This study introduces a mouse model carrying the point

This study introduces a mouse model carrying the point mutation R258W in Ffar1, which abolishes the stimulation of insulin secretion in response to long chain fatty acids. The minimal genetic alteration mirrors the human situation and has the advantage over conventional knockout/congenic mouse models. It also circumvents side effects generated by viral constructs, the removal of additional non-coding regions within the deleted gene, and changes in protein–protein interactions such as receptor G-protein coupling due to complete abrogation of a receptor protein.
Disclosure statement This study was supported by a grant from the German Federal Ministry of Education and Research (BMBF) to the German Center for Diabetes Research (DZD e.V.).
Author contributions GKHP, HUH, MHA, and SU designed the study, SS, SM, and GKHP established the mouse models, SS, GK, FG, TS, and SM generated and analyzed the mouse strains and performed and analyzed the in vivo experiments. GK, FG, MH, ELG, MP, and SU performed the in vitro experiments, analyzed data, and wrote the manuscript. All authors approved the final version.
Acknowledgments
Introduction Diabetes represents a major health concern, especially in developing countries. According to the World Health Organization (WHO), more than 180 million people worldwide have diabetes and this number is expected to reach 366 million in 2030. Half of diabetes-related death cases occur in people under the age of 70 and this number is expected to increase by more than 50% in the next 10 years [1]. Moreover, the number of diabetic patients is continuously increasing due to several factors including population growth, increased life expectancy, increased rates of obesity, and lack of physical activity [2]. The most widely used antidiabetic medications are insulin secretagogues and insulin sensitizers. Examples of insulin secretagogues include sulfonylureas and meglitinides, while metformin and thiazolidinediones (TZDs) are insulin sensitizers. TZDs were introduced in the late 1990s as the first agents that control blood Nystatin level by acting on Peroxisome proliferator-activated receptors (PPARs) [3], [4], [5]. These represent a group of nuclear receptors that control cellular metabolism through the modulation of gene expression [6]. There are three distinct subtypes of PPARs: PPARα, PPARδ, and PPARγ. Activation of PPARγ has been shown to regulate glucose homeostasis, cellular differentiation, apoptosis, and inflammatory responses [7]. Over the past few years, there has been an influx of new antidiabetic agents acting on a variety of cellular targets. Free fatty acid receptors (FFARs) are a family of G-protein coupled receptors (GPCRs) that act as fatty acid sensors and play a crucial role in glucose homeostasis. Recent studies have demonstrated that both dietary fatty acids and synthetic agonists can stimulate glucose-dependent insulin secretion by acting on FFAR1 highly expressed in pancreatic β-cells [8], [9]. Several studies reported that modulation of PPARγ using TZDs was not efficient at controlling diabetes in some patients. This led to the use of combination therapies containing both insulin secreting and insulin sensitizing agents, such as Amaryl M® (glimepiride and metformin) and glucovance® (glibenclamide and metformin) [10]. These findings suggest the need for co-administration of insulin sensitizers and insulin secretagogues for the management of diabetes in some situations. Interestingly, it has been reported that some TZDs activate FFAR1 expressed in human HeLa cells with micromolar potency [11], [12]. In 2007, Owman and co-workers exploited the TZD scaffold for the design of FFAR1 ligands by combining fatty acids substructures with TZD heads. Two of the synthesized compounds in this study showed activity in the micromolar range (compounds A and B, Fig. 1) [13]. In a recent study, 2000 TZDs from the Merck compound collection were screened using the FLIPR assay in human GPR40-CHO cells. This led to the discovery of a partial agonist for GPR40 (compound C, Fig. 1) possessing an EC50 of 0.5 μM. The initial GPR40 activity of this compound was improved after subsequent optimization. However, it was inactive in binding assays against all human PPARα, -δ, and -γ isoforms [14].