Necroptosis is a form of regulated cell death that is linked to various human diseases. Distinct membrane-related, thus lipid-dependent, alterations take place during necroptosis. However, little is known about the roles of specific lipids in this process. We used an untargeted LC-MS-based approach to reveal that distinct lipid species are regulated at the molecular level during necroptosis. We found that ceramides and very long chain fatty acids accumulate during this process. Intrigued by the specificity of very long chain fatty acid accumulation, we focused on characterizing their involvement during necroptosis. Biochemical characterizations suggested that activated fatty acid biosynthesis and elongation could be responsible for these accumulations. We further showed that inhibition of fatty acid biosynthesis and depletion of very long chain fatty acids prevented loss of plasma membrane integrity and cell death, strongly suggesting that very long chain fatty acids are functionally involved in necroptosis.

Necroptosis is a form of regulated cell death which results in loss of plasma membrane integrity, release of intracellular contents, and an associated inflammatory response. We previously found that saturated very long chain fatty acids (VLCFAs), which contain ≥20 carbons, accumulate during necroptosis. Here, we show that genetic knockdown of Fatty Acid (FA) Elongase 7 (ELOVL7) reduces accumulation of specific very long chain FAs during necroptosis, resulting in reduced necroptotic cell death and membrane permeabilization. Conversely, increasing the expression of ELOVL7 increases very long chain fatty acids and membrane permeabilization. In vitro, introduction of the VLCFA C24 FA disrupts bilayer integrity in liposomes to a greater extent than a conventional C16 FA. To investigate the microscopic origin of these observations, atomistic Molecular Dynamics (MD) simulations were performed. MD simulations suggest that fatty acids cause clear differences in bilayers based on length and that it is the interdigitation of C24 FA between the individual leaflets that results in disorder in the region and, consequently, membrane disruption. We synthesized clickable VLCFA analogs and observed that many proteins were acylated by VLCFAs during necroptosis. Taken together, these results confirm the active role of VLCFAs during necroptosis and point to multiple potential mechanisms of membrane disruption including direct permeabilization via bilayer disruption and permeabilization by targeting of proteins to cellular membranes by fatty acylation.

No abstract

Although apoptosis has long dominated the spotlight, studies in the past two decades have expanded the repertoire of programmed cell death (PCD). Several forms of non-apoptotic regulated cell death have been identified, with important links to organismal homeostasis and different disease pathologies. Necroptosis, ferroptosis, pyroptosis, and NETosis are the major forms of PCD that have attracted attention. Clear biochemical distinctions differentiate these forms of non-apoptotic PCD at the protein and membrane levels. For instance, pore formation at the plasma membrane is a hallmark of necroptosis and pyroptosis; however, different proteins facilitate pore formation in these processes. Here, we will highlight the role of lipids in different forms of non-apoptotic PCD. In particular, we discuss how lipids can trigger or facilitate the membrane-related changes that result in cell death. We also highlight the use of small molecules in elucidating the mechanisms of non-apoptotic PCD and the potential of lipid biosynthetic pathways to perturb these processes for therapeutic applications as a future avenue of research.

Lipids are a diverse class of biomolecules. The biosynthesis and transport of these molecules are controlled by a considerable number of proteins, which facilitate spatiotemporal regulation of lipids during different fundamental cellular processes. Although lipids are traditionally considered as molecules for energy storage and as structural components of membranes, they are being increasingly recognized for their signaling roles. There is a growing appreciation of lipids' chemical diversity, which approaches that of proteins. In this Perspective, we discuss recent studies that suggest novel functions for distinct lipid species during different cellular processes. In particular, we discuss findings from our laboratory that illuminate the involvement of ceramides, polyunsaturated triacylglycerols, and very long chain fatty acids in different cellular fates. We also highlight recent innovative methods that have enabled the recognition of previously unknown lipid classes and/or roles of these molecules in different biological processes. We envision that advances in lipid identification, visualization, and perturbation will pave the way for broader investigations into this fascinating and influential class of biomolecules.