Condensation of the ß-cell secretory granule luminal cargoes pro/insulin and ICA512 RESP18 homology domain.

ICA512/PTPRN is a receptor tyrosine-like phosphatase implicated in the biogenesis and turnover of the insulin secretory granules (SGs) in pancreatic islet beta cells. Previously we found biophysical evidence that its luminal RESP18 homology domain (RESP18HD) forms a biomolecular condensate and interacts with insulin in vitro at close-to-neutral pH, that is, in conditions resembling those present in the early secretory pathway. Here we provide further evidence for the relevance of these findings by showing that at pH 6.8 RESP18HD interacts also with proinsulin-the physiological insulin precursor found in the early secretory pathway and the major luminal cargo of ß-cell nascent SGs. Our light scattering analyses indicate that RESP18HD and proinsulin, but also insulin, populate nanocondensates ranging in size from 15 to 300 nm and 10e2 to 10e6 molecules. Co-condensation of RESP18HD with proinsulin/insulin transforms the initial nanocondensates into microcondensates (size >1 µm). The intrinsic tendency of proinsulin to self-condensate implies that, in the ER, a chaperoning mechanism must arrest its spontaneous intermolecular condensation to allow for proper intramolecular folding. These data further suggest that proinsulin is an early driver of insulin SG biogenesis, in a process in which its co-condensation with RESP18HD participates in their phase separation from other secretory proteins in transit through the same compartments but destined to other routes. Through the cytosolic tail of ICA512, proinsulin co-condensation with RESP18HD may further orchestrate the recruitment of cytosolic factors involved in membrane budding and fission of transport vesicles and nascent SGs.

Novel Flow Cytometric Immunoassay for Detection of Proinsulin Autoantibodies in Diabetes Mellitus Employing a Recombinant Autoantigen Expressed in E. coli.

Introduction: Insulin and proinsulin autoantibodies (IAA/PAA) are usually the first markers to appear in patients with type 1 Diabetes Mellitus (T1DM) and their prevalence ranges from 10 to 60% in the child-adolescent population. The reference method for IAA/PAA detection is the Radioligand Binding Assay (RBA), a highly specific and sensitive technique, but expensive and polluting. The aim of this work was to develop a novel flow cytometric microsphere-based immunoassay (FloCMIA) for PAA detection, employing recombinant human proinsulin (PI), as an alternative method to RBA, less expensive and harmful to the environment. Materials and Methods: Human PI was expressed as Thioredoxin fusion protein (TrxPI) in E. coli and a fraction was biotinylated. A double paratope model was used in which samples were incubated with TrxPI-biotin and microspheres adsorbed with TrxPI. The immune complexes were revealed using Streptavidin-Phycoerythrin. The geometric mean of the signals was analyzed, and the results were expressed as Standard Deviation scores (SDs). Sera from 100 normal human control and from 111 type 1 diabetic patients were evaluated by FloCMIA. To correlate the novel assay with RBA, 51 diabetic patients were selected, spanning a wide range of PAA reactivity by RBA. Results: The study of ROC curves allowed choosing a cut-off value of 3.0 SDs and the AUC was 0.705, indicating that FloCMIA has fair ability to distinguish between samples from each group. A prevalence of 50% for PAA was obtained in the population of diabetic patients studied. The specificity was 96% and the analytical sensitivity (percentage of patients RBA positive, also positive by FloCMIA) was 69%. There was a substantial agreement between methods (kappa statistic=0.700). Conclusions: A novel immunoassay based on flow cytometry that uses easy-to produce recombinant PI was developed. This assay constitutes an innovative and cost-effective alternative to RBA for the determination of PAA in patients' sera. The method developed here, presents good performance and a wide dynamic range together with a small required sample volume. Furthermore, these results make it possible to develop multiplex immunoassays that allow the combined detection of autoantibodies present in T1DM and other related autoimmune diseases.

Transgenic Expression and Identification of Recombinant Human Proinsulin in Peanut

The increased incidence of diabetes, coupled with the introduction of alternative insulin delivery methods that rely on higher doses, is expected to result in a substantial escalation in the future demand for affordable insulin. Plant-based systems offer a safe and economical method for producing pharmaceutical proteins. We used peanut (Arachis hypogaea L.) as bio-reactors to express biosafe, stable proinsulin. We designed two proinsulin analogues (FAIA and LAIA) with substitutions in their amino acid sequences. The fast-acting insulin analogue (FAIA) contains a Gly inserted between Cys19 and Gly20, as well as a Pro28Asp substitution, in the B chain. The long-acting insulin analogue (LAIA) contains a Gly inserted between Cys19 and Gly20 and two Arg residues inserted into the terminus of the B chain, as well as an Asn21Gly substitution in the A chain. Four plasmids were constructed: pROKII-Flag-FAIA, pROKII-Flag-LAIA, pCAMBIA2301-Oleosin-FAIA and pCAMBIA2301-Oleosin-LAIA. These plasmids were transferred into peanut to produce recombinant proinsulin. Western blot and GUS staining analysis indicated that some transgenic peanut successfully expressed exogenous proinsulin. Peanut seeds can act as insulin storage sites, which is the foundation for further production of recombinant proinsulin from peanut seeds.

Hypothyroidism decreases proinsulin gene expression and the attachment of its mRNA and eEF1A protein to the actin cytoskeleton of INS-1E cells

The actions of thyroid hormone (TH) on pancreatic beta cells have not been thoroughly explored, with current knowledge being limited to the modulation of insulin secretion in response to glucose, and beta cell viability by regulation of pro-mitotic and pro-apoptotic factors. Therefore, the effects of TH on proinsulin gene expression are not known. This led us to measure: a) proinsulin mRNA expression, b) proinsulin transcripts and eEF1A protein binding to the actin cytoskeleton, c) actin cytoskeleton arrangement, and d) proinsulin mRNA poly(A) tail length modulation in INS-1E cells cultured in different media containing: i) normal fetal bovine serum - FBS (control); ii) normal FBS plus 1 µM or 10 nM T3, for 12 h, and iii) FBS depleted of TH for 24 h (Tx). A decrease in proinsulin mRNA content and attachment to the cytoskeleton were observed in hypothyroid (Tx) beta cells. The amount of eEF1A protein anchored to the cytoskeleton was also reduced in hypothyroidism, and it is worth mentioning that eEF1A is essential to attach transcripts to the cytoskeleton, which might modulate their stability and rate of translation. Proinsulin poly(A) tail length and cytoskeleton arrangement remained unchanged in hypothyroidism. T3 treatment of control cells for 12 h did not induce any changes in the parameters studied. The data indicate that TH is important for proinsulin mRNA expression and translation, since its total amount and attachment to the cytoskeleton are decreased in hypothyroid beta cells, providing evidence that effects of TH on carbohydrate metabolism also include the control of proinsulin gene expression.

Association between proinsulin, insulin, proinsulin/insulin ratio, and insulin resistance status with the metabolic syndrome

The Metabolic Syndrome (MS) constitutes an independent risk factor of cardiovascular disease. There is evidence that proinsulin blood levels and the proinsulin/insulin ratio are associated to the MS. The purpose of this study was to compare proinsulin and insulin, insulin resistance index, and the proinsulin/insulin ratio as predictors of MS. This is a cross-sectional study involving 440 men and 556 women with a mean age of 24 years. Diagnosis of MS was made according to the National Cholesterol Education Program Adult Treatment Panel III. Blood levels of insulin and proinsulin were measured, and the insulin resistance status was estimated using the homeostatic model assessment (HOMA-IR). The prevalence of MS was 10.1 percent. HOMA-IR was the best MS risk factor for both women and men (OR = 2.04; 95 percent CI: 1.68-2.48 and 1.09; 95 percent CI: 1.05-1.13, respectively). HOMA-IR presented the best positive predictive value for MS: 22 percent and 36 percent for men and women, respectively, and was the best MS indicator. The proinsulin/insulin ratio did not show significant association with MS. HOMA-IR, proinsulin, and insulin presented good negative predictive values for both genders that could be used to identify an at-risk population.

A síndrome metabólica (SM) constitui um fator de risco independente para doenças cardiovasculares. Existem evidências de que níveis sangüíneos de proinsulina e o índice proinsulina/insulina estão associados com a presença da SM. O objetivo deste trabalho foi comparar proinsulina e insulina, índice de resistência insulínica e o fator proinsulina/insulina para predizer a presença da SM. Este é um estudo transversal envolvendo 440 homens e 556 mulheres com média de 24 anos de idade. O diagnóstico da SM foi feito de acordo com o Painel III do programa de tratamento nacional educacional de colesterol para adultos. Níveis sangüíneos de insulina e proinsulina foram medidos, o índice de resistência insulínica foi estimado através do modelo de avaliação hemostático (HOMA-IR). A prevalência da SM foi de 10 por cento. HOMA-IR demonstrou ser o melhor fator de risco da SM em homens e mulheres (OR = 2,04; 95 por cento CI: 1,68-2,48 e 1,09; 95 por cento CI: 1,05-1,13, respectivamente). HOMA-IR apresentou o melhor valor preditivo positivo para SM: 22 por cento e 36 por cento para homens e mulheres, respectivamente, e foi o melhor indicador da SM. O índice proinsulina/insulina não apresentou associação significativa com SM. HOMA-IR, proinsulina e insulina apresentaram bons valores preditivos negativos para ambos sexos, o que poderia ser usado para identificar uma população de risco.