Hepatocytes deficient in nuclear envelope protein lamina-associated polypeptide 1 are an ideal mammalian system to study intranuclear lipid droplets

Abstract

Lipid droplets (LDs) are generally considered to be synthesized in the ER and utilized in the cytoplasm. However, LDs have been observed inside nuclei in some cells, although recent research on nuclear LDs has focused on cultured cell lines. To better understand nuclear LDs that occur in vivo, here we examined LDs in primary hepatocytes from mice following depletion of the nuclear envelope protein lamina-associated polypeptide 1 (LAP1). Microscopic image analysis showed that LAP1-depleted hepatocytes contain frequent nuclear LDs, which differ from cytoplasmic LDs in their associated proteins. We found type 1 nucleoplasmic reticula, which are invaginations of the inner nuclear membrane, are often associated with nuclear LDs in these hepatocytes. Furthermore, in vivo depletion of the nuclear envelope proteins lamin A and C from mouse hepatocytes led to severely abnormal nuclear morphology, but significantly fewer nuclear LDs than were observed upon depletion of LAP1. In addition, we show both high fat diet feeding and fasting of mice increased cytoplasmic lipids in LAP1-depleted hepatocytes, but reduced nuclear LDs, demonstrating a relationship of LD formation with nutritional state. Finally, depletion of microsomal triglyceride transfer protein did not change the frequency of nuclear LDs in LAP1-depleted hepatocytes, suggesting that it is not necessary for the biogenesis of nuclear LDs in these cells. Together, these data show that LAP1-depleted hepatocytes represent an ideal mammalian system to investigate the biogenesis of nuclear LDs and their partitioning between the nucleus and cytoplasm in response to changes in nutritional state and cellular metabolism in vivo.

Nuclear Lipid Droplets Exit to the Cytoplasm: A Novel Mechanism of non-nuclear pore-dependent material exchange

“…The presence of nLDs in various species, including yeast, nematode, mouse, and human cells (Jin et al, 2020;R and P, 2013;Romanauska and Koehler, 2021;Romanauska and Kohler, 2018;Soltysik et al, 2019;Soltysik et al, 2021)，has sparked interest in their origin and functions. Notably, the number of nLDs significantly increases in specific environments, such as in hepatocytes of mice with NAFLD (Ostlund et al, 2022;Shin et al, 2019). Recent studies have shown that the intranuclear membrane synthesizes lipids and serves as the site of nLD generation (Romanauska and Kohler, 2018).…”

“…Moreover, conditions of elevated unsaturated fatty acids or impaired cellular phosphatidylcholine synthesis have led to the emergence of nLDs Kohler, 2018, 2021;Soltysik et al, 2019;Soltysik et al, 2021). The importance of these dynamics is emphasized by observations of abnormal nLD formation in pathological conditions, such as nonalcoholic fatty liver disease (NAFLD), a widespread and often debilitating condition that links disrupted cellular lipid metabolism with nLD formation (Ostlund et al, 2022;Shin et al, 2019).…”