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Regulation of lipid droplet size in mammary epithelial cells by remodeling of membrane lipid composition-a potential mechanism.

Cohen BC, Shamay A, Argov-Argaman N - PLoS ONE (2015)

Bottom Line: Mitochondrial quantity and expression levels of genes associated with mitochondrial biogenesis and polar lipid composition were determined.When cultured with oleic acid, 22% of the cells contained large lipid droplets (>3 μm) and phosphatidylethanolamine concentration was higher by 23 and 63% compared with that in the control and palmitic acid treatments, respectively (P < 0.0001).Triglyceride secretion in the oleic acid treatment was 2- and 12-fold higher compared with that in the palmitic acid and control treatments, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Jerusalem, Israel.

ABSTRACT
Milk fat globule size is determined by the size of its precursors-intracellular lipid droplets-and is tightly associated with its composition. We examined the relationship between phospholipid composition of mammary epithelial cells and the size of both intracellular and secreted milk fat globules. Primary culture of mammary epithelial cells was cultured in medium without free fatty acids (control) or with 0.1 mM free capric, palmitic or oleic acid for 24 h. The amount and composition of the cellular lipids and the size of the lipid droplets were determined in the cells and medium. Mitochondrial quantity and expression levels of genes associated with mitochondrial biogenesis and polar lipid composition were determined. Cells cultured with oleic and palmitic acids contained similar quantities of triglycerides, 3.1- and 3.8-fold higher than in controls, respectively (P < 0.0001). When cultured with oleic acid, 22% of the cells contained large lipid droplets (>3 μm) and phosphatidylethanolamine concentration was higher by 23 and 63% compared with that in the control and palmitic acid treatments, respectively (P < 0.0001). In the presence of palmitic acid, only 4% of the cells contained large lipid droplets and the membrane phosphatidylcholine concentration was 22% and 16% higher than that in the control and oleic acid treatments, respectively (P < 0.0001). In the oleic acid treatment, approximately 40% of the lipid droplets were larger than 5 μm whereas in that of the palmitic acid treatment, only 16% of the droplets were in this size range. Triglyceride secretion in the oleic acid treatment was 2- and 12-fold higher compared with that in the palmitic acid and control treatments, respectively. Results imply that membrane composition of bovine mammary epithelial cells plays a role in controlling intracellular and secreted lipid droplets size, and that this process is not associated with cellular triglyceride content.

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Suggested mechanism for free fatty acids effect on intracellular and secreted lipid droplets in mammary gland epithelial cells.The presence of free palmitic or oleic acid in the culture medium increased Tg amount in mammary epithelial cells. In addition oleic acid induced changes in the PGC-1 coactivators transcription pattern which increased mitochondria number. Consequently, higher conversion rates of PS to PE occurred and resulted in altered membrane composition. The higher PE content in the membrane induced fusion of intracelllular lipid droplets which results in larger lipid droplets in the cytoplasm. The higher PE also increased plasma membrane curvature and hence increased the secretion rates of the large lipid droplets which resulted in higher Tg concentration in cultrue medium after incubation with oleic acid. In the presence of palmitic acid (left hand side of the illustration) in the culture medium Tg content was also elevated and also proffered incorporation of palmitic acid into PC increased its content in the cellular membranes. PC induced membrane stability which inhibited the fusion rates of intracellular lipid droplets and resulted in small intracelluar and secreted lipid droplets. This suggested mechanism may explain the reason for the association between the size of the milk fat globules and the membrane phospholipid composition of mammary epithelial cells. C16:0- palmitic acid. C18:1- oleic acid. PGC1- PPAR gamma coactivator 1.PS- Phosphatidylserine. PE- Phosphatidylethanolamine. PC- Phosphatidylcholine. Tg- Triglyceride. Orange arrows- pathways induced by oleate. Yellow arrows- pathways induced by palmitate. Blue arrows- pathways induced by both oleate and palmitate. Membrane composition: Green- phoaphatidylinositol. Red- Phosphatidylchole. Pink- Phosphatidylserine. Yellow- Phosphatidylethanolamine. Blue- Sphingomyelin.
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pone.0121645.g008: Suggested mechanism for free fatty acids effect on intracellular and secreted lipid droplets in mammary gland epithelial cells.The presence of free palmitic or oleic acid in the culture medium increased Tg amount in mammary epithelial cells. In addition oleic acid induced changes in the PGC-1 coactivators transcription pattern which increased mitochondria number. Consequently, higher conversion rates of PS to PE occurred and resulted in altered membrane composition. The higher PE content in the membrane induced fusion of intracelllular lipid droplets which results in larger lipid droplets in the cytoplasm. The higher PE also increased plasma membrane curvature and hence increased the secretion rates of the large lipid droplets which resulted in higher Tg concentration in cultrue medium after incubation with oleic acid. In the presence of palmitic acid (left hand side of the illustration) in the culture medium Tg content was also elevated and also proffered incorporation of palmitic acid into PC increased its content in the cellular membranes. PC induced membrane stability which inhibited the fusion rates of intracellular lipid droplets and resulted in small intracelluar and secreted lipid droplets. This suggested mechanism may explain the reason for the association between the size of the milk fat globules and the membrane phospholipid composition of mammary epithelial cells. C16:0- palmitic acid. C18:1- oleic acid. PGC1- PPAR gamma coactivator 1.PS- Phosphatidylserine. PE- Phosphatidylethanolamine. PC- Phosphatidylcholine. Tg- Triglyceride. Orange arrows- pathways induced by oleate. Yellow arrows- pathways induced by palmitate. Blue arrows- pathways induced by both oleate and palmitate. Membrane composition: Green- phoaphatidylinositol. Red- Phosphatidylchole. Pink- Phosphatidylserine. Yellow- Phosphatidylethanolamine. Blue- Sphingomyelin.

Mentions: The data from this study suggest that membrane phospholipid composition plays a role in regulating MFG size. The association of a specific membrane composition with lipid droplet phenotype provides novel insight into the biochemical mechanism underlying the regulation of MFG size. The results enhance our understanding of how MFG size can be regulated and consequently, how lipid composition of milk can be determined and the suggested mechanism is illustrated in Fig. 8. Data presented herein may provide a novel means of controlling, and ultimately improving milk lipid composition.


Regulation of lipid droplet size in mammary epithelial cells by remodeling of membrane lipid composition-a potential mechanism.

Cohen BC, Shamay A, Argov-Argaman N - PLoS ONE (2015)

Suggested mechanism for free fatty acids effect on intracellular and secreted lipid droplets in mammary gland epithelial cells.The presence of free palmitic or oleic acid in the culture medium increased Tg amount in mammary epithelial cells. In addition oleic acid induced changes in the PGC-1 coactivators transcription pattern which increased mitochondria number. Consequently, higher conversion rates of PS to PE occurred and resulted in altered membrane composition. The higher PE content in the membrane induced fusion of intracelllular lipid droplets which results in larger lipid droplets in the cytoplasm. The higher PE also increased plasma membrane curvature and hence increased the secretion rates of the large lipid droplets which resulted in higher Tg concentration in cultrue medium after incubation with oleic acid. In the presence of palmitic acid (left hand side of the illustration) in the culture medium Tg content was also elevated and also proffered incorporation of palmitic acid into PC increased its content in the cellular membranes. PC induced membrane stability which inhibited the fusion rates of intracellular lipid droplets and resulted in small intracelluar and secreted lipid droplets. This suggested mechanism may explain the reason for the association between the size of the milk fat globules and the membrane phospholipid composition of mammary epithelial cells. C16:0- palmitic acid. C18:1- oleic acid. PGC1- PPAR gamma coactivator 1.PS- Phosphatidylserine. PE- Phosphatidylethanolamine. PC- Phosphatidylcholine. Tg- Triglyceride. Orange arrows- pathways induced by oleate. Yellow arrows- pathways induced by palmitate. Blue arrows- pathways induced by both oleate and palmitate. Membrane composition: Green- phoaphatidylinositol. Red- Phosphatidylchole. Pink- Phosphatidylserine. Yellow- Phosphatidylethanolamine. Blue- Sphingomyelin.
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pone.0121645.g008: Suggested mechanism for free fatty acids effect on intracellular and secreted lipid droplets in mammary gland epithelial cells.The presence of free palmitic or oleic acid in the culture medium increased Tg amount in mammary epithelial cells. In addition oleic acid induced changes in the PGC-1 coactivators transcription pattern which increased mitochondria number. Consequently, higher conversion rates of PS to PE occurred and resulted in altered membrane composition. The higher PE content in the membrane induced fusion of intracelllular lipid droplets which results in larger lipid droplets in the cytoplasm. The higher PE also increased plasma membrane curvature and hence increased the secretion rates of the large lipid droplets which resulted in higher Tg concentration in cultrue medium after incubation with oleic acid. In the presence of palmitic acid (left hand side of the illustration) in the culture medium Tg content was also elevated and also proffered incorporation of palmitic acid into PC increased its content in the cellular membranes. PC induced membrane stability which inhibited the fusion rates of intracellular lipid droplets and resulted in small intracelluar and secreted lipid droplets. This suggested mechanism may explain the reason for the association between the size of the milk fat globules and the membrane phospholipid composition of mammary epithelial cells. C16:0- palmitic acid. C18:1- oleic acid. PGC1- PPAR gamma coactivator 1.PS- Phosphatidylserine. PE- Phosphatidylethanolamine. PC- Phosphatidylcholine. Tg- Triglyceride. Orange arrows- pathways induced by oleate. Yellow arrows- pathways induced by palmitate. Blue arrows- pathways induced by both oleate and palmitate. Membrane composition: Green- phoaphatidylinositol. Red- Phosphatidylchole. Pink- Phosphatidylserine. Yellow- Phosphatidylethanolamine. Blue- Sphingomyelin.
Mentions: The data from this study suggest that membrane phospholipid composition plays a role in regulating MFG size. The association of a specific membrane composition with lipid droplet phenotype provides novel insight into the biochemical mechanism underlying the regulation of MFG size. The results enhance our understanding of how MFG size can be regulated and consequently, how lipid composition of milk can be determined and the suggested mechanism is illustrated in Fig. 8. Data presented herein may provide a novel means of controlling, and ultimately improving milk lipid composition.

Bottom Line: Mitochondrial quantity and expression levels of genes associated with mitochondrial biogenesis and polar lipid composition were determined.When cultured with oleic acid, 22% of the cells contained large lipid droplets (>3 μm) and phosphatidylethanolamine concentration was higher by 23 and 63% compared with that in the control and palmitic acid treatments, respectively (P < 0.0001).Triglyceride secretion in the oleic acid treatment was 2- and 12-fold higher compared with that in the palmitic acid and control treatments, respectively.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Jerusalem, Israel.

ABSTRACT
Milk fat globule size is determined by the size of its precursors-intracellular lipid droplets-and is tightly associated with its composition. We examined the relationship between phospholipid composition of mammary epithelial cells and the size of both intracellular and secreted milk fat globules. Primary culture of mammary epithelial cells was cultured in medium without free fatty acids (control) or with 0.1 mM free capric, palmitic or oleic acid for 24 h. The amount and composition of the cellular lipids and the size of the lipid droplets were determined in the cells and medium. Mitochondrial quantity and expression levels of genes associated with mitochondrial biogenesis and polar lipid composition were determined. Cells cultured with oleic and palmitic acids contained similar quantities of triglycerides, 3.1- and 3.8-fold higher than in controls, respectively (P < 0.0001). When cultured with oleic acid, 22% of the cells contained large lipid droplets (>3 μm) and phosphatidylethanolamine concentration was higher by 23 and 63% compared with that in the control and palmitic acid treatments, respectively (P < 0.0001). In the presence of palmitic acid, only 4% of the cells contained large lipid droplets and the membrane phosphatidylcholine concentration was 22% and 16% higher than that in the control and oleic acid treatments, respectively (P < 0.0001). In the oleic acid treatment, approximately 40% of the lipid droplets were larger than 5 μm whereas in that of the palmitic acid treatment, only 16% of the droplets were in this size range. Triglyceride secretion in the oleic acid treatment was 2- and 12-fold higher compared with that in the palmitic acid and control treatments, respectively. Results imply that membrane composition of bovine mammary epithelial cells plays a role in controlling intracellular and secreted lipid droplets size, and that this process is not associated with cellular triglyceride content.

Show MeSH