Learning theories reveal loss of pancreatic electrical connectivity in diabetes as an adaptive response

Cells of almost all solid tissues are connected with gap junctions which permit the direct transfer of ions and small molecules, integral to regulating coordinated function in the tissue. The pancreatic islets of Langerhans are responsible for secreting the hormone insulin in response to glucose stimulation. Gap junctions are the only electrical contacts between the beta-cells in the tissue of these excitable islets. It is generally believed that they are responsible for synchrony of the membrane voltage oscillations among beta-cells, and thereby pulsatility of insulin secretion. Most attempts to understand connectivity in islets are often interpreted, bottom-up, in terms of measurements of gap junctional conductance. This does not, however explain systematic changes, such as a diminished junctional conductance in type 2 diabetes. We attempt to address this deficit via the model presented here, which is a learning theory of gap junctional adaptation derived with analogy to neural systems. Here, gap junctions are modelled as bonds in a beta-cell network, that are altered according to homeostatic rules of plasticity. Our analysis reveals that it is nearly impossible to view gap junctions as homogeneous across a tissue. A modified view that accommodates heterogeneity of junction strengths in the islet can explain why, for example, a loss of gap junction conductance in diabetes is necessary for an increase in plasma insulin levels following hyperglycemia.Comment: 15 pages, 5 figures. To appear in PLoS One (2013

The Use of Maps in the Analysis of Networks of Coupled Neuronal Oscillators

In this thesis we study aspects of periodic activity in model mutually-coupled oscillators inspired by the nervous system. We define and use maps describing the timing of activity on successive cycles. The central theme here is to examine emergent behavior in networks through the properties of the individual oscillators.In the first chapter, we describe Phase Response Curves (PRCs), which map the changes in theperiod of an oscillator to perturbations at dierent phases along the cycle. We consider various networks of oscillators, pulse-coupled through their PRCs: rings, chains, arrays, and global coupling.We study conditions under which stable patterns, such as synchrony and waves, may be found.In the second and third chapters, we model beta (12-30 Hz) and gamma (30-80 Hz) rhythmsin the nervous system in reduced networks of excitatory and inhibitory neurons. We look at theintriguing results of experiments that show increases in beta band activity in human MEGs upon taking the sedative Diapam. We show that the model network is able to mimic the experimental data. The model then clarifies the inhibitory action of the drug in tissue.We look at another experiment that finds disruption of long-range synchrony of gamma oscillations in transgenic mice with altered excitatory kinetics. We study this behavior in a reduced network that encodes for conduction delays across spatially distal sites. The model provides an explanation of this phenomenon in terms of the properties of the cells involved in generating the rhythm.In our analyses, we use maps to study stability of the patterns of activity

Longitudinal Height Growth in Children and Adolescents with Type-1 Diabetes Mellitus Compared to Controls in Pune, India

Background: Height growth is affected by longterm childhood morbidity.// Objectives: To compare the growth curves of Indian children diagnosed with Type-1 diabetes mellitus (T1DM) and a control group of children without diabetes, and to see how parental height and disease severity affect the growth pattern. // Subjects and Methods: The data came from: (i) the Sweetlings T1DM (STDM) study with 460 subjects aged 4–19 years, previously diagnosed with T1DM and followed for 2–6 (median 3) years, with repeat measurements of height and glycated hemoglobin (HbA1c), and (ii) the Pune School-Children Growth (PSCG) study with 1,470 subjects aged 4–19 years, and height measured annually for median 6 years. Height growth was modeled using SuperImposition by Translation and Rotation (SITAR), a mixed effects model which fits a cubic spline mean curve and summarizes individual growth in terms of differences in mean size, and pubertal timing and intensity.// Results: SITAR explained 99% of the variance in height, the mean curves by sex showing that compared to controls, the children with diabetes were shorter (by 4/5 cm for boys/girls), with a later (by 1/6 months) and less intense (−5%/−10%) pubertal growth spurt. Adjusted for mean height, timing and intensity, the diabetic and control mean curves were very similar in shape. SITAR modeling showed that mean HbA1c peaked at 10.5% at age 15 years, 1.0% higher than earlier in childhood. Individual growth patterns were highly significantly related to parental height, age at diabetes diagnosis, diabetes duration, and mean HbA1c. Mean height was 3.4 cm more per + 1 SD midparental height, and in girls, 2 cm less per + 1 SD HbA1c. Conclusion. The results show that the physiological response to T1DM is to grow more slowly, and to delay and extend the pubertal growth spurt. The effects are dose-related, with more severe disease associated with greater growth faltering

Comprehensive mutations analyses of FTO (fat mass and obesity-associated gene) and their effects on FTO’s substrate binding implicated in obesity

An excessive amount of fat deposition in the body leads to obesity which is a complex disease and poses a generic threat to human health. It increases the risk of various other diseases like diabetes, cardiovascular disease, and multiple types of cancer. Genomic studies have shown that the expression of the fat mass obesity (FTO) gene was highly altered and identified as one of the key biomarkers for obesity. This study has been undertaken to investigate the mutational profile of the FTO gene and elucidates its effect on the protein structure and function. Harmful effects of various missense mutations were predicted using different independent tools and it was observed that all mutations were highly pathogenic. Molecular dynamics (MD) simulations were performed to study the structure and function of FTO protein upon different mutations and it was found that mutations decreased the structure stability and affected protein conformation. Furthermore, a protein residue network analysis suggested that the mutations affected the overall residues bonding and topology. Finally, molecular docking coupled with MD simulation suggested that mutations affected FTO substrate binding by changing the protein-ligand affinity. Hence, the results of this finding would help in an in-depth understanding of the molecular biology of the FTO gene and its variants and lead to the development of effective therapeutics against associated diseases and disorders

Quantification of joint mobility limitation in adult type 1 diabetes

AimsDiabetic cheiroarthropathies limit hand mobility due to fibrosis and could be markers of a global profibrotic trajectory. Heterogeneity in definitions and lack of a method to measure it complicate studying associations with organ involvement and treatment outcomes. We measured metacarpophalangeal (MCP) joint extension as a metric and describe magnetic resonance (MR) imaging determinants of MCP restriction.MethodsAdults with type 1 diabetes were screened for hand manifestations using a symptom questionnaire, clinical examination, and function [Duruoz hand index (DHI) and grip strength]. Patients were segregated by mean MCP extension (<20°, 20°–40°, 40°–60°, and >60°) for MR imaging (MRI) scanning. Patients in the four groups were compared using ANOVA for clinical features and MRI tissue measurements (tenosynovial, skin, and fascia thickness). We performed multiple linear regression for determinants of MCP extension.ResultsOf the 237 patients (90 men), 79 (33.8%) with cheiroarthropathy had MCP extension limitation (39° versus 61°, p < 0.01). Groups with limited MCP extension had higher DHI (1.9 vs. 0.2) but few (7%) had pain. Height, systolic blood pressure, and nephropathy were associated with mean MCP extension. Hand MRI (n = 61) showed flexor tenosynovitis in four patients and median neuritis in one patient. Groups with MCP mobility restriction had the thickest palmar skin; tendon thickness or median nerve area did not differ. Only mean palmar skin thickness was associated with MCP extension angle on multiple linear regression.ConclusionJoint mobility limitation was quantified by restricted mean MCP extension and had structural correlates on MRI. These can serve as quantitative measures for future associative and interventional studies

Deletion of Nedd4-2 results in progressive kidney disease in mice

NEDD4-2 (NEDD4L), a ubiquitin protein ligase of the Nedd4 family, is a key regulator of cell surface expression and activity of the amiloride-sensitive epithelial Na⁺ channel (ENaC). While hypomorphic alleles of Nedd4-2 in mice show salt-sensitive hypertension, complete knockout results in pulmonary distress and perinatal lethality due to increased cell surface levels of ENaC. We now show that Nedd4-2 deficiency in mice also results in an unexpected progressive kidney injury phenotype associated with elevated ENaC and Na⁺Cl⁻ cotransporter expression, increased Na⁺ reabsorption, hypertension and markedly reduced levels of aldosterone. The observed nephropathy is characterized by fibrosis, tubule epithelial cell apoptosis, dilated/cystic tubules, elevated expression of kidney injury markers and immune cell infiltration, characteristics reminiscent of human chronic kidney disease. Importantly, we demonstrate that the extent of kidney injury can be partially therapeutically ameliorated in mice with nephron-specific deletions of Nedd4-2 by blocking ENaC with amiloride. These results suggest that increased Na⁺ reabsorption via ENaC causes kidney injury and establish a novel role of NEDD4-2 in preventing Na⁺-induced nephropathy. Contrary to some recent reports, our data also indicate that ENaC is the primary in vivo target of NEDD4-2 and that Nedd4-2 deletion is associated with hypertension on a normal Na⁺ diet. These findings provide further insight into the critical function of NEDD4-2 in renal pathophysiology.Tanya L Henshall, Jantina A Manning, Omri S Alfassy, Pranay Goel, Natasha A Boase, Hiroshi Kawabe and Sharad Kuma

Characterisation of pathophysiological function of NEDD4-2 in kidney

Nedd4-2 (NEDD4L, neural precursor cell expressed, developmentally down regulated 4-like) belongs to the Nedd4 family of ubiquitin ligases. These ligases aid in maintaining cellular homeostasis by binding to, and ubiquitinating a number of membrane proteins to initiate their internalization and turnover. Previous work from our laboratory has suggested that Nedd4-2 plays an essential role in regulating ion channels, especially the epithelial sodium channel and voltage gated sodium channels. The misregulation of these channels has been implicated in multiple channelopathies, including hypertension and cystic fibrosis like disease. This study characterises a previously unknown function of Nedd4-2 in the kidney. In order to understand this significance of Nedd4-2 in renal homeostasis, the previously generated Nedd4-2⁻ʹ⁻ (Nedd4-2 knockout) mice (Boase et al., 2011) were characterised. The initial histological examination of postnatal kidneys suggested renal cyst formation in Nedd4-2⁻ʹ⁻ animals. Further analysis revealed that Nedd4-2 loss results in renal dysplasia. Nedd4-2⁻ʹ⁻ mice showed variable renal cystic index, onset of cyst formation starting from postnatal day 2 and progressing until the Nedd4-2⁻ʹ⁻ animals die due to respiratory distress around day 19-21. To investigate the prevalence of the cystic phenotype in other tissues histological analysis was performed in pancreas, liver, spleen, colon, stomach and thymus with no significant pathological differences observed in the knockout mice. The Nedd4-2⁻ʹ⁻ kidneys showed increased cell proliferation, with no apoptotic differences in the cells lining the cystic epithelia suggesting an imbalance between cell proliferation and apoptosis in cyst formation. The cyst formation and kidney development disorders are associated with malformation in the kidney tissue leading to extracellular matrix modification with enhanced accumulation of collagens causing increased interstitial fibrosis. The Nedd4-2⁻ʹ⁻ kidneys showed increased interstitial fibrosis, collagen-1 accumulation and expression during progression of the disease. The renal tissue membrane is made up of polysaccharides, glycogen and mucin, the Nedd4-2⁻ʹ⁻ kidneys were found to have decreased accumulation of polysaccharides. The cysts in the Nedd4-2⁻ʹ⁻ kidneys originated from different parts within the nephron. The larger cysts originated from loop of Henle and with the smaller cysts from collecting ducts and distal convoluted tubules. The cystic progression is dependent on cAMP flux initiated by fluid secretion within the cyst. The postnatal day 19 cystic kidneys in Nedd4-2⁻ʹ⁻ animals showed increased cAMP levels suggesting cystic disease progression. As renal cystic disorders may arise from abnormal cilia, ciliary anomalies were found in the Nedd4-2⁻ʹ⁻ around the cysts suggesting importance of cilia in kidney cyst formation. Polycystins are known to be involved in renal cyst development with polycystin-1 and polycystin-2 together known to form calcium ion channel. To investigate the role of Nedd4-2 in the regulation of these polycystins, in vitro and in vivo studies were conducted. In vitro studies suggested that depletion of Nedd4-2 results in increased expression of polycystin-1 on the cell membrane with a decrease in polycystin-2 levels. Further, polycystin-1 was found to be ubiquitinated by Nedd4-2 in vitro providing the first evidence of Nedd4-2-mediated regulation of polycystins. In vivo Polycystin-1 was up-regulated in the Nedd4-2⁻ʹ⁻ kidneys suggesting an important role of Nedd4-2 in regulation of polycystins in cyst formation. To analyse the transcriptional signature of the phenotype seen in the knockout kidneys, postnatal day 19 kidneys from wild-type and Nedd4-2⁻ʹ⁻ mice were subjected to RNA sequencing highlighting 537 genes that were differentially expressed between wild-type and knockout kidneys, with 167 genes down-regulated and 370 genes significantly up-regulated in the absence of Nedd4-2. DAVID and Ingenuity pathway analyses was used to highlight the importance of genes involved in extracellular matrix modification, cell junction formation and cell-cell communication. The work presented in this thesis thus provides new information on the pathophysiological role of Nedd4-2 in kidney and identifies polycystin-1 as a Nedd4-2 target, along with transcriptional changes which may partially explain the cystic phenotype associated with renal dysplasia.Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Medicine, 2016