Project description:Obesity is associated with an increase in β-cell mass in response to the rising demand for insulin. β-cell plasticity is essential to maintaining glucose homeostasis, however, the cellular and molecular mechanisms by which β-cell mass is regulated remain poorly understood. Recently, we described the existence of a crosstalk between the peripancreatic adipose tissue and β-cells as a novel mechanism that participates in the regulation of β-cell plasticity. Here, we identify the secreted frizzled-related protein (Sfrp) 5 as down-regulated in the pancreatic islets of obese rats as well as in the pancreatic islets of human obese patients. Our results demonstrate that the silencing of Sfrp5 induces an increase in β-cell proliferation, which we correlate with the activation of Wnt signaling and of the MAPK and PI3 kinase pathways. Together, these findings expand our understanding of the mechanisms underlying β-cell proliferation under conditions of obesity. Furthermore, this study opens new insights into the specific targeting of Sfrp5 as a novel therapeutic strategy for balancing β-cell mass.
Project description:Obesity is associated with an increase in β-cell mass in response to the rising demand for insulin. β-cell plasticity is essential to maintaining glucose homeostasis, however, the cellular and molecular mechanisms by which β-cell mass is regulated remain poorly understood. Recently, we described the existence of a crosstalk between the peripancreatic adipose tissue and β-cells as a novel mechanism that participates in the regulation of β-cell plasticity. Here, we identify the secreted frizzled-related protein (Sfrp) 5 as down-regulated in the pancreatic islets of obese rats as well as in the pancreatic islets of human obese patients. Our results demonstrate that the silencing of Sfrp5 induces an increase in β-cell proliferation, which we correlate with the activation of Wnt signaling and of the MAPK and PI3 kinase pathways. Together, these findings expand our understanding of the mechanisms underlying β-cell proliferation under conditions of obesity. Furthermore, this study opens new insights into the specific targeting of Sfrp5 as a novel therapeutic strategy for balancing β-cell mass.
Project description:Obesity is associated with an increase in β-cell mass in response to the rising demand for insulin. β-cell plasticity is essential to maintaining glucose homeostasis, however, the cellular and molecular mechanisms by which β-cell mass is regulated remain poorly understood. Recently, we described the existence of a crosstalk between the peripancreatic adipose tissue and β-cells as a novel mechanism that participates in the regulation of β-cell plasticity. Here, we identify the secreted frizzled-related protein (Sfrp) 5 as down-regulated in the pancreatic islets of obese rats as well as in the pancreatic islets of human obese patients. Our results demonstrate that the silencing of Sfrp5 induces an increase in β-cell proliferation, which we correlate with the activation of Wnt signaling and of the MAPK and PI3 kinase pathways. Together, these findings expand our understanding of the mechanisms underlying β-cell proliferation under conditions of obesity. Furthermore, this study opens new insights into the specific targeting of Sfrp5 as a novel therapeutic strategy for balancing β-cell mass. Adult male Wistar rats (Charles River Laboratories, Wilmington, MA), 7 wk old (weighing 225–250 g), were caged individually in a 12-h light, 12-h dark cycle in a temperature- and humidity-controlled environment. Animals were divided into two dietary sets for 10 days. One group was fed with standard chow diet (supplying 8% of calories as fat; type AO4 from Panlab, Barcelona, Spain). The second group was fed with a cafeteria diet (66% of calories as fat), as previously described (Endocrinology 2012;153:177-87). Pancreatic islets were isolated through collagenase perfusion of the pancreas, Histopaque gradient and hand-picking under microscopic guidance. Ten micrograms of total RNA from islets were converted into cRNA, biotinylated, fragmented, and hybridized to GeneChip Rat Genome 230 2.0 (Affymetrix, Santa Clara, CA). Ten microarrays were hybridized, five with independent samples coming from rats fed with standard chow (lean group) and five with independent samples coming from rats fed with the cafeteria diet (obese group).
Project description:The matricellular protein Fibulin-5 (Fbln5) is a secreted protein that is essential for elastic fiber formation, and pancreatic islets are usually surrounded by the extracellular matrix (ECM), which includes elastic fibers. However, much uncertainty remains regarding the function of the ECM and its components in β-cells. Here, we describe the role of Fbln5 in β-cell replication. Fbln5 expression was increased upon glucose stimulation in β-cells of mouse and human islets. β-Cell-specific Fbln5-knockout (βFbln5KO) mice exhibit significantly reduced β-cell proliferation in vivo but not in vitro. Secreted extracellular Fbln5 enhances β-cell replication. Fbln5-deficient β-cells exhibit downregulated expression of the gene encoding polo-like kinase 1 (PLK1), which is accompanied by ERK-mediated FoxM1 nuclear export. These data suggest that Fbln5 is secreted from β-cells in response to glucose and plays important roles in the appropriate maintenance of β-cell functions in an autocrine or paracrine manner.
Project description:Secreted epidermal proteins play pivotal roles in cell-cell communication, extracellular matrix remodeling, and antimicrobial defense. However, the complete spectrum of secreted proteins in the epidermis has not been experimentally defined. In this study, we performed mass spectrometry on conditioned media from primary human keratinocytes, identifying 406 proteins that constitute the keratinocyte secretome. To assess functional impacts of uncharacterized secreted proteins on epidermal stem cell behavior, we devised a colony formation assay-based CRISPR screen. The screen identified six candidate proteins that promoted proliferation of epidermal progenitors and two proteins that inhibited it. Secreted frizzled related protein-1 (SFRP1), an inhibitor of Wnt signaling, was the most potent inhibitor of progenitor proliferation in the screen. We discovered that in addition to regulating Wnt activity, SFRP1 restrained epidermal stem cell proliferation by inhibiting ectopic expression of leukemia inhibitory factor (LIF). Collectively, our study defines the keratinocyte secretome, demonstrates the application of a CRISPR screen to assess the function of non-cell autonomous factors, and highlights SFRP1’s role in regulating epidermal balance.
Project description:Secreted epidermal proteins play pivotal roles in cell-cell communication, extracellular matrix remodeling, and antimicrobial defense. However, the complete spectrum of secreted proteins in the epidermis has not been experimentally defined. In this study, we performed mass spectrometry on conditioned media from primary human keratinocytes, identifying 406 proteins that constitute the keratinocyte secretome. To assess functional impacts of uncharacterized secreted proteins on epidermal stem cell behavior, we devised a colony formation assay-based CRISPR screen. The screen identified six candidate proteins that promoted proliferation of epidermal progenitors and two proteins that inhibited it. Secreted frizzled related protein-1 (SFRP1), an inhibitor of Wnt signaling, was the most potent inhibitor of progenitor proliferation in the screen. We discovered that in addition to regulating Wnt activity, SFRP1 restrained epidermal stem cell proliferation by inhibiting ectopic expression of leukemia inhibitory factor (LIF). Collectively, our study defines the keratinocyte secretome, demonstrates the application of a CRISPR screen to assess the function of non-cell autonomous factors, and highlights SFRP1’s role in regulating epidermal balance.