupture, especially at high strain rate

Abstract

Nuclear rupture has long been associated with deficits or defects in lamins, with recent results also indicating a role for actomyosin stress, but key physical determinants of rupture remain unclear. Here, lamin-B stably interacts with the nuclear membrane at sites of low Gaussian curvature yet dilutes at high-curvature to favor rupture, whereas lamin-A depletes similarly but only at high strain-rates. Live cell imaging of lamin-B1 gene-edited cancer cells is complemented by fixed-cell imaging of ruptured nuclei in: iPS-derived cells from progeria patients, cells within beating chick embryo hearts, and cancer cells that develop multiple ruptures in migrating through small pores. Dilution and curvature-dependent rupture fit a parsimonious model of a stiff filament that detaches from a curved surface, suggesting an elastic-type response of lamin-B, but rupture is also modestly suppressed by inhibiting myosin-II and by hypotonic stress, which slow the strain rates. Lamin-A dilution and nuclear rupture likelihood indeed increase above a threshold rate of pulling into small pipettes, suggesting a viscoplastic coupling to the envelope for protection against nuclear rupture.

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

“…U2OS osteosarcoma cells are an MSC-derived lineage that have been used to study adipogenic processes (Mohseny et al, 2011), and they express more Lamin A,C than Lamin-B (Pfeifer et al, 2022). Adding high concentrations of monounsaturated Oleic Acid to U2OS cultures produces some FD’s in just a day (Brasaemle and Wolins, 2017) (Mannik et al, 2014); and FD’s of ∼1.5 μm median diameter eventually fill a similar area of cytoplasm as the nucleus ( Fig.1B-i ) and modestly suppress F-actin levels ( Fig.1B-i-inset ).…”

“…FD’s form in various cell types including some cancers and are viewed as potentially damaging (Cruz et al, 2020) – but a cell-type dependence could in particular reflect the ability of small FD’s to be suitably localized to a perinuclear location. Nuclear indentation by physiologically-relevant FD’s generates inward Gaussian curvature, as does AFM probing, whereas lamin-B1 dilution during nuclear rupture in other standard 2D cultures is observed at sites of outward curvature – and often with lamins that are mutated and/or suppressed (Xia et al, 2018) (Earle et al, 2020), (Pfeifer et al, 2022). The fit of our single filament model to the Lamin-B1 dilution results ( Fig.1C-iii ) is a first and anticipates rupture because similar parameters fit well to outward curvature rupture of progeria-derived MSCs in 2D culture (Cho et al, 2018) and of U2OS cells in transwell migration through pores (Pfeifer et al, 2022); the fit also suggests a complementary limit to lamin-A,C accumulation of several-fold, consistent with past results (Cho et al, 2018) but motivating further study.…”

“…Nuclear indentation by physiologically-relevant FD’s generates inward Gaussian curvature, as does AFM probing, whereas lamin-B1 dilution during nuclear rupture in other standard 2D cultures is observed at sites of outward curvature – and often with lamins that are mutated and/or suppressed (Xia et al, 2018) (Earle et al, 2020), (Pfeifer et al, 2022). The fit of our single filament model to the Lamin-B1 dilution results ( Fig.1C-iii ) is a first and anticipates rupture because similar parameters fit well to outward curvature rupture of progeria-derived MSCs in 2D culture (Cho et al, 2018) and of U2OS cells in transwell migration through pores (Pfeifer et al, 2022); the fit also suggests a complementary limit to lamin-A,C accumulation of several-fold, consistent with past results (Cho et al, 2018) but motivating further study. The lamina response to Gaussian curvature nonetheless begins to address a paradox as to why fat tissues, which are soft to the touch, possess high lamin levels – except in cases of lipodystrophy caused by lamin-A mutations or drug perturbations that keep it in a farnesylated form similar to lamin-B1’s.…”

“…As previously described (Xia et al, 2019), (Pfeifer et al, 2022), our parsimonious model considers a single stiff lamin-B1 filament with an in situ length L fil and persistence length 𝓁 p (Turgay et al, 2017). The filament is either attached to or detached from the nuclear membrane; thus the following partition function for the filament is obtained: …”

“…U2OS osteosarcoma cells are an MSC-derived lineage that have been used to study adipogenic processes (Mohseny et al, 2011), and they express more Lamin A,C than Lamin-B (Pfeifer et al, 2022).…”