Many cell processes that are disrupted in aging skeletal muscle are also regulated by AMP‐activated protein kinase (AMPK). However, the effect of aging on skeletal muscle AMPK activation is controversial and unclear. Our purpose was to determine the effect of old‐age on endurance‐type contraction‐induced AMPK activation in skeletal muscle. Gastrocnemius muscles from YA (8 mo old) and O (30 mo old) male Fischer344 x Brown Norway F1 hybrid rats were removed after 10 minutes of electrically stimulated in situ contractions (STIM). Muscles from the resting legs served as controls (REST). AMPK phosphorylation and AMPKα2 activity were 63% and 19% lower, respectively, in O vs. YA muscles after STIM. AMPKα1 activity was unaffected by STIM in YA, but increased by 30% in O muscles. AMPK α1 protein concentration was 45% greater, while α2 content was 18% lower in O vs. YA muscles. AMPK β1, β2, and γ1 proteins were unaffected by age, but AMPK γ2 and γ3 concentrations were 75% and 85% lower in O vs. YA muscles, respectively. In conclusion, AMPKα2 activation is impaired while AMPKα1 activation is enhanced after endurance‐type in situ contractions in aged skeletal muscle. This work was funded by NIAMSD Grant AR‐51928.
In liver, the AMP-activated protein kinase kinase (AMPKK) complex was identified as the association of liver kinase B1 (LKB1), mouse protein 25 (MO25α/β), and Ste-20-related adaptor protein (STRADα/β); however, this complex has yet to be characterized in skeletal muscle. We demonstrate the expression of the LKB1-MO25-STRAD complex in skeletal muscle, confirm the absence of mRNA splice variants, and report the relative mRNA expression levels of these proteins in control and muscle-specific LKB1 knockout (LKB1(-/-)) mouse muscle. LKB1 detection in untreated control and LKB1(-/-) muscle lysates revealed two protein bands (50 and 60 kDa), although only the heavier band was diminished in LKB1(-/-) samples [55 ± 2.5 and 13 ± 1.5 arbitrary units (AU) in control and LKB1(-/-), respectively, P < 0.01], suggesting that LKB1 is not represented at 50 kDa, as previously cited. The 60-kDa LKB1 band was further confirmed following purification using polyethylene glycol (43 ± 5 and 8.4 ± 4 AU in control and LKB1(-/-), respectively, P < 0.01) and ion-exchange fast protein liquid chromatography. Mass spectrometry confirmed LKB1 protein detection in the 60-kDa protein band, while none was detected in the 50-kDa band. Coimmunoprecipitation assays demonstrated LKB1-MO25-STRAD complex formation. Quantitative PCR revealed significantly reduced LKB1, MO25α, and STRADβ mRNA in LKB1(-/-) muscle. These findings demonstrate that the LKB1-MO25-STRAD complex is the principal AMPKK in skeletal muscle.
Clinical conditions are described where in dilatation or perforation of an organ or viscus commonly occurs. These include arterial aneurysm, low colon obstruction, ureteropelvic junction obstruction, gastric perforation, hydrocephalus, and bullae. Many fluid or air-containing structures in the body are basically cylinders or spheres. On the basis of the bursting force principle and observations in the above conditions, it is postulated that for a given uniform pressure in a fluid-or air-filled organ, the force tending to expand or burst the organ is greatest at the site of the largest radius of curvature. Weaker or diseased wall areas are predisposed to expansion or rupture and in some instances this may be more important than the difference in bursting forces.
