Stefan Momma

Increased generation of neuronal progenitors after ischemic injury in the aged adult human forebrain.

The adult human brain retains the capacity to generate new neurons in the hippocampal formation (Eriksson et al., 1998) and neuronal progenitor cells (NPCs) in the forebrain (Bernier et al., 2000), but to what extent it is capable of reacting to injuries, such as ischemia, is not known. We analyzed postmortem tissue from normal and pathological human brain tissue (n = 54) to study the cellular response to ischemic injury in the forebrain. We observed that cells expressing the NPC marker polysialylated neural adhesion cell molecule (PSA-NCAM) are continuously generated in the adult human subventricular zone (SVZ) and migrate along the olfactory tracts. These cells were not organized in migrating chains as in the adult rodent rostral migratory stream, and their number was lower in the olfactory tracts of brains from old (56–81 years of age) compared with young (29 + 36 years of age) individuals. Moreover, we show that in brains of patients of advanced age (60–87 years of age), ischemia led to an elevated number of Ki-67-positive cells in the ipsilateral SVZ without concomitant apoptotic cell death. Additionally, ischemia led to an increased number of PSA-NCAM-positive NPCs close to the lateral ventricular walls, compared with brains of comparable age without obvious neuropathologic changes. These results suggest that the adult human brain retains a capacity to respond to ischemic injuries and that this capacity is maintained even in old age.

Neural precursor cells induce cell death of high-grade astrocytomas through stimulation of TRPV1

Primary astrocytomas of grade 3 or 4 according to the classification system of the World Health Organization (high-grade astrocytomas or HGAs) are preponderant among adults and are almost invariably fatal despite the use of multimodal therapy. Here we show that the juvenile brain has an endogenous defense mechanism against HGAs. Neural precursor cells (NPCs) migrate to HGAs, reduce glioma expansion and prolong survival time by releasing endovanilloids that activate the vanilloid receptor (transient receptor potential vanilloid subfamily member-1 or TRPV1) on HGA cells. TRPV1 is highly expressed in tumor and weakly expressed in tumor-free brain. TRPV1 stimulation triggers tumor cell death through the branch of the endoplasmic reticulum stress pathway that is controlled by activating transcription factor-3 (ATF3). The antitumorigenic response of NPCs is lost with aging. NPC-mediated tumor suppression can be mimicked in the adult brain by systemic administration of the synthetic vanilloid arvanil, suggesting that TRPV1 agonists have potential as new HGA therapeutics.

Obstacles and opportunities in the functional analysis of extracellular vesicle RNA – an ISEV position paper

ABSTRACT The release of RNA-containing extracellular vesicles (EV) into the extracellular milieu has been demonstrated in a multitude of different in vitro cell systems and in a variety of body fluids. RNA-containing EV are in the limelight for their capacity to communicate genetically encoded messages to other cells, their suitability as candidate biomarkers for diseases, and their use as therapeutic agents. Although EV-RNA has attracted enormous interest from basic researchers, clinicians, and industry, we currently have limited knowledge on which mechanisms drive and regulate RNA incorporation into EV and on how RNA-encoded messages affect signalling processes in EV-targeted cells. Moreover, EV-RNA research faces various technical challenges, such as standardisation of EV isolation methods, optimisation of methodologies to isolate and characterise minute quantities of RNA found in EV, and development of approaches to demonstrate functional transfer of EV-RNA in vivo. These topics were discussed at the 2015 EV-RNA workshop of the International Society for Extracellular Vesicles. This position paper was written by the participants of the workshop not only to give an overview of the current state of knowledge in the field, but also to clarify that our incomplete knowledge – of the nature of EV(-RNA)s and of how to effectively and reliably study them – currently prohibits the implementation of gold standards in EV-RNA research. In addition, this paper creates awareness of possibilities and limitations of currently used strategies to investigate EV-RNA and calls for caution in interpretation of the obtained data.

Bone morphogenetic protein-7 release from endogenous neural precursor cells suppresses the tumourigenicity of stem-like glioblastoma cells

Glioblastoma cells with stem-like properties control brain tumour growth and recurrence. Here, we show that endogenous neural precursor cells perform an anti-tumour response by specifically targeting stem-like brain tumour cells. In vitro, neural precursor cells predominantly express bone morphogenetic protein-7; bone morphogenetic protein-7 is constitutively released from neurospheres and induces canonical bone morphogenetic protein signalling in stem-like glioblastoma cells. Exposure of human and murine stem-like brain tumour cells to neurosphere-derived bone morphogenetic protein-7 induces tumour stem cell differentiation, attenuates stem-like marker expression and reduces self-renewal and the ability for tumour initiation. Neurosphere-derived or recombinant bone morphogenetic protein-7 reduces glioblastoma expansion from stem-like cells by down-regulating the transcription factor Olig2. In vivo, large numbers of bone morphogenetic protein-7-expressing neural precursors encircle brain tumours in young mice, induce canonical bone morphogenetic protein signalling in stem-like glioblastoma cells and can thereby attenuate tumour formation. This anti-tumour response is strongly reduced in older mice. Our results indicate that endogenous neural precursor cells protect the young brain from glioblastoma by releasing bone morphogenetic protein-7, which acts as a paracrine tumour suppressor that represses proliferation, self-renewal and tumour-initiation of stem-like glioblastoma cells.

LGR5 is a marker of poor prognosis in glioblastoma and is required for survival of brain cancer stem-like cells

In various types of cancers including glioblastoma, accumulating evidence show the existence of cancer stem‐like cells (CSCs), characterized by stem cell marker expression, capability of differentiation and self‐renewal, and high potential for tumor propagation in vivo. LGR5, whose expression is positively regulated by the Wnt signaling pathway, is a stem cell marker in intestinal mucosa and hair follicle in the skin. As Wnt signaling is also involved in brain development, the function of LGR5 in the maintenance of brain CSCs is to be assessed. Our study showed that the LGR5 transcript level was increased in CSCs. Co‐immunofluorescence staining demonstrated the co‐localization of CD133‐ and LGR5‐positive cells in glioblastoma tissue sections. Functionally, silencing of LGR5 by lentiviral shRNA‐mediated knockdown induced apoptosis in brain CSCs. Moreover, LGR5 depletion led to a downregulation of L1 cell adhesion molecule expression. In line with an important function in glioma tumorigenesis, LGR5 expression increased with glioma progression and correlated with an adverse outcome. Our findings suggest that LGR5 plays a role in maintenance and/or survival of brain CSCs.

Pseudotyping vesicular stomatitis virus with lymphocytic choriomeningitis virus glycoproteins enhances infectivity for glioma cells and minimizes neurotropism

ABSTRACT Vesicular stomatitis virus (VSV)-based oncolytic virotherapy has the potential to significantly improve the prognosis of aggressive malignancies such as brain cancer. However, VSVs inherent neurotoxicity has hindered clinical development so far. Given that this neurotropism is attributed to the glycoprotein VSV-G, VSV was pseudotyped with the nonneurotropic envelope glycoprotein of the lymphocytic choriomeningitis virus (LCMV-GP→VSV-GP). Compared to VSV, VSV-GP showed enhanced infectivity for brain cancer cells in vitro while sparing primary human and rat neurons in vitro and in vivo, respectively. In conclusion, VSV-GP has a much wider therapeutic window than VSV and is thus more suitable for clinical applications, especially in the brain.

Fusion of Hematopoietic Cells with Purkinje Neurons Does Not Lead to Stable Heterokaryon Formation under Noninvasive Conditions

Transplanted hematopoietic cells have previously been shown to contribute to cells of other tissues by cell fusion. We wanted to elucidate whether this phenomenon of cell fusion also occurs under physiological conditions. Using a transgenic mouse reporter system to irreversibly label cells of the hematopoietic lineage, we were able to test their contribution to other tissues in the absence of any additional and potentially confounding factors such as irradiation or chemoablation. We found genetically marked, fused Purkinje neurons as well as hepatocytes in numbers comparable to previous bone marrow transplantation studies. The number of fused Purkinje neurons increased after intrathecal administration of bacterial lipopolysaccharide, suggesting that cell fusion can be induced by inflammation. In contrast to previous studies, however, genetically labeled Purkinje neurons never contained more than one nucleus, and we found only a single cell containing two Y-chromosomes in a male mouse. Consistent with results from the mouse model and unlike human bone marrow transplant recipients, postmortem adult human cerebelli of nontransplanted individuals were devoid of binucleated or polyploid Purkinje neurons. Therefore, our data suggests that fusion of hematopoietic cells with Purkinje neurons is only transient and does not lead to stable heterokaryon formation under noninvasive conditions.

Sox2 Transduction enhances cardiovascular repair capacity of blood-derived mesoangioblasts

Rationale: Complementation of pluripotency genes may improve adult stem cell functions. Objectives: Here we show that clonally expandable, telomerase expressing progenitor cells can be isolated from peripheral blood of children. The surface marker profile of the clonally expanded cells is distinct from hematopoietic or mesenchymal stromal cells, and resembles that of embryonic multipotent mesoangioblasts. Cell numbers and proliferative capacity correlated with donor age. Isolated circulating mesoangioblasts (cMABs) express the pluripotency markers Klf4, c-Myc, as well as low levels of Oct3/4, but lack Sox2. Therefore, we tested whether overexpression of Sox2 enhances pluripotency and facilitates differentiation of cMABs in cardiovascular lineages. Methods and Results: Lentiviral transduction of Sox2 (Sox-MABs) enhanced the capacity of cMABs to differentiate into endothelial cells and cardiomyocytes in vitro. Furthermore, the number of smooth muscle actin positive cells was higher in Sox-MABs. In addition, pluripotency of Sox-MABs was shown by demonstrating the generation of endodermal and ectodermal progenies. To test whether Sox-MABs may exhibit improved therapeutic potential, we injected Sox-MABs into nude mice after acute myocardial infarction. Four weeks after cell therapy with Sox-MABs, cardiac function was significantly improved compared to mice treated with control cMABs. Furthermore, cell therapy with Sox-MABs resulted in increased number of differentiated cardiomyocytes, endothelial cells, and smooth muscle cells in vivo. Conclusions: The complementation of Sox2 in Oct3/4-, Klf4-, and c-Myc-expressing cMABs enhanced the differentiation into all 3 cardiovascular lineages and improved the functional recovery after acute myocardial infarction.

EGF induces CREB and ERK activation at the wall of the mouse lateral ventricles.

The subependymal zone at the lateral ventricular wall represents a major neurogenic niche of the adult mammalian brain and continuously provides new neurons for the olfactory bulb. A mosaic of stem and progenitor cells in this niche has the potential to respond to multiple signals including growth factors such as EGF. Recent studies using long-term ventricular infusion of EGF demonstrate intense cell proliferation around the ventricular wall, implicating the presence of EGF-reactive cells also outside the classical neurogenic lateral niche. Here we show that intraventricular injection of EGF induces within minutes CREB and ERK phosphorylation in astrocyte-like progenitor cells (type B cells) and EGF receptor-expressing transit-amplifying progenitor cells-both in the striatal and septal ventricular walls. EGF infusion for 6 days induced continued CREB and ERK activation in nestin+ cells paralleled by intense periventricular cell proliferation. In addition, the ependyma became EGF receptor-immunoreactive, revealed intense CREB phosphorylation and underwent partial de-differentiation. Our results demonstrate that intraventricular application of EGF induces CREB and ERK phosphorylation along the entire ventricular walls and thus permits a direct identification of EGF-responsive cell types. They further support the notion that not only the striatal ventricular wall where the SEZ is located but also the septal ventricular wall carries latent potential for the formation of neurons and glial cells.

The realized niche of adult neural stem cells.

This review gives an overview of current issues concerning the application of the concept of the stem cell niche to the adult mammalian brain. It describes how the niche manifests itself at different structural levels as well as the main applications that are influenced by this concept. Finally, special regard is given to what is known for the adult human brain and how far the findings from lower animals can be applied in harnessing the regenerative potential of stem cells for therapy.