Cold-induced expression of a truncated adenylyl cyclase 3 acts as rheostat to brown fat function.

Promoting brown adipose tissue (BAT) activity innovatively targets obesity and metabolic disease. While thermogenic activation of BAT is well understood, the rheostatic regulation of BAT to avoid excessive energy dissipation remains ill-defined. Here, we demonstrate that adenylyl cyclase 3 (AC3) is key for BAT function. We identified a cold-inducible promoter that generates a 5' truncated AC3 mRNA isoform (Adcy3-at), whose expression is driven by a cold-induced, truncated isoform of PPARGC1A (PPARGC1A-AT). Male mice lacking Adcy3-at display increased energy expenditure and are resistant to obesity and ensuing metabolic imbalances. Mouse and human AC3-AT are retained in the endoplasmic reticulum, unable to translocate to the plasma membrane and lack enzymatic activity. AC3-AT interacts with AC3 and sequesters it in the endoplasmic reticulum, reducing the pool of adenylyl cyclases available for G-protein-mediated cAMP synthesis. Thus, AC3-AT acts as a cold-induced rheostat in BAT, limiting adverse consequences of cAMP activity during chronic BAT activation.

MarShie: a clearing protocol for 3D analysis of single cells throughout the bone marrow at subcellular resolution.

Analyzing immune cell interactions in the bone marrow is vital for understanding hematopoiesis and bone homeostasis. Three-dimensional analysis of the complete, intact bone marrow within the cortex of whole long bones remains a challenge, especially at subcellular resolution. We present a method that stabilizes the marrow and provides subcellular resolution of fluorescent signals throughout the murine femur, enabling identification and spatial characterization of hematopoietic and stromal cell subsets. By combining a pre-processing algorithm for stripe artifact removal with a machine-learning approach, we demonstrate reliable cell segmentation down to the deepest bone marrow regions. This reveals age-related changes in the marrow. It highlights the interaction between CX3CR1+ cells and the vascular system in homeostasis, in contrast to other myeloid cell types, and reveals their spatial characteristics after injury. The broad applicability of this method will contribute to a better understanding of bone marrow biology.

Age-related oxidative changes in pancreatic islets are predominantly located in the vascular system.

Aged tissues usually show a decreased regenerative capacity accompanied by a decline in functionality. During aging pancreatic islets also undergo several morphological and metabolic changes. Besides proliferative and regenerative limitations, endocrine cells lose their secretory capacity, contributing to a decline in functional islet mass and a deregulated glucose homeostasis. This is linked to several features of aging, such as induction of cellular senescence or the formation of modified proteins, such as advanced glycation end products (AGEs) - the latter mainly examined in relation to hyperglycemia and in disease models. However, age-related changes of endocrine islets under normoglycemic and non-pathologic conditions are poorly investigated. Therefore, a characterization of pancreatic tissue sections as wells as plasma samples of wild-type mice (C57BL/6J) at various age groups (2.5, 5, 10, 15, 21 months) was performed. Our findings reveal that mice at older age are able to secret sufficient amounts of insulin to maintain normoglycemia. During aging the pancreatic islet area increased and the islet size doubled in 21 months old mice when compared to 2.5 months old mice, whereas the islet number was unchanged. This was accompanied by an age-dependent decrease in Ki-67 levels and pancreatic duodenal homeobox-1 (PDX-1), indicating a decline in proliferative and regenerative capacity of pancreatic islets with advancing age. In contrast, the number of p16Ink4a-positive nuclei within the islets was elevated starting from 10 months of age. Interestingly, AGEs accumulated exclusively in the islet blood vessels of old mice associated with increased amounts of inflammatory markers, such as the inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (3-NT). In summary, the age-related increase in islet size and area was associated with the induction of senescence, accompanied by an accumulation of non-enzymatically modified proteins in the islet vascular system.

Lysophosphatidic Acid Inhibits Insulin Signaling in Primary Rat Hepatocytes via the LPA3 Receptor Subtype and is Increased in Obesity.

BACKGROUND/AIMS: Obesity is a main risk factor for the development of hepatic insulin resistance and it is accompanied by adipocyte hypertrophy and an elevated expression of different adipokines such as autotaxin (ATX). ATX converts lysophosphatidylcholine to lysophosphatidic acid (LPA) and acts as the main producer of extracellular LPA. This bioactive lipid regulates a broad range of physiological and pathological responses by activation of LPA receptors (LPA1-6). METHODS: The activation of phosphatidylinositide 3-kinases (PI3K) signaling (Akt and GSK-3ß) was analyzed via western blotting in primary rat hepatocytes. Incorporation of glucose into glycogen was measured by using radio labeled glucose. Real-time PCR analysis and pharmacological modulation of LPA receptors were performed. Human plasma LPA levels of obese (BMI > 30, n = 18) and normal weight individuals (BMI 18.5-25, n = 14) were analyzed by liquid chromatography tandem-mass spectrometry (LC-MS/MS). RESULTS: Pretreatment of primary hepatocytes with LPA resulted in an inhibition of insulin-mediated Gck expression, PI3K activation and glycogen synthesis. Pharmacological approaches revealed that the LPA3-receptor subtype is responsible for the inhibitory effect of LPA on insulin signaling. Moreover, human plasma LPA concentrations (16: 0 LPA) of obese participants (BMI > 30) are significantly elevated in comparison to normal weight individuals (BMI 18.5-25). CONCLUSION: LPA is able to interrupt insulin signaling in primary rat hepatocytes via the LPA3 receptor subtype. Moreover, the bioactive lipid LPA (16: 0) is increased in obesity.

Induction of steatohepatitis (NASH) with insulin resistance in wildtype B6 mice by a western-type diet containing soybean oil and cholesterol.

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are hepatic manifestations of the metabolic syndrome. Many currently used animal models of NAFLD/NASH lack clinical features of either NASH or metabolic syndrome such as hepatic inflammation and fibrosis (e.g. high-fat diets) or overweight and insulin resistance (e.g. methionine-choline-deficient diets) or they are based on monogenetic defects (e.g. ob/ob mice). In the current study, a western-type diet containing soybean oil with high n 6-PUFA and 0.75% cholesterol (SOD+Cho) induced steatosis, inflammation and fibrosis accompanied by hepatic lipid peroxidation and oxidative stress in livers of C57BL/6-mice which in addition showed increased weight gain and insulin resistance, thus displaying a phenotype closely resembling all clinical features of NASH in patients with metabolic syndrome. In striking contrast a soybean oil-containing western-type diet without cholesterol (SOD) induced only mild steatosis but neither hepatic inflammation nor fibrosis, weight gain or insulin resistance. Another high-fat diet mainly consisting of lard and supplemented with fructose in drinking water (LAD+Fru) resulted in more prominent weight gain, insulin resistance and hepatic steatosis than SOD+Cho but livers were devoid of inflammation and fibrosis. Although both LAD+Fru- and SOD+Cho-fed animals had high plasma cholesterol, liver cholesterol was elevated only in SOD+Cho animals. Cholesterol induced expression of chemotactic and inflammatory cytokines in cultured Kupffer cells and rendered hepatocytes more susceptible to apoptosis. Summarizing, dietary cholesterol in SOD+Cho diet may trigger hepatic inflammation and fibrosis. SOD+Cho-fed animals may be a useful disease model displaying many clinical features of patients with the metabolic syndrome and NASH.