De novo synthesis of monounsaturated fatty acids modulates exosome-mediated lipid export from human granulosa cells

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Introduction
The somatic cumulus-granulosa cells surrounding the oocytes play a crucial role in major reproductive events in females, including maturation and release from the gonad during ovulation.These functions occur not only through cell-oocyte contact, but also through paracrine signaling.This communication has a significant impact on oocyte development (Alam and Miyano, 2020).
During in vitro fertilization procedures, the removal of granulosa cell layers and their secretions from the ovarian preovulatory follicles is a common practice.The significant role of granulosa cell-produced sex hormones in ovarian follicle development has long been established.However, even with hormonal supplementation, the fertilization rate of retrieved oocytes and subsequent embryo development are unexpectedly low during infertility treatment cycles.Nonhormonal compounds secreted from somatic granulosa cells may contribute to oocyte development capacity (Fatehi et al., 2002;Richani et al., 2021).
Our previous research demonstrated that lipid metabolism in granulosa cells plays a role in the paracrine activity of immature oocytes, as we showed that cellular de novo lipid unsaturation depended on this activity.The conversion of saturated fatty acids (SFAs) to unsaturated fatty acids by the desaturase enzyme stearoyl-CoA desaturase 1 (SCD1) in granulosa cells is essential for the maturation of adjacent oocytes, suggesting that oleic acid (OA) plays a key role in lipid storage and functional capacity of granulosa cells (S.Fayezi et al., 2018).Several other reports suggest a connection between fatty acid synthase (FASN), mammalian/mechanistic target of rapamycin (mTOR), and Cyclin D2 (CCND2) signaling in somatic cell overgrowth (Khaidakov et al., 2011;Raab et al., 2021;Seo et al., 2020).Our previous studies on human primary granulosa cells also suggested that an inhibitor of SCD1 (SCDinhib) suppresses cell growth and functionality at least in part by reducing the amount of monounsaturated fatty acids (MUFAs) in cellular lipids (S.Fayezi et al., 2018).Further studies have highlighted the importance of cell-derived exosomes in modulating lipid metabolism and cell transformation.Adipocyte exosomes have been found to be important lipid sources for their local microenvironment (Flaherty et al., 2019).
Exosomes are nanoparticles released by cells.These membraneenclosed extracellular vesicles (EVs) carry biomolecules, which facilitate intercellular communication.Dysregulation of exosome secretion due to insufficient intracellular OA availability can contribute to pathophysiological outcomes.Therefore, investigating the modulatory effect of lipid metabolism on the lipidomic profile of exosomes secreted by granulosa cells could provide a better understanding of the supportive role of these cells in oocyte maturation, and human reproduction in general.This study investigated how granulosa cells adapt to fatty acid desaturation deficiency by regulating exosome production and lipogenesis.Our results provided valuable insight into the role of de novo MUFA generation in exosome-mediated lipid export from granulosa cells.

Cell culture
COV434 cells were cultured in high-glucose DMEM supplemented with 0.5 IU/mL HCG, 75 IU/mL rFSH, 10% fetal calf serum (FCS), 1% Lglutamine, and 1% penicillin-streptomycin.Cells were then treated with vehicle, the SCD1inhib CAY10566 (1.25-20 μM), or SCDinhib combined with a fixed concentration of OA (110 μM) for 48 h in 5% CO 2 at 37 • C. A non-toxic concentration of 5 μM SCDinhib was chosen for further experiments.The level of membrane packing was estimated by C-Laurdan imaging (Levental et al., 2020;Sanchez et al., 2012) to determine the saturation level.After fixation with 4% paraformaldehyde, cells were washed with phosphate-buffered saline (PBS) and incubated with 10 μg/mL C-Laurdan for 15 min.Staining data were acquired in two channels at wavelengths of 460-500 and 520-550 nm using a fluorescence microscope (Olympus BX41).Pseudocolored images were generated by subtracting the observed fluorescence intensities using ImageJ (National Institutes of Health, MD).Immortalized human endometrial stromal cells (t-hESCs) were cultured in DMEM/F12 supplemented with 10% FCS and 1.7 g/l sodium bicarbonate.

Cell viability and proliferation assays
To assess cell proliferation, the Cell Counting Kit-8 (CCK-8) viability assay (Merck KGaA, Germany) was used.Cells were grown in 96-well plates and treated with the assay reagent solution for 2 h, followed by incubation in a microplate reader (LEDetect 96; Anthos Mikrosysteme GmbH, Germany), and the optical density of each condition was measured at 450 nm.

Gene expression assays
Cells were harvested in TRIzol reagent to extract total RNA, which was subsequently converted to cDNA using our established procedures (Mestre Citrinovitz, Langer, Strowitzki and Germeyer, 2020).Quantitative PCR (qPCR) was performed with TaqMan primers (Life Technologies GmbH, Germany) and TaqMan universal PCR master mix from Applied Biosystems.The qPCRs were performed on a 7500 real-time PCR system (Applied Biosystems, Life Technologies GmbH, Germany), and the data analysis was performed according to the delta-delta C T method.We used predesigned TaqMan assays for genes (Assay IDs): CCND2 (Hs00153380_m1), KIT-ligand (Hs00241497_m1), PTEN (Hs01920652_s1), DGAT1 (Hs00201385_m1), FASN (Hs01005622_m1), mTOR (Hs00234508_m1), and small ribosomal subunit ribosomal RNA (18S) (Hs99999901_s1).The 18S small ribosomal subunit ribosomal RNA (18S) gene served as an internal control.Detailed information on the specific primers used is provided in Supplementary Table 1.C T values were normalized to the 18S C T value, which served as an internal control, and were utilized for subsequent statistical analysis.The results are shown as dot plots with the geometric means of five independent experiments.Expression levels were calculated as the fold change relative to those in the untreated control condition using the 2 -ΔΔCT method and are shown as log2 values.

Isolation and characterization
COV434 cells were seeded in T175 flasks and grown until they reached ~70% confluency.Cells were then treated with dimethyl sulfoxide (DMSO)/albumin (<0.05%),SCDinhib, or SCDinhib and OA for 48 h.After 48 h, the flasks were washed twice with phosphate-buffered saline (PBS) and cultured for 18 h (18 ml/T175 flask) in medium supplemented with 1% exosome-free FBS.Cell culture supernatants were collected and subjected to serial centrifugation at 4 • C to remove floating cells (480×g, 10 min) and cellular residue (2000×g, 10 min), followed by centrifugation at 10,000×g for 30 min and passage through a 0.45 μM filter to remove microparticle contamination.The supernatant was ultracentrifuged at 100,000×g for 90 min.The resulting pellets were resuspended in 1 ml of PBS and reultracentrifuged at 120,000×g for 90 min.The endpoint exosomal pellets were resuspended in 100 μl of PBS for transmission electron microscopy (TEM), 100 μl of PBS containing 0.5% exosome-free bovine serum albumin for the labeling/uptake experiments of CFSE, 100 μl of lipidomic solubilization buffer for lipidomic analysis, or 100 μl of RIPA buffer for Western blotting.Exosome solutions were stored at − 80 • C and a second thaw was avoided.

Confocal microscopy
To track exosome uptake by confocal microscopy, t-HESCs were seeded in 24-well plates and treated with 50 μl of CFSE-labeled exosomes overnight in the dark at 37 • C in an incubator with 5% CO2.The following day, the medium was discarded and the cells were washed with PBS.The uptake by t-HESCs was analyzed using a fluorescence microscope.

Transmission electron microscopy
To prepare for transmission electron microscopy (TEM), the exosome solutions were thawed and the suspension was left to settle on 200 mesh Formvar-coated copper grids (Plano GmbH, Germany).These grids were then stained with 2% aqueous uranyl acetate using negative staining.After air drying, the analysis was carried out using a JEM-1400 transmission microscope (JEOL Ltd., Japan) at 80 kV equipped with a TemCam-F216 2 K (2048 × 2048 pixel) digital camera (TVIPS, Germany).

Nanoparticle tracking analysis
For nanoparticle tracking analysis (NTA), a NanoSight NS300 analyzer (Malvern Panalytical Ltd., Malvern, UK) (405 nm) was used.Camera adjustment and focus were selected according to sample characteristics and according to the best-practice procedures stated by the company.Five replicas of 60 s were taken for each sample.Before measurement, at least 500 μL of the sample was loaded into a dry stream cell.The syringe pump was adjusted to allow the particles to pass through the measurement zone in 10-12 s.All measurements were carried out at room temperature.The number of particles released was normalized based on the cell count.

Lipid analysis by nanoelectrospray mass spectrometry
Lipid analysis using nanoelectrospray ionization tandem mass spectrometry (nano-ESI-MS/MS) was performed on the exosome samples.To prepare the samples, 3 independent preparations from a 175 cm 2 flask were pooled together.The exosome solutions were then resuspended in 100 μl of NH4HCO3 (150 mM).
Lipid analysis involved the use of an acid liquid-liquid extraction (ABD) method with the addition of internal lipid standards.Plasmalogens, however, were extracted under neutral conditions.ABD was conducted to determine the concentration of phosphatidylcholine (PC) as a bulk membrane lipid and to adapt extraction volumes to similar total lipid amounts.Typically, an average of 2300 pmol of total lipids was extracted.

Statistical analysis
At least three independent experiments were performed per analysis, unless otherwise noted.We used two-way analysis of variance (ANOVA) to analyze the data.Differences between treatments were considered statistically significant if the p value was less than 0.05.Statistical analysis was performed using GraphPad Prism 10.2 software (GraphPad Software, CA).The results are expressed as mean ± standard deviation.

Results
Non-toxic concentrations of SCDinhib for subsequent experiments were determined using a cell viability assay on COV434 ovarian granulosa cells.Cell viability decreased dose-dependently, with notable toxicity resulting in fewer than 50% of cells viable at 20 μM (Fig. 1A).However, after treatment with 5 μM SCDinhib for up to 48 h (Fig. 1B), more than 70% of the cells survived.OA supplementation maintained cell viability in cells treated with SCDinhib over time, with no change observed until 24 h, indicating effective rescue at the chosen concentration of OA.Treatment with SCDinhib increased the intensity of staining for membrane packing, while treatment with SCDinhib + OA reversed the effect of the inhibitor (Fig. 1C), demonstrating the intended modifications in the level of desaturation under the test conditions.
Treatment with SCDinhib reduced FASN expression by up to 47%; however, this reduction did not reach statistical significance (p = 0.07; Fig. 2).Adding OA to SCDinhib treatment further suppressed FASN expression by 67% (p = 0.022), indicating a complementary effect of OA in down-regulating FASN.Although SCDinhib treatment did not significantly alter CCND2 expression, the combination of SCDinhib and OA significantly decreased CCND2 expression by 88% (p = 0.02) compared to cells treated with SCDinhib (Fig. 2).
Although SCDinhib treatment tended to cause a 37% reduction in DGAT1 expression and a 2-fold increase in KIT-ligand expression, these changes did not reach statistical significance (p = 0.11 and p = 0.07, respectively).Similarly, PTEN and mTOR did not change significantly under the conditions of SCDinhib treatment (Fig. 2).
We performed a cellular uptake assay to evaluate the integrity of the isolated particles and confirm their ability to cross the plasma membrane.As shown in Fig. 3A, unlike free dye molecules, which remained scattered throughout the cell, fluorescently labeled exosomes appeared as distinct spots within the recipient cells.This finding indicated that the labeled exosomes were successfully taken up by the recipient cells, enabling the delivery of their cargo.
TEM revealed membrane-bound spherical structures with an average diameter of approximately 100 nm (Fig. 3B).The structures had a cupshaped morphology, with a concave side and a slightly raised rim.The membranes appeared to be electron dense, with occasional invaginations and small protrusions.The general appearance of the exosomes was consistent.Western blot analysis clearly demonstrated enrichment of the tetraspanin cluster of differentiation 81 (CD81) in exosomes derived from COV434 cells compared to cell lysate (Fig. 3C).
We observed a trend towards increased particle production in cells treated with SCDinhib, with a further increase observed in cells treated with SCDinhib combined with OA (Fig. 3D).However, the count and average size of the isolated particles were not significantly different between treated cells, with an average size ranging between 127 and 139 nm.According to the size distribution analysis, significant differences were observed in the 90th percentile population, in which fewer exosomes were produced when cells were treated with SCDinhib or SCDinhib combined with OA (Fig. 3D).

Exosome lipidomics
The exosomes consisted mainly of free cholesterol and phospholipids, comprising more than 80% of all lipids in the exosomes, reflecting their membranous origin (Fig. 4A).TAGs and DAGs tended to be depleted after inhibition of SCD1 with and without OA (Fig. 4B).
The principal component analysis (PCA) revealed different exosome clusters based on their lipidomes in the control conditions, SCDinhib and SCDinhib + OA, with the second axis of the principal component (PC2) accounting for 26% of the variance (Fig. 5A).However, PS was the only significantly altered lipid subclass in exosomes after SCD1 inhibition.The addition of OA significantly elevated the level of PE to a greater extent than that observed under control and SCDinhib conditions (Fig. 5B).The enrichment analysis revealed a relatively consistent pattern across the two conditions (Fayezi, 2024).Both conditions showed significant enrichment in pathways related to glycerophospholipid (ratio ≈ 42, p < 0.001) and linoleic acid metabolism compared to untreated cells (ratio ≈ 155, p = 0.012, Supplementary Figs. 1 and 2).
The lipid entities were sorted as SFA, MUFA, or polyunsaturated fatty acids (PUFA) according to Supplementary Table 3. Exosomes collected from cells treated with SCDinhib did not show alterations in the distribution of SFA, MUFA or PUFA, whereas exosomes collected from cells treated with SCDinhib + OA were enriched in saturated lipid entities and depleted in polyunsaturated entities compared to exosomes collected from control cells.Consequently, the molar ratios of PUFA/ SFA and PUFA/MUFA decreased significantly (Fig. 6).

Discussion
The present study investigated the impact of SCD inhibition on exosome-mediated lipid export from granulosa cells.Particle production increased in treated cells, with notable differences in both the count and average size of the isolated particles observed in cells treated with SCDinhib and OA.Smaller exosomes were produced when cells were treated with SCDinhib or SCDinhib combined with OA.These findings Fig. 3. Characterization of exosomes derived from the human COV434 granulosa cell line.The derived exosomes were labeled with CFSE (green fluorescent dye) and their uptake by recipient immortalized human endometrial stromal cells (t-hESCs) was monitored by confocal microscopy after 24 h.The nuclei were stained with DAPI and the images were merged (A, n = 1).Transmission electron microscopy image of exosomes showing small spherical structures with diameters of 50-150 nm (indicated by arrows) (B).Western blot analysis confirmed the enrichment of the exosome marker CD81 in COV434 cell-derived exosomes compared to cell lysate, with actin used as loading control.Molecular weight markers (kDa) are indicated on the left side of the blot (C, n = 1).Nanosight's nanoparticle tracking analysis was used to determine the particle count, average size, and size distribution of isolated exosomes after treatment with an SCD1 inhibitor (SCDinhib) alone or in combination with oleic acid (OA).Percentiles are denoted by the letter D followed by the percentage value (D, n = 3).*p < 0.05 and ***p < 0.001 versus the control.are consistent with previous observations of enhanced exosome production in palmitic acid-treated hepatocyte cell models (Buratta et al., 2021;Hirsova et al., 2016;Wang et al., 2021), which resembles accumulation of saturated lipids under treatment with the SCDinhib.However, the metabolic consequences of palmitic acid and SCDinhib treatment can vary.
Inhibition of SCD1 was confirmed by the depletion of palmitoleoylcontaining entities, which is consistent with inhibition of the palmitic acid-to-palmitoleic acid conversion pathway (Janikiewicz et al., 2023).Additionally, there was enrichment of saturated lipid entities, leading to the accumulation of palmitic acid and stearic acid, which cannot be metabolized.The elevated release of exosomes containing saturated lipids suggests the need for a cellular strategy to alleviate the excessive accumulation of saturated fatty acids, a condition known for its detrimental effects on lipid metabolism.In particular, although OA supplementation reduced omega-6-enriched lipids, paradoxically triggered a further increase in exosome production.
In our study, we analyzed the expression of genes associated with crucial cellular processes and signaling pathways, including those involved in lipid metabolism, cell cycle regulation, and growth factor signaling.The expression of FASN and CCND2 expression was significantly altered only when SCDinhib was co-incubated with OA.Although trends were observed for the DGAT1 and KIT-ligand, the expression of mTOR and PTEN remained relatively stable.
The suppression of FASN, a key enzyme in de novo fatty acid synthesis (Paiva et al., 2021), has potential therapeutic implications for conditions where aberrant lipid metabolism is a contributing factor.Although SCD inhibition alone tended to reduce FASN and DGAT1 expression, the combination of SCD inhibition with OA substantially reduced FASN expression.One possible explanation for this effect may lie in the preferential utilization of OA for incorporation into cellular lipids in the presence of SCDinhib, which ultimately leads to the suppression of de novo lipid synthesis by down-regulating FASN.Furthermore, altered exosome production can affect FASN in a feedback loop through selective lipid export, which is further enhanced by OA supplementation.In particular, in other cellular models, the impact of OA alone on FASN expression has shown variable effects, as some studies reported no effect (Howell et al., 2009;Huang et al., 2017), while others indicated an inducing effect (Yanting et al., 2018).Interestingly, in a hyperlipidemic context, OA effectively reduced de novo fatty acid synthesis through the suppression of FASN (Ni et al., 2017).These findings underscore our observation that inhibition of SCD led to accumulation of OA precursors comparable to those observed under hyperlipidemic conditions.As no changes in mTOR expression, a central regulator of lipid biogenesis in response to nutritional signals (Marques-Ramos and Cervantes, 2023), were detected, we hypothesize that the complementary effect of OA on FASN occurs downstream of mTOR.
Our observations align with previous studies reporting the ability of OA to down-regulate CCND2 transcripts and SFAs, such as palmitic acid and stearic acid, to up-regulate CCND2 transcripts in bovine primary granulosa cells (Sharma et al., 2019;Yenuganti et al., 2016).CCND2 primarily regulates the progression of the cell cycle in response to extracellular signals (Zhang et al., 2014).Therefore, changes in exosome cargo and production might also affect CCND2 expression by altering the homotypic functional potency of exosomes.Despite modulation of CCND2 by fatty acids, none of the saturated or unsaturated fatty acids induced a significant change in the cell cycle phases in cultured granulosa cells (Sharma et al., 2019).The lack of effect of applied treatments on PTEN expression is consistent with these findings.We observed differences in exosome polar lipid profiles between treatment conditions, with substantial changes in the glycerophospholipid and linoleic acid pathways.In particular, a similar enrichment in glycerophospholipid metabolism was observed in milk lipids of SCD1-deficient goats (Tian et al., 2022), suggesting potential shared mechanisms involved in altered lipid export.Our findings are also consistent with those of a recent study in which an SCDinhib was used to examine the lipid profile of small EVs released by Huh-7 hepatocarcinoma cells (Buratta et al., 2021).In that study, inhibition of SCD1 and OA treatment did not alter the size or number of EV, but modified the lipid composition of the EV.
The altered lipid composition of exosomes released under conditions of desaturase deficiency in our study not only reflects the state of lipid metabolism of the parental cells but also provides insights into lipid export mechanisms through exosomes.Elevated concentrations of phosphoglycerols and sphingolipids in exosome lipids suggest that cells with desaturase deficiency release a significant amount of phospholipids enriched with saturated and polyunsaturated omega-6 fatty acids through exosomes.According to observations in hepatocyte cell models (Buratta et al., 2021), OA supplementation was associated with a substantial decrease in polyunsaturated omega-6 lipid entities, particularly eicosatrienoic acid (20:3) and arachidonic acid (20:4).However, downstream effects of SCD1 were still observed, including the enrichment of saturated entities and the depletion of palmitoleic acid.
We examined how SCDinhib influences cellular lipids in physiologically relevant media.Enrichment in OA-containing lipid entities suggested an increased rate of exogenous OA uptake upon inhibition of SCD1.The difference in the impact on lipid entities containing OA and palmitic acid could arise from the fact that the FBS-containing medium has a substantial amount of 21% OA (Audi et al., 2007), which is roughly the same content as that of saturated palmitic acid 16:0 (28%), while palmitoleic fatty acid represents only 2.4%.
The enrichment of omega-6 fatty acids containing lipids suggested the activation of the omega-6 fatty acid pathway from the essential fatty acid linoleic acid present in FBS (6.8%) (Audi et al., 2007), especially when the omega-9 and omega-7 pathways were negatively regulated.The compensatory pathway, which was previously activated to provide long-chain fatty acids, was no longer needed, as OA became the primary source of fatty acids for lipogenesis, primarily in monounsaturated form.The fatty acid profile after OA synthesis maintained its phenotype: an enrichment in saturated entities in lipids containing palmitoleic acid confirming the effect of the SCDinhib (Fig. 8).
Our findings revealed an inconsistency in the ability of OA to reverse the effects of SCD inhibition.This finding suggested that both OA and SCDinhib may exert independent or even combined, bidirectional effects on cellular lipid metabolism and exosome production.This study aimed to explore the overall influence of SCD1 activity in a physiologically relevant context rather than focusing on its specific metabolic role.Subsequent investigations may consider using serum without fatty acids supplemented with specific saturated fatty acids, such as palmitic acid or stearic acid.While our results were derived from a well-established model in granulosa cell studies, generalizing our findings to in vivo conditions requires further investigation.

Conclusion
The exosomes released by granulosa cells with impaired SCD1 activity showed an enrichment of saturated lipids and omega-6 fatty acids.The latter compensatory effect was reversed by inducing lipogenesis through OA supplementation.This supplementation not only increased the exosome production rate, but also suppressed the expression of the de novo fatty acid synthesis enzyme FASN and the cell cycle progression regulator CCND2.These findings provide insight into potential intercellular communication processes with oocytes and underscore promising potential therapeutic applications.

Fig. 1 .
Fig. 1.Effects of a stearoyl-CoA desaturase 1 (SCD1) inhibitor on the viability of COV434 human granulosa cells, membrane desaturation, and staining indices.Cell viability was determined after treatment with various concentrations (1.25-20 μM) of the CAY10566 SCD1 inhibitor (SCDinhib) for 48 h (A).SCDinhib (5 μM) with or without oleic acid (OA, 110 μM) was used for 24, 48, or 72 h (B).The cells were also stained simultaneously with Laurdan (green) and Hoechst (blue).Pseudo-color images show the intensity of Laurdan dye staining at each pixel position after treatment with 5 μM SCDinhib with or without OA (110 μM) for 48 h (C, n = 1).In each assay, DMSO (1:1000 v/v)/albumin (18.3 μM) served as a control.The results in (A) and (B) are presented as the mean and standard deviation of independent experiments carried out in triplicate on COV434 cells.**p < 0.01 and ****p < 0.0001 versus the control.

Fig. 2 .
Fig. 2. Effects of the stearoyl-CoA desaturase 1 (SCD1) inhibitor on genes associated with cell proliferation, lipogenesis, and lipid storage in COV434 human granulosa cells.Cells were treated with the CAY10566 SCD1 inhibitor (SCDinhib) (5 μM) alone or in combination with oleic acid (OA, 110 μM) for 48 h.Relative gene expression was quantified using TaqMan probes for quantitative real-time PCR.The results are presented as the mean and standard deviation of 5 independent experiments performed in triplicate on COV434 cells.*p < 0.05 versus the control.

Fig. 4 .
Fig. 4. Impact of a stearoyl-CoA desaturase 1 (SCD1) inhibitor on the lipid composition of exosomes derived from the human COV434 granulosa cell line.Concentrations of the main lipid classes (A) and three different groups of neutral lipids (B) within exosomes obtained from COV434 granulosa cells after treatment with the SCD1 inhibitor (SCDinhib), alone or in combination with oleic acid (OA).Abbreviations: CE, cholesteryl ester; DAG, diacylglycerol; FC, free cholesterol; NL, neutral lipid; PL, phospholipid; SL, sphingolipid; TAG, triglyceride.The data are representative of three replicates for each condition.

Fig. 7 .
Fig. 7. Comparison of lipid entities in exosomes.Circular heatmap showing significantly altered surface lipid entities (A).Each circle represents a specific comparison: SCD inhibitor (SCDinhib) condition versus control condition (circle 1) and SCDinhib + OA condition versus control condition (circle 2).In red, the lipid entities were significantly depleted in the control group; in blue, the lipid entities were significantly enriched in the control exosomes.Forest plots showing log 2 -fold changes in lipid entities in treated vs. nontreated exosomes (B).Lipids are expressed as the molar percentage of each total lipid subclass.Lipid types are ordered according to increasing amounts of unsaturation.Colored: significant fold changes; gray: nonsignificant fold changes.LPC, lysophosphatidylcholine; O-, ether phospholipids.; PA, phosphatidic acid; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PI, phosphatidylinositol; PS, phosphatidylserine.

Fig. 8 .
Fig. 8. Inhibition of stearoyl-CoA desaturase (SCD1) activity and the resulting pathway for lipogenesis.Inhibition of SCD1 activity results in the accumulation of saturated fatty acid species while decreasing the levels of 16:1 lipid species.However, oleic acid (OA) bypasses the omega-6 pathway, rendering it nonessential for long-chain fatty acid production.Consequently, OA emerges as the primary fatty acid that facilitates lipogenesis.