Cancer cells possess remarkable abilities to adapt to adverse environmental conditions. Their survival during severe nutrient and oxidative stress depends on their capacity to acquire extracellular lipids and the plasticity of their mechanisms for intracellular lipid synthesis, mobilisation, and recycling. Lipid droplets, cytosolic fat storage organelles present in most cells from yeast to men, are emerging as major regulators of lipid metabolism, trafficking, and signalling in various cells and tissues exposed to stress. Their biogenesis is induced by nutrient and oxidative stress and they accumulate in various cancers. Lipid droplets act as switches that coordinate lipid trafficking and consumption for different purposes in the cell, such as energy production, protection against oxidative stress or membrane biogenesis during rapid cell growth. They sequester toxic lipids, such as fatty acids, cholesterol and ceramides, thereby preventing lipotoxic cell damage and engage in a complex relationship with autophagy. Here, we focus on the emerging mechanisms of stress-induced lipid droplet biogenesis; their roles during nutrient, lipotoxic, and oxidative stress; and the relationship between lipid droplets and autophagy. The recently discovered principles of lipid droplet biology can improve our understanding of the mechanisms that govern cancer cell adaptability and resilience to stress.

Lipid droplets (LDs) are dynamic organelles involved in the management of fatty acid trafficking and metabolism. Recent studies suggest that autophagy and LDs serve complementary roles in the protection against nutrient stress, but the autophagy–LD interplay in cancer cells is not well understood. Here, we examined the relationship between autophagy and LDs in starving HeLa cervical cancer- and MDA-MB-231 breast cancer cells. We found that acute amino acid depletion induces autophagy and promotes diacylglycerol acyltransferase 1 (DGAT1)-mediated LD accumulation in HeLa cells. Inhibition of autophagy via late-stage autophagy inhibitors, or by knocking down autophagy-related 5 (ATG5), reduced LD accumulation in amino acid-starved cancer cells, suggesting that autophagy contributes to LD biogenesis. On the contrary, knockdown of adipose triglyceride lipase (ATGL) increased LD accumulation, suggesting that LD breakdown is mediated by lipolysis under these conditions. Concurrent inhibition of autophagy by silencing ATG5 and of LD biogenesis using DGAT inhibitors was effective in killing starving HeLa cells, whereas cell survival was not compromised by suppression of ATGL-mediated lipolysis. Autophagy-dependent LD biogenesis was also observed in the aggressive triple-negative MDA-MB-231 breast cancer cells deprived of amino acids, but these cells were not sensitized to starvation by the combined inhibition of LD biogenesis and autophagy. These findings reveal that while targeting autophagy-driven and DGAT-mediated LD biogenesis reduces the resilience of HeLa cervical cancer cells to amino acid deprivation, this strategy may not be successful in other cancer cell types.

Pulsed field ablation (PFA) is a promising new treatment for atrial fibrillation (AF), in which pulmonary vein isolation is achieved by irreversible electroporation. Electroporation causes ATP to leak through the permeabilized membrane. ATP is required both for the healing of the cell membrane and for the functioning of ion pumps, such as sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) or Na⁺,K⁺-ATPase (NKA), which play a key role in maintaining continuous contractions of the heart muscle. We investigated the effects of electroporation on the expression of ion pumps and possible correlations with the activation of AMPK, the main energy sensor in cells. H9c2 rat cardiac cells were exposed to either monopolar or bipolar (H-FIRE) pulses. Cells lysed 4 or 24 h after electroporation were used for mRNA and protein expression analyses. Overall, both pulse protocols caused a dose-dependent downregulation of crucial SERCA and NKA isoforms, except for NKAα2 and β3, which were upregulated after 24 h. Monopolar pulses also decreased the phosphorylation of FXYD1, which may cause an inhibition of NKA activity. Both pulse protocols caused an increased AMPK activity, which may decrease both SERCA and NKA activity via calcium/calmodulin-dependent protein kinase. Our results provide important new insights into what happens in surviving cardiomyocytes after they are exposed to PFA.