Expression profiling of the {gamma}-subunit isoforms of AMP-activated protein kinase suggests a major role for {gamma}3 in white skeletal muscle

1 Arexis AB, SE-413 46 Gothenburg; 2 Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, and 4 Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala Biomedical Center, SE-751 23 Uppsala; and 3 Department of Surgical Sciences, Karolinska Institutet, SE-171 77 Stockholm, Sweden Submitted 3 April 2003 ; accepted in final form 6 October 2003 Expression patterns of the three isoforms of the regulatory -subunit of AMP-activated protein kinase (AMPK) were determined in various tissues from adult humans, mice, and rats, as well as in human primary muscle cells. Real-time PCR-based quantification of mRNA showed similar expression patterns in the three species and a good correlation with protein expression in mice and rats. The 3-isoform appeared highly specific to skeletal muscle, whereas 1 and 2 showed broad tissue distributions. Moreover, the proportion of white, type IIb fibers in the mouse and rat muscle samples, as indicated by real-time PCR quantification of Atp1b2 mRNA, showed a strong positive correlation with the expression of 3. In samples of white skeletal muscle, 3 clearly appeared to be the most abundant -isoform. Differentiation of human primary muscle cells from myoblasts into multinucleated myotubes was accompanied by upregulation of 3 mRNA expression, whereas levels of 1 and 2 remained largely unchanged. However, even in these cultured myotubes, 2 was the most highly expressed isoform, indicating a considerable difference compared with adult skeletal muscle. Immunoblot analysis of mouse gastrocnemius and quadriceps muscle extracts precipitated with a 3-specific antibody showed that 3 was exclusively associated with the 2- and 2-subunit isoforms. The observation that the AMPK 3 isoform is expressed primarily in white skeletal muscle, in which it is the predominant -isoform, strongly suggests that 3 has a key role in this tissue. adenosine monophosphate; real-time polymerase chain reaction; antibodies; mouse; rat; human Address for reprint requests and other correspondence: S. Marklund, Dept. of Animal Breeding and Genetics, Swedish Univ. of Agricultural Sciences, Uppsala Biomedical Center, Box 597, SE-751 24 Uppsala, Sweden (E-mail: Stefan.Marklund{at}bmc.uu.se ).