The role of insulin C-peptide in the coevolution analyses of the insulin signaling pathway: a hint for its functions

Proinsulin folding and trafficking defects trigger a common pathological disturbance of endoplasmic reticulum homeostasis

Primary defects in folding of mutant proinsulin can cause dominant-negative proinsulin accumulation in the endoplasmic reticulum (ER), impaired anterograde proinsulin trafficking, perturbed ER homeostasis, diminished insulin production, and β-cell dysfunction. Conversely, if primary impairment of ER-to-Golgi trafficking (which also perturbs ER homeostasis) drives misfolding of nonmutant proinsulin-this might suggest bi-directional entry into a common pathological phenotype (proinsulin misfolding, perturbed ER homeostasis, and deficient ER export of proinsulin) that can culminate in diminished insulin storage and diabetes. Here, we've challenged β-cells with conditions that impair ER-to-Golgi trafficking, and devised an accurate means to assess the relative abundance of distinct folded/misfolded forms of proinsulin using a novel nonreducing SDS-PAGE/immunoblotting protocol. We confirm abundant proinsulin misfolding upon introduction of a diabetogenic INS mutation, or in the islets of db/db mice. Whereas blockade of proinsulin trafficking in Golgi/post-Golgi compartments results in intracellular accumulation of properly-folded proinsulin (bearing native disulfide bonds), impairment of ER-to-Golgi trafficking (regardless whether such impairment is achieved by genetic or pharmacologic means) results in decreased native proinsulin with more misfolded proinsulin. Remarkably, reversible ER-to-Golgi transport defects (such as treatment with brefeldin A or cellular energy depletion) upon reversal quickly restore the ER folding environment, resulting in the disappearance of pre-existing misfolded proinsulin while preserving proinsulin bearing native disulfide bonds. Thus, proper homeostatic balance of ER-to-Golgi trafficking is linked to a more favorable proinsulin folding (as well as trafficking) outcome.

Development of a custom next-generation sequencing panel for the determination of bladder cancer risk in a Tunisian cohort

BACKGOUND

Bladder cancer (BCa) is a heterogeneous disease caused by the interaction between environmental and genetic risk factors. The goal of this case-control study was to evaluate the implication of a selected SNP panel in the risk of BCa development in a Tunisian cohort. We were also interested in studying the interaction between this predictive panel and environmental risk factors.

METHODS

The case/control cohort was composed with 249 BCa cases and 255 controls. The designed Bladder cancer hereditary panel (BCHP) was composed of 139 selected variants. These variants were genotyped by an amplification-based targeted Next-Generation Sequencing (NGS) on the Ion Torrent Proton sequencer (Life Technologies, Ion Torrent technology).

RESULTS

We have found that rs162555, rs2228000, rs10936599, rs710521, rs3752645, rs804276, rs4639, rs4881400 and rs288980 were significantly associated with decreased risk of bladder cancer. However the homozygous genotypes for VPS37C (rs7104333, A/A), MPG (rs1013358, C/C) genes or the heterozygous genotype for ARNT gene (rs1889740, rs2228099, rs2256355, rs2864873), GSTA4 (rs17614751) and APOBR/IL27 (rs17855750) were significantly associated with increased risk of bladder cancer development compared to reference group (OR 2.53, 2.34, 1.99, 2.00, 2.00, 1.47, 1.96 and 2.27 respectively). We have also found that non-smokers patients harboring heterozygous genotypes for ARNT/rs2864873 (A > G), ARNT/ rs1889740 (C > T) or GSTA4/rs17614751 (G-A) were respectively at 2.775, 3.069 and 6.608-fold increased risk of Bca development compared to non-smokers controls with wild genotypes. Moreover the ARNT CT (rs1889740), ARNT CG (rs2228099), ARNT TC (rs2864873) and GSS GA genotypes were associated with an increased risk of BCa even in absence of professional risk factors. Finally the decision-tree analysis produced a three major BCa classes. These three classes were essentially characterized by an intensity of tobacco use more than 20 pack years (PY) and the CYP1A2 (rs762551) genotype.

CONCLUSIONS

The determined association between environmental factors, genetic variations and the risk of Bca development may provide additional information to urologists that may help them for clinical assessment and treatment decisions. Nevertheless, the underlying mechanisms through which these genes or SNPs affect the clinical behavior of BCas require further studies.

Biological activity versus physiological function of proinsulin C-peptide

Proinsulin C-peptide (C-peptide) has drawn much research attention. Even if the peptide has turned out not to be important in the treatment of diabetes, every phase of C-peptide research has changed our view on insulin and peptide hormone biology. The first phase revealed that peptide hormones can be subject to processing, and that their pro-forms may involve regulatory stages. The second phase revealed the possibility that one prohormone could harbor more than one activity, and that the additional activities should be taken into account in the development of hormone-based therapies. In the third phase, a combined view of the evolutionary patterns in hormone biology allowed an assessment of C-peptide´s role in physiology, and of how biological activities and physiological functions are shaped by evolutionary processes. In addition to this distinction, C-peptide research has produced further advances. For example, C-peptide fragments are successfully administered in immunotherapy of type I diabetes, and plasma C-peptide levels remain a standard for measurement of beta cell activity in patients. Even if the concept of C-peptide as a hormone is presently not supported, some of its bioactivities continue to influence our understanding of evolutionary changes of also other peptides.

Hormonal and metabolic indicators before and after farrowing in sows affected with postpartum dysgalactia syndrome

BACKGROUND

Postpartum dysgalactia syndrome (PDS) in sows is difficult to diagnose and the pathogenesis is obscure. Hormonal changes related to the disease are often difficult to distinguish from those found in the normal transition period from gestation to lactation. The study aimed to investigate metabolic and hormonal changes related to PDS with the goal of identifying potential biomarkers in sows suffering from PDS (PDS+). Selected biomarkers were examined by comparing 38 PDS+ sows with 38 PDS negative (PDS-) sows. The sows were sampled every 24 h from 60 h ante partum (a.p.) to 36 h post partum (p.p.).

RESULTS

Compared to the baseline (60 to 36 h a.p.), cortisol in serum and saliva and fasting blood glucose concentrations increased in PDS+ as well as PDS- sows. C-peptide decreased relative to the baseline in PDS+ sows, and prolactin and 8-epi prostaglandin F2 alpha (8-epi-PGF2α) decreased in PDS- sows. Concentrations of cortisol in serum and saliva, salivary chromogranin A (CgA), fasting blood glucose, C-peptide, and 8-epi-PGF2α differed significantly between PDS+ and PDS- sows, with levels of cortisol in serum and saliva, salivary CgA, and 8-epi-PGF2α in serum being different in the two groups already before parturition. Concentrations of salivary CgA were significantly lower in PDS- sows than in PDS+ sows during the entire study period.

CONCLUSIONS

The results suggest that salivary CgA, cortisol and serum 8-epi-PGF2α may potentially serve as early diagnostic indicators for PDS. The consistently higher salivary CgA concentration in PDS+ sows compared to PDS- sows may indicate that homeostatic disturbances are present between 36 to 60 h before parturition in sows developing PDS. The higher serum and saliva cortisol concentration in PDS+ sows compared to PDS- sows could reflect an early sign of inflammation or stress. The significantly lower C-peptide in PDS+ sows compared to PDS- sows may reflect a lower food intake. Our results contribute to the understanding of the pathogenesis of PDS, and the homeostatic disturbances detected before parturition warrants further investigation. The diagnostic potential of the markers identified in this study should be investigated further in a larger population of sows.

Coevolution of RAC Small GTPases and their Regulators GEF Proteins

RAC proteins are small GTPases involved in important cellular processes in eukaryotes, and their deregulation may contribute to cancer. Activation of RAC proteins is regulated by DOCK and DBL protein families of guanine nucleotide exchange factors (GEFs). Although DOCK and DBL proteins act as GEFs on RAC proteins, DOCK and DBL family members are evolutionarily unrelated. To understand how DBL and DOCK families perform the same function on RAC proteins despite their unrelated primary structure, phylogenetic analyses of the RAC, DBL, and DOCK families were implemented, and interaction patterns that may suggest a coevolutionary process were searched. Interestingly, while RAC and DOCK proteins are very well conserved in humans and among eukaryotes, DBL proteins are highly divergent. Moreover, correlation analyses of the phylogenetic distances of RAC and GEF proteins and covariation analyses between residues in the interacting domains showed significant coevolution rates for both RAC–DOCK and RAC–DBL interactions.

C-peptide evolution: generation from few structural restrictions of bioactivities not necessarily functional

The proinsulin C-peptide has molecular, cellular and organismal activities but lacks disease-associated mutations or short-term loss-of-function effects. This dilemma between activity and function may be explained from its evolutionary setting with insulin as an ancestral partner. The charge, approximate length and flexibility of C-peptide are all that is required for the insulin interactions, while remaining aspects are free to evolve, where new bioactivities can emerge. They can initially be transient, weak, and non-functional, but may gradually be consolidated. In this manner, C-peptide may have acquired multiple bioactivities, explaining why some yet have limited functions but could represent early-stage hormonal-like activities.

Association of insulin-related serum factors with colorectal polyp number and type in adult males

BACKGROUND

Dysregulated insulin signaling is thought to contribute to cancer risk.

METHODS

To determine if insulin-related serum factors are associated with colon polyps, 126 asymptomatic men (48-65 years) were recruited at colonoscopy. Blood was collected. Odds ratios were determined using polytomous logistic regression for polyp number and type.

RESULTS

Males with serum C-peptide concentration >3.3 ng/mL were 3.8 times more likely to have an adenoma relative to no polyp than those with C-peptide ≤1.8 ng/mL. As C-peptide tertile increased, an individual was 2 times more likely to have an adenoma (P = 0.01) than no polyp. There were no associations between insulin-like growth factor or its binding proteins with polyp number or type. Males with soluble receptor for advanced glycation end products (sRAGE) concentration >120.4 pg/mL were 0.25 times less likely to have ≥3 polyps relative to no polyps compared with males with sRAGE ≤94.5 pg/mL. For each increase in sRAGE tertile, a man was 0.5 times less likely to have ≥3 polyps than no polyps (P = 0.03). Compared with males with a serum vascular endothelial growth factor (VEGF) concentration ≤104.7 pg/mL, males with a serum VEGF concentration >184.2 pg/mL were 3.4 times more likely to have ≥3 polyps relative to no polyps. As the VEGF tertile increased, a man was 1.9 times more likely to have ≥3 polyps than no polyps (P = 0.049).

CONCLUSIONS

Serum concentrations of C-peptide, sRAGE, and VEGF may indicate which men could benefit most from colonoscopy.

IMPACT

Identification of biomarkers could reduce medical costs through the elimination of colonoscopies on low-risk individuals.