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Aims/hypothesis. We examined the properties of a mutant insulin receptor (IR) with an Arg252 to Cys (IRR252C) substitution in the α-subunit originally identified in a patient with extreme insulin resistance and acanthosis nigricans. Methods. We studied IR cell biology and signalling pathways in Chinese Hamster Ovary cells overexpressing this IRR252C. Results. Our investigation showed an impairment in insulin binding to IRR252C related mostly to a reduced affinity of the receptor for insulin and to a reduced rate of IRR252C maturation; an inhibition of IRR252C-mediated endocytosis resulting in a decreased insulin degradation and insulin-induced receptor down-regulation; a maintenance of IRR252C on microvilli even in the presence of insulin; a similar autophosphorylation of mutant IRR252C followed by IRS 1/IRS 2 phosphorylation, p85 association with IRS 1 and IRS 2 and Akt phosphorylation similar to those observed in cells expressing wild type IR (IRwt); and finally, a reduced insulin-induced Shc phosphorylation accompanied by decreased ERK1/2 phosphorylation and activity and of thymidine incorporation into DNA in cells expressing IRR252C as compared to cells expressing IRwt. Conclusion/interpretation. These observations suggest that: parameters other than tyrosine kinase activation participate in or control the first steps of IR internalisation or both; IR-mediated IRS 1/2 phosphorylation can be achieved from the cell surface and microvilli in particular; Shc phosphorylation and its subsequent signalling pathway might require IR internalisation; defective IR endocytosis correlates with an enhancement of some biological responses to insulin and attenuation of others. [ABSTRACT FROM AUTHOR]

Following initial binding to specific cell surface receptors insulin is internalized in target cells. The fate of the internalized insulin-receptor complexes and how the processes involved are regulated is reviewed. The implications of these events in the effects of insulin on its target cells and in the physiopathology of diabetes and insulin resistance states are also considered. [ABSTRACT FROM AUTHOR]

By quantitative electron microscopic autoradiographic technique, we have previously shown thatI-insulin initially localizes to the plasma membrane of isolated rat hepatocytes and is subsequently internalized in a limited region of the peripheral cytoplasm. In the present study, we have shown that when cells are incubated at 20 °C, steady state binding is reached by 60 minutes and maintained up until 120 minutes of incubation while at 37 °C steady state binding is reached by 10 minutes and maintained for 30 minutes. Under both of these conditions, internalization of the labelled material occurs as a constant function of the binding. These data suggest that under normal conditions the binding of the ligand is an important rate limiting determinant of the internalization process. [ABSTRACT FROM AUTHOR]

Replicas of the freeze-fracture surfaces of the internodal myelin membranes of large sciatic nerve fibres from normal and diabetic rats were compared by quantitative electron microscopy. The internodal myelin of the diabetics was examined 14 days after streptozotocin (70 mg/kg IV) induced persistent hyperglycaemia, conditions under which sciatic motor nerve conduction velocity (MNCV) is consistently decreased by 20%. The number of intramembranous particles per unit area of both the P-face and the E-face of the internodal myelin membrane was significantly decreased in the diabetics. This alteration in the structure of the internodal myelin membrane was not found in large sciatic nerve fibres from diabetic rats treated with insulin from day 3 through 14, or from diabetic rats fed a diet containing 1% myoinositol; these are conditions under which the development of decreased sciatic MNCV is prevented or ameliorated. An alteration in internodal myelin structure occurs in acute streptozotocin diabetes which may explain the associated decreased sciatic MNCV. [ABSTRACT FROM AUTHOR]

The aim of the present investigation was to determine in patients with idiopathic haemochromatosis whether diabetes is of the primary type or secondary to pancreatic injury due to iron deposition. For this purpose, plasma glucagon concentrations were determined following arginine infusion or an oral glucose load in eight patients with diabetes and idiopathic haemochromatosis. The enhanced glucagon response to arginine and the nonsuppressibility of glucagon secretion by oral glucose found in these patients were similar to the results found in the same tests performed in our previous series of patients with 'idiopathic' diabetes and at variance with those reported by others in patients with chronic pancreatitis. [ABSTRACT FROM AUTHOR]

As judged by autoradiographic criteria at the optical level, rat islet cells progressively accumulate H-glibenclamide over 1 to 30 min incubation at 24°C. The labeled material associates with all endocrine cells, but is preferentially seen within B cells. The total uptake of H-glibenclamide (1.0 μmol/l) is little affected by the presence of unlabeled glibenclamide (0.2 mmol/l), but is significantly decreased at 4°C (p < 0.05). At the electron microscopic level, less than 15% of the autoradiographic grains are located at the B cell plasma membrane and 72-79% of the grains found over the cytoplasm are associated with insulin secretory granules. Such a pattern is observed both after short (1 min) or prolonged (30 min) incubation, and at 4 or 24 °C. It is proposed that the insulinotropic action of glibenclamide is not necessarily attributable to primary events located solely at the cell surface. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Diabetes is characterised by progressive loss of functional pancreatic beta cells. None of the therapeutic agents used to treat diabetes arrest this process; preventing beta cell loss remains a major unmet need. We have previously shown that serum from eight young healthy male participants who exercised for 8 weeks protected human islets and insulin-producing EndoC-βH1 cells from apoptosis induced by proinflammatory cytokines or the endoplasmic reticulum (ER) stressor thapsigargin. Whether this protective effect is influenced by sex, age, training modality, ancestry or diabetes is unknown., Methods: We enrolled 82 individuals, male or female, non-diabetic or diabetic, from different origins, in different supervised training protocols for 8-12 weeks (including training at home during the COVID-19 pandemic). EndoC-βH1 cells were treated with 'exercised' serum or with the exerkine clusterin to ascertain cytoprotection from ER stress., Results: The exercise interventions were effective and improved [Formula: see text] values in both younger and older, non-obese and obese, non-diabetic and diabetic participants. Serum obtained after training conferred significant beta cell protection (28% to 35% protection after 4 and 8 weeks of training, respectively) from severe ER stress-induced apoptosis. Cytoprotection was not affected by the type of exercise training or participant age, sex, BMI or ancestry, and persisted for up to 2 months after the end of the training programme. Serum from exercised participants with type 1 or type 2 diabetes was similarly protective. Clusterin reproduced the beneficial effects of exercised sera., Conclusions/interpretation: These data uncover the unexpected potential to preserve beta cell health by exercise training, opening a new avenue to prevent or slow diabetes progression through humoral muscle-beta cell crosstalk., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

By quantitative electron microscopic autoradiographic technique, we have previously shown that 125I-insulin initially localizes to the plasma membrane of isolated rat hepatocytes and is subsequently internalized in a limited region of the peripheral cytoplasm. In the present study, we have shown that when cells are incubated at 20 degrees C, steady state binding is reached by 60 minutes and maintained up until 120 minutes of incubation while at 37 degrees C steady state binding is reached by 10 minutes and maintained for 30 minutes. Under both of these conditions, internalization of the labelled material occurs as a constant function of the binding. These data suggest that under normal conditions the binding of the ligand is an important rate limiting determinant of the internalization process.