α-Synuclein promotes IAPP fibril formation in vitro and ß-cell amyloid formation in vivo in mice.

Type 2 diabetes (T2D), alike Parkinson's disease (PD), belongs to the group of protein misfolding diseases (PMDs), which share aggregation of misfolded proteins as a hallmark. Although the major aggregating peptide in ß-cells of T2D patients is Islet Amyloid Polypeptide (IAPP), alpha-synuclein (αSyn), the aggregating peptide in substantia nigra neurons of PD patients, is expressed also in ß-cells. Here we show that αSyn, encoded by Snca, is a component of amyloid extracted from pancreas of transgenic mice overexpressing human IAPP (denoted hIAPPtg mice) and from islets of T2D individuals. Notably, αSyn dose-dependently promoted IAPP fibril formation in vitro and tail-vein injection of αSyn in hIAPPtg mice enhanced ß-cell amyloid formation in vivo whereas ß-cell amyloid formation was reduced in hIAPPtg mice on a Snca -/- background. Taken together, our findings provide evidence that αSyn and IAPP co-aggregate both in vitro and in vivo, suggesting a role for αSyn in ß-cell amyloid formation.

PAN-AMPK activator O304 improves glucose homeostasis and microvascular perfusion in mice and type 2 diabetes patients.

AMPK activated protein kinase (AMPK), a master regulator of energy homeostasis, is activated in response to an energy shortage imposed by physical activity and caloric restriction. We here report on the identification of PAN-AMPK activator O304, which - in diet-induced obese mice - increased glucose uptake in skeletal muscle, reduced ß cell stress, and promoted ß cell rest. Accordingly, O304 reduced fasting plasma glucose levels and homeostasis model assessment of insulin resistance (HOMA-IR) in a proof-of-concept phase IIa clinical trial in type 2 diabetes (T2D) patients on Metformin. T2D is associated with devastating micro- and macrovascular complications, and O304 improved peripheral microvascular perfusion and reduced blood pressure both in animals and T2D patients. Moreover, like exercise, O304 activated AMPK in the heart, increased cardiac glucose uptake, reduced cardiac glycogen levels, and improved left ventricular stroke volume in mice, but it did not increase heart weight in mice or rats. Thus, O304 exhibits a great potential as a novel drug to treat T2D and associated cardiovascular complications.

Hyperinsulinemia Enhances Hepatic Expression of the Fatty Acid Transporter Cd36 and Provokes Hepatosteatosis and Hepatic Insulin Resistance.

Hepatosteatosis is associated with the development of both hepatic insulin resistance and Type 2 diabetes. Hepatic expression of Cd36, a fatty acid transporter, is enhanced in obese and diabetic murine models and human nonalcoholic fatty liver disease, and thus it correlates with hyperinsulinemia, steatosis, and insulin resistance. Here, we have explored the effect of hyperinsulinemia on hepatic Cd36 expression, development of hepatosteatosis, insulin resistance, and dysglycemia. A 3-week sucrose-enriched diet was sufficient to provoke hyperinsulinemia, hepatosteatosis, hepatic insulin resistance, and dysglycemia in CBA/J mice. The development of hepatic steatosis and insulin resistance in CBA/J mice on a sucrose-enriched diet was paralleled by increased hepatic expression of the transcription factor Pparγ and its target gene Cd36 whereas that of genes implicated in lipogenesis, fatty acid oxidation, and VLDL secretion was unaltered. Additionally, we demonstrate that insulin, in a Pparγ-dependent manner, is sufficient to directly increase Cd36 expression in perfused livers and isolated hepatocytes. Mouse strains that display low insulin levels, i.e. C57BL6/J, and/or lack hepatic Pparγ, i.e. C3H/HeN, do not develop hepatic steatosis, insulin resistance, or dysglycemia on a sucrose-enriched diet, suggesting that elevated insulin levels, via enhanced CD36 expression, provoke fatty liver development that in turn leads to hepatic insulin resistance and dysglycemia. Thus, our data provide evidence for a direct role for hyperinsulinemia in stimulating hepatic Cd36 expression and thus the development of hepatosteatosis, hepatic insulin resistance, and dysglycemia.

Type 1 fimbriae, a colonization factor of uropathogenic Escherichia coli, are controlled by the metabolic sensor CRP-cAMP.

Type 1 fimbriae are a crucial factor for the virulence of uropathogenic Escherichia coli during the first steps of infection by mediating adhesion to epithelial cells. They are also required for the consequent colonization of the tissues and for invasion of the uroepithelium. Here, we studied the role of the specialized signal transduction system CRP-cAMP in the regulation of type 1 fimbriation. Although initially discovered by regulating carbohydrate metabolism, the CRP-cAMP complex controls a major regulatory network in Gram-negative bacteria, including a broad subset of genes spread into different functional categories of the cell. Our results indicate that CRP-cAMP plays a dual role in type 1 fimbriation, affecting both the phase variation process and fimA promoter activity, with an overall repressive outcome on fimbriation. The dissection of the regulatory pathway let us conclude that CRP-cAMP negatively affects FimB-mediated recombination by an indirect mechanism that requires DNA gyrase activity. Moreover, the underlying studies revealed that CRP-cAMP controls the expression of another global regulator in Gram-negative bacteria, the leucine-responsive protein Lrp. CRP-cAMP-mediated repression is limiting the switch from the non-fimbriated to the fimbriated state. Consistently, a drop in the intracellular concentration of cAMP due to altered physiological conditions (e.g. growth in presence of glucose) increases the percentage of fimbriated cells in the bacterial population. We also provide evidence that the repression of type 1 fimbriae by CRP-cAMP occurs during fast growth conditions (logarithmic phase) and is alleviated during slow growth (stationary phase), which is consistent with an involvement of type 1 fimbriae in the adaptation to stress conditions by promoting biofilm growth or entry into host cells. Our work suggests that the metabolic sensor CRP-cAMP plays a role in coupling the expression of type 1 fimbriae to environmental conditions, thereby also affecting subsequent attachment and colonization of host tissues.