Calcium plays a fundamental role as second messenger in intracellular signaling and bone serves as the body's calcium reserve to tightly maintain blood calcium levels. Calcium in ingested meal is the main supply and inadequate calcium intake causes osteoporosis and bone fracture. Here, we describe a novel mechanism of how ingested calcium is deposited on bone. Meal ingestion elicits secretion of the gut hormone gastric inhibitory polypeptide (GIP) from endocrine K cells in the duodenum. Bone histomorphometrical analyses revealed that bone formation parameters in the mice lacking GIP receptor (GIPR(-/-)) were significantly lower than those of wild-type (GIPR(+/+)) mice, and that the number of osteoclasts, especially multinuclear osteoclasts, was significantly increased in GIPR(-/-) mice, indicating that GIPR(-/-) mice have high-turnover osteoporosis. In vitro examination showed the percentage of osteoblastic cells undergoing apoptosis to be significantly decreased in the presence of GIP. Because GIPR(-/-) mice exhibited an increased plasma calcium concentration after meal ingestion, GIP directly links calcium contained in meal to calcium deposition on bone.

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Osteoclasts are generated from monocyte/macrophage-lineage precursors in response to colony-stimulating factor 1 (CSF-1) and receptor activator of nuclear factor-κB ligand (RANKL). CSF-1-mutated CSF-1 op/op mice as well as RANKL −/− mice exhibit osteopetrosis (OP) caused by osteoclast deficiency. We previously identified RANKL receptor (RANK)/CSF-1 receptor (CSF-1R) double-positive cells as osteoclast precursors (OCPs), which existed in bone in RANKL −/− mice. Here we show that OCPs do not exist in bone but in spleen in CSF-1 op/op mice, and spleen acts as their reservoir. IL-34, a newly discovered CSF-1R ligand, was highly expressed in vascular endothelial cells in spleen in CSF-1 op/op mice. Vascular endothelial cells in bone also expressed IL-34, but its expression level was much lower than in spleen, suggesting a role of IL-34 in the splenic generation of OCPs. Splenectomy (SPX) blocked CSF-1-induced osteoclastogenesis in CSF-1 op/op mice. Osteoclasts appeared in aged CSF-1 op/op mice with up-regulation of IL-34 expression in spleen and bone. Splenectomy blocked the age-associated appearance of osteoclasts. The injection of 2-methylene-19-nor-(20S)-1α,25(OH) 2 D 3 (2MD), a potent analog of 1α,25-dihidroxyvitamin D 3 , into CSF-1 op/op mice induced both hypercalcemia and osteoclastogenesis. Administration of 2MD enhanced IL-34 expression not only in spleen but also in bone through a vitamin D receptor-mediated mechanism. Either splenectomy or siRNA-mediated knockdown of IL-34 suppressed 2MD-induced osteoclastogenesis. These results suggest that IL-34 plays a pivotal role in maintaining the splenic reservoir of OCPs, which are transferred to bone in response to diverse stimuli, in CSF-1 op/op mice. The present study also suggests that the IL-34 gene in vascular endothelial cells is a unique target of vitamin D. CSF-1 is the most potent growth factor for monocytes/macrophages (3), but its synthesis by osteoblasts occurs independently of PTH and 1α,25(OH) 2 D 3 (2). CSF-1 op/op mice cannot produce a functionally active CSF-1 (4), and therefore, exhibit monocytopenia and osteopetrosis (OP) (5, 6). However, several curious phenomena have been observed in CSF-1 op/op mice. First, osteoclasts are totally absent in young CSF-1 op/op mice, but appear in aged CSF-1 op/op mice (7). Second, osteopetrotic characteristics of CSF-1R −/− mice are more severe than those of CSF-1 op/op mice (8). Third, F4/80 + [F4/80(+)] macrophages exist in the splenic red pulp in CSF-1 op/op mice as well as in WT mice, and their number is regulated by a mechanism independently of CSF-1 (9, 10). Fourth, the administration of vascular endothelial growth factor (VEGF) rescues osteopetrosis in CSF-1 op/op mice (11, 12), but VEGF cannot substitute for CSF-1 to induce osteoclast formation in vitro (13).Recently, Lin et al. (14) discovered IL-34, as a new ligand for CSF-1R. The amino acid sequence of IL-34 was quite different from that of CSF-1, but IL-34 promoted macrophage colony formation like CSF-1 did. IL-34 was specifically expressed in splen...

Recommender systems aim to increase user actions such as clicks and purchases. Typical evaluations of recommenders regard the purchase of a recommended item as a success. However, the item may have been purchased even without the recommendation. An uplift is defned as an increase in user actions caused by recommendations. Situations with and without a recommendation cannot both be observed for a specifc user-item pair at a given time instance, making uplift-based evaluation and optimization challenging. This paper proposes new evaluation metrics and optimization methods for the uplift in a recommender system. We apply a causal inference framework to estimate the average uplift for the ofine evaluation of recommenders. Our evaluation protocol leverages both purchase and recommendation logs under a currently deployed recommender system, to simulate the cases both with and without recommendations. This enables the ofine evaluation of the uplift for newly generated recommendation lists. For optimization, we need to defne positive and negative samples that are specifc to an uplift-based approach. For this purpose, we deduce four classes of items by observing purchase and recommendation logs. We derive the relative priorities among these four classes in terms of the uplift and use them to construct both pointwise and pairwise sampling methods for uplift optimization. Through dedicated experiments with three public datasets, we demonstrate the efectiveness of our optimization methods in improving the uplift. CCS CONCEPTS • Information systems → Recommender systems; • Computing methodologies → Learning from implicit feedback.