Increased adipose tissue lipolysis in dairy cows with fatty liver is associated with enhanced autophagy activity

Dietary supplementation with citrus peel extract in transition period improves rumen microbial composition and ameliorates energy metabolism and lactation performance of dairy cows

BACKGROUND

During the transition period, excessive negative energy balance (NEB) lead to metabolic disorders and reduced milk yield. Rumen microbes are responsible for resolving plant material and producing volatile fatty acids (VFA), which are the primary energy source for cows. In this study, we aimed to investigate the effect of citrus peel extract (CPE) supplementation on rumen microbiota composition, energy metabolism and milk performance of peripartum dairy cows.

METHODS

Dairy cows were fed either a basal diet (CON group) or the same basal diet supplemented with CPE via intragastric administration (4 g/d, CPE group) for 6 weeks (3 weeks before and 3 weeks after calving; n = 15 per group). Samples of serum, milk, rumen fluid, adipose tissue, and liver were collected to assess the effects of CPE on rumen microbiota composition, rumen fermentation parameters, milk performance, and energy metabolic status of dairy cows.

RESULTS

CPE supplementation led to an increase in milk yield, milk protein and lactose contents, and serum glucose levels, while reduced serum concentrations of non-esterified fatty acid, β-hydroxybutyric acid, insulin, aspartate aminotransferase, alanine aminotransferase, and haptoglobin during the first month of lactation. CPE supplementation also increased the content of ruminal VFA. Compared to the CON group, the abundance of Prevotellaceae, Methanobacteriaceae, Bacteroidales_RF16_group, and Selenomonadaceae was found increased, while the abundance of Oscillospiraceae, F082, Ruminococcaceae, Christensenellaceae, Muribaculaceae UCG-011, Saccharimonadaceae, Hungateiclostridiaceae, and Spirochaetaceae in the CPE group was found decreased. In adipose tissue, CPE supplementation decreased lipolysis, and inflammatory response, while increased insulin sensitivity. In the liver, CPE supplementation decreased lipid accumulation, increased insulin sensitivity, and upregulated expression of genes involved in gluconeogenesis.

CONCLUSIONS

Our findings suggest that CPE supplementation during the peripartum period altered rumen microbiota composition and increased ruminal VFA contents, which further improved NEB and lactation performance, alleviated lipolysis and inflammatory response in adipose tissue, reduced lipid accumulation and promoted gluconeogenesis in liver. Thus, CPE might contribute to improve energy metabolism and consequently lactation performance of dairy cows during the transition period.

Dissecting loci that underpin the genetic correlations between production, fertility, and urea traits in Australian Holstein cattle

Unfavorable genetic correlations between milk production, fertility, and urea traits have been reported. However, knowledge of the genomic regions associated with these unfavorable correlations is limited. Here, we used the correlation scan method to identify and investigate the regions driving or antagonizing the genetic correlations between production vs. fertility, urea vs. fertility, and urea vs. production traits. Driving regions produce an estimate of correlation that is in the same direction as the global correlation. Antagonizing regions produce an estimate in the opposite direction of the global estimates. Our dataset comprised 6567, 4700, and 12,658 Holstein cattle with records of production traits (milk yield, fat yield, and protein yield), fertility (calving interval) and urea traits (milk urea nitrogen and blood urea nitrogen predicted using milk-mid-infrared spectroscopy), respectively. Several regions across the genome drive the correlations between production, fertility, and urea traits. Antagonizing regions were confined to certain parts of the genome and the genes within these regions were mostly involved in preventing metabolic dysregulation, liver reprogramming, metabolism remodeling, and lipid homeostasis. The driving regions were enriched for QTL related to puberty, milk, and health-related traits. Antagonizing regions were mostly related to muscle development, metabolic body weight, and milk traits. In conclusion, we have identified genomic regions of potential importance for dairy cattle breeding. Future studies could investigate the antagonizing regions as potential genomic regions to break the unfavorable correlations and improve milk production as well as fertility and urea traits.

Role of diacylglycerol O-acyltransferase 1 (DGAT1) in lipolysis and autophagy of adipose tissue from ketotic dairy cows

High-yielding dairy cows in early lactation often encounter difficulties in meeting the energy requirements essential for maintaining milk production. This is primarily attributed to insufficient dry matter intake, which consequently leads to sustained lipolysis of adipose tissue. Fatty acids released by lipolysis can disrupt metabolic homeostasis. Autophagy, an adaptive response to intracellular environmental changes, is considered a crucial mechanism for regulating lipid metabolism and maintaining a proper cellular energy status. Despite its close relationship with aberrant lipid metabolism and cytolipotoxicity in animal models of metabolic disorders, the precise function of diacylglycerol o-acyltransferase 1 (DGAT1) in bovine adipose tissue during periods of negative energy balance is not fully understood, particularly regarding its involvement in lipolysis and autophagy. The objective of the present study was to assess the effect of DGAT1 on both lipolysis and autophagy in bovine adipose tissue and isolated adipocytes. Adipose tissue and blood samples were collected from cows diagnosed as clinically ketotic (n = 15) or healthy (n = 15) following a veterinary evaluation based on clinical symptoms and serum concentrations of BHB, which were 3.19 mM (interquartile range = 0.20) and 0.50 mM (interquartile range = 0.06), respectively. Protein abundance of DGAT1 and phosphorylation levels of unc-51-like kinase 1 (ULK1), were greater in adipose tissue from cows with ketosis, whereas phosphorylation levels of phosphoinositide 3-kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) were lower. Furthermore, when adipocytes isolated from the harvested adipose tissue of 15 healthy cows were transfected with DGAT1 overexpression adenovirus or DGAT1 small interfering RNA followed by exposure to epinephrine (EPI), it led to greater ratios and protein abundance of phosphorylated hormone-sensitive triglyceride lipase (LIPE) to total LIPE and adipose triglyceride lipase (ATGL), while inhibiting the protein phosphorylation levels of ULK1, PI3K, AKT, and mTOR. Overexpression of DGAT1 in EPI-treated adipocytes reduced lipolysis and autophagy, whereas silencing DGAT1 further exacerbated EPI-induced lipolysis and autophagy. Taken together, these findings indicate that upregulation of DGAT1 may function as an adaptive response to suppress adipocytes lipolysis, highlighting the significance of maintaining metabolic homeostasis in dairy cows during periods of negative energy balance.

Subclinical ketosis leads to lipid metabolism disorder by downregulating the expression of acetyl-coenzyme A acetyltransferase 2 in dairy cows

Ketosis is a metabolic disease that often occurs in dairy cows postpartum and is a result of disordered lipid metabolism. Acetyl-coenzyme A (CoA) acetyltransferase 2 (ACAT2) is important for balancing cholesterol and triglyceride (TG) metabolism; however, its role in subclinical ketotic dairy cows is unclear. This study aimed to explore the potential correlation between ACAT2 and lipid metabolism disorders in subclinical ketotic cows through in vitro and in vivo experiments. In the in vivo experiment, liver tissue and blood samples were collected from healthy cows (CON, n = 6, β-hydroxybutyric acid [BHBA] concentration <1.0 mM) and subclinical ketotic cows (subclinical ketosis [SCK], n = 6, BHBA concentration = 1.2-3.0 mM) to explore the effect of ACAT2 on lipid metabolism disorders in SCK cows. For the in vitro experiment, bovine hepatocytes (BHEC) were used as the model. The effects of BHBA on ACAT2 and lipid metabolism were investigated via BHBA concentration gradient experiments. Subsequently, the relation between ACAT2 and lipid metabolism disorder was explored by transfection with siRNA of ACAT2. Transcriptomics showed an upregulation of differentially expression genes during lipid metabolism and significantly lower ACAT2 mRNA levels in the SCK group. Compared with the CON group in vivo, the SCK group showed significantly higher expression levels of peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulator element binding protein 1c (SREBP1c) and significantly lower expression levels of peroxisome proliferator-activated receptor α (PPARα), carnitine palmitoyl-transferase 1A (CPT1A), sterol regulatory element binding transcription factor 2 (SREBP2), and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR). Moreover, the SCK group had a significantly higher liver TG content and significantly lower plasma total cholesterol (TC) and free cholesterol content. These results were indicative of TG and cholesterol metabolism disorders in the liver of dairy cows with SCK. Additionally, the SCK group showed an increased expression of perilipin-2 (PLIN2), decreased expression of apolipoprotein B, and decreased plasma concentration of very low-density lipoproteins (VLDL) and low-density lipoproteins cholesterol (LDL-C) by downregulating ACAT2, which indicated an accumulation of TG in liver. In vitro experiments showed that BHBA induced an increase in the TG content of BHEC, decreased content TC, increased expression of PPARγ and SREBP1c, and decreased expression of PPARα, CPT1A, SREBP2, and HMGCR. Additionally, BHBA increased the expression of PLIN2 in BHEC, decreased the expression and fluorescence intensity of ACAT2, and decreased the VLDL and LDL-C contents. Furthermore, silencing ACAT2 expression increased the TG content; decreased the TC, VLDL, and LDL-C contents; decreased the expression of HMGCR and SREBP2; and increased the expression of SREBP1c; but had no effect on the expression of PLIN2. These results suggest that ACAT2 downregulation in BHEC promotes TG accumulation and inhibits cholesterol synthesis, leading to TG and cholesterol metabolic disorders. In conclusion, ACAT2 downregulation in the SCK group inhibited cholesterol synthesis, increased TG synthesis, and reduced the contents of VLDL and LDL-C, eventually leading to disordered TG and cholesterol metabolism.

Steatosis in metabolic diseases: A focus on lipolysis and lipophagy

Fatty acids (FAs), as part of lipids, are involved in cell membrane composition, cellular energy storage, and cell signaling. FAs can also be toxic when their concentrations inside and/or outside the cell exceed physiological levels, which is called "lipotoxicity", and steatosis is a form of lipotoxity. To facilitate the storage of large quantities of FAs in cells, they undergo a process called lipolysis or lipophagy. This review focuses on the effects of lipolytic enzymes including cytoplasmic "neutral" lipolysis, lysosomal "acid" lipolysis, and lipophagy. Moreover, the impact of related lipolytic enzymes on lipid metabolism homeostasis and energy conservation, as well as their role in lipid-related metabolic diseases. In addition, we describe how they affect lipid metabolism homeostasis and energy conservation in lipid-related metabolic diseases with a focus on hepatic steatosis and cancer and the pathogenesis and therapeutic targets of AMPK/SIRTs/FOXOs, PI3K/Akt, PPARs/PGC-1α, MAPK/ERK1/2, TLR4/NF-κB, AMPK/mTOR/TFEB, Wnt/β-catenin through immune inflammation, oxidative stress and autophagy-related pathways. As well as the current application of lipolytic enzyme inhibitors (especially Monoacylglycerol lipase (MGL) inhibitors) to provide new strategies for future exploration of metabolic programming in metabolic diseases.

An affinity tool for the isolation of endogenous active mTORC1 from various cellular sources

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of mammalian cell growth that is dysregulated in a number of human diseases, including metabolic syndromes, aging and cancer. Structural, biochemical and pharmacological studies that have increased our understanding of how mTORC1 executes growth control often relied upon purified mTORC1 protein. However, current immunoaffinity-based purification methods are expensive, inefficient, and do not necessarily isolate endogenous mTORC1, hampering their overall utility in research. Here we present a simple tool to isolate endogenous mTORC1 from various cellular sources. By recombinantly expressing and isolating mTORC1-binding Rag GTPases from E. Coli and using them as affinity probes, we demonstrate that mTORC1 can be isolated from mouse, bovine and human sources. Our results indicate that mTORC1 isolated by this relatively inexpensive method is catalytically active and amenable to scaling. Collectively, this tool may be utilized to isolate mTORC1 from various cellular sources, organs, and disease contexts, aiding mTORC1-related research.

Dietary supplementation with calcium propionate could beneficially alter rectal microbial composition of early lactation dairy cows

Dietary supplementation with calcium propionate can effectively alleviate negative energy balance and hypocalcemia of dairy cows in early lactation. The objective of this study was to investigate the effects of calcium propionate feeding levels on the immune function, liver function, and fecal microbial composition of dairy cows in early lactation. Thirty-two multiparous Holstein cows were randomly assigned to four treatments after calving. Treatments were a basal diet plus 0, 200, 350, and 500 g calcium propionate per cow per day throughout a 5-week trial period. Cows were milked three times a day, and blood was sampled to measure immune function and liver function on d 7, 21, and 35. The rectal contents were sampled and collected on d 35 to analyze the microbial composition using 16S rRNA gene sequencing. The results indicated that increasing amounts of calcium propionate did not affected the serum concentrations of total protein, IgG, IgM, and calcium, but the concentrations of albumin and IgA changed quadratically. With the increase of calcium propionate, the activity of serum alanine transaminase and aspartate aminotransferase increased linearly, in contrast, the activity of alkaline phosphatase decreased linearly. Moreover, dietary supplementation with increasing levels of calcium propionate tended to quadratically decrease the relative abundance of Firmicutes while quadratically increased the abundance of Bacteroidetes, and consequently linearly decreased the Firmicutes/Bacteroidetes ratio in the rectal microbiota. Additionally, the supplementation of calcium propionate increased the relative abundances of Ruminococcaceae_UCG-005 and Prevotellaceae_UCG-004 linearly, and Ruminococcaceae_UCG-014 quadratically, but decreased the relative abundances of Lachnospiraceae_NK3A20_group and Family_XIII_AD3011_group quadratically. Compared with the CON group, the calcium propionate supplementation significantly decreased the relative abundance of Acetitomaculum but increased the abundances of Rikenellaceae_RC9_gut_group and Alistipes. In summary, these results suggested that the supplementation of calcium propionate to dairy cows in early lactation could beneficially alter the rectal microbiota.