1
|
Firdos, Mittal A. Secretory Conservation in Insulin Producing Cells: Is There a System-Level Law of Mass Action in Biology? ACS OMEGA 2023; 8:37573-37583. [PMID: 37954232 PMCID: PMC10635588 DOI: 10.1021/acsomega.3c06058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 09/19/2023] [Indexed: 11/14/2023]
Abstract
Altered secretion of insulin from pancreatic β-cells can manifest into disorders. For example, a lack of endogenously produced and/or secreted insulin results in Type 1 diabetes (and other associated subtypes). Pancreatic β-cells are the endocrine secretory cells that promote insulin secretion in response to glucose stimulation. Secretion in response to extracellular triggers is an interplay among various signaling pathways, transcription factors, and molecular mechanisms. The Mouse Insulinoma 6 (MIN6) cell line serves as a model system for gaining mechanistic insights into pancreatic β-cell functions. It is obvious that higher glucose consumption and increased insulin secretion are correlated. However, it has been reported that intracellular ATP levels remain ∼ constant beyond the extracellular glucose (EG) concentration of 10 mM. Therefore, any cause-effect relationship between glucose consumption (GC) and enhanced insulin secretion (eIS) remains unclear. We also found that total cellular protein, as well as total protein content in the culture "supernatant," remains constant regardless of varying EG concentrations. This indicated that eIS may be at the cost of (a) intracellular synthesis of other proteins and (b) secretion of other secretory proteins, or both (a) and (b), somehow coupled with GC by cells. To gain insights into the above, we carried out a transcriptome study of MIN6 cells exposed to hypoglycemic (HoG = 2.8 mM EG) and hyperglycemic (HyG = 25 mM EG) conditions. Expression of transcripts was analyzed in terms of Fragments Per Kilobase of transcript per Million mapped reads and Transcripts Per Million (FPKM and TPM) as well as values obtained by normalizing w.r.t. "∑(FPKM)" and "∑(TPM)." We report that HyG extracellular conditions lead to an ∼2-fold increase in insulin secretion compared to HoG measured by the enzyme-linked immunosorbent assay (ELISA) and transcripts of secreted proteins as well as their isoforms decreased in HyG conditions compared to HoG. Our results show for the first time that eIS in HyG conditions is at the cost of reduced transcription of other secreted proteins and is coupled with higher GC. The higher GC at increased extracellular glucose also indicates a yet undiscovered role of glucose molecules enhancing insulin secretion, since ATP levels resulting from glucose metabolism have been reported to be constant above an EG concentration of 10 mM. While extrapolation of our results to clinical implications is ambitious at best, this work reports novel cellular level aspects that seem relevant in some clinical observations pertaining to Type 1 diabetes. In addition, the conservatory nature of cellular secretions in insulin-secreting cells, discovered here, may be a general feature in cell biology.
Collapse
Affiliation(s)
- Firdos
- Kusuma
School of Biological Sciences, Indian Institute
of Technology Delhi (IIT Delhi), Hauz Khas, New Delhi 110016, India
| | - Aditya Mittal
- Kusuma
School of Biological Sciences, Indian Institute
of Technology Delhi (IIT Delhi), Hauz Khas, New Delhi 110016, India
- Supercomputing
Facility for Bioinformatics and Computational Biology (SCFBio), IIT Delhi, Hauz Khas, New Delhi 110016, India
| |
Collapse
|
2
|
Tarasov AI, Galvanovskis J, Rorsman O, Hamilton A, Vergari E, Johnson PRV, Reimann F, Ashcroft FM, Rorsman P. Monitoring real-time hormone release kinetics via high-content 3-D imaging of compensatory endocytosis. LAB ON A CHIP 2018; 18:2838-2848. [PMID: 30083680 PMCID: PMC6250124 DOI: 10.1039/c8lc00417j] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 07/26/2018] [Indexed: 05/02/2023]
Abstract
High-content real-time imaging of hormone secretion in tissues or cell populations is a challenging task, which is unlikely to be resolved directly, despite immense translational value. We approach this problem indirectly, using compensatory endocytosis, a process that closely follows exocytosis in the cell, as a surrogate read-out for secretion. The tissue is immobilized in an open-air perifusion chamber and imaged using a two-photon microscope. A fluorescent polar tracer, perifused through the experimental circuit, gets trapped into the cells via endocytosis, and is quantified using a feature-detection algorithm. The signal of the tracer that accumulates into the endocytotic system reliably reflects stimulated exocytosis, which is demonstrated via co-imaging of the latter using existing reporters. A high signal-to-noise ratio and compatibility with multisensor imaging affords the real-time quantification of the secretion at the tissue/population level, whereas the cumulative nature of the signal allows imprinting of the "secretory history" within each cell. The technology works for several cell types, reflects disease progression and can be used for human tissue.
Collapse
Affiliation(s)
- Andrei I Tarasov
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK. and Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford OX3 7LE, UK
| | - Juris Galvanovskis
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK.
| | - Olof Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK.
| | - Alexander Hamilton
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK.
| | - Elisa Vergari
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK.
| | - Paul R V Johnson
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK.
| | - Frank Reimann
- Metabolic Research Laboratories, Wellcome Trust-MRC Institute of Metabolic Science, Addenbrooke's Hospital, Cambridge, CB2 0QQ UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Parks road, Oxford, OX1 3PT, UK
| | - Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, Churchill Hospital, University of Oxford, Headington, OX3 7LE, Oxford, UK. and Oxford National Institute for Health Research, Biomedical Research Centre, Churchill Hospital, Oxford OX3 7LE, UK and Institute of Neuroscience of Physiology, Department of Physiology, Metabolic Research Unit, University of Göteborg, Box 430, SE-405 30 Göteborg, Sweden
| |
Collapse
|