Cystic Fibrosis-Related Diabetes Workshop: Research Priorities Spanning Disease Pathophysiology, Diagnosis, and Outcomes.

Cystic fibrosis (CF) is a recessive disorder arising from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR is expressed in numerous tissues, with high expression in the airways, small and large intestine, pancreatic and hepatobiliary ducts, and male reproductive tract. CFTR loss in these tissues disrupts regulation of salt, bicarbonate, and water balance across their epithelia, resulting in a systemic disorder with progressive organ dysfunction and damage. Pancreatic exocrine damage ultimately manifests as pancreatic exocrine insufficiency that begins as early as infancy. Pancreatic remodeling accompanies this early damage, during which abnormal glucose tolerance can be observed in toddlers. With increasing age, however, insulin secretion defects progress such that CF-related diabetes (CFRD) occurs in 20% of teens and up to half of adults with CF. The relevance of CFRD is highlighted by its association with increased morbidity, mortality, and patient burden. While clinical research on CFRD has greatly assisted in the care of individuals with CFRD, key knowledge gaps on CFRD pathogenesis remain. Furthermore, the wide use of CFTR modulators to restore CFTR activity is changing the CFRD clinical landscape and the field's understanding of CFRD pathogenesis. For these reasons, the National Institute of Diabetes and Digestive and Kidney Diseases and the Cystic Fibrosis Foundation sponsored a CFRD Scientific Workshop, 23-25 June 2021, to define knowledge gaps and needed research areas. This article describes the findings from this workshop and plots a path for CFRD research that is needed over the next decade.

Cystic Fibrosis-Related Diabetes Workshop: Research Priorities Spanning Disease Pathophysiology, Diagnosis, and Outcomes.

Cystic fibrosis (CF) is a recessive disorder arising from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR is expressed in numerous tissues, with high expression in the airways, small and large intestine, pancreatic and hepatobiliary ducts, and male reproductive tract. CFTR loss in these tissues disrupts regulation of salt, bicarbonate, and water balance across their epithelia, resulting in a systemic disorder with progressive organ dysfunction and damage. Pancreatic exocrine damage ultimately manifests as pancreatic exocrine insufficiency that begins as early as infancy. Pancreatic remodeling accompanies this early damage, during which abnormal glucose tolerance can be observed in toddlers. With increasing age, however, insulin secretion defects progress such that CF-related diabetes (CFRD) occurs in 20% of teens and up to half of adults with CF. The relevance of CFRD is highlighted by its association with increased morbidity, mortality, and patient burden. While clinical research on CFRD has greatly assisted in the care of individuals with CFRD, key knowledge gaps on CFRD pathogenesis remain. Furthermore, the wide use of CFTR modulators to restore CFTR activity is changing the CFRD clinical landscape and the field's understanding of CFRD pathogenesis. For these reasons, the National Institute of Diabetes and Digestive and Kidney Diseases and the Cystic Fibrosis Foundation sponsored a CFRD Scientific Workshop, 23-25 June 2021, to define knowledge gaps and needed research areas. This article describes the findings from this workshop and plots a path for CFRD research that is needed over the next decade.

The fatty acid imbalance of cystic fibrosis exists at birth independent of feeding in pig and ferret models.

Persons with cystic fibrosis (CF) exhibit a unique alteration of fatty acid composition, marked especially among polyunsaturates by relative deficiency of linoleic acid and excess of Mead acid. Relative deficiency of docosahexaenoic acid is variably found. However, the initial development of these abnormalities is not understood. We examined fatty acid composition in young CF ferrets and pigs, finding abnormalities from the day of birth onward including relative deficiency of linoleic acid in both species. Fatty acid composition abnormalities were present in both liver and serum phospholipids of newborn CF piglets even prior to feeding, including reduced linoleic acid and increased Mead acid. Serum fatty acid composition evolved over the first weeks of life in both non-CF and CF ferrets, though differences between CF and non-CF persisted. Although red blood cell phospholipid fatty acid composition was normal in newborn animals, it became perturbed in juvenile CF ferrets including relative deficiencies of linoleic and docosahexaenoic acids and excess of Mead acid. In summary, fatty acid composition abnormalities in CF pigs and ferrets exist from a young age including at birth independent of feeding and overlap extensively with the abnormalities found in humans with CF. That the abnormalities exist prior to feeding implies that dietary measures alone will not address the mechanisms of imbalance.

Oxidative stress and impaired insulin secretion in cystic fibrosis pig pancreas.

Cystic fibrosis-related diabetes (CFRD) is one the most common comorbidities in cystic fibrosis (CF). Pancreatic oxidative stress has been postulated in the pathogenesis of CFRD, but no studies have been done to show an association. The main obstacle is the lack of suitable animal models and no immediate availability of pancreas tissue in humans. In the CF porcine model, we found increased pancreatic total glutathione (GSH), glutathione disulfide (GSSG), 3-nitrotyrosine- and 4-hydroxynonenal-modified proteins, and decreased copper zinc superoxide dismutase (CuZnSOD) activity, all indicative of oxidative stress. CF pig pancreas demonstrated increased DHE oxidation (as a surrogate marker of superoxide) in situ compared to non-CF and this was inhibited by a SOD-mimetic (GC4401). Catalase and glutathione peroxidase activities were not different between CF and non-CF pancreas. Isolated CF pig islets had significantly increased DHE oxidation, peroxide production, reduced insulin secretion in response to high glucose and diminished secretory index compared to non-CF islets. Acute treatment with apocynin or an SOD mimetic failed to restore insulin secretion. These results are consistent with the hypothesis that CF pig pancreas is under significant oxidative stress as a result of increased O2 ●- and peroxides combined with reduced antioxidant defenses against reactive oxygen species (ROS). We speculate that insulin secretory defects in CF may be due to oxidative stress.

Lack of CFTR alters the ferret pancreatic ductal epithelial secretome and cellular proteome: Implications for exocrine/endocrine signaling.

BACKGROUND: Cystic fibrosis (CF) related diabetes is the most common comorbidity for CF patients and associated with islet dysfunction. Exocrine pancreas remodeling in CF alters the microenvironment in which islets reside. Since CFTR is mainly expressed in pancreatic ductal epithelium, we hypothesized altered CF ductal secretions could impact islet function through paracrine signals. METHOD: We evaluated the secretome and cellular proteome of polarized WT and CF ferret ductal epithelia using quantitative ratiometric mass spectrometry. Differentially secreted proteins (DSPs) or expressed cellular proteins were used to mine pathways, upstream regulators and the CFTR interactome to map candidate CF-associated alterations in ductal signaling and phenotype. Candidate DSPs were evaluated for their in vivo pancreatic expression patterns and their functional impact on islet hormone secretion. RESULTS: The secretome and cellular proteome of CF ductal epithelia was significantly altered relative to WT and implicated dysregulated TGFß, WNT, and BMP signaling pathways. Cognate receptors of DSPs from CF epithelia were equally distributed among endocrine, exocrine, and stromal pancreatic cell types. IGFBP7 was a downregulated DSP in CF ductal epithelia in vitro and exhibited reduced CF ductal expression in vivo. IGFBP7 also altered WT islet insulin secretion in response to glucose. Many CFTR-associated proteins, including SLC9A3R1, were differentially expressed in the CF cellular proteome. Upstream regulators of the differential CF ductal proteome included TGFß, PDX1, AKT/PTEN, and INSR signaling. Data is available via ProteomeXchange with identifier PXD025126. CONCLUSION: These findings provide a proteomic roadmap for elucidating disturbances in autocrine and paracrine signals from CF pancreatic ducts and how they may alter islet function and maintenance.

Glycemia and ß-cell function before and after elexacaftor/tezacaftor/ivacaftor in youth and adults with cystic fibrosis.

Background: Diabetes is prevalent among people with CF (PwCF) and associated with worse clinical outcomes. CFTR modulators are highly effective in improving the disease course of CF. However, the effects of elexacaftor/tezacaftor/ivacaftor (ETI) on glucose metabolism in PwCF are unclear. Methods: Twenty youth and adults with CF underwent frequently sampled oral glucose tolerance tests (fsOGTT) before and after ETI initiation. Glucose, insulin, and C-peptide were collected at 0, 10, 30, 60, 90, and 120 min after 1.75 g/kg (max 75 g) of dextrose. HbA1c and continuous glucose monitoring (CGM) were collected in a subset. Estimates of insulin secretion (C-peptide index), insulin resistance (HOMA2 IR and IS(OGTT Cpep)), and ß-cell function (C-peptide oral disposition index, oDIcoeo), were compared before and after ETI. Results: Participants were a median (IQR) of 20.4 (14.1, 28.6) years old, 75 % male. Follow-up occurred 10.5 (10.0, 12.3) months after ETI initiation. BMI z-score increased from 0.3 (-0.3, 0.8) to 0.8 (0.4, 1.5), p = 0.013 between visits. No significant differences were observed in glucose tolerance, glucose area under the curve, nor fsOGTT glucose concentrations before and after ETI. Median (IQR) C-peptide index increased from 5.7 (4.1, 8.3) to 8.8 (5.5, 10.8) p = 0.013 and HOMA2 IR increased (p < 0.001), while oDIcoeo was unchanged (p = 0.67). HbA1c decreased from 5.5 % (5.5, 5.8) to 5.4 % (5.2, 5.6) (p = 0.003) while CGM variables did not change. Conclusions: BMI z-score and measures of both insulin resistance and insulin secretion increased within the first year of ETI initiation. ß-cell function adjusted for insulin sensitivity (oDIcoeo) did not change.

Acute pancreatitis-induced islet dysfunction in ferrets.

BACKGROUND: /Objectives: The pathogenesis of hyperglycemia during acute pancreatitis (AP) remains unknown due to inaccessibility of human tissues and lack of animal models. We aimed to develop an animal model to study the mechanisms of hyperglycemia and impaired glucose tolerance in AP. METHODS: We injected ferrets with intraperitoneal cerulein (50 µg/kg, 9 hourly injections) or saline. Blood samples were collected for glucose (0, 4, 8, 12, 24h); TNF-α, IL-6 (6h); amylase, lipase, insulin, glucagon, pancreatic polypeptide (PP), glucagon-like peptide-1 (GLP-1), and gastric inhibitory polypeptide (GIP) (24h). Animals underwent oral glucose tolerance test (OGTT), mixed meal tolerance test (MMTT) at 24h or 3 months, followed by harvesting pancreas for histopathology and immunostaining. RESULTS: Cerulein-injected ferrets exhibited mild pancreatic edema, neutrophil infiltration, and elevations in serum amylase, lipase, TNF-α, IL-6, consistent with AP. Plasma glucose was significantly higher in ferrets with AP at all time points. Plasma glucagon, GLP-1 and PP were significantly higher in cerulein-injected animals, while plasma insulin was significantly lower compared to controls. OGTT and MMTT showed abnormal glycemic responses with higher area under the curve. The hypoglycemic response to insulin injection was completely lost, suggestive of insulin resistance. OGTT showed low plasma insulin; MMTT confirmed low insulin and GIP; abnormal OGTT and MMTT responses returned to normal 3 months after cerulein injection. CONCLUSIONS: Acute cerulein injection causes mild acute pancreatitis in ferrets and hyperglycemia related to transient islet cell dysfunction and insulin resistance. The ferret cerulein model may contribute to the understanding of hyperglycemia in acute pancreatitis.

Exposure to Static Magnetic and Electric Fields Treats Type 2 Diabetes.

Aberrant redox signaling underlies the pathophysiology of many chronic metabolic diseases, including type 2 diabetes (T2D). Methodologies aimed at rebalancing systemic redox homeostasis have had limited success. A noninvasive, sustained approach would enable the long-term control of redox signaling for the treatment of T2D. We report that static magnetic and electric fields (sBE) noninvasively modulate the systemic GSH-to-GSSG redox couple to promote a healthier systemic redox environment that is reducing. Strikingly, when applied to mouse models of T2D, sBE rapidly ameliorates insulin resistance and glucose intolerance in as few as 3 days with no observed adverse effects. Scavenging paramagnetic byproducts of oxygen metabolism with SOD2 in hepatic mitochondria fully abolishes these insulin sensitizing effects, demonstrating that mitochondrial superoxide mediates induction of these therapeutic changes. Our findings introduce a remarkable redox-modulating phenomenon that exploits endogenous electromagneto-receptive mechanisms for the noninvasive treatment of T2D, and potentially other redox-related diseases.

A tale of two pancreases: exocrine pathology and endocrine dysfunction.

The islets of Langerhans are well embedded within the exocrine pancreas (the latter comprised of ducts and acini), but the nature of interactions between these pancreatic compartments and their role in determining normal islet function and survival are poorly understood. However, these interactions appear to be critical, as when pancreatic exocrine disease occurs, islet function and insulin secretion frequently decline to the point that diabetes ensues, termed pancreatogenic diabetes. The most common forms of pancreatogenic diabetes involve sustained exocrine disease leading to ductal obstruction, acinar inflammation, and fibro-fatty replacement of the exocrine pancreas that predates the development of dysfunction of the endocrine pancreas, as seen in chronic pancreatitis-associated diabetes and cystic fibrosis-related diabetes and, more rarely, MODY type 8. Intriguingly, a form of tumour-induced diabetes has been described that is associated with pancreatic ductal adenocarcinoma. Here, we review the similarities and differences among these forms of pancreatogenic diabetes, with the goal of highlighting the importance of exocrine/ductal homeostasis for the maintenance of pancreatic islet function and survival and to highlight the need for a better understanding of the mechanisms underlying these diverse conditions. Graphical abstract.

Incretin dysfunction and hyperglycemia in cystic fibrosis: Role of acyl-ghrelin.

BACKGROUND: Insulin secretion is insufficient in cystic fibrosis (CF), even before diabetes is present, though the mechanisms involved remain unclear. Acyl-ghrelin (AG) can diminish insulin secretion and is elevated in humans with CF. METHODS: We tested the hypothesis that elevated AG contributes to reduced insulin secretion and hyperglycemia in CF ferrets. RESULTS: Fasting AG was elevated in CF versus non-CF ferrets. Similar to its effects in other species, AG administration in non-CF ferrets acutely reduced insulin, increased growth hormone, and induced hyperglycemia. During oral glucose tolerance testing, non-CF ferrets had responsive insulin, glucagon like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP) levels and maintained normal glucose levels, whereas CF ferrets had insufficient responses and became hyperglycemic. Interestingly in wild-type ferrets, the acyl-ghrelin receptor antagonist [D-Lys3]-GHRP-6 impaired glucose tolerance, and abolished insulin, GLP-1, and GIP responses during glucose tolerance testing. By contrast, in CF ferrets [D-Lys3]-GHRP-6 improved glucose tolerance, enhanced the insulin-to-glucose ratio, but did not impact the already low GLP-1 and GIP levels. CONCLUSIONS: These results suggest a mechanism by which elevated AG contributes to CF hyperglycemia through inhibition of insulin secretion, an effect magnified by low GLP-1 and GIP. Interventions that lower ghrelin, ghrelin action, and/or raise GLP-1 or GIP might improve glycemia in CF.

Survival in a bad neighborhood: pancreatic islets in cystic fibrosis.

In cystic fibrosis (CF), ductal plugging and acinar loss result in rapid decline of exocrine pancreatic function. This destructive process results in remodeled islets, with only a modest reduction in insulin producing ß cells. However, ß-cell function is profoundly impaired, with decreased insulin release and abnormal glucose tolerance being present even in infants with CF. Ultimately, roughly half of CF subjects develop diabetes (termed CF-related diabetes, CFRD). Importantly, CFRD increases CF morbidity and mortality via worsening catabolism and pulmonary disease. Current accepted treatment options for CFRD are aimed at insulin replacement, thereby improving glycemia as well as preventing nutritional losses and lung decline. CFRD is a unique form of diabetes with a distinct pathophysiology that is as yet incompletely understood. Recent studies highlight emerging areas of interest. First, islet inflammation and lymphocyte infiltration are common even in young children with CF and may contribute to ß-cell failure. Second, controversy exists in the literature regarding the presence/importance of ß-cell intrinsic functions of CFTR and its direct role in modulating insulin release. Third, loss of the CF transmembrane conductance regulator (CFTR) from pancreatic ductal epithelium, the predominant site of its synthesis, results in paracrine effects that impair insulin release. Finally, the degree of ß-cell loss in CFRD does not appear sufficient to explain the deficit in insulin release. Thus, it may be possible to enhance the function of the remaining ß cells using strategies such as targeting islet inflammation or ductal CFTR deficiency to effectively treat or even prevent CFRD.

PyMINEr Finds Gene and Autocrine-Paracrine Networks from Human Islet scRNA-Seq.

Toolsets available for in-depth analysis of scRNA-seq datasets by biologists with little informatics experience is limited. Here, we describe an informatics tool (PyMINEr) that fully automates cell type identification, cell type-specific pathway analyses, graph theory-based analysis of gene regulation, and detection of autocrine-paracrine signaling networks in silico. We applied PyMINEr to interrogate human pancreatic islet scRNA-seq datasets and discovered several features of co-expression graphs, including concordance of scRNA-seq-graph structure with both protein-protein interactions and 3D genomic architecture, association of high-connectivity and low-expression genes with cell type enrichment, and potential for the graph structure to clarify potential etiologies of enigmatic disease-associated variants. We further created a consensus co-expression network and autocrine-paracrine signaling networks within and across islet cell types from seven datasets. PyMINEr correctly identified changes in BMP-WNT signaling associated with cystic fibrosis pancreatic acinar cell loss. This proof-of-principle study demonstrates that the PyMINEr framework will be a valuable resource for scRNA-seq analyses.

Development of a polarized pancreatic ductular cell epithelium for physiological studies.

Pancreatic ductular epithelial cells comprise the majority of duct cells in pancreas, control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate ([Formula: see text]) secretion, but are difficult to grow as a polarized monolayer. Using NIH-3T3-J2 fibroblast feeder cells and a Rho-associated kinase inhibitor, we produced well-differentiated and polarized porcine pancreatic ductular epithelial cells. Cells grown on semipermeable filters at the air-liquid interface developed typical epithelial cell morphology and stable transepithelial resistance and expressed epithelial cell markers (zona occludens-1 and ß-catenin), duct cell markers (SOX-9 and CFTR), but no acinar (amylase) or islet cell (chromogranin) markers. Polarized cells were studied in Ussing chambers bathed in Krebs-Ringer [Formula: see text] solution at 37°C gassed with 5% CO2 to measure short-circuit currents ( Isc). Ratiometric measurement of extracellular pH was performed with fluorescent SNARF-conjugated dextran at 5% CO2. Cells demonstrated a baseline Isc (12.2 ± 3.2 µA/cm2) that increased significantly in response to apical forskolin-IBMX (∆ Isc: 35.4 ± 3.8 µA/cm2, P < 0.001) or basolateral secretin (∆ Isc: 31.4 ± 2.5 µA/cm2, P < 0.001), both of which increase cellular levels of cAMP. Subsequent addition of apical GlyH-101, a CFTR inhibitor, decreased the current (∆ Isc: 20.4 ± 3.8 µA/cm2, P < 0.01). Extracellular pH and [Formula: see text] concentration increased significantly after forskolin-IBMX (pH: 7.18 ± 0.23 vs. 7.53 ± 0.19; [Formula: see text] concentration, 14.5 ± 5.9 vs. 31.8 ± 13.4 mM; P < 0.05 for both). We demonstrate the development of a polarized pancreatic ductular epithelial cell epithelium with CFTR-dependent [Formula: see text] secretion in response to secretin and cAMP. This model is highly relevant, as porcine pancreas physiology is very similar to humans and pancreatic damage in the cystic fibrosis pig model recapitulates that of humans. NEW & NOTEWORTHY Pancreas ductular epithelial cells control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate secretion. Their function is critical because when CFTR is deficient in cystic fibrosis bicarbonate secretion is lost and the pancreas is damaged. Mechanisms that control pancreatic bicarbonate secretion are incompletely understood. We generated well-differentiated and polarized porcine pancreatic ductular epithelial cells and demonstrated feasibility of bicarbonate secretion. This novel method will advance our understanding of pancreas physiology and mechanisms of bicarbonate secretion.

SWELL1 is a glucose sensor regulating ß-cell excitability and systemic glycaemia.

Insulin secretion is initiated by activation of voltage-gated Ca2+ channels (VGCC) to trigger Ca2+-mediated insulin vesicle fusion with the ß-cell plasma membrane. The firing of VGCC requires ß-cell membrane depolarization, which is regulated by a balance of depolarizing and hyperpolarizing ionic currents. Here, we show that SWELL1 mediates a swell-activated, depolarizing chloride current (ICl,SWELL) in both murine and human ß-cells. Hypotonic and glucose-stimulated ß-cell swelling activates SWELL1-mediated ICl,SWELL and this contributes to membrane depolarization and activation of VGCC-dependent intracellular calcium signaling. SWELL1 depletion in MIN6 cells and islets significantly impairs glucose-stimulated insulin secretion. Tamoxifen-inducible ß-cell-targeted Swell1 KO mice have normal fasting serum glucose and insulin levels but impaired glucose-stimulated insulin secretion and glucose tolerance; and this is further exacerbated in mild obesity. Our results reveal that ß-cell SWELL1 modulates insulin secretion and systemic glycaemia by linking glucose-mediated ß-cell swelling to membrane depolarization and activation of VGCC-triggered calcium signaling.

Pancreatic and Islet Remodeling in Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Knockout Ferrets.

In cystic fibrosis (CF), there is early destruction of the exocrine pancreas, and this results in a unique form of diabetes that affects approximately half of adult CF individuals. An animal model of cystic fibrosis-related diabetes has been developed in the ferret, which progresses through phases of glycemic abnormalities because of islet remodeling during and after exocrine destruction. Herein, we quantified the pancreatic histopathological changes that occur during these phases. There was an increase in percentage ductal, fat, and islet area in CF ferrets over time compared with age-matched wild-type controls. We also quantified islet size, shape, islet cell composition, cell proliferation (Ki-67), and expression of remodeling markers (matrix metalloprotease-7, desmin, and α-smooth muscle actin). Pancreatic ducts were dilated with scattered proliferating cells and were surrounded by activated stellate cells, indicative of tissue remodeling. The timing of islet and duct proliferation, stellate cell activation, and matrix remodeling coincided with the previously published stages of glycemic crisis and inflammation. This mapping of remodeling events in the CF ferret pancreas provides insights into early changes that control glycemic intolerance and subsequent recovery during the evolution of CF pancreatic disease.

CFTR Influences Beta Cell Function and Insulin Secretion Through Non-Cell Autonomous Exocrine-Derived Factors.

Although ß-cell dysfunction in cystic fibrosis (CF) leads to diabetes, the mechanism by which the cystic fibrosis transmembrane conductance regulator (CFTR) channel influences islet insulin secretion remains debated. We investigated the CFTR-dependent islet-autonomous mechanisms affecting insulin secretion by using islets isolated from CFTR knockout ferrets. Total insulin content was lower in CF as compared with wild-type (WT) islets. Furthermore, glucose-stimulated insulin secretion (GSIS) was impaired in perifused neonatal CF islets, with reduced first, second, and amplifying phase secretion. Interestingly, CF islets compensated for reduced insulin content under static low-glucose conditions by secreting a larger fraction of islet insulin than WT islets, probably because of elevated SLC2A1 transcripts, increased basal inhibition of adenosine triphosphate-sensitive potassium channels (K-ATP), and elevated basal intracellular Ca2+. Interleukin (IL)-6 secretion by CF islets was higher relative to WT, and IL-6 treatment of WT ferret islets produced a CF-like phenotype with reduced islet insulin content and elevated percentage insulin secretion in low glucose. CF islets exhibited altered expression of INS, CELA3B, and several ß-cell maturation and proliferation genes. Pharmacologic inhibition of CFTR reduced GSIS by WT ferret and human islets but similarly reduced insulin secretion and intracellular Ca2+ in CFTR knockout ferret islets, indicating that the mechanism of action is not through CFTR. Single-molecule fluorescent in situ hybridization, on isolated ferret and human islets and ferret pancreas, demonstrated that CFTR RNA colocalized within KRT7+ ductal cells but not endocrine cells. These results suggest that CFTR affects ß-cell function via a paracrine mechanism involving proinflammatory factors secreted from islet-associated exocrine-derived cell types.

Abnormal Glucose Tolerance in Infants and Young Children with Cystic Fibrosis.

RATIONALE: In cystic fibrosis, abnormal glucose tolerance is associated with decreased lung function and worsened outcomes. Translational evidence indicates that abnormal glucose tolerance may begin in early life. OBJECTIVES: To determine whether very young children with cystic fibrosis have increased abnormal glucose tolerance prevalence compared with control subjects. The secondary objective was to compare area under the curve for glucose and insulin in children with cystic fibrosis with control subjects. METHODS: This is a prospective multicenter study in children ages 3 months to 5 years with and without cystic fibrosis. MEASUREMENTS AND MAIN RESULTS: Oral glucose tolerance testing with glucose, insulin, and C-peptide was sampled at 0, 10, 30, 60, 90, and 120 minutes. Twenty-three children with cystic fibrosis and nine control subjects had complete data. All control subjects had normal glucose tolerance. Nine of 23 subjects with cystic fibrosis had abnormal glucose tolerance (39%; P = 0.03). Of those, two met criteria for cystic fibrosis-related diabetes, two indeterminate glycemia, and six impaired glucose tolerance. Children with cystic fibrosis failed to exhibit the normal increase in area under the curve insulin with age observed in control subjects (P < 0.01), despite increased area under the curve glucose (P = 0.02). CONCLUSIONS: Abnormal glucose tolerance is notably prevalent among young children with cystic fibrosis. Children with cystic fibrosis lack the normal increase in insulin secretion that occurs in early childhood despite increased glucose. These findings demonstrate that glycemic abnormalities begin very early in cystic fibrosis, possibly because of insufficient insulin secretion.

A Transient Metabolic Recovery from Early Life Glucose Intolerance in Cystic Fibrosis Ferrets Occurs During Pancreatic Remodeling.

Cystic fibrosis (CF)-related diabetes in humans is intimately related to exocrine pancreatic insufficiency, yet little is known about how these 2 disease processes simultaneously evolve in CF. In this context, we examined CF ferrets during the evolution of exocrine pancreatic disease. At 1 month of age, CF ferrets experienced a glycemic crisis with spontaneous diabetic-level hyperglycemia. This occurred during a spike in pancreatic inflammation that was preceded by pancreatic fibrosis and loss of ß-cell mass. Surprisingly, there was spontaneous normalization of glucose levels at 2-3 months, with intermediate hyperglycemia thereafter. Mixed meal tolerance was impaired at all ages, but glucose intolerance was not detected until 4 months. Insulin secretion in response to hyperglycemic clamp and to arginine was impaired. Insulin sensitivity, measured by euglycemic hyperinsulinemic clamp, was normal. Pancreatic inflammation rapidly diminished after 2 months of age during a period where ß-cell mass rose and gene expression of islet hormones, peroxisome proliferator-activated receptor-γ, and adiponectin increased. We conclude that active CF exocrine pancreatic inflammation adversely affects ß-cells but is followed by islet resurgence. We predict that very young humans with CF may experience a transient glycemic crisis and postulate that pancreatic inflammatory to adipogenic remodeling may facilitate islet adaptation in CF.

Regulation of glucose tolerance and sympathetic activity by MC4R signaling in the lateral hypothalamus.

Melanocortin 4 receptor (MC4R) signaling mediates diverse physiological functions, including energy balance, glucose homeostasis, and autonomic activity. Although the lateral hypothalamic area (LHA) is known to express MC4Rs and to receive input from leptin-responsive arcuate proopiomelanocortin neurons, the physiological functions of MC4Rs in the LHA are incompletely understood. We report that MC4R(LHA) signaling regulates glucose tolerance and sympathetic nerve activity. Restoring expression of MC4Rs specifically in the LHA improves glucose intolerance in obese MC4R-null mice without affecting body weight or circulating insulin levels. Fluorodeoxyglucose-mediated tracing of whole-body glucose uptake identifies the interscapular brown adipose tissue (iBAT) as a primary source where glucose uptake is increased in MC4R(LHA) mice. Direct multifiber sympathetic nerve recording further reveals that sympathetic traffic to iBAT is significantly increased in MC4R(LHA) mice, which accompanies a significant elevation of Glut4 expression in iBAT. Finally, bilateral iBAT denervation prevents the glucoregulatory effect of MC4R(LHA) signaling. These results identify a novel role for MC4R(LHA) signaling in the control of sympathetic nerve activity and glucose tolerance independent of energy balance.