"Macro transcobalamin causing raised vitamin B12: Case-based laboratory investigation".

Determination of plasma vitamin B12 (B12) is a frequently requested laboratory analysis, mainly employed to establish B12 deficiency. However, an increased level of B12 is a common unexpected finding that may be related to an increased concentration of one of the B12 binding proteins, haptocorrin or transcobalamin. This paper describes the extensive laboratory evaluation of a patient with an elevated level of plasma B12 with various well-established assays. Initial studies suggested the presence of a macromolecule consisting of haptocorrin bound B12. Specific determinations of the B12-binding proteins revealed normal amounts of haptocorrin but a markedly increase in both total and B12 saturated transcobalamin (holo-TC). The results are in accord with the presence of macro-transcobalamin. These experiments reveal that determination of the nature of the B12-macromolecules is troublesome due to differences in assays applied to measure these proteins. In addition, this publication creates awareness of macro-holo-TC as a cause of an unexplained increased B12 level.

In vivo and in vitro Approaches Reveal Novel Insight Into the Ability of Epicardium-Derived Cells to Create Their Own Extracellular Environment.

Human epicardium-derived cells (hEPDCs) transplanted in the NOD-SCID mouse heart after myocardial infarction (MI) are known to improve cardiac function, most likely orchestrated by paracrine mechanisms that limit adverse remodeling. It is not yet known, however, if hEPDCs contribute to preservation of cardiac function via the secretion of matrix proteins and/or matrix proteases to reduce scar formation. This study describes the ability of hEPDCs to produce human collagen type I after transplantation into the infarct border zone, thereby creating their own extracellular environment. As the in vivo environment is too complex to investigate the mechanisms involved, we use an in vitro set-up, mimicking biophysical and biochemical cues from the myocardial tissue to unravel hEPDC-induced matrix remodeling. The in vivo contribution of hEPDCs to the cardiac extracellular matrix (ECM) was assessed in a historical dataset of the NOD-SCID murine model of experimentally induced MI and cell transplantation. Analysis showed that within 48 h after transplantation, hEPDCs produce human collagen type I. The build-up of the human collagen microenvironment was reversed within 6 weeks. To understand the hEPDCs response to the pathologic cardiac microenvironment, we studied the influence of cyclic straining and/or transforming growth beta (TGFß) signaling in vitro. We revealed that 48 h of cyclic straining induced collagen type I production via the TGFß/ALK5 signaling pathway. The in vitro approach enables further unraveling of the hEPDCs ability to secrete matrix proteins and matrix proteases and the potential to create and remodel the cardiac matrix in response to injury.

The roadmap of WT1 protein expression in the human fetal heart.

The transcription factor Wilms' Tumor-1 (WT1) is essential for cardiac development. Deletion of Wt1 in mice results in disturbed epicardial and myocardial formation and lack of cardiac vasculature, causing embryonic lethality. Little is known about the role of WT1 in the human fetal heart. Therefore, as a first step, we analyzed the expression pattern of WT1 protein during human cardiac development from week 4 till week 20. WT1 expression was apparent in epicardial, endothelial and endocardial cells in a spatiotemporal manner. The expression of WT1 follows a pattern starting at the epicardium and extending towards the lumen of the heart, with differences in timing and expression levels between the atria and ventricles. The expression of WT1 in cardiac arterial endothelial cells reduces in time, whereas WT1 expression in the endothelial cells of cardiac veins and capillaries remains present at all stages studied. This study provides for the first time a detailed description of the expression of WT1 protein during human cardiac development, which indicates an important role for WT1 also in human cardiogenesis.

Part and Parcel of the Cardiac Autonomic Nerve System: Unravelling Its Cellular Building Blocks during Development.

The autonomic nervous system (cANS) is essential for proper heart function, and complications such as heart failure, arrhythmias and even sudden cardiac death are associated with an altered cANS function. A changed innervation state may underlie (part of) the atrial and ventricular arrhythmias observed after myocardial infarction. In other cardiac diseases, such as congenital heart disease, autonomic dysfunction may be related to disease outcome. This is also the case after heart transplantation, when the heart is denervated. Interest in the origin of the autonomic nerve system has renewed since the role of autonomic function in disease progression was recognized, and some plasticity in autonomic regeneration is evident. As with many pathological processes, autonomic dysfunction based on pathological innervation may be a partial recapitulation of the early development of innervation. As such, insight into the development of cardiac innervation and an understanding of the cellular background contributing to cardiac innervation during different phases of development is required. This review describes the development of the cANS and focuses on the cellular contributions, either directly by delivering cells or indirectly by secretion of necessary factors or cell-derivatives.

The epicardium as modulator of the cardiac autonomic response during early development.

The cardiac autonomic nervous system (cANS) modulates heart rate, contraction force and conduction velocity. The embryonic chicken heart already responds to epinephrine prior to establishment of the cANS. The aim of this study was to define the regions of the heart that might participate in modulating the early autonomic response to epinephrine. Immunofluorescence analysis reveals expression of neural markers tubulin beta-3 chain and neural cell adhesion molecule in the epicardium during early development. In addition, expression of the ß2 adrenergic receptor, the receptor for epinephrine, was found in the epicardium. Ex-ovo micro-electrode recordings in hearts with inhibition of epicardial outgrowth showed a significantly reduced response of the heart rate to epinephrine compared to control hearts. This study suggests a role for the epicardium as autonomic modulator during early cardiac development.

Regional differences in WT-1 and Tcf21 expression during ventricular development: implications for myocardial compaction.

BACKGROUND: Morphological and functional differences of the right and left ventricle are apparent in the adult human heart. A differential contribution of cardiac fibroblasts and smooth muscle cells (populations of epicardium-derived cells) to each ventricle may account for part of the morphological-functional disparity. Here we studied the relation between epicardial derivatives and the development of compact ventricular myocardium. RESULTS: Wildtype and Wt1CreERT2/+ reporter mice were used to study WT-1 expressing cells, and Tcf21lacZ/+ reporter mice and PDGFRα-/-;Tcf21LacZ/+ mice to study the formation of the cardiac fibroblast population. After covering the heart, intramyocardial WT-1+ cells were first observed at the inner curvature, the right ventricular postero-lateral wall and left ventricular apical wall. Later, WT-1+ cells were present in the walls of both ventricles, but significantly more pronounced in the left ventricle. Tcf21-LacZ + cells followed the same distribution pattern as WT-1+ cells but at later stages, indicating a timing difference between these cell populations. Within the right ventricle, WT-1+ and Tcf21-lacZ+ cell distribution was more pronounced in the posterior inlet part. A gradual increase in myocardial wall thickness was observed early in the left ventricle and at later stages in the right ventricle. PDGFRα-/-;Tcf21LacZ/+ mice showed deficient epicardium, diminished number of Tcf21-LacZ + cells and reduced ventricular compaction. CONCLUSIONS: During normal heart development, spatio-temporal differences in contribution of WT-1 and Tcf21-LacZ + cells to right versus left ventricular myocardium occur parallel to myocardial thickening. These findings may relate to lateralized differences in ventricular (patho)morphology in humans.

Cardiac endothelial cells express Wilms' tumor-1: Wt1 expression in the developing, adult and infarcted heart.

Myocardial infarction is the leading cause of death worldwide. Due to their limited regenerative capacity lost cardiomyocytes are replaced by a non-contractile fibrotic scar tissue. The epicardial layer of the heart provides cardiac progenitor cells during development. Because this layer regains embryonic characteristics in the adult heart after cardiac injury, it could serve as a promising source for resident cardiac progenitor cells. Wilms' tumor-1 (Wt1) is associated with the activation and reactivation of the epicardium and therefore potentially important for the differentiation and regenerative capacity of the epicardium. To gain more insight into the regulation of Wt1 we examined the spatiotemporal expression pattern of Wt1 during murine development and after cardiac injury. Interestingly, we found that Wt1 is expressed in the majority of the cardiac endothelial cells within the myocardial ventricular layer of the developing heart from E12.5 onwards. In the adult heart only a subset of coronary endothelial cells remains positive for Wt1. After myocardial infarction Wt1 is temporally upregulated in the endothelial cells of the infarcted area and the border zone of the heart. In vitro experiments show that endothelial Wt1 expression can be induced by hypoxia. We show that Wt1 is associated with endothelial cell proliferation: Wt1 expression is higher in proliferating endothelial cells, Wt1 knockdown inhibits the proliferation of endothelial cells, and Wt1 regulates CyclinD1 expression. Finally, endothelial cells lacking Wt1 are not capable to establish a proper vascular network in vitro. Together, these results suggest a possible role for Wt1 in cardiac vessel formation in development and disease.

TGFß and BMP signaling in cardiac cushion formation: lessons from mice and chicken.

Cardiac cushion formation is crucial for both valvular and septal development. Disruption in this process can lead to valvular and septal malformations, which constitute the largest part of congenital heart defects. One of the signaling pathways that is important for cushion formation is the TGFß superfamily. The involvement of TGFß and BMP signaling pathways in cardiac cushion formation has been intensively studied using chicken in vitro explant assays and in genetically modified mice. In this review, we will summarize and discuss the role of TGFß and BMP signaling components in cardiac cushion formation.