Tissue chaperoning—the expanded functions of fetuin-A beyond inhibition of systemic calcification

Accelerated calciprotein crystallization time (T50) is correlated with impaired lung diffusion capacity in systemic sclerosis

Background

Systemic sclerosis (SSc) is a complex auto-immune disease characterized by vascular damage, inflammation, fibrosis and calcinosis, where pulmonary involvement is the leading cause of mortality. Calciprotein particles (CPPs) are increasingly formed upon disbalance of the physiological mineral buffering system and induce pro-inflammatory effects. This exploratory study investigated whether functional indicators of the endogenous mineral buffering system are dysregulated in SSc and linked to disease activity.

Methods

T50 (calciprotein crystallization test or serum calcification propensity) and hydrodynamic radius of secondary CPPs (CPP2) were determined in serum samples from 78 SSc patients and 44 controls without SSc, and were associated with disease activity markers of SSc.

Results

T50 was reduced and CPP2 radius was increased in SSc patients as compared to controls, indicating a deranged mineral buffering system. This was accompanied by slightly higher serum phosphate and PTH levels in SSc patients, while iFGF23 was not significantly modified. Longitudinally, all parameters remained unchanged over time in SSc patients, only iFGF23 increased. While the modified Rodnan skin score showed some inconsistent correlations with mineral buffering indicators, their association was not independent of other factors. However, lower T50 was significantly correlated to reduced lung diffusion capacity and this association remained significant in a multivariate linear regression model.

Conclusion

This study provides indications for a disturbed mineral buffering system in SSc. Increased serum calcification propensity (lower T50) is correlated with impaired lung diffusion capacity, suggesting a possible role of deranged mineral buffering in disease progression. Further studies are required to confirm these observations in larger cohorts and to investigate a putative functional relevance.

Association of serum zinc with mineral stress in chronic kidney disease

Background

The excessive cardiovascular mortality of patients with chronic kidney disease (CKD) could be linked to mineral stress, the biological consequence of calcium-phosphate nanoparticle exposure. This study investigated whether zinc is associated with mineral stress markers in CKD.

Methods

Zinc and T50 (serum calcification propensity) as well as hydrodynamic radius of secondary calciprotein particles (CPP2) were measured in blood donors and CKD patients with/out dialysis.

Results

Serum zinc concentrations and T50 were reduced, while CPP2 radius was increased in CKD patients. Serum zinc levels positively correlated with T50 and inversely correlated with CPP2 radius. In a hierarchical linear regression model, T50 was associated with age, calcium, phosphate, magnesium and albumin. Addition of zinc significantly improved prediction of the model, confirming an additional contribution of zinc to T50. Similar observations were made for the association of zinc and CPP2 radius, but spiking experiments indicated that zinc may stronger modify T50 than CPP2 radius. Also, urinary zinc excretion was increased in patients with kidney disease and correlated to T50 and CPP2 radius. Serum zinc further correlated with markers of arterial stiffness in blood donors and CKD patients, but these associations did not remain significant in a multivariate linear regression model.

Conclusions

Reduced serum zinc levels in CKD appear directly linked to lower T50 and associated with larger CPP2 radius. Further studies on the associations of zinc and mineral stress as well as putative therapeutic benefits of zinc supplementation are required.

COVID-19 Recovery and Cardiovascular Health: The Interplay Between Fetuin-A and Blood Pressure

INTRODUCTION

COVID-19 has been shown to impair cardiovascular function, and further studies have proven that this effect can be long-term on several cardiovascular biomarkers. Fetuin-A, a multifunctional protein involved in calcification and inflammation, has emerged as an important biomarker in this process. This study investigates the relationship between recovery from COVID-19, cardiovascular health, and concentrations of fetuin-A in patients with high blood pressure.

METHODS

Seventy-nine men and 36 women were admitted to the Nasiriyah Heart Center in Iraq between March and August 2023, with ages ranging from 5 to 93 years. Clinical data were collected on admission along with blood samples, and serum levels of fetuin-A were measured using an enzyme-linked immunosorbent assay (ELISA). The results were analyzed using Python libraries Pandas and SciPy to perform independent sample t-tests to determine mean levels of fetuin-A in various patient subgroups. A p-value of less than 0.05 was considered statistically significant.

RESULTS

The study showed that patients who had survived COVID-19 had significantly higher levels of fetuin-A compared to healthy controls, with a mean concentration of 103.64 mg/L versus 19.199 mg/L (p < 0.001). Additionally, it was found that patients with high blood pressure had increased levels of fetuin-A compared to those without high blood pressure, with a mean concentration of 109.01 mg/L versus 95.88 mg/L (p = 0.025). These results suggest that COVID-19 may alter the usual relationship between blood pressure and cardiovascular biomarkers.

CONCLUSION

This study emphasizes the complex interaction between recovery from COVID-19 and cardiovascular health, primarily through the levels of fetuin-A. The increase in fetuin-A among hypertensive patients suggests that COVID-19 may enhance cardiovascular risk, highlighting the need for stricter monitoring and tailored treatment strategies. Further studies are needed to elucidate the underlying mechanisms, which will help develop effective clinical guidelines for managing cardiovascular health in COVID-19 survivors.

Pioglitazone treatment mitigates cardiovascular bioprosthetic degeneration in a chronic kidney disease model

Aims

Chronic kidney disease (CKD) is a risk factor for the development of cardiovascular diseases, e.g., atherosclerosis and calcific aortic valve disease, leading inevitably to valve replacement surgery. CKD patients with bioprosthetic cardiovascular grafts, in turn, have a higher risk of premature graft degeneration. Peroxisome proliferator-activated receptor gamma (PPARγ) activation by pioglitazone has cardio-renal protective properties, and research using a heterotopic valve implantation model has shown anti-degenerative effects of PPARγ activation on bioprosthetic valved grafts (BVG) in rats. The present work aims to analyze a potential protective effect of pioglitazone treatment on BVG in an adenine-induced rat model of CKD.

Methods and Results

BVG of Sprague Dawley rats were heterotopically implanted in Wistar rats in an infrarenal position for 4 and 8 weeks. Animals were distributed into three groups for each time point: 1) control group receiving standard chow, 2) CKD group receiving 0.25% adenine and 3) CKD + pioglitazone group (300 mg per kg of 0.25% adenine chow). BVG function was analyzed by echocardiography. Plasma analytes were determined and explanted grafts were analyzed by semi-quantitative real-time PCR, Western blot analysis, histology and immunohistology.PPARγ activation significantly reduced CKD-induced calcification of aortic and valvular segments of BVG by 44% and 53%, respectively. Pioglitazone treatment significantly also reduced CKD-induced intima hyperplasia by 60%. Plasma analysis revealed significantly attenuated potassium and phosphate levels after pioglitazone treatment. Moreover, PPARγ activation led to significantly decreased interleukin-6 gene expression (by 57%) in BVG compared to CKD animals. Pioglitazone treatment leads to functional improvement of BVG.

Conclusion

This study broadens the understanding of the potential value of PPARγ activation in cardio-renal diseases and delineates pioglitazone treatment as a valuable option to prevent bioprosthetic graft failure in CKD. Further mechanistic studies, e.g., using small molecules activating PPARγ signaling pathways, are necessary for the evaluation of involved mechanisms. Additionally, the translation into pre-clinical studies using large animals is intended as the next research project.

Invited review: Modeling milk stability

Novel insights into the stability of milk and milk products during storage and processing result from describing caseins near neutral pH as hydrophilic, intrinsically disordered, proteins. Casein solubility is strongly influenced by pH and multivalent ion binding. Solubility is high at a neutral pH or above, but decreases as the casein net charge approaches zero, allowing a condensed casein phase or gel to form, then increases at lower pH. Of particular importance for casein micelle stability near neutral pH is the proportion of free caseins in the micelle (i.e., caseins not bound directly to nanoclusters of calcium phosphate). Free caseins are more soluble and better able to act as molecular chaperones (to prevent casein and whey protein aggregation) than bound caseins. Some free caseins are highly phosphorylated and can also act as mineral chaperones to inhibit the growth of calcium phosphate phases and prevent mineralized deposits from forming on membranes or heat exchangers. Thus, casein micelle stability is reduced when free caseins bind to amyloid fibrils, destabilized whey proteins or calcium phosphate. The multivalent-binding model of the casein micelle quantitatively describes these and other factors affecting the stability of milk and milk protein products during manufacture and storage.

Evaluation of atherosclerotic risk in rosacea patients through serum fetuin-A and carotid intima media thickness

BACKGROUND

The link between rosacea and various systemic conditions has been growing in prominence, even though the relationship between rosacea and cardiovascular disease remains a subject of debate in current research.

AIMS

Detecting the connection between rosacea and subclinical atherosclerosis using laboratory and ultrasonographic parameters.

METHODS

Fifty rosacea patients and 49 control were included in the study. Demographic, clinical, and laboratory data, including serum high sensitivity C-reactive protein (hs-CRP), fetuin-A (FA), and matrix gla protein levels were assessed. Carotid intima-media thickness (CIMT) was measured by carotid ultrasonography.

RESULTS

Serum hs-CRP levels (p = 0.009) and mean CIMT (p = 0.001) were significantly higher, while serum FA levels were significantly lower (p < 0.001) in the rosacea patients compared with control. The number of patients with mean CIMT>75th percentile according to age and sex were significantly higher in the rosacea group (p = 0.001). Rosacea patients with ocular involvement exhibited significantly higher hs-CRP values in comparison to those without ocular involvement (p = 0.008). No significant correlation was detected between disease duration, severity, subtype and the study parameters.

CONCLUSIONS

This study results suggest that rosacea poses an independent risk for subclinical atherosclerosis regardless of its severity, duration, or subtype. Therefore, individuals diagnosed with rosacea should receive careful evaluation and monitoring to detect possible cardiovascular complications promptly. Furthermore, our study hints at a potential elevated risk of subclinical inflammation in rosacea patients with ocular involvement, warranting additional attention and further investigation.

Current and Emerging Markers and Tools Used in the Diagnosis and Management of Chronic Kidney Disease-Mineral and Bone Disorder in Non-Dialysis Adult Patients

Chronic kidney disease (CKD) is a significant public health concern associated with significant morbidity and has become one of the foremost global causes of death in recent years. A frequent comorbidity of CKD is secondary hyperparathyroidism (SHPT), exemplified by high serum parathyroid hormone (PTH) levels. The mineral metabolism disturbances resulting from CKD and progression to SHPT are currently considered part of the definition of chronic kidney disease-mineral and bone disorder (CKD-MBD). However, CKD-MBD does not only include abnormalities in laboratory-measured parameters; it is a complex condition characterized by dysregulation of bone turnover, mineralization, growth and strength, accompanied by vascular or another soft-tissue calcification. Together, this increases the risk of bone fractures, cardiovascular disease, and overall mortality in CKD-MBD patients. Monitoring serum markers is essential in diagnosing SHPT and CKD-MBD, and there are several recognized indicators for prognosis, optimal clinical management and treatment response in late-stage kidney disease patients receiving dialysis. However, far fewer markers have been established for patients with non-dialysis CKD. This review provides an overview of current and emerging markers and tools used in the diagnosis and management of CKD-MBD in non-dialysis adult patients.

The Complex Relationship between Hypoxia Signaling, Mitochondrial Dysfunction and Inflammation in Calcific Aortic Valve Disease: Insights from the Molecular Mechanisms to Therapeutic Approaches

Calcific aortic valve stenosis (CAVS) is among the most common causes of cardiovascular mortality in an aging population worldwide. The pathomechanisms of CAVS are such a complex and multifactorial process that researchers are still making progress to understand its physiopathology as well as the complex players involved in CAVS pathogenesis. Currently, there is no successful and effective treatment to prevent or slow down the disease. Surgical and transcatheter valve replacement represents the only option available for treating CAVS. Insufficient oxygen availability (hypoxia) has a critical role in the pathogenesis of almost all CVDs. This process is orchestrated by the hallmark transcription factor, hypoxia-inducible factor 1 alpha subunit (HIF-1α), which plays a pivotal role in regulating various target hypoxic genes and metabolic adaptations. Recent studies have shown a great deal of interest in understanding the contribution of HIF-1α in the pathogenesis of CAVS. However, it is deeply intertwined with other major contributors, including sustained inflammation and mitochondrial impairments, which are attributed primarily to CAVS. The present review aims to cover the latest understanding of the complex interplay effect of hypoxia signaling pathways, mitochondrial dysfunction, and inflammation in CAVS. We propose further hypotheses and interconnections on the complexity of these impacts in a perspective of better understanding the pathophysiology. These interplays will be examined considering recent studies that shall help us better dissect the molecular mechanism to enable the design and development of potential future therapeutic approaches that can prevent or slow down CAVS processes.

Reconsidering the role of albumin towards amorphous calcium phosphate-based calciprotein particles formation and stability from a physico-chemical perspective

The formation of calciprotein particles (CPPs) in serum is a physiological phenomenon fundamental to prevent the rise of ectopic calcifications. CPPs are colloidal hybrid particles made of amorphous calcium phosphate stabilized by a protein, fetuin-A. Since albumin is the most abundant protein present in serum, we aimed at understanding if it plays a synergic action together with fetuin-A towards CPPs formation and stability. CPPs were prepared using a constant fetuin-A concentration (5 µM) and different concentrations of albumin (0-606 µM). The stability of CPPs, their crystallization and sedimentation were followed in situ by combining turbidimetry, precipitation analysis and dynamic light scattering. The morphology was investigated by scanning electron microscopy and cryo-transmission electron microscopy, while crystallinity was inspected by infrared spectroscopy. The effect of albumin on the amount of formed CPPs was also studied, as well as the amount of protein adsorbed on CPPs. We found that albumin is not able to prolong the lifetime of the amorphous phase, but it is very effective in delaying the sedimentation of CPPs after crystallization. Albumin also significantly decreases the amount and size of CPPs when present in their synthetic medium, likely playing a fundamental role in our organism together with fetuin-A towards the stabilization of CPPs.

Cardiac Hepatopathy: New Perspectives on Old Problems through a Prism of Endogenous Metabolic Regulations by Hepatokines

Cardiac hepatopathy refers to acute or chronic liver damage caused by cardiac dysfunction in the absence of any other possible causative reasons of liver injury. There is a large number of evidence of the fact that cardiac hepatopathy is associated with poor clinical outcomes in patients with acute or actually decompensated heart failure (HF). However, the currently dominated pathophysiological background does not explain a role of metabolic regulative proteins secreted by hepatocytes in progression of HF, including adverse cardiac remodeling, kidney injury, skeletal muscle dysfunction, osteopenia, sarcopenia and cardiac cachexia. The aim of this narrative review was to accumulate knowledge of hepatokines (adropin; fetuin-A, selenoprotein P, fibroblast growth factor-21, and alpha-1-microglobulin) as adaptive regulators of metabolic homeostasis in patients with HF. It is suggested that hepatokines play a crucial, causative role in inter-organ interactions and mediate tissue protective effects counteracting oxidative stress, inflammation, mitochondrial dysfunction, apoptosis and necrosis. The discriminative potencies of hepatokines for HF and damage of target organs in patients with known HF is under on-going scientific discussion and requires more investigations in the future.

Application of the mineral-binding protein fetuin-A for the detection of calcified lesions

Rationale: Calcium plays an essential role in the biology of vertebrates. Calcium content in body fluids is maintained within a narrow physiologic range by feedback control. Phosphate is equally important for metabolism and is likewise controlled, albeit over a wider range. This results in a nearly supersaturated state of calcium phosphate in body liquids driving mineral precipitation in soft tissues, which is actively prevented by calcification inhibitors. The hepatic plasma protein fetuin-A is a circulating mineralization inhibitor regulating calcium phosphate crystal growth and calcified matrix metabolism. Ectopic mineralization is associated with many pathological conditions aggravating their outcome. Current diagnostic methods lack sensitivity towards microcalcifications representing the initial stages of the process. Given the irreversibility of established calcifications, novel diagnostic tools capable of detecting nascent calcium phosphate deposits are highly desirable. Methods: We designed fluorescent fusion proteins consisting of fetuin-A coupled to a green or red fluorescent protein derivate, mEmerald or mRuby3, respectively. The proteins were expressed in mammalian cell lines. Sequence optimization resolved folding issues and increased sensitivity of mineral binding. Chimeric proteins were tested for their ability to detect calcifications in cell cultures and tissue sections retrieved from calcification-prone mice. Results: We employed novel genetically labeled fetuin-A-based fluorescent proteins for the detection of ectopic calcifications. We show that fetuin-A-based imaging agents are non-toxic and suitable for live imaging of microcalcifications beyond the detection limit of conventional staining techniques. The ability of fetuin-A to preferentially bind nascent calcium phosphate crystals allowed the resolution of histopathological detail of early kidney damage that went previously undetected. Endogenous expression of fetuin-A fluorescent fusion proteins allowed extended live imaging of calcifying cells with unprecedented sensitivity and specificity. Conclusion: Ectopic microcalcifications represent a major clinical concern lacking effective diagnostic and treatment options. In this paper, we describe novel highly sensitive fetuin-A-based fluorescent probes for imaging microcalcifications. We show that fusion proteins consisting of a fetuin-A mineral binding moiety and a fluorescent protein are superior to the routine methods for detecting calcifications. They also surpass in continuous live cell imaging the chemically fluorescence labeled fetuin-A, which we established previously.

Protein arginine deiminase 2 (PAD2) modulates the polarization of THP-1 macrophages to the anti-inflammatory M2 phenotype

Background

Macrophages are effector cells of the innate immune system that undergo phenotypical changes in response to organ injury and repair. These cells are most often classified as proinflammatory M1 and anti-inflammatory M2 macrophages. Protein arginine deiminase (PAD), which catalyses the irreversible conversion of protein-bound arginine into citrulline, is expressed in macrophages. However, the substrates of PAD and its role in immune cells remain unclear. This study aimed to investigate the role of PAD in THP-1 macrophage polarization to the M1 and M2 phenotypes and identify the citrullinated proteins and modified arginines that are associated with this biological switch using mass spectrometry.

Results

Our study showed that PAD2 and, to a lesser extent, PAD1 and PAD4 were predominantly expressed in M1 macrophages. We showed that inhibiting PAD expression with BB-Cl-amidine decreased macrophage polarization to the M1 phenotype (TNF-α, IL-6) and increased macrophage polarization to the M2 phenotype (MRC1, ALOX15). This process was mediated by the downregulation of proteins involved in the NF-κβ pathway. Silencing PAD2 confirmed the activation of M2 macrophages by increasing the antiviral innate immune response and interferon signalling. A total of 192 novel citrullination sites associated with inflammation, cell death and DNA/RNA processing pathways were identified in M1 and M2 macrophages.

Conclusions

We showed that inhibiting PAD activity using a pharmacological inhibitor or silencing PAD2 with PAD2 siRNA shifted the activation of macrophages towards the M2 phenotype, which can be crucial for designing novel macrophage-mediated therapeutic strategies. We revealed a major citrullinated proteome and its rearrangement following macrophage polarization, which after further validation could lead to significant clinical benefits for the treatment of inflammation and autoimmune diseases.

Post-translational modifications glycosylation and phosphorylation of the major hepatic plasma protein fetuin-A are associated with CNS inflammation in children

Fetuin-A is a liver derived plasma protein showing highest serum concentrations in utero, preterm infants, and neonates. Fetuin-A is also present in cerebrospinal fluid (CSF). The origin of CSF fetuin-A, blood-derived via the blood-CSF barrier or synthesized intrathecally, is presently unclear. Fetuin-A prevents ectopic calcification by stabilizing calcium and phosphate as colloidal calciprotein particles mediating their transport and clearance. Thus, fetuin-A plays a suppressive role in inflammation. Fetuin-A is a negative acute-phase protein under investigation as a biomarker for multiple sclerosis (MS). Here we studied the association of pediatric inflammatory CNS diseases with fetuin-A glycosylation and phosphorylation. Paired blood and CSF samples from 66 children were included in the study. Concentration measurements were performed using a commercial human fetuin-A/AHSG ELISA. Of 60 pairs, 23 pairs were analyzed by SDS-PAGE following glycosidase digestion with PNGase-F and Sialidase-AU. Phosphorylation was analyzed in 43 pairs by Phos-TagTM acrylamide electrophoresis following alkaline phosphatase digestion. Mean serum and CSF fetuin-A levels were 0.30 ± 0.06 mg/ml and 0.644 ± 0.55 μg/ml, respectively. This study showed that serum fetuin-A levels decreased in inflammation corroborating its role as a negative acute-phase protein. Blood-CSF barrier disruption was associated with elevated fetuin-A in CSF. A strong positive correlation was found between the CSF fetuin-A/serum fetuin-A quotient and the CSF albumin/serum albumin quotient, suggesting predominantly transport across the blood-CSF barrier rather than intrathecal fetuin-A synthesis. Sialidase digestion showed increased asialofetuin-A levels in serum and CSF samples from children with neuroinflammatory diseases. Desialylation enhanced hepatic fetuin-A clearance via the asialoglycoprotein receptor thus rapidly reducing serum levels during inflammation. Phosphorylation of fetuin-A was more abundant in serum samples than in CSF, suggesting that phosphorylation may regulate fetuin-A influx into the CNS. These results may help establish Fetuin-A as a potential biomarker for neuroinflammatory diseases.