Insulin Signaling in Liver and Adipose Tissues in Periparturient Dairy Cows Supplemented with Dietary Nicotinic Acid

Nicotinamide benefited amino acid metabolism and rumen fermentation pattern to improve growth performance of growing lambs

OBJECTIVE

Nicotinamide (NAM) is easily degraded in the rumen, but the rumen-protected NAM (RPN) supplementation might enable the use of NAM in ruminants. This study aimed to elucidate the effects of RPN supplementation on growth performance, rumen fermentation, antioxidant status and amino acid (AA) metabolism in growing lambs.

METHODS

A total of 128 healthy and similar lambs (21.3±0.28 kg, 70±6.3 days of age) were allotted to 1 of 4 groups. The treatments were 0, 0.5, 1, and 2 g/d RPN supplementation. The RPN products (50% bioavailability) were fed at 0700 h every day for 12 weeks. All lambs were fed the same pelleted total mixed rations to allow ad libitum consumption and had free access to water.

RESULTS

The RPN tended to increase the average daily gain and feed efficiency. The tendencies of RPN×day interaction were found for dry matter intake during the entire study (p = 0.078 and 0.073, respectively). The proportions of acetic acid, isobutyric acid and isovaleric acid were decreased, whereas the proportions of propionic acid and valeric acid were increased (p<0.05). The ratio of acetic acid to propionic acid was decreased (p<0.05). Moreover, the antioxidative status was enhanced and the glucose concentration was increased by RPN (p<0.05). In addition, 17 AAs were detected in plasma, of which 11 AAs were increased by RPN (p<0.05). Plasma metabolomics analysis identified 1,395 compounds belonging to 15 classes, among which 7 peptides were significantly changed after RPN supplementation.

CONCLUSION

Overall, the results suggested that RPN supplementation favoured the rumen fermentation pattern to propionic acid-type with benefited glucose metabolism, enhanced antioxidant capacity, and changed the AA and small peptide metabolism. This study provides a new perspective for studying the relationship between vitamin and AA metabolism.

Lipolysis inhibition as a treatment of clinical ketosis in dairy cows: Effects on adipose tissue metabolic and immune responses

Dairy cows with clinical ketosis (CK) exhibit excessive adipose tissue (AT) lipolysis and systemic inflammation. Lipolysis in cows can be induced by the canonical (hormonally induced) and inflammatory lipolytic pathways. Currently, the most common treatment for CK is oral propylene glycol (PG); however, PG does not reduce lipolysis or inflammation. Niacin (NIA) can reduce the activation of canonical lipolysis, whereas cyclooxygenase inhibitors such as flunixin meglumine (FM) can limit inflammation and inhibit the inflammatory lipolytic pathway. The objective of this study was to determine the effects of including NIA and FM in the standard PG treatment for postpartum CK on AT function. Multiparous Jersey cows (n = 18; 7.1 ± 3.8 DIM) were selected from a commercial dairy. Inclusion criteria were CK symptoms (lethargy, depressed appetite, and drop in milk yield) and high blood levels of BHB (≥1.2 mmol/L). Cows with CK were randomly assigned to one of 3 treatments: (1) PG: 310 g administered orally once per day for 5 d, (2) PG+NIA: 24 g administered orally once per day for 3 d, and (3) PG+NIA+FM: 1.1 mg/kg administered IV once per day for 3 d. Healthy control cows (HC; n = 6) matched by lactation and DIM (±2 d) were sampled. Subcutaneous AT explants were collected at d 0 and d 7 relative to enrollment. To assess AT insulin sensitivity, explants were treated with insulin (1 µL/L) during lipolysis stimulation with a β-adrenergic receptor agonist (isoproterenol, 1 µM). Lipolysis was quantified by glycerol release in the media. Lipid mobilization and inflammatory gene networks were evaluated using quantitative PCR. Protein biomarkers of lipolysis, insulin signaling, and AT inflammation, including hormone-sensitive lipase, protein kinase B (Akt), and ERK1/2, were quantified by capillary immunoassays. Flow cytometry of AT cellular components was used to characterize macrophage inflammatory phenotypes. Statistical significance was determined by a nonparametric t-test when 2 groups (HC vs. CK) were analyzed and an ANOVA test with Tukey adjustment when 3 treatment groups (PG vs. PG+NIA vs. PG+NIA+FM) were evaluated. At d 0, AT from CK cows showed higher mRNA expression of lipolytic enzymes ABHD5, LIPE, and LPL, as well as increased phosphorylation of hormone-sensitive lipase compared with HC. At d 0, insulin reduced lipolysis by 41% ± 8% in AT from HC, but CK cows were unresponsive (-2.9 ± 4%). Adipose tissue from CK cows exhibited reduced Akt phosphorylation compared with HC. Cows with CK had increased AT expression of inflammatory gene markers, including CCL2, IL8, IL10, TLR4, and TNF, along with ERK1/2 phosphorylation. Adipose tissue from CK cows showed increased macrophage infiltration compared with HC. By d 7, AT from PG+NIA+FM cows had a more robust response to insulin, as evidenced by reduced glycerol release (36.5% ± 8% compared with PG at 26.9% ± 7% and PG+NIA at 7.4% ± 8%) and enhanced phosphorylation of Akt. By d 7, PG+NIA+FM cows presented lower inflammatory markers, including ERK1/2 phosphorylation, and reduced macrophage infiltration, compared with PG and PG+NIA. These data suggest that including NIA and FM in CK treatment improves AT insulin sensitivity and reduces AT inflammation and macrophage infiltration.

Insulin signaling in insulin-dysregulated Icelandic horses

The underlying molecular mechanisms leading to insulin dysregulation are poorly understood in horses. Therefore, this study aimed to determine if insulin dysregulation is associated with an altered basal expression and extent of phosphorylation of key proteins of the insulin signaling cascade in liver (LT), muscle (MT), and subcutaneous adipose tissue (AT) under basal and stimulated conditions. Twelve Icelandic horses were subjected (1) to an oral glucose (Gluc PO) challenge and (2) to an intravenous (Ins IV) insulin challenge in a crossover study. Biopsies of LT, MT, and AT were taken in vivo under basal conditions and after Gluc PO and Ins IV stimulation. Corresponding insulin levels were measured by an equine optimized ELISA (Mercodia AB, Uppsala). Insulin levels ≥ 110 µIU/mL at 120 min indicated that six horses were insulin dysregulated (HI), while six were not (NI). Gluc PO stimulation resulted in a more pronounced hyperinsulinemia and hyperglycemia in HI horses compared to NI horses. Western blot analysis of key proteins of the insulin signaling cascade revealed an enhanced phosphorylation of the insulin receptor (InsR) under Gluc PO (P = 0.001) and Ins IV stimulation (P = 0.017) within LT, but not in MT and AT. Phosphorylation of protein kinase B was enhanced under Gluc PO stimulation in all tissues and under Ins IV stimulation in MT and AT, while phosphorylation of adenosine monophosphate protein kinase α was reduced after glucose administration (P = 0.005) in all horses. Interestingly, HI horses had significantly higher amounts of phosphorylated mechanistic target of rapamycin (mTOR) in MT (P = 0.049), irrespective of any stimulation. In LT, the amount of phosphorylated mTOR decreased under Gluc PO conditions in HI horses, while an increase was observed in NI horses (P = 0.015). A major limitation was the inclusion of only Icelandic horses of advanced age since insulin dysregulation could be related to both the equine metabolic syndrome and/or pituitary pars intermedia dysfunction. In summary, insulin signaling appeared to be maintained in both HI and NI Icelandic horses, although post-receptor alterations were observed. Thus, ID might be an equine-specific metabolic condition, in which alterations of the mTOR signaling pathway may play a crucial role, as emphasized by higher mTOR phosphorylation in HI horses.

Investigating circulating miRNA in transition dairy cows: What miRNAomics tells about metabolic adaptation

In the current study, we investigated dairy cows’ circulating microRNA (miRNA) expression signature during several key time points around calving, to get insights into different aspects of metabolic adaptation. In a trial with 32 dairy cows, plasma samples were collected on days −21, 1, 28, and 63 relative to calving. Individually extracted total RNA was subjected to RNA sequencing using NovaSeq 6,000 (Illumina, CA) on the respective platform of IGA Technology Services, Udine, Italy. MiRDeep2 was used to identify known and novel miRNA according to the miRbase collection. Differentially expressed miRNA (DEM) were assessed at a threshold of fold-change &gt; 1.5 and false discovery rate &lt; 0.05 using the edgeR package. The MiRWalk database was used to predict DEM targets and their associated KEGG pathways. Among a total of 1,692 identified miRNA, 445 known miRNA were included for statistical analysis, of which 84, 59, and 61 DEM were found between days −21 to 1, 1 to 28, and 28 to 63, respectively. These miRNA were annotated to KEGG pathways targeting the insulin, MAPK, Ras, Wnt, Hippo, sphingolipid, T cell receptor, and mTOR signaling pathways. MiRNA-mRNA network analysis identified miRNA as master regulators of the biological process including miR-138, miR-149-5p, miR-2466-3p, miR-214, miR-504, and miR-6523a. This study provided new insights into the miRNA signatures of transition to the lactation period. Calving emerged as a critical time point when miRNA were most affected, while the following period appeared to be recovering from massive parturition changes. The primarily affected pathways were key signaling pathways related to establishing metabolic and immune adaptations.

Ceramide metabolism associated with chronic dietary nutrient surplus and diminished insulin sensitivity in the liver, muscle, and adipose tissue of cattle

High dietary energy and protein supply is common practice in livestock nutrition, aiming to maximize growth and production performance. However, a chronic nutritional surplus induces obesity, promotes insulin insensitivity, and triggers low-grade inflammation. Thirty Holstein bulls were randomly assigned to two groups, low energy and protein (LEP), and high energy and protein (HEP) intake, provided from the 13th to the 20th month of life. Body weight, carcass composition, laminitis score, and circulating insulin and glucose concentrations were assessed. The expression and extent of phosphorylation of insulin signaling proteins were measured in the liver, muscle, and adipose tissue. The sphingolipid metabolome was quantified by a targeted liquid chromatography-mass spectrometry based metabolomics approach. The HEP bulls were obese, had hyperinsulinemia with euglycemia, and expressed clinical signs of chronic laminitis. In the liver, protein kinase B (PKB) phosphorylation was decreased and this was associated with a higher tissue concentration of ceramide 16:0, a sphingolipid that diminishes insulin action by dephosphorylating PKB. In the adipose tissue, insulin receptor expression was lower in HEP bulls, associated with higher concentration of hexosylceramide, which reduces the abundance of functional insulin receptors. Our findings confirm that diet-induced metabolic inflammation triggers ceramide accumulation and disturbs insulin signaling. As insulin insensitivity exacerbates metabolic inflammation, this self-reinforcing cycle could explain the deterioration of metabolic health apparent as chronic laminitis. By demonstrating molecular relationships between insulin signaling and sphingolipid metabolism in three major tissues, our data extend our mechanistic understanding of the role of ceramides in diet-induced metabolic inflammation.

The sphingolipidome of plasma, liver, and adipose tissues and its association with insulin response to oral glucose testing in Icelandic horses

Insulin dysregulation (ID) is a determinant of equine metabolic syndrome. Among the sphingolipids, ceramides contribute to the development of ID; however, the crosstalk between the liver and adipose tissue (AT) depots and the variation among AT depots in terms of ceramide metabolism are not well-understood. We aimed to characterize the sphingolipidome of plasma, liver, and AT (nuchal, NUAT; subcutaneous, SCAT; omental, OMAT; retroperitoneal, RPAT) and their associations with insulin response to oral glucose testing (OGT) in normoinsulinemic and hyperinsulinemic horses. Plasma, liver, and AT samples were collected from 12 Icelandic horses upon euthanasia and analyzed by liquid chromatography-mass spectrometry. Eighty-four targeted compounds were effectively quantified. Comparing the AT depots, greater (FDR < 0.05) ceramide, dihydroceramide, and sphingomyelin concentrations and lower glucosyl- and galactosyl-ceramides were found in RPAT and OMAT than in NUAT and SCAT. Hyperinsulinemic response to OGT was associated with sphingolipidome alterations primarily in the RPAT and OMAT, while the NUAT sphingolipidome did not show signs of ceramide accumulation, which was inconsistent with the previously proposed role of nuchal adiposity in ID. The plasma sphingolipidome was not significantly associated with the liver or AT sphingolipidomes, indicating that plasma profiles are determined by an interplay of various organs. Further, hepatic sphingolipid profiles were not correlated with the profiles of AT depots. Finally, statistically valid partial least square regression models predicting insulin response were found in the plasma (Q²= 0.58, R²= 0.98), liver (Q²= 0.64, R²= 0.74), and RPAT (Q²= 0.68, R²= 0.79) sphingolipidome, but not in the other adipose tissues.

Effect of precalving body condition score on insulin signaling and hepatic inflammatory state in grazing dairy cattle

During postpartum, high-production dairy cows show a temporary period of insulin resistance, during which glucose uptake by peripheral tissues is reduced to prioritize milk production. However, this can further increase their negative energy balance by compromising liver function, especially in cows with excessive body condition score (BCS) and a pro-inflammatory state. Based on this, the aim of this study was to evaluate the hepatic expression of proteins of the insulin signaling pathway (PI3K) and of the cytokines TNFα, IL-6 and NF-κB, as well as the plasma concentrations of non-esterified fatty acids (NEFA), beta-hydroxybutyrate, glucose, triglycerides (TAG), insulin and insulin-like growth factor-1, insulin sensitivity indexes, and the hepatic content of TAG during the transition period in cows with different BCS. Sixteen Holstein cows were selected 14 days before the expecting calving date and classified into 2 groups: low BCS (LBCS) ≤ 3.25 (n = 9) and high BCS (HBCS) ≥ 3.5 (n = 7). Blood and liver samples were obtained 14 (±3) days before the expected calving date and 4 (±3), 14 (±3) and 28 (±3) days after calving. The concentration of NEFA was higher in the HBCS group than in the LBCS group. Glucose concentration showed an interaction effect, with a greater concentration on day 28 in HBCS. Insulin concentration showed no changes. While the pAkt/total Akt ratio was lower in the HBCS group, the TNFα protein expression was higher only on day 4 postcalving in the HBCS group. In agreement with these results, the insulin sensitivity indexes RQUICKI and RQUICKI_BHBA were lower in the HCBS group. The results suggest an insulin resistance and a pro-inflammatory state in the liver of cows with HBCS.

Gain and loss of subcutaneous and abdominal adipose tissue depot mass of German Holstein dairy cows with different body conditions during the transition period

Subcutaneous adipose tissue (SCAT) and abdominal adipose tissue (AAT) depots are mobilized during the fresh cow period (FCP) and early lactation period (ELP) to counteract the negative energy balance (NEB). Earlier studies suggested that fat depots contribute differently to lipomobilization and may vary in functionality. Differences between the adipose depots might influence the development of metabolic disorders. Thus, the gain and loss of subcutaneous and abdominal adipose depot masses in Holstein cows with lower and higher body condition (mean body condition scores: 3.48 and 3.87, respectively) were compared in the period from d -42 to d 70 relative to parturition in this study. Animals of the 2 experimental groups represented adequately conditioned and overconditioned cows. Estimated depot mass (eDM) of SCAT, AAT, retroperitoneal, omental, and mesenteric adipose depots of 31 pluriparous German Holstein cows were determined via ultrasonography at d -42, 7, 28, and 70 relative to parturition. The cows were grouped according to the eDM of SCAT on d -42 [low body condition (LBC) group: n = 16, mean eDM 8.6 kg; high body condition (HBC) group: n = 15, mean eDM 15.6 kg]. Average daily change (prepartum gain and postpartum loss) in depot masses during dry period (DP; from d -42 to d 7), FCP (d 7 to d 28), and ELP (d 28 to d 70) were calculated and daily dry matter intake and lactation performance recorded. Cows of this study stored about 2 to 3 times more fat in AAT than in SCAT depots. After parturition, on average more adipose tissue mass was lost from the AAT than the SCAT depot (0.23 kg/d vs. 0.14 kg/d). Cows with high compared with low body condition had similar gains in AAT (0.33 kg/d) and SCAT (0.14 kg/d) masses during the DP but mobilized significantly more adipose tissue mass from both depots after calving (AAT, HBC vs. LBC: 0.30 vs. 0.17 kg/d; SCAT, HBC vs. LBC: 0.19 vs. 0.10 kg/d). Correlation analysis indicated a functional disparity between AAT and SCAT. In the case of AAT (R² = 0.36), the higher the gain in adipose mass during DP, the higher the loss in FCP, but this was not the case for SCAT. During FCP, a greater NEB resulted in greater loss of mass from SCAT (R² = 0.18). In turn, greater mobilization of SCAT mass led to a higher calculated feed efficiency (R² = 0.18). However, AAT showed no such correlations. On the other hand, during ELP, loss of both SCAT and AAT mass correlated positively with feed efficiency (R² = 0.35 and 0.33, respectively). The results indicate that feed efficiency may not be an adequate criterion for performance evaluation in cows during NEB. Greater knowledge of functional disparities between AAT and SCAT depots may improve our understanding of excessive lipomobilization and its consequences for metabolic health and performance of dairy cows during the transition period.

Insulin signaling and insulin response in subcutaneous and retroperitoneal adipose tissue in Holstein cows during the periparturient period

Adipose tissue response to endocrine stimuli, such as insulin, is crucial for metabolic adaptation at the onset of lactation in dairy cows. However, the exact molecular mechanisms behind this response are not well understood. Thus, the aim of this study was to determine the dynamics in protein expression and phosphorylation of key components in insulin signaling in subcutaneous (SCAT) and retroperitoneal (RPAT) adipose tissues of Holstein dairy cows. Furthermore, by ex vivo examinations, response to insulin was assessed in SCAT and RPAT at different time points during the periparturient period. Biopsy samples were taken 42 d prepartum, and 1, 21, and 100 d postpartum. Insulin and glucose concentrations were measured in blood serum in consecutive serum samples from d -42 until d +100. After parturition, the majority of the key components were downregulated in both adipose tissues but recovered by d +100. The extent of hormone-sensitive lipase phosphorylation increased postpartum and remained high throughout the experimental period. Strong differences in molecular response were observed between the 2 depots. The RPAT expressed a remarkably greater extent of AMP-activated kinase phosphorylation compared with SCAT, indicating that AMP-activated kinase as an energy sensor is highly active particularly in RPAT in times of energy scarcity. Consequently, this depot expressed a greater extent of hormone-sensitive lipase phosphorylation over the whole experimental period. Insulin response after parturition appeared to be greater in RPAT too, due to the significantly greater expression of the insulin receptor at d +21 and +100. Although insulin concentrations in plasma were low postpartum, the depot-specific changes in molecular modulation of insulin signaling and insulin response suggested that both adipose tissue depots studied were contributing to the periparturient homeorhetic adaptation, although most likely to a different extent.