ABSTRACT
BACKGROUND: Adipocyte renewal from preadipocytes occurs throughout the lifetime and contributes to obesity. To date, little is known about the mechanisms that control preadipocyte proliferation and differentiation. Prokineticin-2 is an angiogenic and anorexigenic hormone that activate two G protein-coupled receptors (GPCRs): PKR1 and PKR2. Prokineticin-2 regulates food intake and energy metabolism via central mechanisms (PKR2). The peripheral effect of prokineticin-2 on adipocytes/preadipocytes has not been studied yet. METHODOLOGY/PRINCIPAL FINDINGS: Since adipocytes and preadipocytes express mainly prokineticin receptor-1 (PKR1), here, we explored the role of PKR1 in adipose tissue expansion, generating PKR1-null (PKR1(-/-)) and adipocyte-specific (PKR1(ad-/-)) mutant mice, and using murine and human preadipocyte cell lines. Both PKR1(-/-) and PKR1(ad-/-) had excessive abdominal adipose tissue, but only PKR1(-/-) mice showed severe obesity and diabetes-like syndrome. PKR1(ad-/-)) mice had increased proliferating preadipocytes and newly formed adipocyte levels, leading to expansion of adipose tissue. Using PKR1-knockdown in 3T3-L1 preadipocytes, we show that PKR1 directly inhibits preadipocyte proliferation and differentiation. These PKR1 cell autonomous actions appear targeted at preadipocyte cell cycle regulatory pathways, through reducing cyclin D, E, cdk2, c-Myc levels. CONCLUSIONS/SIGNIFICANCE: These results suggest PKR1 to be a crucial player in the preadipocyte proliferation and differentiation. Our data should facilitate studies of both the pathogenesis and therapy of obesity in humans.
Subject(s)
Adipocytes/metabolism , Adipocytes/pathology , Cell Differentiation , Obesity/pathology , Receptors, G-Protein-Coupled/metabolism , 3T3-L1 Cells , Abdominal Fat/pathology , Adipogenesis , Animals , Cell Proliferation , Diabetes Mellitus/pathology , Humans , Male , Mice , Mice, Inbred C57BL , Mice, KnockoutABSTRACT
OBJECTIVE: Prokineticins are potent angiogenic hormones that use 2 receptors, prokineticin receptor-1 (PKR1) and PKR2, with important therapeutic use in anticancer therapy. Observations of cardiac and renal toxicity in cancer patients treated with antiangiogenic compounds led us to explore how PKR1 signaling functioned in heart and kidney in vivo. METHODS AND RESULTS: We generated mice with a conditional disruption of the PKR1 gene. We observed that PKR1 loss led to cardiomegaly, severe interstitial fibrosis, and cardiac dysfunction under stress conditions, accompanied by renal tubular dilation, reduced glomerular capillaries, urinary phosphate excretion, and proteinuria at later ages. Abnormal mitochondria and increased apoptosis were evident in both organs. Perturbation of capillary angiogenesis in both organs was restored at the adult stage potentially via upregulation of hypoxia-inducible factor-1 and proangiogenic factors. Compensatory mechanism could not revoke the epicardial and glomerular capillary networks, because of increased apoptosis and reduced progenitor cell numbers, consistent with an endogenous role of PKR1 signaling in stimulating epicardin+ progenitor cell proliferation and differentiation. CONCLUSIONS: Here, we showed for the first time that the loss of PKR1 causes renal and cardiac structural and functional changes because of deficits in survival signaling, mitochondrial, and progenitor cell functions in found both organs.
Subject(s)
Gene Silencing , Heart Diseases/genetics , Kidney Diseases/genetics , Kidney/metabolism , Myocardium/metabolism , Receptors, G-Protein-Coupled/genetics , Aging , Animals , Apoptosis , Cell Differentiation , Cell Proliferation , Cells, Cultured , Genetic Predisposition to Disease , Heart Diseases/metabolism , Heart Diseases/pathology , Heart Diseases/physiopathology , Kidney/pathology , Kidney Diseases/metabolism , Kidney Diseases/pathology , Kidney Diseases/physiopathology , Mice , Mice, Inbred C57BL , Mice, Knockout , Mitochondria, Heart/metabolism , Mitochondria, Heart/pathology , Myocardium/pathology , Neovascularization, Physiologic , Phenotype , Receptors, G-Protein-Coupled/metabolism , Signal Transduction , Stem Cells/metabolism , Stem Cells/pathology , Ventricular Function, LeftABSTRACT
BACKGROUND: Ca2+ is a ubiquitous messenger that has been shown to be responsible for controlling numerous cellular processes including cell growth and cell death. Whereas the involvement of IP3-induced Ca2+ signalling (IICS) in the physiological activity of numerous cell types is well documented, the role of IICS in cancer cells is still largely unknown. Our purpose was to characterize the role of IICS in the control of growth of the estrogen-dependent human breast cancer epithelial cell line MCF-7 and its potential regulation by 17beta-estradiol (E2). RESULTS: Our results show that the IP3 receptor (IP3R) inhibitors caffeine, 2-APB and xestospongin C (XeC) inhibited the growth of MCF-7 stimulated by 5% foetal calf serum or 10 nM E2. Furthermore, Ca2+ imaging experiments showed that serum and E2 were able to trigger, in a Ca2+-free medium, an elevation of internal Ca2+ in a 2-APB and XeC-sensitive manner. Moreover, the phospholipase C (PLC) inhibitor U-73122 was able to prevent intracellular Ca2+ elevation in response to serum, whereas the inactive analogue U-73343 was ineffective. Western-blotting experiments revealed that the 3 types of IP3Rs are expressed in MCF-7 cells and that a 48 hours treatment with 10 nM E2 elevated IP3R3 protein expression level in an ICI-182,780 (a specific estrogen receptor antagonist)-dependent manner. Furthermore, IP3R3 silencing by the use of specific small interfering RNA was responsible for a drastic modification of the temporal feature of IICS, independently of a modification of the sensitivity of the Ca2+ release process and acted to counteract the proliferative effect of 10 nM E2. CONCLUSIONS: Altogether, our results are in favour of a role of IICS in MCF-7 cell growth, and we hypothesize that the regulation of IP3R3 expression by E2 is involved in this effect.
