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.

Separation and characterization of an IgG2 antibody containing a cyclic imide in CDR1 of light chain by hydrophobic interaction chromatography and mass spectrometry.

Hydrophobic interaction chromatography (HIC) was used to separate populations of recombinant IgG2 antibody that were created as a result of prolonged incubation at 40 degrees C. Antibody was separated by HIC into three major and seven minor fractions. All but one fraction was composed of antibody with distinct chemical modifications that resulted from exposure to elevated temperature. The results of intact and reduced mass analysis as well as peptide map data derived from the three major HIC fractions indicated that the antibody was being chromatographically separated into populations containing a succinimidyl intermediate in complementarity determining region 1 (CDR1) on zero, one, and two light chain arms. Lower level species purified by HIC were analyzed by intact and reduced mass analysis and laser-induced fluorescence capillary electrophoresis (CE-LIF) and consisted of an antibody that was clipped in four different places in the heavy chain as well as misfolded and aggregated antibody. The potency of the recombinant antibody containing a succinimidyl intermediate on zero, one, and two light chain arms was analyzed by LANCE binding assay and a cell based in vitro bioassay, and the occurrence of this modification on one or both light chain arms was associated with a reduction in the binding affinity of the molecule to the target by approximately 10%. We show that HIC has the unique ability as a first step purification method to separate populations of antibody which are covalently modified under stability programs. The method conditions that have been developed for the HIC assay are ideal for purifying antibodies with labile modifications for the purpose of further characterization.

Sclerostin inhibition of Wnt-3a-induced C3H10T1/2 cell differentiation is indirect and mediated by bone morphogenetic proteins.

High bone mass diseases are caused both by activating mutations in the Wnt pathway and by loss of SOST, a bone morphogenetic protein (BMP) antagonist, leading to the activation of BMP signaling. Given the phenotypic similarity between mutations that activate these signaling pathways, it seems likely that BMPs and Wnts operate in parallel or represent components of the same pathway, modulating osteoblast differentiation. In this study, we show that in C3H10T1/2 cells, Wnt-3A and BMP-6 proteins were inducers of osteoblast differentiation, as measured by alkaline phosphatase (ALP) induction. Surprisingly, sclerostin, noggin, and human BMP receptor 1A (BMPR1A)-FC fusion proteins blocked Wnt-3A-induced ALP as well as BMP-6-induced ALP activity. Dkk-1, a Wnt inhibitor, blocked Wnt-induced ALP activity but not BMP-induced ALP activity. Early Wnt-3A signaling as measured by beta-catenin accumulation was not affected by the BMP antagonists but was blocked by Dkk-1. Wnt-3A induced the appearance of BMP-4 mRNA 12 h prior to that of ALP in C3H10T1/2 cells. We propose that sclerostin and other BMP antagonists do not block Wnt signaling directly. Sclerostin blocks Wnt-induced ALP activity by blocking the activity of BMP proteins produced by Wnt treatment. The expression of BMP proteins in this autocrine loop is essential for Wnt-3A-induced osteoblast differentiation.

Noggin and sclerostin bone morphogenetic protein antagonists form a mutually inhibitory complex.

Noggin and sclerostin are bone morphogenetic protein (BMP) antagonists that modulate mitogenic activity through sequestering BMPs. Little is known of the interactions among this class of proteins. We show that recombinant sclerostin and noggin bound to each other with high affinity (K(D) = 2.92 nm). This observation has been extended to naturally expressed noggin and sclerostin from the rat osteosarcoma cell line, ROS 17/2.8, supporting a role for the complex in natural systems. The noggin-sclerostin complex was competitive with BMP binding and mutually attenuated the activity of each BMP antagonist. Collectively, the data demonstrate a novel and exquisite paradigm for the regulation of BMP activity through direct neutralization of the BMP and activation by co-localized BMP antagonist expression. The pleiotrophic nature of noggin and sclerostin represents a novel mechanism for the fine-tuning of BMP activity in bone homeostasis.

Osteocyte control of bone formation via sclerostin, a novel BMP antagonist.

There is an unmet medical need for anabolic treatments to restore lost bone. Human genetic bone disorders provide insight into bone regulatory processes. Sclerosteosis is a disease typified by high bone mass due to the loss of SOST expression. Sclerostin, the SOST gene protein product, competed with the type I and type II bone morphogenetic protein (BMP) receptors for binding to BMPs, decreased BMP signaling and suppressed mineralization of osteoblastic cells. SOST expression was detected in cultured osteoblasts and in mineralizing areas of the skeleton, but not in osteoclasts. Strong expression in osteocytes suggested that sclerostin expressed by these central regulatory cells mediates bone homeostasis. Transgenic mice overexpressing SOST exhibited low bone mass and decreased bone strength as the result of a significant reduction in osteoblast activity and subsequently, bone formation. Modulation of this osteocyte-derived negative signal is therapeutically relevant for disorders associated with bone loss.