Ellagic acid (EA), because of its remarkable health-promoting
ability,
has aroused widespread interest in the fields of nutrition and medicine.
However, no reports showed that EA regulates mitochondrial biogenesis
as well as muscle fiber-type composition in pigs. Our study found
that dietary 75 and 150 mg/kg EA obviously augmented the slow myosin
heavy chain (MyHC) protein level, the number of slow-twitch muscle
fibers, and the activity of malate dehydrogenase (MDH) in the longissimus
thoracis (LT) muscle of growing-finishing pigs. In contrast, dietary
75 and 150 mg/kg EA decreased the fast MyHC level, the number of fast-twitch
muscle fibers, and the activity of lactate dehydrogenase (LDH) in
the LT muscle. In addition, our further study found that dietary 75
and 150 mg/kg EA promoted the mitochondrial DNA (mtDNA) content, the
mRNA expressions of ATP synthase (ATP5G), mtDNA transcription
factor A (TFAM), AMP-activated protein kinase α1
(AMPKα1), peroxisome proliferator-activated
receptor-γ coactivator-1α (PGC-1α)
and sirtuin 1 (Sirt1), and the level of phospho-LKB1
(P-LKB1), phospho-AMPK (P-AMPK), Sirt1, and PGC-1α in the LT
muscle. In vitro, 5, 10, and 20 μmol/L EA treatment
upregulated the level of slow MyHC, but only 10 μmol/L EA treatment
decreased fast MyHC protein expression in porcine skeletal muscle
satellite cells (PSCs). In addition, our data again found that 10
μmol/L EA treatment promoted the mtDNA content, the mRNA levels
of ATP5G, mitochondrial transcription factor b1 (TFB1M), citrate synthase (Cs), AMPKα1, PGC-1α,
and Sirt1, and the protein expressions of P-AMPK,
P-LKB1, PGC-1α, and Sirt1 in PSCs. What is more, inhibition
of the AMPK signaling pathway by AMPKα1 siRNA significantly
eliminated the improvement of EA on muscle fiber-type composition
as well as the mtDNA content in PSCs. In conclusion, EA altered muscle
fiber-type composition and promoted mitochondrial biogenesis through
the AMPK signaling pathway.