Cystatin C in adipose tissue and stimulation of its production by growth hormone and triiodothyronine in 3T3-L1 cells

Human visceral adipose tissue microvascular endothelial cell isolation and establishment of co-culture with white adipocytes to analyze cell-cell communication

Communication between adipocytes and endothelial cells (EC) is suggested to play an important role in the metabolic function of white adipose tissue. In order to generate tools to investigate in detail the physiology and communication of EC and adipocytes, a method for isolation of adipose microvascular EC from visceral adipose tissue (VAT) biopsies of subjects with obesity was developed. Moreover, mature white adipocytes were isolated from the VAT biopsies by a method adapted from a previously published Membrane aggregate adipocytes culture (MAAC) protocol. The identity and functionality of the cultivated and isolated adipose microvascular EC (AMvEC) was validated by imaging their morphology, analyses of mRNA expression, fluorescence activated cell sorting (FACS), immunostaining, low-density lipoprotein (LDL) uptake, and in vitro angiogenesis assays. Finally, we established a new trans filter co-culture system (membrane aggregate adipocyte and endothelial co-culture, MAAECC) for the analysis of communication between the two cell types. EC-adipocyte communication in this system was validated by omics analyses, revealing several altered proteins belonging to pathways such as metabolism, intracellular transport and signal transduction in adipocytes co-cultured with AMvEC. In reverse experiments, induction of several pathways including endothelial development and functions was found in AMvEC co-cultured with adipocytes. In conclusion, we developed a robust method to isolate EC from small quantities of human VAT. Furthermore, the MAAECC system established during the study enables one to study the communication between primary white adipocytes and EC or vice-versa and could also be employed for drug screening.

Adipose tissue is associated with kidney function parameters

Obesity is characterized by the accumulation of adipose tissue in different body compartments. Whether adipose tissue directly affects kidney function is still unknown. We aimed to investigate the role of the adipose tissue and circulating creatinine, cystatin C and kidney function in subjects free of cardio-renal diseases. In the KORA-MRI population-based study, 377 subjects (mean age 56.2 ± 9.2 years; 41.6% female) underwent whole-body 3T-MRI examination. Adipose tissue defined as visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were quantified from T1-DIXON sequence using a semi-automatic algorithm. Serum creatinine and cystatin C were measured using standard laboratory and estimated glomerular filtration rate (e-GFR) was performed based on creatinine (e-GFR_crea), cystatin C (e-GFR_cys) and creatinine-cystatin C (e-GFR_cc). Linear regression analysis, adjusted for risk factors, was used to investigate the relationship between adipose tissue and circulating creatinine, cystatin C, and kidney function. In multivariate analyses VAT was inversely associated with eGFR_cys (ß = - 4.88, p =  < 0.001), and positively associated with serum cystatin C (ß = 0.05, p =  < 0.001), respectively. No association was found between other adipose parameters such as total adipose tissue (TAT) and subcutaneous adipose tissue (SAT) and serum creatinine, urine microalbumin and eGFR_crea. Stratified analyses according to BMI revealed confirmatory results for category of BMI > 30. VAT is positively associated with serum cystatin C and inversely with eGFR based on cystatin C, suggesting a direct involvement of visceral adipose tissue in increased metabolism of cystatin C and consequently decreased kidney function.

Increased fat mass index is associated with decreased glomerular filtration rate estimated from cystatin C. Data from Malmö Diet and Cancer cohort

Background

This study aims to describe associations of obesity and CKD in a Swedish urban population. The impact of fat mass, from bioimpedance analysis, on eGFR based on cystatin C and/or creatinine is studied.

Methods

5049 participants from Malmö Diet and Cancer Study the cardiovascular arm (MDCS‐CV) with available body mass composition (single frequency bioimpedance analysis) and cystatin C measured at baseline were selected. Body mass index (kg/m²) was used to define overweight/obesity. eGFR was calculated using cystatin C (eGFR_CYS) and creatinine (eGFR_CR) equations: Chronic Kidney Disease Epidemiology Collaboration 2012 (CKD-EPI_CR, CKD-EPI_CYS, CKD-EPI_CR-CYS)_, eGFR_CYS based on Caucasian, Asian, pediatric, and adult cohorts (CAPA), the Lund-Malmö revised equation (LMrev), and Modified Full Age Spectrum creatinine-based equation (EKFC_CR). Two different fat mass index (FMI) z-scores were calculated: FMI z-score_Larsson and FMI z-score_Lee.

Results

Lower eGFR_CYS and eGFR_CR-CYS following multiple adjustments were prevalent in overweight/obese subjects. Increase in FMI z-score_Larsson or FMI z-score_Lee was related to decrease in predicted CAPA, CKD-EPI_CYS, CKD-EPI_CR-CYS and CAPA-LMrev equation.

Conclusion

eGFR_CYS, in contrast to combined eGFR_CR-CYS and eGFR_CR, demonstrate the strongest association between FMI and kidney function.

Cystatin C relates to metabolism in healthy, pubertal adolescents

INTRODUCTION

The cystatin C (CysC) serum level is a marker of glomerular filtration rate and depends on age, gender, and pubertal stage. We hypothesize that CysC might overall reflect energy homeostasis and be regulated by components of the endocrine system and metabolites in pubertal adolescents.

METHODS

Serum CysC levels and further possible effector parameters in 5355 fasting, morning venous blood samples from 2035 healthy participants of the LIFE Child cohort study (age 8 to 18 years) were analyzed. Recruitment started in 2011, with probands followed up once a year. Linear univariate and stepwise multivariate regression analyses were performed.

RESULTS

Annual growth rate, serum levels of thyroid hormones, parathyroid hormone, insulin-like growth factor 1, hemoglobin A1c (HbA1c), uric acid, and alkaline phosphatase show relevant and significant associations with CysC serum concentrations (p <0.001). Furthermore, male probands' CysC correlated with the body mass index and testosterone among other sexual hormones. Multivariate analyses revealed that uric acid and HbA1c are associated variables of CysC independent from gender (p <0.001). In males, alkaline phosphatase (p <0.001) is additionally significantly associated with CysC. Thyroid hormones show significant correlations only in multivariate analyses in females (p <0.001).

CONCLUSIONS

The described associations strongly suggest an impact of children's metabolism on CysC serum levels. These alterations need to be considered in kidney diagnostics using CysC in adolescents. Additionally, further studies are needed on CysC in children.

A New Panel-Estimated GFR, Including β2-Microglobulin and β-Trace Protein and Not Including Race, Developed in a Diverse Population

RATIONALE AND OBJECTIVE

Glomerular filtration rate (GFR) estimation based on creatinine and cystatin C (eGFRcr-cys) is more accurate than estimated GFR (eGFR) based on creatinine or cystatin C alone (eGFRcr or eGFRcys, respectively), but the inclusion of creatinine in eGFRcr-cys requires specification of a person's race. β2-Microglobulin (B2M) and β-trace protein (BTP) are alternative filtration markers that appear to be less influenced by race than creatinine is.

STUDY DESIGN

Study of diagnostic test accuracy.

SETTING AND PARTICIPANTS

Development in a pooled population of 7 studies with 5,017 participants with and without chronic kidney disease. External validation in a pooled population of 7 other studies with 2,245 participants.

TESTS COMPARED

Panel eGFR using B2M and BTP in addition to cystatin C (3-marker panel) or creatinine and cystatin C (4-marker panel) with and without age and sex or race.

OUTCOMES

GFR measured as the urinary clearance of iothalamate, plasma clearance of iohexol, or plasma clearance of [51Cr]EDTA.

RESULTS

Mean measured GFRs were 58.1 and 83.2 mL/min/1.73 m2, and the proportions of Black participants were 38.6% and 24.0%, in the development and validation populations, respectively. In development, addition of age and sex improved the performance of all equations compared with equations without age and sex, but addition of race did not further improve the performance. In validation, the 4-marker panels were more accurate than the 3-marker panels (P < 0.001). The 3-marker panel without race was more accurate than eGFRcys (percentage of estimates greater than 30% different from measured GFR [1 - P30] of 15.6% vs 17.4%; P = 0.01), and the 4-marker panel without race was as accurate as eGFRcr-cys (1 - P30 of 8.6% vs 9.4%; P = 0.2). Results were generally consistent across subgroups.

LIMITATIONS

No representation of participants with severe comorbid illness and from geographic areas outside of North America and Europe.

CONCLUSIONS

The 4-marker panel eGFR is as accurate as eGFRcr-cys without requiring specification of race. A more accurate race-free eGFR could be an important advance.

Obesity-Induced Increase in Cystatin C Alleviates Tissue Inflammation

We recently demonstrated that removal of one kidney (uninephrectomy [UniNx]) in mice reduced high-fat diet (HFD)-induced adipose tissue inflammation, thereby improving adipose tissue and hepatic insulin sensitivity. Of note, circulating cystatin C (CysC) levels were increased in UniNx compared with sham-operated mice. Importantly, CysC may have anti-inflammatory properties, and circulating CysC levels were reported to positively correlate with obesity in humans and as shown here in HFD-fed mice. However, the causal relationship of such observation remains unclear. HFD feeding of CysC-deficient (CysC knockout [KO]) mice worsened obesity-associated adipose tissue inflammation and dysfunction, as assessed by proinflammatory macrophage accumulation. In addition, mRNA expression of proinflammatory mediators was increased, whereas markers of adipocyte differentiation were decreased. Similar to findings in adipose tissue, expression of proinflammatory cytokines was increased in liver and skeletal muscle of CysC KO mice. In line, HFD-induced hepatic insulin resistance and impairment of glucose tolerance were further aggravated in KO mice. Consistently, chow-fed CysC KO mice were more susceptible to lipopolysaccharide-induced adipose tissue inflammation. In people with obesity, circulating CysC levels correlated negatively with adipose tissue Hif1α as well as IL6 mRNA expression. Moreover, healthy (i.e., insulin-sensitive) subjects with obesity had significantly higher mRNA expression of CysC in white adipose tissue. In conclusion, CysC is upregulated under obesity conditions and thereby counteracts inflammation of peripheral insulin-sensitive tissues and, thus, obesity-associated deterioration of glucose metabolism.