Dietary Arthrospira platensis modulates autophagy-related markers in breast muscle of heat-stressed broilers and chicken primary myoblasts.

Previous study showed that Arthrospira platensis (Spirulina, SP) enhanced breast yield in heat-stressed broilers via modulation of proteostasis network. As autophagy is a fundamental component of this cellular process, the objective of this study was to determine the effect of SP supplementation on autophagy machinery in breast muscle of heat-stressed broilers. one-day old male Cobb 500 broilers (n=600) were randomly allocated to 12 environmental chambers (2 floor pens/chamber, 24 pens in total, 25 birds/pen) and fed two diets (standard control diet, C vs. SP-supplemented diet at 0.5% inclusion rate). On day 29 to 42, birds were exposed to 2 environmental conditions (thermoneutral, TN, 24°C vs. cyclic HS 36°C, 8h/day). A pair-fed group was included to distinguish between the effect of HS per se and the effect associated with feed depression-induced by HS. In vitro studies were conducted to test the effect of SP compounds, quercetin (QCT, 10μM) and benzoic acid (BA, 50μM) separately or combined, on autophagy machinery in heat-stressed (45°C for 6h) and/or starved (HBSS) chicken primary embryonic myoblasts (CPEM). Untreated CPEM cells maintained at 37°C were used as control. Expression of Genes and proteins involved in autophagy processes were determined by qPCR and Western blot, respectively (n =6 birds/group). Data were analyzed by two-way ANOVA and Tukey's HSD test, and significance was set at P < 0.05. Compared to control diet, in-feed SP supplementation modulated autophagy nucleation and initiation via reducing p-ULK1Ser555 (P = 0.0002) in TN, HS, and PF conditions, and ATG13 (P = 0.0385) protein levels in HS-broiler breasts. Supplementation of SP significantly decreased Rab7 protein expression in breast of HS broilers, indicating an inhibition of autophagosome maturation and fusion. Treatment with QCT and BA combined, recapitulated some of SP effects, by significantly modulating ATG13, ATG5, ATG7, LC3, and P62 protein levels in heat-stressed and starved CPEM cells. Collectively, this is the first report showing that SP and its compound (QCT, BA) modulated the autophagy processes in heat-stressed broiler breasts and CPEM, which might explain its beneficial effect on breast yield enhancement.