Objective: The gene TSPAN8 was recently identified in a genome-wide association study as the most likely causal gene in a locus that was correlated with the risk of type 2 diabetes (T2D) in northern European individuals. To assess whether Tspan8 is the actual T2D-causal gene in this locus, we ablated its expression in mice and determined the consequences of this ablation on a multitude of metabolic traits. Results: We found that genetic ablation of Tspan8 in mice results in a reduction (À15.6%) in the body weight of males fed a normal chow diet and that this deficiency results in a resistance to body weight gain (À13.7%) upon feeding a high fat and high carbohydrate diet. The differences in body weight could only be detected in male mice and were the consequence of both a decrease in fat deposition, and a decrease in lean body mass (16.9 and 11%, respectively). In spite of the significant body weight difference, no changes in fasting insulin and glucose levels could be detected in Tspan8 knockout mice, nor could we identify changes in the clearance of glucose or sensitivity to insulin in oral glucose tolerance test and intraperitoneal insulin sensitivity test studies, respectively. In addition, male Tspan8 knockout mice showed significantly lower bone mineral density and phosphorus levels (6.2 and 16.6%, respectively). Expression of Tspan8 in mouse was highest in digestive tissues, but virtually absent from the pancreas. In contrast, expression of human TSPAN8 was substantial in digestive tissues, as well as pancreatic cells. Conclusions: Our results argue for a role for Tspan8 in body-weight regulation in males, but do not show differences in T2D-associated traits that were anticipated from previous human genome-wide association studies. Differences in Tspan8 expression levels in mouse and human tissues suggest that Tspan8 could fulfill different or additional physiological functions in these organisms.

Lipoprotein(a) [Lp(a)] has recently been recognized as an independent risk factor for coronary heart disease. While plasma Lp(a) levels are correlated with cardiovascular risk, the mechanism by which this particle contributes to atherosclerosis is largely unknown. Although humanized transgenic mouse model has recently been described to study Lp(a) biology, non-human primates (NHP) are the only preclinical model available that allow study of the role of Lp(a) in atherosclerosis in an innate setting. We describe targeting of LPA using lipid nanoparticle formulated short interfering RNAs (siRNAs) in lean rhesus macaque monkeys. We show >90 % LPA mRNA lowering in the liver and >95 % Lp(a) plasma reduction for over 3 weeks after a single siRNA dose. Given the potency of LPA siRNAs, siRNA approach may enable chronic reduction of Lp(a) in atherosclerotic NHP and help to unmask the role for Lp(a) in the genesis and progression of atherosclerosis in man.