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The Role of Triacylglycerols and Lipid Droplets During Apoptosis.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	The Role of Triacylglycerols and Lipid Droplets During Apoptosis./
Author:	Li-Purcell, Nasi.
Description:	1 online resource (158 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 81-05, Section: B.
Contained By:	Dissertations Abstracts International81-05B.
Subject:	Chemistry. -
Online resource:	click for full text (PQDT)
ISBN:	9781088367728

The Role of Triacylglycerols and Lipid Droplets During Apoptosis.
Li-Purcell, Nasi.

The Role of Triacylglycerols and Lipid Droplets During Apoptosis. - 1 online resource (158 pages)

Source: Dissertations Abstracts International, Volume: 81-05, Section: B.

Thesis (Ph.D.)--State University of New York at Buffalo, 2019.

Includes bibliographical references

Apoptosis, a form of programmed cell death, is an essential cellular process. Deregulation of apoptosis is linked to many diseases, including cancer. Many efforts have been dedicated in understanding the molecular mechanism involved in apoptosis. The majority of these efforts focused on proteins; however, the involvement of lipids is still poorly understood. Thus, the aim of this study is to investigate the functional involvement of specific lipid structures and their regulation in apoptosis.As a first step to understand the changes in lipids at the molecular level during apoptosis, we utilized mass-spectrometry (MS)-based untargeted lipidomics and compared the lipidome of control and 5-fluorouracil-treated apoptotic HCT-116 cells. We found that TAGs containing polyunsaturated fatty acyl chains (PUFA-TAGs) show profound accumulation in 5-fluorouracil-treated apoptotic cells. We then induced apoptosis using other apoptotic inducers (i.e. staurosporine and doxorubicin) in HCT-116 cells and another cell line (MCF-7 cells), and we observed PUFA-TAG accumulation in these conditions as well. Our data suggest that PUFA-TAG accumulation can be generalized to apoptosis. To understand the enzymatic regulation behind the lipid changes we observed, we studied the key enzymes involved in TAG biosynthesis. We found that diacylglycerol acyltransferases, the enzymes catalyze the last step of TAG biosynthesis, are activated during apoptosis, suggesting the observed TAG accumulation during apoptosis could be due to the activation of these enzymes.Next, we studied the localization of these accumulated PUFA-TAGs during apoptosis. Our results suggest that these lipids are stored in lipid droplets, endoplasmic reticulum derived structures. Since membrane-residing PUFA-phospholipids can undergo oxidation and form reactive species under increased oxidative stress, we hypothesized that incorporation of PUFAs to PUFA-TAGs and their localization within lipid droplets during apoptosis limits the toxicity during this process. Indeed, exogenous delivery of a polyunsaturated fatty acid resulted in a profound accumulation of PUFA-phospholipids and rendered cells more sensitive to oxidative stress, causing reduced viability. Our data suggest that PUFA-TAG and lipid droplet accumulation could serve to limit lipid-induced cell death during apoptosis.Given that TAG and lipid droplet accumulation could serve to limit cell death in apoptosis, it is important to identify the upstream regulators and pathways that activate their biosynthesis during apoptosis. We investigated the role of p53 activation on TAG accumulation using p53 gene lacking cells, p53-/- and we found that TAG accumulation occurred downstream of p53 activation. Also, we used RNAseq and identified p38 MAPK as a lipid-related pathway that was upregulated during apoptosis by gene enrichment studies. Inhibition of p38 MAPK activity using a small molecule inhibitor decreased the mRNA expression of diacylglycerol acyltransferase1, and caused a depletion in TAG levels during apoptosis. This suggests that p38 MAPK can regulate triacylglycerol biosynthesis through diacylglycerol acyltransferase1 during apoptosis. We also showed that p38 MAPK could affect lipid droplet and PUFA-TAG accumulation during this process through additional downstream targets, including perilipin 2 and cytosolic phospholipase A2delta. Our data show a new mechanism that regulate glycerolipid biosynthesis during apoptosis.Finally, we performed initial investigation on the changes and the biochemical regulations of 1-O-acylcermides, which are derivatives of pro-apoptotic ceramides. We developed a high resolution mass spectrometry (Orbitrap) based method for their analysis and we characterized the cellular 1-O-acylceramide pools. Our results show that endogenous 1-O-acylcermides demonstrate accumulation during apoptosis, potentially through activated DGATs. Future investigations are needed to study their localization and functional role during apoptosis.Overall, our results showed that PUFA-TAGs accumulate during apoptosis with important functional roles. Specifically, sequestering polyunsaturated fatty acids in lipid droplets as TAGs limits lipid peroxide-induced membrane damage under increased oxidative stress during apoptosis. At a broader sense, it is possible that targeting at DGATs or their upstream regulators in cancer cells might represent a new approach to promote cell death during apoptosis.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9781088367728Subjects--Topical Terms:

593913
Chemistry.
Subjects--Index Terms:

ApoptosisIndex Terms--Genre/Form:

554714
Electronic books.

The Role of Triacylglycerols and Lipid Droplets During Apoptosis.
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504 $a Includes bibliographical references
520 $a Apoptosis, a form of programmed cell death, is an essential cellular process. Deregulation of apoptosis is linked to many diseases, including cancer. Many efforts have been dedicated in understanding the molecular mechanism involved in apoptosis. The majority of these efforts focused on proteins; however, the involvement of lipids is still poorly understood. Thus, the aim of this study is to investigate the functional involvement of specific lipid structures and their regulation in apoptosis.As a first step to understand the changes in lipids at the molecular level during apoptosis, we utilized mass-spectrometry (MS)-based untargeted lipidomics and compared the lipidome of control and 5-fluorouracil-treated apoptotic HCT-116 cells. We found that TAGs containing polyunsaturated fatty acyl chains (PUFA-TAGs) show profound accumulation in 5-fluorouracil-treated apoptotic cells. We then induced apoptosis using other apoptotic inducers (i.e. staurosporine and doxorubicin) in HCT-116 cells and another cell line (MCF-7 cells), and we observed PUFA-TAG accumulation in these conditions as well. Our data suggest that PUFA-TAG accumulation can be generalized to apoptosis. To understand the enzymatic regulation behind the lipid changes we observed, we studied the key enzymes involved in TAG biosynthesis. We found that diacylglycerol acyltransferases, the enzymes catalyze the last step of TAG biosynthesis, are activated during apoptosis, suggesting the observed TAG accumulation during apoptosis could be due to the activation of these enzymes.Next, we studied the localization of these accumulated PUFA-TAGs during apoptosis. Our results suggest that these lipids are stored in lipid droplets, endoplasmic reticulum derived structures. Since membrane-residing PUFA-phospholipids can undergo oxidation and form reactive species under increased oxidative stress, we hypothesized that incorporation of PUFAs to PUFA-TAGs and their localization within lipid droplets during apoptosis limits the toxicity during this process. Indeed, exogenous delivery of a polyunsaturated fatty acid resulted in a profound accumulation of PUFA-phospholipids and rendered cells more sensitive to oxidative stress, causing reduced viability. Our data suggest that PUFA-TAG and lipid droplet accumulation could serve to limit lipid-induced cell death during apoptosis.Given that TAG and lipid droplet accumulation could serve to limit cell death in apoptosis, it is important to identify the upstream regulators and pathways that activate their biosynthesis during apoptosis. We investigated the role of p53 activation on TAG accumulation using p53 gene lacking cells, p53-/- and we found that TAG accumulation occurred downstream of p53 activation. Also, we used RNAseq and identified p38 MAPK as a lipid-related pathway that was upregulated during apoptosis by gene enrichment studies. Inhibition of p38 MAPK activity using a small molecule inhibitor decreased the mRNA expression of diacylglycerol acyltransferase1, and caused a depletion in TAG levels during apoptosis. This suggests that p38 MAPK can regulate triacylglycerol biosynthesis through diacylglycerol acyltransferase1 during apoptosis. We also showed that p38 MAPK could affect lipid droplet and PUFA-TAG accumulation during this process through additional downstream targets, including perilipin 2 and cytosolic phospholipase A2delta. Our data show a new mechanism that regulate glycerolipid biosynthesis during apoptosis.Finally, we performed initial investigation on the changes and the biochemical regulations of 1-O-acylcermides, which are derivatives of pro-apoptotic ceramides. We developed a high resolution mass spectrometry (Orbitrap) based method for their analysis and we characterized the cellular 1-O-acylceramide pools. Our results show that endogenous 1-O-acylcermides demonstrate accumulation during apoptosis, potentially through activated DGATs. Future investigations are needed to study their localization and functional role during apoptosis.Overall, our results showed that PUFA-TAGs accumulate during apoptosis with important functional roles. Specifically, sequestering polyunsaturated fatty acids in lipid droplets as TAGs limits lipid peroxide-induced membrane damage under increased oxidative stress during apoptosis. At a broader sense, it is possible that targeting at DGATs or their upstream regulators in cancer cells might represent a new approach to promote cell death during apoptosis.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2024
538 $a Mode of access: World Wide Web
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653 $a Apoptosis
653 $a Lipid structures
653 $a Enzymes
653 $a Endoplasmic reticulum
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690 $a 0485
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710 2 $a State University of New York at Buffalo. $b Chemistry. $3 1474406
773 0 $t Dissertations Abstracts International $g 81-05B.
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