Global investigation of estrogen-responsive genes regulating lipid metabolism in the liver of laying hens

Dietary silymarin improves performance by altering hepatic lipid metabolism and cecal microbiota function and its metabolites in late laying hens

BACKGROUND

Liver lipid dysregulation is one of the major factors in the decline of production performance in late-stage laying hens. Silymarin (SIL), a natural flavonolignan extracted from milk thistle, is known for its hepatoprotective and lipid-lowering properties in humans. This study evaluates whether SIL can provide similar benefits to late-stage laying hens. A total of 480 68-week-old Lohmann Pink laying hens were randomly assigned into 5 groups, each group consisting of 6 replicates with 16 hens each. The birds received a basal diet either without silymarin (control) or supplemented with silymarin at concentrations of 250, 500, 750, or 1,000 mg/kg (SIL250, SIL500, SIL750, SIL1000) over a 12-week period.

RESULTS

The CON group exhibited a significant decline in laying rates from weeks 9 to 12 compared to the initial 4 weeks (P = 0.042), while SIL supplementation maintained consistent laying rates throughout the study (P > 0.05). Notably, the SIL500 and SIL750 groups showed higher average egg weight than the CON group during weeks 5 to 8 (P = 0.049). The SIL750 group had a significantly higher average daily feed intake across the study period (P < 0.05), and the SIL500 group saw a marked decrease in the feed-to-egg ratio from weeks 5 to 8 (P = 0.003). Furthermore, the SIL500 group demonstrated significant reductions in serum ALT and AST levels (P < 0.05) and a significant decrease in serum triglycerides and total cholesterol at week 12 with increasing doses of SIL (P < 0.05). SIL also positively influenced liver enzyme expression (FASN, ACC, Apo-VLDL II, FXR, and CYP7A1; P < 0.05) and altered the cecal microbiota composition, enhancing species linked to secondary bile acid synthesis. Targeted metabolomics identified 9 metabolites predominantly involved in thiamin metabolism that were significantly different in the SIL groups (P < 0.05).

CONCLUSIONS

Our study demonstrated that dietary SIL supplementation could ameliorate egg production rate in late stage laying hens, mechanistically, this effect was via improving hepatic lipid metabolism and cecal microbiota function to achieve. Revealed the potentially of SIL as a feed supplementation to regulate hepatic lipid metabolism dysregulation. Overall, dietary 500 mg/kg SIL had the best effects.

miRNA-seq analysis of liver tissue from largemouth bass (Micropterus salmoides) in response to oxytetracycline and enzyme-treated soy protein

The specific miRNA regulation triggered by enzyme-treated soybean protein in response to well-known stressors, such as the prophylactic use of the antimicrobial oxytetracycline, remains unknown. Hence, this study aimed to evaluate the regulatory changes of hepatic miRNAs induced by oxytetracycline and enzyme-treated soybean protein in largemouth bass dietary formulations. The experiment was designed with three groups: the normal control (NC), the oxytetracycline exposure treatment group (OTC), and the pre-treatment with enzyme-treated soybean protein before oxytetracycline exposure group (ETSP). miRNA sequencing was employed to characterize the differences between these groups. In conclusion, the NC group exhibited up-regulation of 13 host miRNAs and down-regulation of 1 miRNA compared to the OTC group, whereas the ETSP group showed an increasing trend of 36 host miRNAs and a decreasing trend of 13 host miRNAs compared to the OTC group. Nine miRNAs were identified as prudential targets for enzyme-treated soy protein, protecting the largemouth bass liver from oxytetracycline. Furthermore, gene ontology analysis revealed nine key miRNAs that mediate signaling pathways with significant differences. The cellular lipid metabolic process was identified as the most important biological process, and the propanoate metabolism pathway was highlighted as significant. These results will facilitate further exploration of the mechanism by which enzyme-treated soy protein alleviates the effects of oxytetracycline on largemouth bass in water environments.

Exposure to microplastics affects fatty acid composition in the Japanese quail depending on sex and particle size

Plastic ingestion in birds is a widespread phenomenon of increasing concern. However, little is known about how exposure to microplastics (MP) affects the health of birds. In other organisms, MP exposure alters lipid metabolism and composition. If also true in birds, this could affect their fitness, especially since birds heavily rely on lipids during migration and egg production. Therefore, the aim of this study was to determine if ingestion of MP (polypropylene and polyethylene collected in nature) in two size ranges, large (3 mm) and small (<125 μm), affects lipid metabolism in the Japanese quail (Coturnix japonica). We orally exposed 55 one-week-old quail during 5 weeks to a total of 600 mg of MP in sizes of either large, small, or a mixture of both. After the exposure period, females fed small MP had higher liver masses compared to control females (on average ± SD, 8.95 ± 2.3 g vs. 6.34 ± 1.0 g), while liver lipid content did not differ in either males or females. The levels of monounsaturated fatty acids were lower in females exposed to large MP and the mixture of both MP sizes compared to controls. Females exposed to MP also had different levels of oleic- (18:1) and palmitoleic (16:1) acid compared to controls dependent on MP size. Exposure to small MP increased levels of palmitic- (16:0) and palmitoleic (16:1) acid in both males and females suggesting a possible increase in de novo fatty acid synthesis. Taken together, our results point towards a sex-specific sensitivity to MP as well as size-dependent MP effects on lipid metabolism in birds. Disruption of fatty acid composition could affect important life stages in female birds, such as migration and egg-laying. We stress the importance of further research focused on determining the mechanisms of action of MP on lipid metabolism.

miR-19b-3p regulated by estrogen controls lipid synthesis through targeting MSMO1 and ELOVL5 in LMH cells

miR-19b-3p is reported to undertake various biological role, while its function and action mechanism in chicken hepatic lipid metabolism is unclear. Conservation analysis and tissue expression pattern of miR-19b-3p and its target gene were evaluated, respectively. Dual luciferase reporter system and Western blot technologies were adopted to validate miR-19b-3p target gene. Overexpression and knockdown assays were done to explore the biological functions of miR-19b-3p and target gene in Leghorn Male Hepatoma cell line (LMH). Regulatory approaches of estrogen on miR-19b-3p and target gene expressions are analyzed through site-directed mutation combined with estrogen receptors antagonist treatment assays. The results showed that chicken miR-19b-3p mature sequences are highly conserved among Capra hircus, Columba livia, Rattus norvegicus, Mus musculus, Cricetulus griseus, Danio rerio, Danio novaehollandiae, Orycodylus porosus, Crocodylus porosus, Gadus morhua, and widely expressed in lung, ovary, spleen, duodenum, kidney, heart, liver, leg muscle, and pectoral muscle tissues. miR-19b-3p could significantly increase intracellular triglyceride (TG) content and decrease intracellular cholesterol (TC) content via targeting methylsterol monooxygenase 1 (MSMO1) and elongase of very long chain fatty acids 5 (ELOVL5), which are highly conserved among species, in both mRNA and protein levels. Estrogen could inhibit miR-19b-3p expression, but directly promoted MSMO1 transcription via estrogen receptor α (ERα) and indirectly regulated ELOVL5 expression at the transcription level. Meanwhile, estrogen could also upregulate MSMO1 and ELOVL5 expression through inhibiting miR-19b-3p expression at the post-transcription level. Taken together, these results highlight the role and regulatory mechanism of miR-19b-3p in hepatic lipid metabolism in chicken, and might produce useful comparative information for human obesity studies and biomedical research.

LncHLEF promotes hepatic lipid synthesis through miR-2188-3p/GATA6 axis and encoding peptides and enhances intramuscular fat deposition via exosome

Long noncoding RNAs (lncRNAs) have emergingly been implicated in mammalian lipid metabolism. However, their biological functions and regulatory mechanisms underlying adipogenesis remain largely elusive in chicken. Here, we systematically characterized the genome-wide full-length lncRNAs in the livers of pre- and peak-laying hens, and identified a novel intergenic lncRNA, lncHLEF, an RNA macromolecule with a calculated molecular weight of 433 kDa. lncHLEF was primarily distributed in cytoplasm of chicken hepatocyte and significantly up-regulated in livers of peak-laying hens. Functionally, lncHLEF could promote hepatocyte lipid droplet formation, triglycerides and total cholesterol contents. Mechanistically, lncHLEF could not only serve as a competitive endogenous RNA to modulate miR-2188-3p/GATA6 axis, but also encode three small functional polypeptides that directly interact with ACLY protein to enable its stabilization. Importantly, adeno-associated virus-mediated liver-specific lncHLEF overexpression resulted in increased hepatic lipid synthesis and intramuscular fat (IMF) deposition, but did not alter abdominal fat (AbF) deposition. Furthermore, hepatocyte lncHLEF could be delivered into intramuscular and abdominal preadipocytes via hepatocyte-secreted exosome to enhance intramuscular preadipocytes differentiation without altering abdominal preadipocytes differentiation. In conclusion, this study revealed that the lncHLEF could promote hepatic lipid synthesis through two independent regulatory mechanisms, and could enhance IMF deposition via hepatocyte-adipocyte communications mediated by exosome.

Dietary naringin supplementation on hepatic yolk precursors formation and antioxidant capacity of Three-Yellow breeder hens during the late laying period

In this study, the effects of naringin on hepatic yolk precursors formation and antioxidant capacity of Three-Yellow breeder hens during late laying period were evaluated. A total of 480 (54-wk-old) Three-Yellow breeder hens were randomly assigned to 4 groups (6 replicates of 20 hens): nonsupplemented control diet (C), and control diet supplemented with 0.1%, 0.2%, and 0.4% of naringin (N1, N2, and N3), respectively. Results showed that dietary supplemented with 0.1%, 0.2%, and 0.4% of naringin for 8 wk promoted the cell proliferation and attenuated the excessive fat accumulation in the liver. Compared with C group, increased concentrations of triglyceride (TG), total cholesterol (T-CHO), high-density lipoprotein cholesterol (HDL-C), and very low-density lipoprotein (VLDL), and decreased contents of low-density lipoprotein cholesterol (LDL-C) were detected in liver, serum and ovarian tissues (P < 0.05). After 8 wk of feeding with naringin (0.1%, 0.2%, and 0.4%), serum estrogen (E₂) level, expression levels of proteins and genes of estrogen receptors (ERs) increased significantly (P < 0.05). Meanwhile, naringin treatment regulated expression of genes related to yolk precursors formation (P < 0.05). Furthermore, dietary naringin addition increased the antioxidants, decreased the oxidation products, and up-regulated transcription levels of antioxidant genes in liver tissues (P < 0.05). These results indicated that dietary supplemented with naringin could improve hepatic yolk precursors formation and hepatic antioxidant capacity of Three-Yellow breeder hens during the late laying period. Doses of 0.2% and 0.4% are more effective than dose of 0.1%.

Interacting Networks of the Hypothalamic-Pituitary-Ovarian Axis Regulate Layer Hens Performance

Egg production is a vital biological and economic trait for poultry breeding. The 'hypothalamic-pituitary-ovarian (HPO) axis' determines the egg production, which affects the layer hens industry income. At the organism level, the HPO axis is influenced by the factors related to metabolic and nutritional status, environment, and genetics, whereas at the cellular and molecular levels, the HPO axis is influenced by the factors related to endocrine and metabolic regulation, cytokines, key genes, signaling pathways, post-transcriptional processing, and epigenetic modifications. MiRNAs and lncRNAs play a critical role in follicle selection and development, atresia, and ovulation in layer hens; in particular, miRNA is known to affect the development and atresia of follicles by regulating apoptosis and autophagy of granulosa cells. The current review elaborates on the regulation of the HPO axis and its role in the laying performance of hens at the organism, cellular, and molecular levels. In addition, this review provides an overview of the interactive network regulation mechanism of the HPO axis in layer hens, as well as comprehensive knowledge for successfully utilizing their genetic resources.

Alleviation effect of conjugated linoleic acid on estradiol benzoate induced fatty liver hemorrhage syndrome in Hy-line male chickens

The purpose of this study was to explore whether conjugated linoleic acid (CLA) could alleviate fatty liver hemorrhagic syndrome (FLHS) induced by estradiol benzoate intramuscular injection in laying hens. One hundred male Hy-Line white chickens were randomly divided into two groups, namely, the control (CON) and estradiol benzoate (E) groups, and both groups were fed the same basal diet. After injections of estradiol benzoate at 2 mg/kg every two days for a total of 7 times, chickens in the E group showed FLHS symptoms, including liver enlargement, hemorrhage, and steatosis. Then half of the chickens in the E group received an additional diet containing 5000 mg/kg CLA for 8 weeks. The results of morphological observations, hematoxylin and eosin staining, and Oil Red O staining showed that CLA alleviated liver enlargement, hemorrhage, and lipid accumulation in FLHS chickens. In addition, we measured liver function and lipid metabolism indicators, including ALT, AST, TG, TCH, HDL-C, and LDL-C, which further suggested that CLA mitigated the disturbance of serum and liver metabolism in FLHS chickens. Mechanistically, CLA inhibited hepatic de novo lipogenesis, cholesterol synthesis, and TG accumulation and increased TG hydrolysis in FLHS chickens by regulating the gene expression of CD36, ACC, FAS, SCD 1, DGAT2, LIPE, ATGL, CPT1A, SREBP-1c, SREBP-2, PPARγ, and PPARα. Furthermore, CLA ameliorated hepatic oxidative stress and inhibited NF-κB signaling pathway-mediated inflammation in FLHS chickens. In conclusion, CLA regulated lipid metabolism, thus further alleviating oxidative stress and inflammation to alleviate FLHS induced by estrogen in chickens.

Hepatic Transcriptomic Responses to Ethinylestradiol in Two Life Stages of Japanese Quail

Chemical risk assessment for avian species typically depends on information from toxicity tests performed in adult birds. Early-life stage (ELS) toxicity tests have been proposed as an alternative, but incorporation of these data into existing frameworks will require knowledge about the similarities/differences between ELS and adult responses. The present study uses transcriptomics to assess hepatic gene expression in ELS and adult Japanese quail following exposure to ethinylestradiol (EE2). Prior to incubation, ELS quail were dosed with measured EE2 concentrations of 0.54, 6.3, and 54.2 µg/g egg weight via air cell injection. Adult quail were fed a single dose of EE2 at nominal concentrations of 0, 0.5, and 5 mg/kg body weight by gavage. Liver tissue was collected from five to six individuals per dose group at mid-incubation for ELS quail and 4 days after dosing for adults. A total of 283 and 111 differentially expressed genes (DEGs) were detected in ELS and adult quail, respectively, 16 of which were shared across life stages. Shared DEGs included estrogenic biomarkers such as vitellogenin genes and apovitellenin-1. For the dose groups that resulted in the highest number of DEGs (ELS, 6.3 µg/g; adult, 5 mg/kg), 21 and 35 Kyoto Encyclopedia of Genes and Genomes pathways were enriched, respectively. Ten of these pathways were shared between life stages, including pathways involved with signaling molecules and interaction and the endocrine system. Taken together, our results suggest conserved mechanisms of action following estrogenic exposure across two life stages, with evidence from differential expression of key biomarker genes and enriched pathways. The present study contributes to the development and evaluation of ELS tests and toxicogenomic approaches and highlights their combined potential for screening estrogenic chemicals. Environ Toxicol Chem 2022;41:2769-2781. © 2022 SETAC.

ELOVL gene family plays a virtual role in response to breeding selection and lipid deposition in different tissues in chicken (Gallus gallus)

Background

Elongases of very long chain fatty acids (ELOVLs), a family of first rate-limiting enzymes in the synthesis of long-chain fatty acids, play an essential role in the biosynthesis of complex lipids. Disrupting any of ELOVLs affects normal growth and development in mammals. Genetic variations in ELOVLs are associated with backfat or intramuscular fatty acid composition in livestock. However, the effects of ELOVL gene family on breeding selection and lipid deposition in different tissues are still unknown in chickens.

Results

Genetic variation patterns and genetic associations analysis showed that the genetic variations of ELOVL genes were contributed to breeding selection of commercial varieties in chicken, and 14 SNPs in ELOVL2-6 were associated with body weight, carcass or fat deposition traits. Especially, one SNP rs17631638T > C in the promoter of ELOVL3 was associated with intramuscular fat content (IMF), and its allele frequency was significantly higher in native and layer breeds compared to that in commercial broiler breeds. Quantitative real-time PCR (qRT-PCR) determined that the ELOVL3 expressions in pectoralis were affected by the genotypes of rs17631638T > C. In addition, the transcription levels of ELOVL genes except ELOVL5 were regulated by estrogen in chicken liver and hypothalamus with different regulatory pathways. The expression levels of ELOVL1-6 in hypothalamus, liver, abdominal fat and pectoralis were correlated with abdominal fat weight, abdominal fat percentage, liver lipid content and IMF. Noteworthily, expression of ELOVL3 in pectoralis was highly positively correlated with IMF and glycerophospholipid molecules, including phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol and phospholipids inositol, rich in ω-3 and ω-6 long-chain unsaturated fatty acids, suggesting ELOVL3 could contribute to intramuscular fat deposition by increasing the proportion of long-chain unsaturated glycerophospholipid molecules in pectoralis.

Conclusions

In summary, we demonstrated the genetic contribution of ELOVL gene family to breeding selection for specialized varieties, and revealed the expression regulation of ELOVL genes and their potential roles in regulating lipid deposition in different tissues. This study provides new insights into understanding the functions of ELOVL family on avian growth and lipid deposition in different tissues and the genetic variation in ELOVL3 may aid the marker-assisted selection of meat quality in chicken.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08932-8.

GPNMB promotes abdominal fat deposition in chickens: genetic variation, expressional profile, biological function, and transcriptional regulation

Glycoprotein nonmetastatic melanoma protein B (GPNMB) is a vital secreted factor that promotes the occurrence of obesity in mammals. However, the effects of GPNMB on abdominal fat deposition is still unknown in chickens. In this study, we looked into the genetic and expression association of GPNMB gene with abdominal fat traits in chicken, and found that a genetic variation rs31126482 in GPNMB promoter was significantly associated with abdominal fat weight (AFW, P < 0.05) and abdominal fat percentage (AFP, P < 0.01). Express profile analysis of the GPNMB indicated that the gene was mainly expressed in abdominal fat tissue, and its expression level was strongly positively correlated with AFW (R² = 0.6356, P = 4.10E−05) and AFP (R² = 0.6450, P = 2.90E−05). We then investigated biological function of GPNMB on adipogenesis in chicken, and found that GPNMB could inhibit abdominal preadipocyte proliferation, but promote abdominal preadipocyte differentiation and lipid deposition. Furthermore, we explored regulatory mechanism of GPNMB gene in chicken, and detected one nonclassical estrogen regulatory element (AP1) and one peroxisome proliferator-activated receptor α (PPARα) responsive element in the 2 kb promoter region of GPNMB gene, and demonstrated that estrogen could up-regulate GPNMB mRNA expression in adipose tissue and primary abdominal preadipocytes, while PPARα could down-regulate GPNMB expression in primary preadipocytes. Taken together, this study brings new insights into understanding the function and transcriptional control of GPNMB gene, and provides genetic markers for breeding selection to improve abdominal fat traits in chicken.

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

Deficiency of PSRC1 accelerates atherosclerosis by increasing TMAO production via manipulating gut microbiota and flavin monooxygenase 3

Maladaptive inflammatory and immune responses are responsible for intestinal barrier integrity and function dysregulation. Proline/serine-rich coiled-coil protein 1 (PSRC1) critically contributes to the immune system, but direct data on the gut microbiota and the microbial metabolite trimethylamine N-oxide (TMAO) are lacking. Here, we investigated the impact of PSRC1 deletion on TMAO generation and atherosclerosis. We first found that PSRC1 deletion in apoE^-/- mice accelerated atherosclerotic plaque formation, and then the gut microbiota and metabolites were detected using metagenomics and untargeted metabolomics. Our results showed that PSRC1 deficiency enriched trimethylamine (TMA)-producing bacteria and functional potential for TMA synthesis and accordingly enhanced plasma betaine and TMAO production. Furthermore, PSRC1 deficiency resulted in a proinflammatory colonic phenotype that was significantly associated with the dysregulated bacteria. Unexpectedly, hepatic RNA-seq indicated upregulated flavin monooxygenase 3 (FMO3) expression following PSRC1 knockout. Mechanistically, PSRC1 overexpression inhibited FMO3 expression in vitro, while an ERα inhibitor rescued the downregulation. Consistently, PSRC1-knockout mice exhibited higher plasma TMAO levels with a choline-supplemented diet, which was gut microbiota dependent, as evidenced by antibiotic treatment. To investigate the role of dysbiosis induced by PSRC1 deletion in atherogenesis, apoE^-/- mice were transplanted with the fecal microbiota from either apoE^-/- or PSRC1^-/-apoE^-/- donor mice. Mice that received PSRC1-knockout mouse feces showed an elevation in TMAO levels, as well as plaque lipid deposition and macrophage accumulation, which were accompanied by increased plasma lipid levels and impaired hepatic cholesterol transport. Overall, we identified PSRC1 as an atherosclerosis-protective factor, at least in part, attributable to its regulation of TMAO generation via a multistep pathway. Thus, PSRC1 holds great potential for manipulating the gut microbiome and alleviating atherosclerosis.

Liver Transcriptome Response to Heat Stress in Beijing You Chickens and Guang Ming Broilers

Heat stress is one of the most prevalent issues in poultry production that reduces performance, robustness, and economic gains. Previous studies have demonstrated that native chickens are more tolerant of heat than commercial breeds. However, the underlying mechanisms of the heat tolerance observed in native chicken breeds remain unelucidated. Therefore, we performed a phenotypical, physiological, liver transcriptome comparative analysis and WGCNA in response to heat stress in one native (Beijing You, BY) and one commercial (Guang Ming, GM) chicken breed. The objective of this study was to evaluate the heat tolerance and identify the potential driver and hub genes related to heat stress in these two genetically distinct chicken breeds. In brief, 80 BY and 60 GM, 21 days old chickens were submitted to a heat stress experiment for 5 days (33 °C, 8 h/day). Each breed was divided into experimental groups of control (Ctl) and heat stress (HS). The results showed that BY chickens were less affected by heat stress and displayed reduced DEGs than GM chickens, 365 DEGs and 382 DEGs, respectively. The transcriptome analysis showed that BY chickens exhibited enriched pathways related to metabolism activity, meanwhile GM chickens’ pathways were related to inflammatory reactions. CPT1A and ANGPTL4 for BY chickens, and HSP90B1 and HSPA5 for GM chickens were identified as potential candidate genes associated with HS. The WGCNA revealed TLR7, AR, BAG3 genes as hub genes, which could play an important role in HS. The results generated in this study provide valuable resources for studying liver transcriptome in response to heat stress in native and commercial chicken lines.

In Vitro Investigations of miR-33a Expression in Estrogen Receptor-Targeting Therapies in Breast Cancer Cells

(1) Background: Increased fatty acid synthesis leads to the aggressive phenotype of breast cancer and renders efficiency of therapeutics. Regulatory microRNAs (miRNAs) on lipid biosynthesis pathways as miR-33a have potential to clarify the exact mechanism. (2) Methods: We determined miR-33a expression levels following exposure of MCF-7 and MDA-MB-231 breast cancer cells to estrogen receptor (ER) activator (estradiol-17β, E2) or anti-estrogens (ICI 182,780, Fulvestrant, FUL) at non-cytotoxic concentrations. We related miR-33a expression levels in the cells to cellular lipid biosynthesis-related pathways through immunoblotting. (3) Results: miR-33a mimic treatment led to significantly downregulation of fatty acid synthase (FASN) in MCF-7 cells but not in MDA-MB-231 cells in the presence of estradiol-17β (E2) or Fulvestrant (FUL). In contrast to the miR-33a inhibitor effect, miR-33a mimic co-transfection with E2 or FUL led to diminished AMP-activated protein kinase α (AMPKα) activity in MCF-7 cells. E2 increases FASN levels in MDA-MB-231 cells regardless of miR-33a cellular levels. miR-33a inhibitor co-treatment suppressed E2-mediated AMPKα activity in MDA-MB-231 cells. (4) Conclusions: The cellular expression levels of miR-33a are critical to understanding differential responses which include cellular energy sensors such as AMPKα activation status in breast cancer cells.