Renal function is a major predictor of circulating acyl-CoA-binding protein/diazepam-binding inhibitor

Objective

Acyl-CoA-binding protein (ACBP)/diazepam-binding inhibitor has lately been described as an endocrine factor affecting food intake and lipid metabolism. ACBP is dysregulated in catabolic/malnutrition states like sepsis or systemic inflammation. However, regulation of ACBP has not been investigated in conditions with impaired kidney function, so far.

Design/methods

Serum ACBP concentrations were investigated by enzyme-linked immunosorbent assay i) in a cohort of 60 individuals with kidney failure (KF) on chronic haemodialysis and compared to 60 individuals with a preserved kidney function; and ii) in a human model of acute kidney dysfunction (AKD). In addition, mACBP mRNA expression was assessed in two CKD mouse models and in two distinct groups of non-CKD mice. Further, mRNA expression of mACBP was measured in vitro in isolated, differentiated mouse adipocytes - brown and white - after exposure to the uremic agent indoxyl sulfate.

Results

Median [interquartile range] serum ACBP was almost 20-fold increased in KF (514.0 [339.3] µg/l) compared to subjects without KF (26.1 [39.1] µg/l) (p<0.001). eGFR was the most important, inverse predictor of circulating ACBP in multivariate analysis (standardized β=-0.839; p<0.001). Furthermore, AKD increased ACBP concentrations almost 3-fold (p<0.001). Increased ACBP levels were not caused by augmented mACBP mRNA expression in different tissues of CKD mice in vivo or in indoxyl sulfate-treated adipocytes in vitro.

Conclusions

Circulating ACBP inversely associates with renal function, most likely through renal retention of the cytokine. Future studies need to investigate ACBP physiology in malnutrition-related disease states, such as CKD, and to adjust for markers of renal function.

Leptin Receptor-Deficient db/db Mice Show Significant Heterogeneity in Response to High Non-heme Iron Diet

Recent studies have shown an association between iron homeostasis, obesity and diabetes. In this work, we investigated the differences in the metabolic status and inflammation in liver, pancreas and visceral adipose tissue of leptin receptor-deficient db/db mice dependent on high iron concentration diet. 3-month-old male BKS-Leprdb/db/JOrlRj (db/db) mice were divided into two groups, which were fed with different diets containing high iron (29 g/kg, n = 57) or standard iron (0.178 g/kg; n = 42) concentrations for 4 months. As anticipated, standard iron-fed db/db mice developed obesity and diabetes. However, high iron-fed mice exhibited a wide heterogeneity. By dividing into two subgroups at the diabetes level, non-diabetic subgroup 1 (<13.5 mmol/l, n = 30) significantly differed from diabetic subgroup two (>13.5 mmol/l, n = 27). Blood glucose concentration, HbA1c value, inflammation markers interleukin six and tumor necrosis factor α and heme oxygenase one in visceral adipose tissue were reduced in subgroup one compared to subgroup two. In contrast, body weight, C-peptide, serum insulin and serum iron concentrations, pancreatic islet and signal ratio as well as cholesterol, LDL and HDL levels were enhanced in subgroup one. While these significant differences require further studies and explanation, our results might also explain the often-contradictory results of the metabolic studies with db/db mice.

Classification of Microglial Morphological Phenotypes Using Machine Learning

Microglia are the brain's immunocompetent macrophages with a unique feature that allows surveillance of the surrounding microenvironment and subsequent reactions to tissue damage, infection, or homeostatic perturbations. Thereby, microglia's striking morphological plasticity is one of their prominent characteristics and the categorization of microglial cell function based on morphology is well established. Frequently, automated classification of microglial morphological phenotypes is performed by using quantitative parameters. As this process is typically limited to a few and especially manually chosen criteria, a relevant selection bias may compromise the resulting classifications. In our study, we describe a novel microglial classification method by morphological evaluation using a convolutional neuronal network on the basis of manually selected cells in addition to classical morphological parameters. We focused on four microglial morphologies, ramified, rod-like, activated and amoeboid microglia within the murine hippocampus and cortex. The developed method for the classification was confirmed in a mouse model of ischemic stroke which is already known to result in microglial activation within affected brain regions. In conclusion, our classification of microglial morphological phenotypes using machine learning can serve as a time-saving and objective method for post-mortem characterization of microglial changes in healthy and disease mouse models, and might also represent a useful tool for human brain autopsy samples.

Treatment-Induced Neuropathy in Diabetes (TIND)-Developing a Disease Model in Type 1 Diabetic Rats

Treatment-induced neuropathy in diabetes (TIND) is defined by the occurrence of an acute neuropathy within 8 weeks of an abrupt decrease in glycated hemoglobin-A1c (HbA1c). The underlying pathogenic mechanisms are still incompletely understood with only one mouse model being explored to date. The aim of this study was to further explore the hypothesis that an abrupt insulin-induced fall in HbA1c may be the prime causal factor of developing TIND. BB/OKL (bio breeding/OKL, Ottawa Karlsburg Leipzig) diabetic rats were randomized in three groups, receiving insulin treatment by implanted subcutaneous osmotic insulin pumps for 3 months, as follows: Group one received 2 units per day; group two 1 unit per day: and group three 1 unit per day in the first month, followed by 2 units per day in the last two months. We serially examined blood glucose and HbA1c levels, motor- and sensory/mixed afferent conduction velocities (mNCV and csNCV) and peripheral nerve morphology, including intraepidermal nerve fiber density and numbers of Iba-1 (ionized calcium binding adaptor molecule 1) positive macrophages in the sciatic nerve. Only in BB/OKL rats of group three, with a rapid decrease in HbA1c of more than 2%, did we find a significant decrease in mNCV in sciatic nerves (81% of initial values) after three months of treatment as compared to those group three rats with a less marked decrease in HbA1c <2% (mNCV 106% of initial values, p ≤ 0.01). A similar trend was observed for sensory/mixed afferent nerve conduction velocities: csNCV were reduced in BB/OKL rats with a rapid decrease in HbA1c >2% (csNCV 90% of initial values), compared to those rats with a mild decrease <2% (csNCV 112% of initial values, p ≤ 0.01). Moreover, BB/OKL rats of group three with a decrease in HbA1c >2% showed significantly greater infiltration of macrophages by about 50% (p ≤ 0.01) and a decreased amount of calcitonin gene related peptide (CGRP) positive nerve fibers as compared to the animals with a milder decrease in HbA1c. We conclude that a mild acute neuropathy with inflammatory components was induced in BB/OKL rats as a consequence of an abrupt decrease in HbA1c caused by high-dose insulin treatment. This experimentally induced neuropathy shares some features with TIND in humans and may be further explored in studies into the pathogenesis and treatment of TIND.

Pro-neurotensin depends on renal function and is related to all-cause mortality in chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) have a high risk of premature cardiovascular diseases (CVD) and show increased mortality. Pro-neurotensin (Pro-NT) was associated with metabolic diseases and predicted incident CVD and mortality. However, Pro-NT regulation in CKD and its potential role linking CKD and mortality have not been investigated, so far.

METHODS

In a central lab, circulating Pro-NT was quantified in three independent cohorts comprising 4715 participants (cohort 1: patients with CKD; cohort 2: general population study; and cohort 3: non-diabetic population study). Urinary Pro-NT was assessed in part of the patients from cohort 1. In a 4th independent cohort, serum Pro-NT was further related to mortality in patients with advanced CKD. Tissue-specific Nts expression was further investigated in two mouse models of diabetic CKD and compared to non-diabetic control mice.

RESULTS

Pro-NT significantly increased with deteriorating renal function (P < 0.001). In meta-analysis of cohorts 1-3, Pro-NT was significantly and independently associated with estimated glomerular filtration rate (P ≤ 0.002). Patients in the middle/high Pro-NT tertiles at baseline had a higher all-cause mortality compared to the low Pro-NT tertile (Hazard ratio: 2.11, P = 0.046). Mice with severe diabetic CKD did not show increased Nts mRNA expression in different tissues compared to control animals.

CONCLUSIONS

Circulating Pro-NT is associated with impaired renal function in independent cohorts comprising 4715 subjects and is related to all-cause mortality in patients with end-stage kidney disease. Our human and rodent data are in accordance with the hypotheses that Pro-NT is eliminated by the kidneys and could potentially contribute to increased mortality observed in patients with CKD.

COMP-Ang-1 Improves Glucose Uptake in db/db Mice with Type 2 Diabetes

Cartilage oligomeric matrix protein (COMP)-Angiopoietin-1 is a potent angiopoietin-1 (Ang-1) variant that possesses therapeutic potential in angiogenesis and vascular endothelial dysfunction. Noteworthy, we have shown that COMP-Ang-1 improves hyperglycemia and neuroregeneration in ob/ob mice. However, the mechanism of the antidiabetic effect of COMP-Ang-1 is completely unknown. Therefore, we elucidated the diabetes protective molecular mechanisms of COMP-Ang-1 in diabetic db/db mouse model. COMP-Ang-1 (0.5 ng/g body weight) or aqueous NaCl solution was injected intraperitoneally per day in 21 consecutive days into 3-month old, male db/db mice (n=10 per group). Blood glucose and HbA1c levels were determined at baseline and 21 days after COMP-Ang-1 or NaCl treatment. The effect of COMP-Ang-1 on glucose uptake was investigated by euglycemic-hyperinsulinemic clamp studies and key genes of glucose metabolism were studied by Western blot analysis. Our findings indicate that COMP-Ang-1 improves glucose metabolism in a tissue specific manner by regulating HIF-1α transcriptional genes of GLUT-1 expression.

The brown fat-secreted adipokine neuregulin 4 is decreased in human and murine chronic kidney disease

OBJECTIVE

Neuregulin 4 (NRG4) has recently been introduced as a novel brown adipose tissue (BAT)-secreted adipokine with beneficial metabolic effects in mice. However, regulation of Nrg4 in end-stage kidney disease (ESKD) and type 2 diabetes mellitus (T2DM) has not been elucidated, so far.

DESIGN/METHODS

Serum NRG4 levels were quantified by ELISA in 60 subjects with ESKD on chronic hemodialysis as compared to 60 subjects with an estimated glomerular filtration rate >50 mL/min/1.73 m2 in a cross-sectional cohort. Within both groups, about half of the patients had a T2DM. Furthermore, mRNA expression of Nrg4 was determined in two mouse models of diabetic kidney disease (DKD) as compared to two different groups of non-diabetic control mice. Moreover, mRNA expression of Nrg4 was investigated in cultured, differentiated mouse brown and white adipocytes, as well as hepatocytes, after treatment with the uremic toxin indoxyl sulfate.

RESULTS

Median serum NRG4 was significantly lower in patients with ESKD compared to controls and the adipokine was independently associated with a beneficial renal, glucose and lipid profile. In mice with DKD, Nrg4 mRNA expression was decreased in all adipose tissue depots compared to control mice. The uremic toxin indoxyl sulfate did not significantly alter Nrg4 mRNA expression in adipocytes and hepatocytes, in vitro.

CONCLUSIONS

Circulating NRG4 is independently associated with a preserved renal function and mRNA expression of -Nrg4 is reduced in adipose tissue depots of mice with DKD. The BAT-secreted adipokine is further associated with a beneficial glucose and lipid profile supporting NRG4 as potential treatment target in metabolic and renal disease states.

Up-regulated autophagy: as a protective factor in adipose tissue of WOKW rats with metabolic syndrome

BACKGROUND

Wistar Ottawa Karlsburg W (RT1u) rats (WOKW) are a model of the metabolic syndrome (MetS). Adipose tissue (AT) and peripheral nerves of WOKW rats exhibit up-regulated autophagy and inflammation corresponding with decreased apoptosis rate. The aim of this study was to characterize AT in WOKW rats in relation to autophagic activity.

METHODS

mRNA and protein expression of adiponectin, pro-inflammatory and pro-apoptotic markers including MCP1, TNFα, cleaved caspase-3 and RNF157, a new candidate gene regulated through autophagy, were analyzed in adipocytes isolated from visceral and subcutaneous AT of 5-month old WOKW rats with MetS and LEW.1W controls in response to pharmacological inhibition of autophagy. Immunohistochemistry was performed to detect adiponectin and RNF157 protein in cultured adipocytes.

RESULTS

Inhibition of autophagy by LY294002 was associated with a fourfold up-regulation of adiponectin expression and a decrease of RNF157 protein and pro-inflammatory markers-MCP-1 and TNFα predominantly in visceral adipocytes of obese WOKW rats compared to LEW.1W rats. Moreover, inhibition of autophagic activity correlates with an activation of cleaved caspase-3 apoptotic signaling pathway.

CONCLUSIONS

Up-regulated autophagy in obese WOKW rats contributes to the regulation of visceral AT function and involves an altered balance between pro-inflammatory and protective adipokine expression. Our data suggest that activation of AT autophagy protects against adipocyte apoptosis at least under conditions of obesity related MetS in WOKW rats.

The role of nerve inflammation and exogenous iron load in experimental peripheral diabetic neuropathy (PDN)

BACKGROUND

Iron is an essential but potentially toxic metal in mammals. Here we investigated a pathogenic role of exogenous iron in peripheral diabetic neuropathy (PDN) in an animal model for type 1 diabetes.

METHODS

Diabetes was induced by a single injection of streptozotocin (STZ) in 4-month-old Sprague-Dawley rats. STZ-diabetic rats and non-diabetic rats were fed with high, standard, or low iron diet. After three months of feeding, animals were tested.

RESULTS

STZ-rats on standard iron diet showed overt diabetes, slowed motor nerve conduction, marked degeneration of distal intraepidermal nerve fibers, mild intraneural infiltration with macrophages and T-cells in the sciatic nerve, and increased iron levels in serum and dorsal root ganglion (DRG) neurons. While motor fibers were afflicted in all STZ-groups, only a low iron-diet led also to reduced sensory conduction velocities in the sciatic nerve. In addition, only STZ-rats on a low iron diet showed damaged mitochondria in numerous DRG neurons, a more profound intraepidermal nerve fiber degeneration indicating small fiber neuropathy, and even more inflammatory cells in sciatic nerves than seen in any other experimental group.

CONCLUSIONS

These results indicate that dietary iron-deficiency rather than iron overload, and mild inflammation may both promote neuropathy in STZ-induced experimental PDN.

Autophagy in adipose tissue of patients with obesity and type 2 diabetes

BACKGROUND

Pathophysiology of obesity is closely associated with enhanced autophagy in adipose tissue (AT). Autophagic process can promote survival or activate cell death. Therefore, we examine the occurrence of autophagy in AT of type 2 diabetes (T2D) patients in comparison to obese and lean individuals without diabetes.

METHODOLOGY/PRINCIPAL FINDINGS

Numerous autophagosomes accumulated within adipocytes were visualized by electron transmission microscopy and by immunofluorescence staining for autophagy marker LC3 in obese and T2D patients. Increased autophagy was demonstrated by higher LC3-II/LC3-I ratio, up-regulated expression of LC3 and Atg5 mRNA, along with decreased p62 and mTOR protein levels. Increased autophagy occurred together with AT inflammation.

CONCLUSIONS

Our data suggest fat depot-related differences in autophagy regulation. In subcutaneous AT, increased autophagy is accompanied by increased markers of apoptosis in patients with obesity independently of T2D. In contrast, in visceral AT only in T2D patients increased autophagy was related to higher markers of apoptosis.

Upregulation of Bcl-2 at the foetal-maternal interface from mice undergoing abortion

Several burning questions remain unanswered in pregnancy-related research. Pro- and anti-inflammatory cytokines orchestrate an intriguing interaction leading either to the development of a normal individual or to its rejection. Augmented Th1 cytokines' production is involved in immunological rejection of the foetus. Excessive production of Th1 cytokines, particularly of tumour necrosis factor (TNF)-alpha, also triggers apoptosis. Thus, in the present work we investigated the incidence of apoptosis in a well-known experimental model of Th1-induced abortion, characterized by increased local TNF-alpha levels. Apoptosis of lymphocytes as well as their Th1 and Th2 cytokine production were analysed by flow cytometry. TNF-alpha mRNA levels were additionally analysed by real time reverse transcription-polymerase chain reaction (RT-PCR) in placental and decidual samples. Total placental apoptosis activity was investigated by measuring caspase-3 activity and by TdT-mediated dUTP nick end label staining. Immunohistochemistry, Western blot and real time RT-PCR were used to localize and quantify several anti- and pro-apoptotic molecules at the foetal-maternal interface. Despite elevated Th1 levels at the foetal-maternal interface, mice undergoing abortion presented comparable apoptotic rates. Interestingly, we found a significant upregulation of the anti-apoptotic Bcl-2 protein at the foetal-maternal interface from abortion-prone mice, while no changes could be observed for pro-apoptotic molecules. In the light of our results, we conclude that there is no evidence of increased apoptosis in mice undergoing immunological abortion in spite of elevated TNF-alpha levels. This is probably due to a selective upregulation of anti-apoptotic pathways (i.e. Bcl-2) at the foetal-maternal interface as a compensatory and/or protective mechanism.