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

Abstract

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 g 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 g 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.

Active microrheology with a single, time-shared laser trap

“…5b), 2) they are ≈ 1µm in diameter to maximize trapping stiffness[53, 19] (Fig. 5c) and, 3) they are sufficiently stiff to be able to indent the desired target [50, 52]. We thus isolated lipid droplet from C. elegans using established procedures[54] and used iodixanol (idx) as index matching media [55] to determine their refractive index.…”

“…Due to the difficulty in introducing microspheres into adult tissues without affecting animal physiology, we first established the use of endogenous lipid droplets as mechanical stress probes. Recent data demonstrates that cellular lipid droplets resist deformation when subjected to forces [50], cause itself nuclear indentations [50,51] and activation of mechanotransduction pathways leading to hepatocyte differentiation [51]. Such droplets are abundant in various C. elegans tissues, including the intestinal epithelium (Fig.…”

Delayed localization of A-type lamins to the rupture sites in Hutchinson–Gilford progeria syndrome

“…Next, to examine the effect of this mutation on recovery from forced NE rupture, single-cell compression by AFM indentation was applied to these cells, and the nuclear reentry of NLS-sfCherry was observed by time-lapse imaging before and after the induction of the rupture (Fig. 1 B) (Ivanovska et al ., 2023). Interestingly, G609G/+ cells showed a significantly slow reentry compared to the WT cells which had a ∼50% recovery from the original fluorescence intensity ∼4 min after the rupture (Fig.…”

Lipid droplets in steatotic liver disease

“…Increased lipid droplet number and size in hepatocytes cause liver anatomical changes, engendering the compression of sinusoidal cells and the reduction of blood flow, ultimately leading to hypoxia and increased portal pressure. Although not yet shown in hepatocytes, recent work also suggests that small lipid droplets (micron-sized) may also indent the nucleus and potentially trigger nuclear rupture [27 ▪▪ ]. Such cellular events are thought to cause a loss of DNA repair factors, increase DNA damage, supress the expression of hepatocyte nuclear factor 4 alpha (HNF4α) and may contribute to the development of a pro-carcinogenic environment [27 ▪▪ ].…”

“…Although not yet shown in hepatocytes, recent work also suggests that small lipid droplets (micron-sized) may also indent the nucleus and potentially trigger nuclear rupture [27 ▪▪ ]. Such cellular events are thought to cause a loss of DNA repair factors, increase DNA damage, supress the expression of hepatocyte nuclear factor 4 alpha (HNF4α) and may contribute to the development of a pro-carcinogenic environment [27 ▪▪ ]. We have attempted to summarize the emerging evidence linking lipid droplet induced mechanical stress to hepatocyte dysfunction and SLD risk (Fig.…”