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Increase of Calcium Sensing Receptor Expression Is Related to Compensatory Insulin Secretion during Aging in Mice.

ABSTRACT: Type 2 diabetes is caused by both insulin resistance and relative insulin deficiency. To investigate age-related changes in glucose metabolism and development of type 2 diabetes, we compared glucose homeostasis in different groups of C57BL/6J mice ranging in age from 4 months to 20 months (4, 8, 12, 16 and 20 months). Interestingly, we observed that non-fasting glucose levels were not significantly changed, but glucose tolerance gradually increased by 20 months of age, whereas insulin sensitivity declined with age. We found that the size of islets and glucose-stimulated insulin secretion increased with aging. However, mRNA expression of pancreatic and duodenal homeobox 1 and granuphilin was decreased in islets of older mice compared with that of 4-month-old mice. Serum calcium (Ca2+) levels were significantly decreased at 12, 20 and 28 months of age compared with 4 months and calcium sensing receptor (CaSR) mRNA expression in the islets significantly increased with age. An extracellular calcium depletion agent upregulated CaSR mRNA expression and consequently enhanced insulin secretion in INS-1 cells and mouse islets. In conclusion, we suggest that decreased Ca2+ levels and increased CaSR expression might be involved in increased insulin secretion to compensate for insulin resistance in aged mice.

SUBMITTER: Oh YS

PROVIDER: S-EPMC4956240 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Increase of Calcium Sensing Receptor Expression Is Related to Compensatory Insulin Secretion during Aging in Mice.

Oh Yoon Sin YS Seo Eun-Hui EH Lee Young-Sun YS Cho Sung Chun SC Jung Hye Seung HS Park Sang Chul SC Jun Hee-Sook HS

PloS one 20160721 7

Type 2 diabetes is caused by both insulin resistance and relative insulin deficiency. To investigate age-related changes in glucose metabolism and development of type 2 diabetes, we compared glucose homeostasis in different groups of C57BL/6J mice ranging in age from 4 months to 20 months (4, 8, 12, 16 and 20 months). Interestingly, we observed that non-fasting glucose levels were not significantly changed, but glucose tolerance gradually increased by 20 months of age, whereas insulin sensitivit ...[more]

PMID: 27441644

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Project description:Aims/hypothesisIngested protein is a well-recognised stimulus for glucagon-like peptide-1 (GLP-1) release from intestinal L cells. This study aimed to characterise the molecular mechanisms employed by L cells to detect oligopeptides.MethodsGLP-1 secretion from murine primary colonic cultures and Ca(2+) dynamics in L cells were monitored in response to peptones and dipeptides. L cells were identified and purified based on their cell-specific expression of the fluorescent protein Venus, using GLU-Venus transgenic mice. Pharmacological tools and knockout mice were used to characterise candidate sensory pathways identified by expression analysis.ResultsGLP-1 secretion was triggered by peptones and di-/tripeptides, including the non-metabolisable glycine-sarcosine (Gly-Sar). Two sensory mechanisms involving peptide transporter-1 (PEPT1) and the calcium-sensing receptor (CaSR) were distinguishable. Responses to Gly-Sar (10 mmol/l) were abolished in the absence of extracellular Ca(2+) or by the L-type calcium-channel blocker nifedipine (10 ?mol/l) and were PEPT1-dependent, as demonstrated by their sensitivity to pH and 4-aminomethylbenzoic acid and the finding of impaired responses in tissue from Pept1 (also known as Slc15a1) knockout mice. Peptone (5 mg/ml)-stimulated Ca(2+) responses were insensitive to nifedipine but were blocked by antagonists of CaSR. Peptone-stimulated GLP-1 secretion was not impaired in mice lacking the putative peptide-responsive receptor lysophosphatidic acid receptor 5 (LPAR5; also known as GPR92/93).Conclusions/interpretationOligopeptides stimulate GLP-1 secretion through PEPT1-dependent electrogenic uptake and activation of CaSR. Both pathways are highly expressed in native L cells, and likely contribute to the ability of ingested protein to elevate plasma GLP-1 levels. Targeting nutrient-sensing pathways in L cells could be used to mobilise endogenous GLP-1 stores in humans, and could mimic some of the metabolic benefits of bariatric surgery.

Project description:Abstract The dysregulation of systemic calcium homeostasis during malignancy is common in most patients with high-grade tumors. The associated comorbidity is known as cancer-induced hypercalcemia (CIH) which affects up to 30% of cases, in the absence of metastasis. In the course of breast cancer progression, the secretion of parathyroid hormone-related protein (PTHrP) by tumor cells and the associated destruction of bone tissues, leads to a progressive increase in systemic calcium or CIH. The increase in circulating Ca2+ is sensed by the calcium-sensing receptor (CaSR), which plays a significant role in maintaining Ca2+ homeostasis. More than 200 mutations and single nucleotide polymorphisms (SNPs) in the CaSR gene have been described, including the A986S CaSR at rs1801725 and Q1011E CaSR at rs1801726 SNPs with reduced sensitivity to Ca2+. Interestingly, high circulating Ca2+ is associated with aggressive breast tumors in premenopausal women and larger tumors in postmenopausal women; however, the contribution of the CaSR in breast cancer progression remains poorly understood. Unlike SNPs at rs1801726, up to 20% of breast cancer patients with SNPs at rs1801725 may be predisposed to higher circulating Ca2+ in the course of their disease. Since breast cancer frequently metastasizes to Ca2+ rich skeletal tissues, we hypothesize that the development of CIH and subsequent desensitization of the CaSR by sustained high Ca2+ is critical for both the adaptation of TNBC cells to CIH in Ca2+ rich microenvironments and TNBC progression. Our preliminary data reveal that the expression level and mutational status of the CaSR is cell type-specific, and that sustained high Ca2+ desensitizes the receptor, but promotes tumor cell growth and motility. Sustained high Ca2+ also triggers the expression of metastasis promoting genes, including the cancer/testis antigen, MAGEC2, and Plasminogen Activator Inhibitor, PAI-2, potentially via the early response genes FOS/FOSB. In addition, our preliminary data show that the A986S SNP is associated with hypercalcemia, secondary malignancy of bone and respiratory organs, and deficiency of humoral immunity. This study provides novel insights into not only the adaptation of TNBC cells to high circulating Ca2+, but also suggests that mutations of the CaSR at rs1801725 are predictive of the likelihood for metastasis to lungs and bone.

Dataset Information

Increase of Calcium Sensing Receptor Expression Is Related to Compensatory Insulin Secretion during Aging in Mice.

Publications

Increase of Calcium Sensing Receptor Expression Is Related to Compensatory Insulin Secretion during Aging in Mice.

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