Herbert Tempfer

Perivascular cells of the supraspinatus tendon express both tendon- and stem cell-related markers

Tendons and ligaments are often affected by mechanical injuries or chronic impairment but other than muscle or bone they possess a low healing capacity. So far, little is known about regeneration of tendons and the role of tendon precursor cells in that process. We hypothesize that perivascular cells of tendon capillaries are progenitors for functional tendon cells and are characterized by expression of marker genes and proteins typical for mesenchymal stem cells and functional tendon cells. Immunohistochemical characterization of biopsies derived from intact human supraspinatus tendons was performed. From these biopsies perivascular cells were isolated, cultured, and characterized using RT-PCR and Western blotting. We have shown for the first time that perivascular cells within tendon tissue express both tendon- and stem/precursor cell-like characteristics. These findings were confirmed by results from in vitro studies focusing on cultured perivascular cells isolated from human supraspinatus tendon biopsies. The results suggest that the perivascular niche may be considered a source for tendon precursor cells. This study provides further information about the molecular nature and localization of tendon precursor cells, which is the basis for developing novel strategies towards tendon healing and facilitated regeneration.

Effects of crystalline glucocorticoid triamcinolone acetonide on cultered human supraspinatus tendon cells.

Background Rotator cuff tears are a common cause of shoulder pain and impairment. Subacromial glucocorticoid injections are widely used for treatment of epiphenomenons of chronic impingement syndrome with the possible side effects of tendon rupture and impaired tendon healing. Methods Using qRT-PCR, western blot, immunoflourescence, and measurement of 3H-thymidine uptake we investigated the effects of the crystalline glucocorticoid triamcinolone acetonide (TAA) when added to the culture medium of isolated human rotator cuff tendon cells. Results After 2 weeks of incubation, the cells had lost their fibroblastic appearance and parallel orientation, which is characteristic of cellular degeneration in vivo. Moreover, expression and secretion of collagen I was strongly reduced, and there was a decrease in proliferation rate. Cell migration was blocked and the rate of expression of the matrix metalloproteinases MMP2, MMP8, MMP9, and MMP13 was reduced, but expression of TIMP1 (a tissue inhibitor of MMPs) was upregulated, indicating a reduction in the cellular capacity for tendon repair. In addition, changes in cellular differentiation were observed: the number of adipocytes increased and levels of the protein Sox9—a marker of differentiating and mature chondrocytes—were elevated in triamcinolone acetonide treated cells. Interpretation These results may indicate that the use of TAA is one reason for weaker mechanical tendon properties and for the high rate of re-rupture after supraspinatus tendon repair.

New aspects of the molecular constituents of tissue barriers

Epithelial and endothelial tissue barriers are based on tight intercellular contacts (Tight Junctions, TJs) between neighbouring cells. TJs are multimeric complexes, located at the most apical border of the lateral membrane. So far, a plethora of proteins locating at tight intercellular contacts have been discovered, the role of which has just partly been unraveled. Yet, there is convincing evidence that many TJ proteins exert a dual role: They act as structural components at the junctional site and they are involved in signalling pathways leading to alterations of gene expression and cell behaviour (migration, proliferation). This review will shortly summarize the classical functions of TJs and TJ-related proteins and will introduce a new category, termed the “non-classical” functions of junctional proteins. A particular focus will be directed towards the nuclear targeting of junctional proteins and the downstream effects elicited by their intranuclear activities.

Brain pericyte plasticity as a potential drug target in CNS repair

Brain pericytes (BrPCs) are essential cellular components of the central nervous system neurovascular unit involved in the regulation of blood flow, blood-brain barrier function, as well as in the stabilization of the vessel architecture. More recently, it became evident that BrPCs, besides their regulatory activities in brain vessel function and homeostasis, have pleiotropic functions in the adult CNS ranging from stromal and regeneration promoting activities to stem cell properties. This special characteristic confers BrPC cell plasticity, being able to display features of other cells within the organism. BrPCs might also be causally involved in certain brain diseases. Due to these properties BrPCs might be potential drug targets for future therapies of neurological disorders. This review summarizes BrPC properties, disorders in which this cell type might be involved, and provides suggestions for future therapeutic developments targeting BrPCs.

Neural Crest Origin of Retinal and Choroidal Pericytes

PURPOSE The origin of pericytes (PCs) has been controversially discussed and at least three different sources of PCs are proposed: a neural crest, mesodermal, or bone marrow origin. In the present study we investigated a potential neural crest origin of ocular PCs in a transgenic Rosa26-YFP-Sox10-Cre neural crest-specific reporter mouse model at different developmental stages. METHODS The Rosa26-YFP-Sox10-Cre mouse model expresses the yellow fluorescent protein (YFP) reporter in cells with an active Sox10 promoter and was here used for cell fate studies of Sox10-positive neural crest derived progeny cells. Detection of the YFP signal in combination with double and triple immunohistochemistry of chondroitin sulfate proteoglycan (NG2), platelet derived growth factor receptor β (PDGFRβ), α smooth muscle actin (αSMA), oligodendrocyte transcription factor 2 (Olig2), and lectin was performed and analyzed by confocal microscopy. RESULTS Sox10-YFP-positive cells and profiles were detected in the inner nuclear layer, the ganglionic cell layer, and the axons of the nerve fiber layer in postnatal retinas. An additional population has been identified in the retina, optic nerve, and choroid that displays strong perivascular localization. These cells were colocalized with the PC-specific markers NG2 and PDGFRβ in embryonic (E14.5) as well as postnatal (P4, P12, 6-week-old) vasculature. Beside PCs, vascular smooth muscle cells (vSMCs) were also labeled by the Sox10-YFP reporter protein in all ocular tissues investigated. CONCLUSIONS Since YFP-positive PCs and vSMCs are colocalized with NG2 and PDGFRβ, we propose that capillary PCs and vSMCs in the retina and the optic nerve, both parts of the central nervous system, as well as in the choroid, a tissue of mesodermal origin, derive from the neural crest.

Inhibition of leukotriene receptors boosts neural progenitor proliferation.

Neural stem and progenitor cells serve as a reservoir for new neurons in the adult brain throughout lifetime. One of the critical steps determining the net production of new neurons is neural progenitor proliferation, which needs to be tightly controlled. Since inflammation has detrimental effects on neurogenesis and the 5-lipoxygenase/leukotriene pathway is involved in inflammatory processes, we investigated the effects of leukotrienes and montelukast, a small molecule inhibitor of the leukotriene receptors CysLT1R and GPR17, on neural stem and progenitor cell proliferation. We demonstrate expression of the leukotriene receptor GPR17 by neural progenitors and by neural stem cells. Stimulation with excess amounts of leukotrienes did not affect progenitor proliferation, whereas blockade of GPR17 with montelukast strongly elevated neural stem and progenitor proliferation, while maintaining their differentiation fate and potential. This effect was associated with increased ERK1/2 phosphorylation suggesting an involvement of the EGF signaling cascade. Based on our results, montelukast and the inhibition of the 5-LOX pathway might be potent candidates for future therapies employing neurogenesis to promote structural and functional improvement in neurodegeneration, neuropsychiatric disease and ageing.

Tendon Vasculature in Health and Disease.

Tendons represent a bradytrophic tissue which is poorly vascularized and, compared to bone or skin, heal poorly. Usually, a vascularized connective scar tissue with inferior functional properties forms at the injury site. Whether the increased vascularization is the root cause of tissue impairments such as loss of collagen fiber orientation, ectopic formation of bone, fat or cartilage, or is a consequence of these pathological changes remains unclear. This review provides an overview of the role of tendon vasculature in healthy and chronically diseased tendon tissue as well as its relevance for tendon repair. Further, the nature and the role of perivascular tendon stem/progenitor cells residing in the vascular niche will be discussed and compared to multipotent stromal cells in other tissues.

ACL injuries and stem cell therapy

Tears of the anterior cruciate ligament (ACL) are very frequent injuries, particularly in young and active people. Arthroscopic reconstruction using tendon auto- or allograft represents the gold-standard for the management of ACL tears. Interestingly, the ACL has the potential to heal upon intensive non-surgical rehabilitation procedures. Several biological factors influence this healing process as local intraligamentous cytokines and mainly cell repair mechanisms controlled by stem cells or progenitor cells. Understanding the mechanisms of this regeneration process and the cells involved may pave the way for novel, less invasive and biology-based strategies for ACL repair. This review aims to focus on the current knowledge on the mechanisms of ACL healing, the nature and potential of ligament derived stem/progenitor cells as well as on the potential and the limitations of using mesenchymal stem cells (MSCs) for treating injured ACL.

Neuronal stem cells in adults

Neuronal stem cells are like other tissue-specific stem cells, undifferentiated cells which can proliferate and may give rise to glia and neurons. They are present in mammalians throughout the entire life and are supposed to play an important role in renewal of neurons. However, little is known about the origin, phenotypic expression and function of neuronal stem cells in the adult brain. In the present review the occurrence and origin of neuronal stem cells as well as specific markers, which allow their identification in the brain is being described. Finally the role of these cells in the adult brain and their potential use in neuropathy is discussed.

Pericytes Stimulate Oligodendrocyte Progenitor Cell Differentiation during CNS Remyelination

Summary The role of the neurovascular niche in CNS myelin regeneration is incompletely understood. Here, we show that, upon demyelination, CNS-resident pericytes (PCs) proliferate, and parenchymal non-vessel-associated PC-like cells (PLCs) rapidly develop. During remyelination, mature oligodendrocytes were found in close proximity to PCs. In Pdgfbret/ret mice, which have reduced PC numbers, oligodendrocyte progenitor cell (OPC) differentiation was delayed, although remyelination proceeded to completion. PC-conditioned medium accelerated and enhanced OPC differentiation in vitro and increased the rate of remyelination in an ex vivo cerebellar slice model of demyelination. We identified Lama2 as a PC-derived factor that promotes OPC differentiation. Thus, the functional role of PCs is not restricted to vascular homeostasis but includes the modulation of adult CNS progenitor cells involved in regeneration.