The MODY-associated KCNK16 L114P mutation increases islet glucagon secretion and limits insulin secretion resulting in transient neonatal diabetes and glucose dyshomeostasis in adults

The gain-of-function mutation in the TALK-1 K + channel (p.L114P) is associated with maturity-onset diabetes of the young (MODY). TALK-1 is a key regulator of β-cell electrical activity and glucose-stimulated insulin secretion (GSIS). The KCNK16 gene encoding TALK-1, is the most abundant and β-cell-restricted K + channel transcript. To investigate the impact of KCNK16 L114P on glucose homeostasis and confirm its association with MODY, a mouse model containing the Kcnk16 L114P mutation was generated. Heterozygous and homozygous Kcnk16 L114P mice exhibit increased neonatal lethality in the C57BL/6J and the mixed C57BL/6J:CD-1(ICR) genetic background, respectively. Lethality is likely a result of severe hyperglycemia observed in the homozygous Kcnk16 L114P neonates due to lack of glucose-stimulated insulin secretion and can be reduced with insulin treatment. Kcnk16 L114P increased whole-cell β-cell K + currents resulting in blunted glucose-stimulated Ca 2+ entry and loss of glucose-induced Ca 2+ oscillations. Thus, adult Kcnk16 L114P mice have reduced glucose-stimulated insulin secretion and plasma insulin levels, which significantly impaired glucose homeostasis. Taken together, this study shows that the MODY-associated Kcnk16 L114P mutation disrupts glucose homeostasis in adult mice resembling a MODY phenotype and causes neonatal lethality by inhibiting islet hormone secretion during development. These data strongly suggest that TALK-1 is an islet-restricted target for the treatment of diabetes.

TALK-1-mediated alterations of β-cell mitochondrial function and insulin secretion impair glucose homeostasis on a diabetogenic diet

Mitochondrial Ca2+ ([Ca2+]m) homeostasis is critical for β-cell function and becomes disrupted during the pathogenesis of diabetes. [Ca2+]m uptake is dependent on elevations in cytoplasmic Ca2+ ([Ca2+]c) and endoplasmic reticulum Ca2+ ([Ca2+]ER) release, both of which are regulated by the two-pore domain K+ channel TALK-1. Here, utilizing a novel β-cell TALK-1-knockout (β-TALK-1-KO) mouse model, we found that TALK-1 limited β-cell [Ca2+]m accumulation and ATP production. However, following exposure to a high-fat diet (HFD), ATP-linked respiration, glucose-stimulated oxygen consumption rate, and glucose-stimulated insulin secretion (GSIS) were increased in control but not TALK1-KO mice. Although β-TALK-1-KO animals showed similar GSIS before and after HFD treatment, these mice were protected from HFD-induced glucose intolerance. Collectively, these data identify that TALK-1 channel control of β-cell function reduces [Ca2+]m and suggest that metabolic remodeling in diabetes drives dysglycemia.

Gi/o protein-coupled receptor inhibition of beta-cell electrical excitability and insulin secretion depends on Na+/K+ ATPase activation

Gi/o-coupled somatostatin or α2-adrenergic receptor activation stimulated β-cell NKA activity, resulting in islet Ca2+ fluctuations. Furthermore, intra-islet paracrine activation of β-cell Gi/o-GPCRs and NKAs by δ-cell somatostatin secretion slowed Ca2+ oscillations, which decreased insulin secretion. β-cell membrane potential hyperpolarization resulting from Gi/o-GPCR activation was dependent on NKA phosphorylation by Src tyrosine kinases. Whereas, β-cell NKA function was inhibited by cAMP-dependent PKA activity. These data reveal that NKA-mediated β-cell membrane potential hyperpolarization is the primary and conserved mechanism for Gi/o-GPCR control of electrical excitability, Ca2+ handling, and insulin secretion.

Liraglutide increases islet Ca2+ oscillation frequency and insulin secretion by activating hyperpolarization-activated cyclic nucleotide-gated channels

AIM

To determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN) channels impact glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) modulation of islet Ca²⁺ handling and insulin secretion.

METHODS

The impact of liraglutide (GLP-1 analogue) on islet Ca²⁺ handling, HCN currents and insulin secretion was monitored with fluorescence microscopy, electrophysiology and enzyme immunoassays, respectively. Furthermore, liraglutide-mediated β-to-δ-cell cross-communication was assessed following selective ablation of either mouse islet δ or β cells.

RESULTS

Liraglutide increased β-cell Ca²⁺ oscillation frequency in mouse and human islets under stimulatory glucose conditions. This was dependent in part on liraglutide activation of HCN channels, which also enhanced insulin secretion. Similarly, liraglutide activation of HCN channels also increased β-cell Ca²⁺ oscillation frequency in islets from rodents exposed to a diabetogenic diet. Interestingly, liraglutide accelerated Ca²⁺ oscillations in a majority of islet δ cells, which showed synchronized Ca²⁺ oscillations equivalent to β cells; therefore, we assessed if either cell type was driving this liraglutide-mediated islet Ca²⁺ response. Although δ-cell loss did not impact liraglutide-mediated increase in β-cell Ca²⁺ oscillation frequency, β-cell ablation attenuated liraglutide-facilitated acceleration of δ-cell Ca²⁺ oscillations.

CONCLUSION

The data presented here show that liraglutide-induced stimulation of islet HCN channels augments Ca²⁺ oscillation frequency. As insulin secretion oscillates with β-cell Ca²⁺ , these findings have important implications for pulsatile insulin secretion that is probably enhanced by liraglutide activation of HCN channels and therapeutics that target GLP-1Rs for treating diabetes. Furthermore, these studies suggest that liraglutide as well as GLP-1-based therapies enhance δ-cell Ca²⁺ oscillation frequency and somatostatin secretion kinetics in a β-cell-dependent manner.

CXCR4 signaling at the fetal-maternal interface may drive inflammation and syncytia formation during ovine pregnancy†

Early pregnancy features complex signaling between fetal trophoblast cells and maternal endometrium directing major peri-implantation events including localized inflammation and remodeling to establish proper placental development. Proinflammatory mediators are important for conceptus attachment, but a more precise understanding of molecular pathways regulating this process is needed to understand how the endometrium becomes receptive to implantation. Both chemokine ligand 12 (CXCL12) and its receptor CXCR4 are expressed by fetal and maternal tissues. We identified this pair as a critical driver of placental angiogenesis, but their additional importance to inflammation and trophoblast cell survival, proliferation, and invasion imply a role in syncytia formation at the fetal-maternal microenvironment. We hypothesized that CXCL12 encourages both endometrial inflammation and conceptus attachment during implantation. We employed separate ovine studies to (1) characterize endometrial inflammation during early gestation in the ewe, and (2) establish functional implications of CXCL12 at the fetal-maternal interface through targeted intrauterine infusion of the CXCR4 inhibitor AMD3100. Endometrial tissues were evaluated for inflammatory mediators, intracellular signaling events, endometrial modifications, and trophoblast syncytialization using western blotting and immunohistochemistry. Endometrial tissue from ewes receiving CXCR4 inhibitor demonstrated dysregulated inflammation and reduced AKT and NFKB, paired with elevated autophagic activity compared to control. Immunohistochemical observation revealed an impairment in endometrial surface remodeling and diminished trophoblast syncytialization following localized CXCR4 inhibition. These data suggest CXCL12-CXCR4 regulates endometrial inflammation and remodeling for embryonic implantation, and provide insight regarding mechanisms that, when dysregulated, lead to pregnancy pathologies such as intrauterine growth restriction and preeclampsia.

Strongyloides stercoralis eosinophilic granulomatous enterocolitis

Six patients suffering from an unusual form of colitis produced by Strongyloides stercoralis hyperinfection are described. In contrast to the usual Strongyloides hyperinfection syndrome, in which small intestinal and pulmonary manifestations are seen in patients with some forms of immunodeficiency, the patients described here presented with only a characteristic transmural eosinophilic granulomatous inflammation affecting mostly the colonic wall and clinically mimicking ulcerative colitis or Crohn's disease. This Strongyloides eosinophilic granulomatous enterocolitis apparently results from a florid inflammatory response by eosinophils, histiocytes, and giant cells with formation of granulomas that destroy the larvae entering the colon. This morphologic picture differs from that of the well-described hyperinfection syndrome, in which the bulk of the larvae pass through the colonic wall to complete the life cycle, with only a few larvae destroyed in the colon. The probable pathophysiologic mechanism of this unusual manifestation of hyperinfection is discussed based on the anatomic and clinical observations of patients who presented at different stages in the evolution of their condition and whose length of follow-up varied.

Fallibility of transthoracic needle biopsy of anterior mediastinal masses

Percutaneous transthoracic core needle biopsy has been advocated as a highly accurate technique for the diagnosis of anterior mediastinal masses. A patient is described with a large anterior mediastinal mass in whom the diagnosis of mediastinal carcinoid tumour was made by transthoracic core needle biopsy. At definitive surgical resection the tumour proved to be a B cell lymphoma. This case illustrates one of the important limitations of needle biopsy with its potential for sampling error.

Benign mediastinal teratoma masquerading as a large multiloculated effusion

Benign mediastinal teratomas are uncommon germ cell tumors often discovered while still asymptomatic. Almost all arise in the anterosuperior mediastinal compartment, and most symptoms, when present, result from compression of adjacent structures. We report a case of a large teratoma arising from the anterior mediastinum that presented a confusing clinical picture of a multiloculated pleural effusion. It was successfully treated by surgical excision, with no long-term recurrence.

Short-term smoking reduction is associated with reduction in measures of lower respiratory tract inflammation in heavy smokers

The beneficial effect of short-term smoking reduction in reducing lower respiratory tract inflammation was assessed in 15 healthy heavy smokers. All underwent fibreoptic bronchoscopy and bronchoalveolar lavage and were then treated with at least 20 mg of nicotine gum daily. Self-reported cigarette consumption decreased from 50.7 +/- 2.3 to 18.8 +/- 1.5 (p less than 0.001) cigarettes daily, and expired CO decreased from 48.5 +/- 2.5 to 27.3 +/- 2.5 ppm (p less than 0.001). After two months, repeat bronchoscopy and bronchoalveolar lavage revealed that bronchial inflammation, as assessed by direct inspection, neutrophilia of bronchial lavage fluid, and the number of alveolar macrophages, the number of alveolar neutrophils and the concentration of neutrophil elastase alpha 1-antiprotease complex in alveolar lavage fluid, had improved significantly. The present study suggests that smoking reduction may be associated with an improvement in lower respiratory tract inflammation in heavy smokers and may, if persistent, be an alternative for smokers who cannot, or do not wish, to quit.

Personality disorder: a challenge for the future

Young persons with life long pattern of maladaptive behaviour present to the health and social services with multiple disabilities. These include suicidal behaviours, drug abuse (alcohol and opiates), VA, motorvehicle accidents, repeated failure of close personal relationship (including marriage), job failure, repeated delinquency, criminal violence (including battering babies), and failure to cooperate with medical care. Conspicuous parental discord is the major causal influence, thus explaining transmission to successive generations. Regarding marital disharmony as a major public health hazard may diminish expensive human misery and reduce crime.