BackgroundThere is considerable heterogeneity in the rate of lung function decline in chronic obstructive pulmonary disease (COPD), the determinants of which are largely unknown. Observational studies in COPD indicate that low body mass index (BMI) is associated with worse outcomes, and overweight/obesity has a protective effect – the so-called “obesity paradox”. We aimed to determine the relationship between BMI and the rate of FEV1 decline in data from published clinical trials in COPD.MethodsWe performed a systematic review of the literature, and identified 5 randomized controlled trials reporting the association between BMI and FEV1 decline. Four of these were included in the meta-analyses. We analyzed BMI in 4 categories: BMI-I (< 18.5 or <  20 kg/m2), BMI-II (18.5 or 20 to < 25 kg/m2), BMI-III (25 to < 29 or < 30 kg/m2) and BMI-IV (≥29 or ≥ 30 kg/m2). We then performed a meta-regression of all the estimates against the BMI category.ResultsThe estimated rate of FEV1 decline decreased with increasing BMI. Meta-regression of the estimates showed that BMI was significantly associated with the rate of FEV1 decline (linear trend p = 1.21 × 10− 5).ConclusionsThese novel findings support the obesity paradox in COPD: compared to normal BMI, low BMI is a risk factor for accelerated lung function decline, whilst high BMI has a protective effect. The relationship may be due to common but as-of-yet unknown causative factors; further investigation into which may reveal novel endotypes or targets for therapeutic intervention.

In contrast to the human lutropin receptor (hLHR), very few naturally occurring activating mutations of the structurally related human follitropin receptor (hFSHR) have been identified. The present study was undertaken to determine if one aspect underlying this discrepancy might be a general resistance of the hFSHR to mutation-induced constitutive activity. Five different mutations were introduced into both the hLHR and hFSHR (four based on activating mutations of the hLHR gene, one based on an activating mutation of the hFSHR gene). Our results demonstrate that hFSHR constitutively activating mutants (CAMs) were not as active as hLHR CAMs containing the comparable mutation. Furthermore, although all hFSHR CAMs exhibited strong promiscuous activation by high concentrations of the other glycoprotein hormone receptors, hLHR CAMs showed little or no promiscuous activation. Our in vitro findings are consistent with in vivo observations of known pathophysiological conditions associated with hLHR CAMs, but not hFSHR CAMs, and with promiscuous activation of hFSHR CAMs, but not hLHR CAMs. Computational experiments suggest that the mechanisms through which homologous mutations increase the basal activity of the hLHR and the hFSHR are similar. This is particularly true for the strongest CAMs like L460 (3.43) R. Disparate properties of the hLHR versus hFSHR CAMs may, therefore, be due to differences in shape and electrostatics features of the solventexposed cytosolic receptor domains involved in the receptor-G protein interface rather than to differences in the nature of local perturbation at the mutation site or in the way local perturbation is transferred to the putative G protein binding domains. The LH receptor (LHR)4 and FSH receptor (FSHR), collectively termed the gonadotropin receptors, are G protein-coupled receptors whose primary role is mediation of the signal transduction by pituitary LH or placental hCG (LHR) or pituitary FSH (FSHR) in the gonads. The LHR and FSHR are each composed of a serpentine region containing the seven transmembrane helices typical of G protein-coupled receptors as well as a large extracellular domain that confers the high affinity binding of hormone (1, 2). The gonadotropin receptors are members of the leucine-rich glycoprotein receptor subfamily of rhodopsin-like G protein-coupled receptors (3). The gonadotropin receptors of human origin are highly homologous, with the greatest degree of amino acid conservation within the transmembrane helices. Recent crystallographic studies on human FSH (hFSH) bound to the extracellular domain of the hFSHR have tremendously advanced our understanding of the mechanism of hormone binding to the gonadotropin receptors (4). The entire receptor complexed with ligand has yet to be crystallized, however, and it is still unclear how the binding of hormone to the extracellular domain of the gonadotropin receptor causes stabilization of the serpentine region in an active conformation that causes stimulation of G proteins, primarily G s .In the past several year...

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