Jacob D. Brown

Thyroid hormone effects on LKB1, MO25, phospho-AMPK, phospho-CREB, and PGC-1α in rat muscle

Expression of all of the isoforms of the subunits of AMP-activated protein kinase (AMPK) and AMPK activity is increased in skeletal muscle of hyperthyroid rats. Activity of AMPK in skeletal muscle is regulated principally by the upstream kinase, LKB1. This experiment was designed to determine whether the increase in AMPK activity is accompanied by increased expression of the LKB1, along with binding partner proteins. LKB1, MO25, and downstream targets were determined in muscle extracts in control rats, in rats given 3 mg of thyroxine and 1 mg of triiodothyronine per kilogram chow for 4 wk, and in rats given 0.01% propylthiouracil (PTU; an inhibitor of thyroid hormone synthesis) in drinking water for 4 wk (hypothyroid group). LKB1 and MO25 increased in the soleus of thyroid hormone-treated rats vs. the controls. In other muscle types, LKB1 responses were variable, but MO25 increased in all. In soleus, MO25 mRNA increased with thyroid hormone treatment, and STRAD mRNA increased with PTU treatment. Phospho-AMPK and phospho-ACC were elevated in soleus and gastrocnemius of hyperthyroid rats. Thyroid hormone treatment also increased the amount of phospho-cAMP response element binding protein (CREB) in the soleus, heart, and red quadriceps. Four proteins having CREB response elements (CRE) in promoter regions of their genes (peroxisome proliferator-activated receptor-gamma coactivator-1alpha, uncoupling protein 3, cytochrome c, and hexokinase II) were all increased in soleus in response to thyroid hormones. These data provide evidence that thyroid hormones increase soleus muscle LKB1 and MO25 content with subsequent activation of AMPK, phosphorylation of CREB, and expression of mitochondrial protein genes having CRE in their promoters.

Skeletal muscle dysfunction in muscle-specific LKB1 knockout mice

Liver kinase B1 (LKB1) is a tumor-suppressing protein that is involved in the regulation of muscle metabolism and growth by phosphorylating and activating AMP-activated protein kinase (AMPK) family members. Here we report the development of a myopathic phenotype in skeletal and cardiac muscle-specific LKB1 knockout (mLKB1-KO) mice. The myopathic phenotype becomes overtly apparent at 30-50 wk of age and is characterized by decreased body weight and a proportional reduction in fast-twitch skeletal muscle weight. The ability to ambulate is compromised with an often complete loss of hindlimb function. Skeletal muscle atrophy is associated with a 50-75% reduction in mammalian target of rapamycin pathway phosphorylation, as well as lower peroxisome proliferator-activated receptor-alpha coactivator-1 content and cAMP response element binding protein phosphorylation (43 and 40% lower in mLKB1-KO mice, respectively). Maximum in situ specific force production is not affected, but fatigue is exaggerated, and relaxation kinetics are slowed in the myopathic mice. The increased fatigue is associated with a 30-78% decrease in mitochondrial protein content, a shift away from type IIA/D toward type IIB muscle fibers, and a tendency (P=0.07) for decreased capillarity in mLKB1-KO muscles. Hearts from myopathic mLKB1-KO mice exhibit grossly dilated atria, suggesting cardiac insufficiency and heart failure, which likely contributes to the phenotype. These findings indicate that LKB1 plays a critical role in the maintenance of both skeletal and cardiac function.

Effects of voluntary running on oxygen consumption, RQ, and energy expenditure during primary prevention of diet-induced obesity in C57BL/6N mice

Diet-induced obesity (DIO) in C57BL/6 mice is the standard model for studying obesity in mice. The few reports of DIO utilizing voluntary running provide contradictory results with respect to prevention of obesity. However, total energy expenditures associated with voluntary running during DIO are unknown. We hypothesized that voluntary running would increase the amount of total energy expended during DIO. Female C57BL/6N mice were randomly assigned to one of three experimental groups [high-fat diet with voluntary running (HFRun); high-fat diet without running (HFSed); and low-fat diet without running (LFSed)] for a 10-wk period. We confirmed production of obesity in HFSed, and more importantly demonstrated primary prevention of obesity by voluntary running in a group of cohorts (HFRun). Indirect calorimetry was performed to determine oxygen consumption (Vo(2)) and respiratory quotient (RQ). The following novel mechanisms were identified in female C57BL/6N mice: 1) HFRun showed ∼2 times greater total energy expenditures during a day compared with HFSed and LFSed; 2) HFRun had increased Vo(2) compared with HFSed and LFSed, lower RQ in the light period than HFSed, and lower RQ in both light and dark periods than LFSed; and 3) in the HFRun group, the magnitude of change in Vo(2) and RQ differed in dark and light periods during voluntary running. Our data combined with existing literature point to a potential threshold of physical activity that would prevent DIO in this mouse model. These data give a mechanistic explanation to resolve contradictory reports on whether voluntary running can prevent obesity in the DIO mouse model. In conclusion, voluntary running rescues high-fat fed, female C57BL/6N mice from obesity in DIO by doubling energy expenditure during the dark period and significantly increasing energy expenditure during the light cycle.

Early depression of Ankrd2 and Csrp3 mRNAs in the polyribosomal and whole tissue fractions in skeletal muscle with decreased voluntary running

The wheel-lock (WL) model for depressed ambulatory activity in rats has shown metabolic maladies ensuing within 53-173 h after WL begins. We sought to determine if WL beginning after 21-23 days of voluntary running in growing female Wistar rats affected the mRNA profile in the polyribosomal fraction from plantaris muscle shortly following WL. In experiment 1, WL occurred at 0200 and muscles were harvested at 0700 daily at 5 h (WL5h, n = 4), 29 h (WL29h, n = 4), or 53 h (WL53h, n = 4) after WL. Affymetrix Rat Gene 1.0 ST Arrays were used to test the initial question as to whether WL affects mRNA occupancy on skeletal muscle polyribosomes. Using a false discovery rate of 15%, no changes in mRNAs in the polyribosomal fraction were observed at WL29h and eight mRNAs (of over 8,200 identified targets) were altered at WL53h compared with WL5h. Interestingly, two of the six downregulated genes included ankyrin repeat domain 2 (Ankrd2) and cysteine-rich protein 3/muscle LIM protein (Csrp3), both of which encode mechanical stretch sensors and RT-PCR verified their WL-induced decline. In experiment 2, whole muscle mRNA and protein levels were analyzed for Ankrd2 and Csrp3 from the muscles of WL5h (4 original samples + 2 new), WL29h (4 original), WL53h (4 original + 2 new), as well as WL173 h (n = 6 new) and animals that never ran (SED, 4-5 new). Relative to WL5h controls, whole tissue Ankrd2 and Csrp3 mRNAs were lower (P < 0.05) at WL53h, WL173h, and SED; Ankrd2 protein tended to decrease at WL53h (P = 0.054) and Csrp3 protein was less in WL173h and SED rats (P < 0.05). In summary, unique early declines in Ankrd2 and Csrp3 mRNAs were identified with removal of voluntary running, which was subsequently followed by declines in Csrp3 protein levels during longer periods of wheel lock.

Effect of LKB1 deficiency on mitochondrial content, fibre type and muscle performance in the mouse diaphragm

Aim:  The liver kinase B1 (LKB1)/AMP‐activated protein kinase (AMPK) signalling pathway is a major regulator of skeletal muscle metabolic processes. During exercise, LKB1‐mediated phosphorylation of AMPK leads to its activation, promoting mitochondrial biogenesis and glucose transport, among other effects. The roles of LKB1 and AMPK have not been fully characterized in the diaphragm.

Is pornography consumption associated with condom use and intoxication during hookups

In order to examine whether pornography consumption is associated with risky sexual behaviour among emerging adults, we examined two large samples of those who reported hooking up in the past 12 months (combined n = 1216). Pornography use was associated with a higher likelihood of having a penetrative hookup; a higher incidence of intoxication during hookups for men (but a lower incidence of intoxication during hookups for women); increasing levels of intoxication during hookups for men but decreasing levels of intoxication for women; and a higher likelihood of being in the riskiest category of having a penetrative hookup, without a condom, while intoxicated. For each of these outcomes, our point estimates for Study 2 fell within the 95% confidence intervals from Study 1. Controlling for trait self-control, binge drinking frequency, broader problematic patterns of alcohol use, openness to experience, and attitudes toward casual sex did not change the pattern of results. Implications for interventions to reduce sexual risk are discussed.