Adult Neural Stem Cell Regulation by Small Non-coding RNAs: Physiological Significance and Pathological Implications

The adult neurogenic niches are complex multicellular systems, receiving regulatory input from a multitude of intracellular, juxtacrine, and paracrine signals and biological pathways. Within the niches, adult neural stem cells (aNSCs) generate astrocytic and neuronal progeny, with the latter predominating in physiological conditions. The new neurons generated from this neurogenic process are functionally linked to memory, cognition, and mood regulation, while much less is known about the functional contribution of aNSC-derived newborn astrocytes and adult-born oligodendrocytes. Accumulating evidence suggests that the deregulation of aNSCs and their progeny can impact, or can be impacted by, aging and several brain pathologies, including neurodevelopmental and mood disorders, neurodegenerative diseases, and also by insults, such as epileptic seizures, stroke, or traumatic brain injury. Hence, understanding the regulatory underpinnings of aNSC activation, differentiation, and fate commitment could help identify novel therapeutic avenues for a series of pathological conditions. Over the last two decades, small non-coding RNAs (sncRNAs) have emerged as key regulators of NSC fate determination in the adult neurogenic niches. In this review, we synthesize prior knowledge on how sncRNAs, such as microRNAs (miRNAs) and piwi-interacting RNAs (piRNAs), may impact NSC fate determination in the adult brain and we critically assess the functional significance of these events. We discuss the concepts that emerge from these examples and how they could be used to provide a framework for considering aNSC (de)regulation in the pathogenesis and treatment of neurological diseases.

Cell cycle arrest determines adult neural stem cell ontogeny by an embryonic Notch-nonoscillatory Hey1 module

Quiescent neural stem cells (NSCs) in the adult mouse brain are the source of neurogenesis that regulates innate and adaptive behaviors. Adult NSCs in the subventricular zone are derived from a subpopulation of embryonic neural stem-progenitor cells (NPCs) that is characterized by a slower cell cycle relative to the more abundant rapid cycling NPCs that build the brain. Yet, how slow cell cycle can cause the establishment of adult NSCs remains largely unknown. Here, we demonstrate that Notch and an effector Hey1 form a module that is upregulated by cell cycle arrest in slowly dividing NPCs. In contrast to the oscillatory expression of the Notch effectors Hes1 and Hes5 in fast cycling progenitors, Hey1 displays a non-oscillatory stationary expression pattern and contributes to the long-term maintenance of NSCs. These findings reveal a novel division of labor in Notch effectors where cell cycle rate biases effector selection and cell fate.

Mitochondrial Dynamics: impact on adult neural stem cell fate

Neural stem cells (NSCs) are found in discrete regions of the mammalian brain. During adulthood, NSCs can be a source of new neurons and oligodendrocytes in neurological disorders. However, these newborn cells are not sufficient to overcome the neurological deficits involved by neural loss. Therefore, the identification of novel mechanisms responsible for modulating NSC fate represent a major key issue for future brain repair strategies. Several studies suggest that mitochondria have an important role in regulating NSC differentiation and lineage determination. However, the molecular mechanisms involved in this regulation remain unknown. Hence, our work aims to dissect how mitochondria biogenesis and dynamics can modulate the NSC differentiation into neurons or oligodendrocytes. For this, NSCs were obtained by isolating subventricular zone (SVZ) and dentate gyrus (DG) cells from P1-3 mouse models. Seeding density, culture conditions and number of passages were determined. Moreover, the multipotency of SVZ/DG-derived NSPCs, obtained from different passages, was also accessed. Additionally, expression of proteins involved in mitochondrial biogenesis and fusion/fission appear altered during NSPC differentiation, while mitochondrial network revealed different morphologies in cells from different lineages. The results obtained will provide novel findings concerning the role of mitochondrial dynamics in NSC fate.