The interplay between non-esterified fatty acids and bovine peroxisome proliferator-activated receptors: results of an in vitro hybrid approach

Abstract

Background: In dairy cows circulating non-esterified fatty acids (NEFA) increase early post-partum while liver and other tissues undergo adaptation to greater lipid metabolism, mainly regulated by peroxisome proliferator-activated receptors (PPAR). PPAR are activated by fatty acids (FA), but it remains to be demonstrated that circulating NEFA or dietary FA activate bovine PPAR. We hypothesized that circulating NEFA and dietary FA activate PPAR in dairy cows. Methods: The dose-response activation of PPAR by NEFA or dietary FA was assessed using HP300e digital dispenser and luciferase reporter in several bovine cell types. Cells were treated with blood plasma isolated from Jersey cows before and after parturition, NEFA isolated from the blood plasma, FA released from lipoproteins using milk lipoprotein lipase (LPL), and palmitic acid (C16:0). Effect on each PPAR isotype was assessed using specific synthetic inhibitors. Results: NEFA isolated from blood serum activate PPAR linearly up to~4-fold at 400 μmol/L in MAC-T cells but had cytotoxic effect. Addition of albumin to the culture media decreases cytotoxic effects of NEFA but also PPAR activation by~2-fold. Treating cells with serum from peripartum cows reveals that much of the PPAR activation can be explained by the amount of NEFA in the serum (R 2 = 0.91) and that the response to serum NEFA follows a quadratic tendency, with peak activation around 1.4 mmol/L. Analysis of PPAR activation by serum in MAC-T, BFH-12 and BPAEC cells revealed that most of the activation is explained by the activity of PPARδ and PPARγ, but not PPARα. Palmitic acid activated PPAR when added in culture media or blood serum but the activation was limited to PPARδ and PPARα and the response was nil in serum from post-partum cows. The addition of LPL to the serum increased > 1.5-fold PPAR activation. Conclusion: Our results support dose-dependent activation of PPAR by circulating NEFA in bovine, specifically δ and γ isotypes. Data also support the possibility of increasing PPAR activation by dietary FA; however, this nutrigenomics approach maybe only effective in pre-partum but not post-partum cows.

Hepatic transcriptomic adaptation from prepartum to postpartum in dairy cows

“…As Figure 5 shows, it appears that more putative downstream targets of PPARD were affected compared with the putative downstream targets of PPARA. Recent data generated in vitro revealed that PPARD responded to NEFA in bovine hepatocytes, but PPARA did not (Busato and Bionaz, 2020). The high importance of PPAR during the transition, as observed in the present manuscript, or during the response to changes in the energy level in the diet (Loor et al, 2007;McCabe et al, 2012), further supports the importance of PPAR in the adaptation of the liver to the transition period (Bionaz et al, 2013).…”

“…The downregulation or lack of change in expression of PPARA, with a higher change in putative downstream target genes, appears to be a contradiction; however, as previously argued (Bionaz et al, 2015), the activity of a transcription factor is not dependent on its transcription. The increased activation of PPAR in the liver of transition cows is partly explained by increased NEFA, as previously argued (Bionaz et al, 2013) and recently demonstrated in vitro (Busato and Bionaz, 2020). As Figure 5 shows, it appears that more putative downstream targets of PPARD were affected compared with the putative downstream targets of PPARA.…”

In vitro–In vivo Hybrid Approach for Studying Modulation of NRF2 in Immortalized Bovine Mammary Cells

“…It is also of interest the lower overall cell viability in serum collected from post-partum vs. pre-partum cows, suggesting that the former may contain compounds that negatively affect cell viability. Among those compounds, free fatty acids are known to be cytotoxic (Busato and Bionaz, 2020) and are elevated during the early post-partum (Bionaz et al, 2007;Gonçalves-De-Albuquerque et al, 2019). However, blood serum is also known to be cytotoxic by the release of reactive oxygen species when exposed to cell culture environment, as recently reviewed (Boehm and Bourke, 2019).…”

Diet Composition Affects Liver and Mammary Tissue Transcriptome in Primiparous Holstein Dairy Cows

“…Shahzad et al (2014) demonstrated that "PPAR signaling" pathway plays a role in regulating the transcriptomic adaptation of the liver to different levels of dietary energy in prepartum cows [30]. Thus, in the present study, the modest inhibition of PPAR signaling pathway by CS compared to MF can be a response to different dietary energy levels between the two diets (lower in CS vs. MF) but also to the different composition of fatty acids in the diet, with CS having less 16:0 in the diet and less 18:0 intake in CS vs. MF, both with evidence of PPAR activation in dairy cows [29,31].…”

“…The PPAR isotypes are considered important in the whole economy of lipid metabolism in liver of mammals [28]. Recent data indicated PPARδ being the major PPAR isotypes responding to NEFA in bovine liver [29]. Shahzad et al (2014) demonstrated that "PPAR signaling" pathway plays a role in regulating the transcriptomic adaptation of the liver to different levels of dietary energy in prepartum cows [30].…”