Analyzing human knockouts to validate GPR151 as a therapeutic target for reduction of body mass index

Novel drug targets for sustained reduction in body mass index (BMI) are needed to curb the epidemic of obesity, which affects 650 million individuals worldwide and is a causal driver of cardiovascular and metabolic disease and mortality. Previous studies reported that the Arg95Ter nonsense variant of GPR151, an orphan G protein-coupled receptor, is associated with reduced BMI and reduced risk of Type 2 Diabetes (T2D). Here, we further investigate GPR151 with the Pakistan Genome Resource (PGR), which is one of the largest exome biobanks of human homozygous loss-of-function carriers (knockouts) in the world. Among PGR participants, we identify eleven GPR151 putative loss-of-function (plof) variants, three of which are present at homozygosity (Arg95Ter, Tyr99Ter, and Phe175LeufsTer7), with a cumulative allele frequency of 2.2%. We confirm these alleles in vitro as loss-of-function. We test if GPR151 plof is associated with BMI, T2D, or other metabolic traits and find that GPR151 deficiency in complete human knockouts is not associated with clinically significant differences in these traits. Relative to Gpr151+/+ mice, Gpr151-/- animals exhibit no difference in body weight on normal chow and higher body weight on a high-fat diet. Together, our findings indicate that GPR151 antagonism is not a compelling therapeutic approach to treatment of obesity.

In vivo measurement of the acetylation state of sirtuin substrates as a proxy for sirtuin activity

Evaluating the precise catalytic activity of sirtuin proteins in vivo is a challenging endeavor. Enzymological methods, including those employed in commercially available kits, require the isolation of immunopurified protein from cells or tissues, which can perturb regulatory protein-protein interactions as well as remove the enzyme from the reaction-altering effects of intracellular NAD(+), nicotinamide, and O-acetyl-ADP ribose concentrations. As such, the measurement of the steady state acetylation status of select sirtuin substrates in vivo remains an important tool for evaluating changes in sirtuin activity. Here, we describe how to perform the analysis of the acetylation status of key SIRT1 and SIRT3 targets in rodent tissues and cultured cells.

Taurine-induced long-lasting potentiation in the rat hippocampus shows a partial dissociation from total hippocampal taurine content and independence from activation of known taurine transporters

Perfusion with high millimolar levels of taurine evoked a long-lasting potentiation (LLP-TAU) of synaptic transmission in the Schaffer-collateral CA1 region of the rat hippocampus. Although LLP-TAU showed some correlations to increases in the total taurine content of hippocampal slices, it could not be blocked by the taurine transport inhibitor guanidinoethanesulfonic acid (GES), which was able to significantly reduce total slice taurine uptake. Inhibition of GABA transport by either nipecotic acid or beta-guanidinopropionate failed to abolish LLP-TAU and had no significant effect on taurine uptake. The combination of GES and nipecotic acid also had no significant effect on LLP-TAU. Experiments with transportable structural analogs of taurine (beta-aminoisobutyric acid, homotaurine, and isethionic acid) suggest that activation of classical taurine transport pathways does not always yield a robust LLP-TAU. Hippocampal LLP-TAU could be significantly attenuated, however, by pre-incubation with submillimolar levels of taurine. In summary, the development of LLP-TAU in the rat hippocampus appears to be associated with the intracellular accumulation rather than the activation of known transporters of taurine, but the precise means of its accumulation remains to be identified.

Building Biosynthetic Schools: Reviewing Compartmentation of CNS Taurine Synthesis

Taurine is one of the mammalian brain's most abundant and indispensable amino acids. Considerable strides have been made in understanding taurine biosynthesis within the brain, but many disputed issues nonetheless remain. Heading the list is the cellular origin of biosynthetically derived taurine: glial or neuronal? This article reviews the competing theories surrounding cellular compartmentation of taurine biosynthesis in the brain. It concludes that while in vitro systems clearly show astrocytes to be fully capable of taurine synthesis and neurons to be limited to synthesizing taurine from hypotaurine, there is insufficient evidence to attribute these processes to any one cell type in vivo. Instead, there is a growing body of evidence that suggests brain taurine biosynthesis is occurring via a more cooperative metabolic interaction between astrocytes and neurons.

The cytoprotective role of taurine in exercise-induced muscle injury

Intense exercise is thought to increase oxidative stress and damage muscle tissue. Taurine is present in high concentration in skeletal muscle and may play a role in cellular defenses against free radical-mediated damage. The aim of this study was to determine if manipulating muscle levels of taurine would alter markers of free radical damage after exercise-induced injury. Adult male Sprague-Dawley rats were supplemented via the drinking water with either 3% (w/v) taurine (n = 10) or the competitive taurine transport inhibitor, beta-alanine (n = 10), for one month. Controls (n = 20) drank tap water containing 0.02% taurine and all rats were placed on a taurine free diet. All the rats except one group of sedentary controls (n = 10) were subjected to 90 minutes of downhill treadmill running. Markers of cellular injury and free radical damage were determined along with tissue amino acid content. The 3% taurine treatment raised plasma levels about 2-fold and 3% beta-alanine reduced plasma taurine levels about 50%. Taurine supplementation (TS) significantly increased plasma glutamate levels in exercised rats. Exercise reduced plasma methionine levels and taurine prevented its decline. Taurine supplementation increased muscle taurine content significantly in all muscles except the soleus. beta-alanine decreased muscle taurine content about 50% in all the muscles examined. Lipid peroxidation (TBARS) was significantly increased by exercise in the extensor digitorium longus (EDL) and gastrocnemius (GAST) muscles. Both taurine and beta-alanine completely blocked the increase in TBARs in the EDL, but had no effect in the GAST. Muscle content of the cytosolic enzyme, lactate dehydrogenase (LDH) was significantly decreased by exercise in the GAST muscle and this effect was attenuated by both taurine and beta-alanine. Muscle myeloperoxidase (MPO) activity was significantly elevated in the gastrocnemius muscle, but diet had no effect. MPO activity was significantly increased by exercise in the liver and both taurine and beta-alanine blocked this effect. There was no effect of either exercise or the diets on MPO activity in the lung or spleen. Running performance as assessed by a subjective rating scale was improved by taurine supplementation and there was a significant loss in body weight in the beta-alanine-treated rats 24 hours after exercise. In summary, taurine supplementation or taurine depletion had measurable cytoprotective actions to attenuate exercise-induced injury.

Feasibility study on a composite material construction technique for highly stressed components in reciprocal walking orthoses for paraplegic patients

Reciprocal walking for thoracic level paraplegic patients using reciprocal walking orthoses has become a routine treatment option. Two general design options are currently deployed within an overall treatment regime. Research has shown that one has better walking efficiency but is cosmetically less acceptable to the patient. Design analysis and experimental data have shown that a major factor in improved walking efficiency is the lateral stiffness of the body brace section of the orthosis. This is the area where problems of cosmesis in the more efficient orthosis are perceived because of the employment of metallic structures. The use of composite material structures to achieve shapes which are more closely conforming to the patient is an attractive option. However the brittle nature of these materials makes it unlikely that the requirement for the ductile failure mode will be achieved from a straightforward moulding. A new construction technique has been devised which has the potential to provide a safe failure mode with greater stiffness and lighter weight. This feasibility study has been undertaken to demonstrate its potential so that further work can be justified which will provide sufficient evidence to support a patent application. The successful outcome of the study, in which stiffness was increased by 60 per cent with a weight reduction of 50 per cent and a failure mode comparable with the original metal structure, suggests that further work will enable the dilemma in the choice of orthosis to be resolved.