The adult human subventricular zone: partial ependymal coverage and proliferative capacity of cerebrospinal fluid

Neurogenesis continues throughout adulthood in specialized regions of the brain. One of these regions is the subventricular zone. During brain development, neurogenesis is regulated by a complex interplay of intrinsic and extrinsic cues that control stem-cell survival, renewal and cell lineage specification. Cerebrospinal fluid (CSF) is an integral part of the neurogenic niche in development as it is in direct contact with radial glial cells, and it is important in regulating proliferation and migration. Yet, the effect of CSF on neural stem cells in the subventricular zone of the adult human brain is unknown. We hypothesized a persistent stimulating effect of ventricular CSF on neural stem cells in adulthood, based on the literature, describing bulging accumulations of subventricular cells where CSF is in direct contact with the subventricular zone. Here, we show by immunohistochemistry on post-mortem adult human subventricular zone sections that neural stem cells are in close contact with CSF via protrusions through both intact and incomplete ependymal layers. We are the first to systematically quantify subventricular glial nodules denuded of ependyma and consisting of proliferating neural stem and progenitor cells, and showed that they are present from foetal age until adulthood. Neurosphere, cell motility and differentiation assays as well as analyses of RNA expression were used to assess the effects of CSF of adult humans on primary neural stem cells and a human immortalized neural stem cell line. We show that human ventricular CSF increases proliferation and decreases motility of neural stem cells. Our results also indicate that adult CSF pushes neural stem cells from a relative quiescent to a more active state and promotes neuronal over astrocytic lineage differentiation. Thus, CSF continues to stimulate neural stem cells throughout aging.

Resident adult neural stem cells in Parkinson's disease--the brain's own repair system?

One important pathological process in the brain of Parkinson disease (PD) patients is the degeneration of the dopaminergic neurons in the substantia nigra, which leads to a decline in striatal dopamine levels and motor dysfunction. A major clinical problem is that this degenerative process currently cannot be stopped or reversed. Expectations from the restorative capacity of neural stem cells (NSCs) are high, as these cells can potentially replace the degenerating neurons. The discovery of the presence of NSCs in the adult human brain has instigated research into the potential of these cells as a resource to promote brain repair in neurodegenerative diseases. Neural stem and progenitor cells reside in the subventricular zone (SVZ), which is closely situated to the striatum, which is affected in PD. Therefore, restoring the dopamine levels in the striatum of PD patients through stimulating endogenous NSCs in the nearby SVZ to migrate into the striatum and differentiate into dopaminergic neurons might thus be an attractive future therapeutic approach. We will review the reported changes in NSCs in the SVZ of PD animal models and PD patients, which are due to a lack of striatal dopamine. Furthermore, we will summarise the reports that describe efforts to stimulate NSCs to replace dopaminergic cells in the SN and restore striatal dopamine levels. In our opinion, mobilizing the endogenous SVZ NSCs to replenish striatal dopamine is an attractive approach to alleviate the motor symptoms in PD patients, without the ethical and immunological challenges of transplantation of NSCs and foetal brain tissue.

Specific human astrocyte subtype revealed by affinity purified GFAP antibody; unpurified serum cross-reacts with neurofilament-L in Alzheimer

The human GFAP splice variants GFAPΔ164 and GFAPΔexon6 both result in a GFAP protein isoform with a unique out-of-frame carboxy-terminus that can be detected by the GFAP⁺¹ antibody. We previously reported that GFAP⁺¹ was expressed in astrocytes and in degenerating neurons in Alzheimer's disease brains. In this study we aimed at further investigating the neuronal GFAP⁺¹ expression and we started by affinity purifying the GFAP⁺¹ antibody. The purified antibody resulted in a loss of neuronal GFAP⁺¹ signal, although other antibodies directed against the amino- and carboxy-terminus of GFAPα still revealed GFAP-immunopositive neurons, as described before. With an in-depth analysis of a western blot, followed by mass spectrometry we discovered that the previously detected neuronal GFAP⁺¹ expression was due to cross-reactivity of the antibody with neurofilament-L (NF-L). This was confirmed by double-label fluorescent immunohistochemistry and western blotting with the unpurified GFAP⁺¹ antibody and an antibody against NF-L. Our data imply that NF-L can accumulate in some tangle-like structures in Alzheimer brains. More importantly, the purified GFAP⁺¹ antibody clearly revealed a specific subtype of astrocytes in the adult human brain. These large astrocytes are present throughout the brain, e.g., along the subventricular zone, in the hippocampus, in the striatum and in the spinal cord of controls, Alzheimer, and Parkinson patients. The presence of a specific GFAP-isoform suggests a specialized function of these astrocytes.

Subventricular zone neural progenitors from rapid brain autopsies of elderly subjects with and without neurodegenerative disease

In mice and in young adult humans, the subventricular zone (SVZ) contains multipotent, dividing astrocytes, some of which, when cultured, produce neurospheres that differentiate into neurons and glia. It is unknown whether the SVZ of very old humans has this capacity. Here, we report that neural stem/progenitor cells can also be cultured from rapid autopsy samples of SVZ from elderly human subjects, including patients with age-related neurologic disorders. Histological sections of SVZ from these cases showed a glial fibrillary acidic protein (GFAP)-positive ribbon of astrocytes similar to the astrocyte ribbon in human periventricular white matter biopsies that is reported to be a rich source of neural progenitors. Cultures of the SVZ contained 1) neurospheres with a core of Musashi-1-, nestin-, and nucleostemin-immunopositive cells as well as more differentiated GFAP-positive astrocytes; 2) SMI-311-, MAP2a/b-, and beta-tubulin(III)-positive neurons; and 3) galactocerebroside-positive oligodendrocytes. Neurospheres continued to generate differentiated progeny for months after primary culturing, in some cases nearly 2 years postinitial plating. Patch clamp studies of differentiated SVZ cells expressing neuron-specific antigens revealed voltage-dependent, tetrodotoxin-sensitive, inward Na+ currents and voltage-dependent, delayed, slowly inactivating K+ currents, electrophysiologic characteristics of neurons. A subpopulation of these cells also exhibited responses consistent with the kinetics and pharmacology of the h-current. However, although these cells displayed some aspects of neuronal function, they remained immature, insofar as they did not fire action potentials. These studies suggest that human neural progenitor activity may remain viable throughout much of the life span, even in the face of severe neurodegenerative disease.