Hepatic Sirt3 expression declines postpartum in dairy goats

Sirtuin 3 mitigates oxidative-stress-induced apoptosis in bovine mammary epithelial cells

Ketosis is often accompanied by a reduction in milk production in dairy cows, but the molecular mechanism has not been fully elucidated. Ketotic cows possess systemic oxidative stress (OS), which may implicate apoptosis in mammary glands. Sirtuin 3 (SIRT3) is a vital regulator of cellular redox homeostasis and is under the control of AMP-activated protein kinase (AMPK) signaling in nonruminants. Thus, we aimed to investigate (1) the AMPK-SIRT3 and apoptosis status of mammary glands from ketotic cows, (2) the effect of SIRT3 on OS-induced apoptosis in bovine mammary epithelial cells (BMEC), and (3) the role of AMPK signaling on SIRT3-mediated effects on apoptosis. Mammary gland samples were reused from a previous study, which contained healthy and ketotic cows (both n = 15). BMEC were incubated with 0, 0.3, 0.6, or 0.9 mM H2O2 for 6 h with/without a 30 min incubation of an antioxidant MitoQ (1 μM). Then BMEC were incubated with SIRT3 overexpression adenovirus (Ad-SIRT3) for 6 h followed by a 6 h incubation with 0.6 mM H2O2. Finally, BMEC were treated with the AMPK inhibitor Compound C (Cd C,10 μM) for 30 min before the H2O2 challenge, or cells were initially treated with the AMPK agonist MK8722 (10 μM) for 30 min followed by a 30-h culture with/without si-SIRT3 and eventually the H2O2 exposure. Ketotic cows displayed higher levels of Bax, Caspase-3 and Bax/Bcl-2 but lower levels of Bcl-2 in mammary glands. H2O2 incubation displayed similar results, exhibiting a dose-dependent manner between the H2O2 concentration and the apoptosis degree. Mito Q pretreatment reduced cellular reactive oxygen species and rescued cells from apoptosis. Ketotic cows had a lower mammary protein abundance of SIRT3. Similarly, H2O2 incubation downregulated both mRNA and protein levels of SIRT3 in a dose- and time-dependent manner. Ad-SIRT3 infection lowered levels of cellular reactive oxygen species, Bax, Caspase-3 and Bax/Bcl-2 but increased levels of Bcl-2. TUNEL assays confirmed that Ad-SIRT3 infection mitigated H2O2-induced apoptosis. Both ketotic cows and H2O2-induced BMEC had lower levels of p-AMPK and p-AMPK/AMPK. Additionally, Cd C pretreatment decreased SIRT3 and Bcl-2 expression but increased levels of Bax and Caspase-3. Contrary to the inhibitor, MK8722 had opposite effects and reduced the percentage of apoptotic cells. However, these effects of MK8722 were reversed upon SIRT3 silencing. In conclusion, in vivo data confirmed that ketosis is associated with greater apoptosis and restricted AMPK-SIRT3 signaling in mammary glands; in vitro data indicated that SIRT3 mitigates OS-induced apoptosis via AMPK signaling. As such, there may be potential benefits for targeting the AMPK-SIRT3 axis to help counteract the negative effects of mammary glands during ketosis.

Sirtuin 3 inhibits nuclear factor-κB signaling activated by a fatty acid challenge in bovine mammary epithelial cells

Susceptibility to mastitis is highest during the peripartal (transition) period and is often concomitant with other comorbidities such as ketosis. Although infection with pathogenic microorganisms and immune-dysfunction around calving clearly play key roles in mastitis development, other metabolic factors also contribute. Sirtuin 3 (SIRT3), a mitochondrial deacetylase regulating energy and redox homeostasis, antagonizes the lipotoxic effects of nonesterified fatty acids (NEFA). Thus, we hypothesized that increases in circulating NEFA concentrations, as observed in the transition period, provokes inflammatory responses that can be reversed via activation of SIRT3. Here we aimed to study (1) proinflammatory NF-κB signaling and SIRT3 abundance in mammary tissue of ketotic cows and healthy controls, and (2) the effect of SIRT3 on NF-κB activation in bovine mammary epithelial cells (BMEC) treated with high levels of NEFA. The mammary gland biopsy samples were from a previous study, which included 15 healthy cows and 15 ketotic cows. Primary BMEC were isolated from 3 healthy Holstein cows with collagenase III digestion. Purified BMEC were incubated with or without SIRT3 overexpression adenovirus for 48 h, then treated with 0, 0.6, 1.2, or 2.4 mM NEFA for 24 h. Mammary tissue of ketotic cows was associated with lower protein abundance of SIRT3 along with greater NF-κB P65 phosphorylation levels (p-NF-κB P65), p-NF-κB P65:NF-κB P65 ratio, and mRNA abundance of IL1B and IL6. In BMEC, exogenous NEFA dose-dependently reduced protein abundance of SIRT3, but increased p-NF-κB P65, p-NF-κB P65:NF-κB P65 ratio, and mRNA abundance of IL1B and IL6. Compared with green fluorescent protein adenovirus vector + NEFA, overexpression of SIRT3 in NEFA-treated BMEC downregulated p-NF-κB P65 and mRNA abundance of IL1B and IL6. Immunofluorescence indicated that overexpression of SIRT3 inhibited nuclear translocation of NF-κB P65. Overall, our data demonstrated that ketosis is associated with a reduction in SIRT3 abundance and activation of NF-κB signaling in the mammary gland. In vitro data provided evidence that high NEFA concentrations inhibit SIRT3, which contributes to enhanced NF-κB signaling including nuclear translocation and a pro-inflammatory response. The data suggest a promising role of SIRT3 as a target for helping alleviate localized inflammation of the mammary gland resulting from exposure to high concentrations of NEFA.

Sirtuin 3 Restores Synthesis and Secretion of Very Low-Density Lipoproteins in Cow Hepatocytes Challenged with Nonesterified Fatty Acids In Vitro

Fatty liver is closely associated with elevated concentrations of nonesterified fatty acids (NEFA) and a low level of very low-density lipoproteins (VLDL) in blood of dairy cows. High NEFA inhibit the VLDL synthesis and assembly, and cause hepatic triacylglycerol (TAG) deposition. Sirtuin 3 (SIRT3), a mitochondrial deacetylase, antagonizes NEFA-induced TAG accumulation through modulating expressions of fatty acid synthesis and oxidation genes in cow hepatocytes. However, the role of SIRT3 in the VLDL synthesis and assembly was largely unknown. Here we aimed to test whether SIRT3 would recover the synthesis and assembly of VLDL in cow hepatocytes induced by high NEFA. Primary cow hepatocytes were isolated from 3 Holstein cows. Hepatocytes were infected with SIRT3 overexpression adenovirus (Ad-SIRT3), SIRT3-short interfering (si) RNA, or first infected with Ad-SIRT3 and then incubated with 1.0 mM NEFA (Ad-SIRT3 + NEFA). Expressions of key genes in VLDL synthesis and the VLDL contents in cell culture supernatants were measured. SIRT3 overexpression significantly increased the mRNA abundance of microsomal triglyceride transfer protein (MTP), apolipoprotein B100 (ApoB100) and ApoE (p < 0.01), and raised VLDL contents in the supernatants (p < 0.01). However, SIRT3 silencing displayed a reverse effect in comparison to SIRT3 overexpression. Compared with NEFA treatment alone, the Ad-SIRT3 + NEFA significantly upregulated the mRNA abundance of MTP, ApoB100 and ApoE (p < 0.01), and increased VLDL contents in the supernatants (p < 0.01). Our data demonstrated that SIRT3 restored the synthesis and assembly of VLDL in cow hepatocytes challenged with NEFA, providing an in vitro basis for further investigations testing its feasibility against hepatic TAG accumulation in dairy cows during the perinatal period.

Effect of three weaning methods on behavioural, cortisol and weight changes in buffalo calves

Context Calves reared in cow–calf systems separated from their mothers could present various physiological and behavioural changes. Aims The objective of the present study was to examine the effect of different weaning protocols on plasma cortisol concentrations, behavioural responses, and weight gain in water buffalo calves. Methods In total, 40 Murrah buffalo calves (20 males, 20 females) aged 7–8 months and weighing 247.05 ± 33.23 kg were included. The animals were assigned to one of four treatments (10 per group, 5 males, 5 females), as follows: non-weaned calves (NoW); calves weaned abruptly on Day 0 (AW); calves fitted with nose-flaps anti-suckling devices on Day –7 and completely separated from their mothers on Day 0 (NFW); and calves separated from their mothers by a fence line on Day –7 and, then completely separated from their mothers on Day 0 (FENW). Plasma cortisol was measured on Days –7, –6, –4, 0, 1 and 3, while the behavioural variables were measured from Day –7 to Day –4, and from Day 0 to Day 3. The weight of the calves was evaluated on Days –9, –7, 0 and 3. Key results AW calves presented higher cortisol concentrations than did NoW calves (P = 0.0002) and showed a marked increase in walking and decrease in grazing and ruminating on Days 0–3 compared with the other treatments (P &lt; 0.0001). The use of NFW caused behavioural changes after the device placement and after the final separation from the mother (P &lt; 0.0001). In FENW, behavioural changes were observed after the separation by a linear fence but no negative changes were observed after the final separation from the mothers, and positive behaviours such as grazing, rumination and exploration increased. No changes in weight gain were observed (P &gt; 0.05). Conclusions No clear effects were observed in the implementation of alternative weaning, since both NFW and FENW presented changes related to stress at weaning, compared with abrupt weaning. However, in FENW, no behavioural alterations were observed after definitive separation from their mothers. Implications The application of fence-line separation before final separation could be a promising strategy to reduce stress at weaning in water buffalo calves. However, further studies are required to determinate its long-term effect.

Sirtuin 3 improves fatty acid metabolism in response to high nonesterified fatty acids in calf hepatocytes by modulating gene expression

Sirtuin 3 (SIRT3), a mitochondrial deacetylase, is a key regulator of energy metabolism in the liver. In nonruminants, the hepatic abundance of SIRT3 is decreased in individuals with nonalcoholic fatty liver diseases, and recovery of SIRT3 alleviates hepatic triacylglycerol (TG) deposition. However, the level of SIRT3 expression and its effects on lipid metabolism in dairy cows have not been characterized. Here we studied the hepatic expression of SIRT3 in cows with fatty liver and the role of SIRT3 in fatty acid metabolism in bovine hepatocytes. This in vivo study involved 10 healthy cows and 10 cows with fatty liver, from which we collected samples of liver tissue and blood. Primary hepatocytes were isolated from Holstein calves and treated with 0, 0.5, or 1.0 mM nonesterified fatty acids (NEFA) for 24 h or transinfected with SIRT3 overexpression adenovirus (Ad-SIRT3)/SIRT3-short interfering (si)RNA for 48 h. Cows with fatty liver displayed lower serum glucose concentrations but higher serum NEFA and β-hydroxybutyrate concentrations relative to healthy cows. Cows with fatty liver also had significant lower mRNA and protein abundance of hepatic SIRT3. Incubation of primary hepatocytes with NEFA reduced SIRT3 abundance in primary hepatocytes in a dose-dependent manner. Fatty acid (1 mM) treatment also markedly increased the abundance of acetyl-CoA carboxylase 1 (ACC1) and fatty acid synthase (FAS) but significantly decreased the abundance of carnitine palmitoyltransferase I (CPT1A), carnitine palmitoyltransferase II (CPT2), and acyl-CoA oxidase (ACO). Knockdown of SIRT3 by SIRT3-siRNA downregulated the mRNA abundance of CPT1A, CPT2, and ACO. In contrast, overexpression of SIRT3 by Ad-SIRT3 upregulated the mRNA abundance of CPT1A, CPT2, and ACO; downregulated the mRNA abundance of ACC1 and FAS; and consequently, decreased intracellular TG concentrations. Overexpression of SIRT3 ameliorated exogenous NEFA-induced TG accumulation by downregulating the abundance of ACC1 and FAS and upregulating the abundance of CPT1A, CPT2, and ACO in calf hepatocytes. Our data demonstrated that cows with fatty liver had lower hepatic SIRT3 contents, and an increase in SIRT3 abundance by overexpression mitigated TG deposition by modulating the expression of lipid metabolism genes in bovine hepatocytes. These data suggest a possible role of SIRT3 as a therapeutic target for fatty liver disease prevention in periparturient dairy cattle.