Dynamic label-free imaging of lipid droplets and their link to fatty acid and pyruvate oxidation in mouse eggs

In the presence of high abundance of exogenous fatty acids, cells either store fatty acids in lipid droplets or oxidize them in mitochondria. In this study, we aimed to explore a novel and direct role of mitochondrial fission in lipid homeostasis in HeLa cells. We observed the association between mitochondrial morphology and lipid droplet accumulation in response to high exogenous fatty acids. We inhibited mitochondrial fission by silencing dynamin-related protein 1(DRP1) and observed the shift in fatty acid storage-usage balance. Inhibition of mitochondrial fission resulted in an increase in fatty acid content of lipid droplets and a decrease in mitochondrial fatty acid oxidation. Next, we overexpressed carnitine palmitoyltransferase-1 (CPT1), a key mitochondrial protein in fatty acid oxidation, to further examine the relationship between mitochondrial fatty acid usage and mitochondrial morphology. Mitochondrial fission plays a role in distributing exogenous fatty acids. CPT1A controlled the respiratory rate of mitochondrial fatty acid oxidation but did not cause a shift in the distribution of fatty acids between mitochondria and lipid droplets. Our data reveals a novel function for mitochondrial fission in balancing exogenous fatty acids between usage and storage, assigning a role for mitochondrial dynamics in control of intracellular fuel utilization and partitioning.

Download Full-text

ATGL-mediated triglyceride turnover and the regulation of mitochondrial capacity in skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00598.2014 ◽

2015 ◽

Vol 308 (11) ◽

pp. E960-E970 ◽

Cited By ~ 24

Author(s):

Ruth C. R. Meex ◽

Andrew J. Hoy ◽

Rachael M. Mason ◽

Sheree D. Martin ◽

Sean L. McGee ◽

...

Keyword(s):

Skeletal Muscle ◽

Fatty Acid ◽

Lipid Droplets ◽

Target Genes ◽

Control Point ◽

Hormone Sensitive Lipase ◽

Acid Oxidation ◽

Minor Importance ◽

Transcriptional Responses ◽

Mitochondrial Capacity

Emerging evidence indicates that skeletal muscle lipid droplets are an important control point for intracellular lipid homeostasis and that regulating fatty acid fluxes from lipid droplets might influence mitochondrial capacity. We used pharmacological blockers of the major triglyceride lipases, adipose triglyceride lipase (ATGL) and hormone-sensitive lipase, to show that a large proportion of the fatty acids that are transported into myotubes are trafficked through the intramyocellular triglyceride pool. We next tested whether increasing lipolysis from intramyocellular lipid droplets could activate transcriptional responses to enhance mitochondrial and fatty acid oxidative capacity. ATGL was overexpressed by adenoviral and adenoassociated viral infection in C2C12 myotubes and the tibialis anterior muscle of C57Bl/6 mice, respectively. ATGL overexpression in C2C12 myotubes increased lipolysis, which was associated with increased peroxisome proliferator-activated receptor (PPAR)-∂ activity, transcriptional upregulation of some PPAR∂ target genes, and enhanced mitochondrial capacity. The transcriptional responses were specific to ATGL actions and not a generalized increase in fatty acid flux in the myotubes. Marked ATGL overexpression (20-fold) induced modest molecular changes in the skeletal muscle of mice, but these effects were not sufficient to alter fatty acid oxidation. Together, these data demonstrate the importance of lipid droplets for myocellular fatty acid trafficking and the capacity to modulate mitochondrial capacity by enhancing lipid droplet lipolysis in vitro; however, this adaptive program is of minor importance when superimposing the normal metabolic stresses encountered in free-moving animals.

Download Full-text

Tracking the Formation and Degradation of Fatty-Acid-Accumulated Mitochondria Using Label-Free Chemical Imaging

10.21203/rs.3.rs-119989/v1 ◽

2020 ◽

Author(s):

Chi Zhang ◽

Stephen Boppart

Keyword(s):

Fatty Acid ◽

Structural Features ◽

Chemical Imaging ◽

Live Cells ◽

Label Free ◽

Dynamic Changes ◽

Regulatory Processes ◽

Transport Chain ◽

Anti Stokes ◽

First Time

Abstract The mitochondrion is one of the key organelles for maintaining cellular homeostasis. External environmental stimuli and internal regulatory processes alter the metabolism and functions of mitochondria. To understand these activities of mitochondria, it is critical to probe the key metabolic molecules inside these organelles. In this study, we used label-free chemical imaging modalities including coherent anti-Stokes Raman scattering and multiphoton-excited autofluorescence to study the mitochondrial activities in living cancer cells. We found that hypothermia exposure tends to induce fatty-acid (FA) accumulation in some mitochondria of MIAPaCa-2 cells. Autofluorescence images show that the FA-accumulated mitochondria also have abnormal NADH and FAD metabolism, likely induced by the dysfunction of the electron transport chain. We also found that when the cells were re-warmed to physiological temperature after a period of hypothermia, the FA-accumulated mitochondria changed their structural features, likely caused by the mitophagy process. To the best of our knowledge, this is the first time that FA accumulation in mitochondria was observed in live cells. Our research also demonstrates that multimodal label-free chemical imaging is an attractive tool to discover abnormal functions of mitochondria at the single-organelle level and can be used to quantify the dynamic changes of this organelle under perturbative conditions.

Download Full-text

Characterization of emulsions and lipolysis of dietary lipids in the human stomach

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1994.266.3.g372 ◽

1994 ◽

Vol 266 (3) ◽

pp. G372-G381 ◽

Cited By ~ 20

Author(s):

M. Armand ◽

P. Borel ◽

C. Dubois ◽

M. Senft ◽

J. Peyrot ◽

...

Keyword(s):

Fatty Acid ◽

Lipid Droplets ◽

Present Finding ◽

Droplet Diameter ◽

Human Stomach ◽

Dietary Lipids ◽

Gastric Lipase ◽

A Minor ◽

First Time

Fasting subjects were intragastrically intubated and received a coarsely emulsified test meal. Gastric aspirates were collected after 1, 2, 3, and 4 h. During digestion in the stomach, unemulsified lipids (> or = 100 microns) represented a minor fraction. A significant amount of the large 70- to 100-microns lipid droplets disappeared, and fine 1- to 10-microns droplets were generated. The median lipid droplet diameter significantly decreased (21.9 vs. 52.9 microns) after 1 h and kept intermediate values for longer periods of time. The emulsion surface area was 100-120 m2/l and was basically provided by 1- to 100-microns droplets. Lipolysis catalyzed by gastric lipase primarily occurred within the first hour of digestion (11.9%). Smaller droplets were enriched in triglyceride lipolytic products. The free fatty acid concentrations were in the range of 5.6-8.2 mM over 1-4 h. The present finding demonstrates for the first time that in the human stomach most dietary lipids are present in the form of emulsified droplets, in the range of 20-40 microns, and that gastric lipolysis can help to increase emulsification in the stomach.

Download Full-text

Lipid Droplets Are Novel Sites ofN-Acylethanolamine Inactivation by Fatty Acid Amide Hydrolase-2

Journal of Biological Chemistry ◽

10.1074/jbc.m109.058461 ◽

2009 ◽

Vol 285 (4) ◽

pp. 2796-2806 ◽

Cited By ~ 63

Author(s):

Martin Kaczocha ◽

Sherrye T. Glaser ◽

Janiper Chae ◽

Deborah A. Brown ◽

Dale G. Deutsch

Keyword(s):

Fatty Acid ◽

Lipid Droplets ◽

Fatty Acid Amide Hydrolase ◽

Acid Amide ◽

Amide Hydrolase ◽

Fatty Acid Amide

Download Full-text

Rapid and label-free metamaterial-based biosensor for fatty acid detection with terahertz time-domain spectroscopy

Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy ◽

10.1016/j.saa.2019.117736 ◽

2020 ◽

Vol 228 ◽

pp. 117736

Author(s):

Mingjie Tang ◽

Liangping Xia ◽

Dongshan Wei ◽

Shihan Yan ◽

Mingkun Zhang ◽

...

Keyword(s):

Fatty Acid ◽

Time Domain ◽

Label Free ◽

Terahertz Time Domain Spectroscopy ◽

Time Domain Spectroscopy

Download Full-text

Multiplex coherent anti-Stokes Raman scattering microspectroscopy detection of lipid droplets in cancer cells expressing TrkB

Scientific Reports ◽

10.1038/s41598-020-74021-z ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Tiffany Guerenne-Del Ben ◽

Vincent Couderc ◽

Ludovic Duponchel ◽

Vincent Sol ◽

Philippe Leproux ◽

...

Keyword(s):

Cancer Cells ◽

Lipid Droplets ◽

Live Cells ◽

Label Free ◽

Colorectal Cancer Cell Lines ◽

Invasive Method ◽

Dye Staining ◽

Cytoplasmic Lipid Droplets ◽

Anti Stokes ◽

Cell Fixation

Abstract For many years, scientists have been looking for specific biomarkers associated with cancer cells for diagnosis purposes. These biomarkers mainly consist of proteins located at the cell surface (e.g. the TrkB receptor) whose activation is associated with specific metabolic modifications. Identification of these metabolic changes usually requires cell fixation and specific dye staining. MCARS microspectroscopy is a label-free, non-toxic, and minimally invasive method allowing to perform analyses of live cells and tissues. We used this method to follow the formation of lipid droplets in three colorectal cancer cell lines expressing TrkB. MCARS images of cells generated from signal integration of CH2 stretching modes allow to discriminate between lipid accumulation in the endoplasmic reticulum and the formation of cytoplasmic lipid droplets. We found that the number of the latter was related to the TrkB expression level. This result was confirmed thanks to the creation of a HEK cell line which over-expresses TrkB. We demonstrated that BDNF-induced TrkB activation leads to the formation of cytoplasmic lipid droplets, which can be abolished by K252a, an inhibitor of TrkB. So, MCARS microspectroscopy proved useful in characterizing cancer cells displaying an aberrant lipid metabolism.

Download Full-text