Lipid droplets in cultured luteal cells in non-pregnant sheep fed different planes of nutrition

Abstract

Accumulation of lipid droplets (LD) in luteal cells likely is important for energy storage and steroidogenesis in the highly metabolically active corpus luteum (CL). The objective of this study was to determine the effect of plane of nutrition on progesterone (P4) secretion, and lipid droplet number and size in cultured ovine luteal cells. Ewes were randomly assigned to one of three nutritional groups: control (C; 100% NRC requirements, n=9), overfed (O; 2×C, n=12), or underfed (U; 0.6×C, n=10). Superovulation was induced by follicle stimulating hormone injections. At the early and mid-luteal phases of the estrous cycle, CL were dissected from ovaries, and luteal cells isolated enzymatically. Luteal cells were incubated overnight in medium containing serum in chamber slides. Media were then changed to serum-free and after 24h incubation, media were collected for P4 analysis, and cells were fixed in formalin and stained with BODIPY followed by DAPI staining. Z-stacks of optical sections of large and small luteal cells (LLC and SLC, respectively) were obtained using a laser-scanning microscope. Rendered 3D images of individual LLC and SLC were analyzed for cell volume, and total and individual LD volume, number and percentage of cellular volume occupied by LD by using Imaris software. Concentrations of P4 in serum and media were greater (P<0.05) at the mid than early-luteal phase, and were not affected by nutritional plane. LD total volume and number were greater (P<0.001) in LLC than SLC; however, mean volume of individual LD was greater (P<0.02) in SLC than LLC. In LLC, total LD volume was greater (P<0.02) in O than C and U ewes. In SLC, total LD volume and number was greater (P<0.003) at the mid than early-luteal phase, and percentage of cell volume occupied by LD was greater (P<0.002) in U than C and O ewes. These data demonstrate that both stage of luteal development and nutritional plane affect selected LD measurements and thus may affect luteal functions. Furthermore, these data confirm that LD dynamics differ among parenchymal steroidogenic luteal cell types.

Trafficking of cholesterol from lipid droplets to mitochondria in bovine luteal cells: Acute control of progesterone synthesis

“…45,46 The LIPE/HSL mRNA transcripts were enriched 2-fold in small luteal cells compared to theca cell counterparts (P < .05; Figure 1A); and 2.7-fold in large luteal cells when compared to granulosa cells (P < .05; Figure 1A). In keeping with the presence of lipid droplets in luteal cells, 23 large and small luteal cells had 2.3-fold and 4-fold greater PLIN2 transcripts than granulosa and theca cells, respectively (P < .05; Figure 1A). Moreover, STAR transcripts were elevated by 1.4-fold in small luteal cells compared to theca cells (P < .05; Figure 1A); however, we observed much greater transcript expression of STAR in large luteal cells (56-fold) when compared to granulosa cells ( Figure 1A), which is in keeping with the conversion from an estrogen secreting granulosa cell to a progesterone manufacturing luteal cell.…”

Composition of the Lipid Droplets of the Bovine Corpus Luteum

“…Small luteal cells have a mean LD volume 2.4 times greater than large luteal cells; whereas, large luteal cells have three times the number of LDs present in small luteal cells. This finding is in agreement with data by Khanthusaeng et al, who found that ovine large luteal cells have many smaller LDs and small luteal cells have fewer, but larger LDs (43). The difference in LD size and number in the two cell types may relate to the different functions of large and small luteal cells.…”

“…Luteal LDs are a prominent feature of bovine luteal tissue and the presence, prominence, and composition of luteal Luteal tissue of all examined species contain abundant LDs which vary in size and number throughout the normal estrous or menstrual cycle (15)(16)(17)(18)(19). The findings that neutral lipids occupy approximately 5-16% of bovine luteal tissue area is in agreement with other studies examining LD to luteal cell area or volume (27,28,43). In contrast, other tissues rarely contain the same amount of neutral lipids, except during pathological situations (8)(9)(10)(11).…”

Formation and characterization of lipid droplets of the bovine corpus luteum

“…Luteal tissue of all examined species contain abundant LDs, which vary in size and number throughout the normal estrous or menstrual cycle [14][15][16][17][18] . The findings that neutral lipids occupy approximately 5-16% of bovine luteal tissue area is in agreement with other studies examining LD to luteal cell area or volume 26,27,33 . In contrast, other tissues rarely contain the same extant of neutral lipids, except during pathological situations [8][9][10][11] .…”