Metformin rescues migratory deficits of cells derived from patients with periventricular heterotopia.

Periventricular neuronal heterotopia (PH) is one of the most common forms of cortical malformation in the human cortex. We show that human neuronal progenitor cells (hNPCs) derived from PH patients with a DCHS1 or FAT4 mutation as well as isogenic lines had altered migratory dynamics when grafted in the mouse brain. The affected migration was linked to altered autophagy as observed in vivo with an electron microscopic analysis of grafted hNPCs, a Western blot analysis of cortical organoids, and time-lapse imaging of hNPCs in the presence of bafilomycin A1. We further show that deficits in autophagy resulted in the accumulation of paxillin, a focal adhesion protein involved in cell migration. Strikingly, a single-cell RNA-seq analysis of hNPCs revealed similar expression levels of autophagy-related genes. Bolstering AMPK-dependent autophagy by metformin, an FDA-approved drug, promoted migration of PH patients-derived hNPCs. Our data indicate that transcription-independent homeostatic modifications in autophagy contributed to the defective migratory behavior of hNPCs in vivo and suggest that modulating autophagy in hNPCs might rescue neuronal migration deficits in some forms of PH.

Deciphering heterogeneous populations of migrating cells based on the computational assessment of their dynamic properties.

Neuronal migration is a highly dynamic process, and multiple cell movement metrics can be extracted from time-lapse imaging datasets. However, these parameters alone are often insufficient to evaluate the heterogeneity of neuroblast populations. We developed an analytical pipeline based on reducing the dimensions of the dataset by principal component analysis (PCA) and determining sub-populations using k-means, supported by the elbow criterion method and validated by a decision tree algorithm. We showed that neuroblasts derived from the same adult neural stem cell (NSC) lineage as well as across different lineages are heterogeneous and can be sub-divided into different clusters based on their dynamic properties. Interestingly, we also observed overlapping clusters for neuroblasts derived from different NSC lineages. We further showed that genetic perturbations or environmental stimuli affect the migratory properties of neuroblasts in a sub-cluster-specific manner. Our data thus provide a framework for assessing the heterogeneity of migrating neuroblasts.

AMPK-induced autophagy as a key regulator of cell migration.

Cell migration is a highly dynamic and energy-intensive process that ensures the correct targeting of cells during embryonic and postnatal development. In recent work, we highlighted the importance of macroautophagy/autophagy in regulating the dynamics of cell migration under baseline conditions and in response to a diverse set of molecular factors. Genetic suppression of autophagy-related genes induced longer stationary phases in migrating cells and cell stalling at the beginning of the migratory stream. We also showed that autophagy is required for recycling of the focal adhesion molecule PXN (paxillin), and is induced by energy levels of cells via AMPK activation. This recent study revealed the importance of autophagy in the maintenance of cell migration, and showed that the dynamic interplay between autophagy and energy levels is required to sustain neuronal migration and to cope with diverse micro-environmental factors.

The dynamic interplay between ATP/ADP levels and autophagy sustain neuronal migration in vivo.

Cell migration is a dynamic process that entails extensive protein synthesis and recycling, structural remodeling, and considerable bioenergetic demand. Autophagy is one of the pathways that maintain cellular homeostasis. Time-lapse imaging of autophagosomes and ATP/ADP levels in migrating cells in the rostral migratory stream of mouse revealed that decreases in ATP levels force cells into the stationary phase and induce autophagy. Pharmacological or genetic impairments of autophagy in neuroblasts using either bafilomycin, inducible conditional mice, or CRISPR/Cas9 gene editing decreased cell migration due to the longer duration of the stationary phase. Autophagy is modulated in response to migration-promoting and inhibiting molecular cues and is required for the recycling of focal adhesions. Our results show that autophagy and energy consumption act in concert in migrating cells to dynamically regulate the pace and periodicity of the migratory and stationary phases to sustain neuronal migration.

Developmental Potential and Plasticity of Olfactory Epithelium Stem Cells Revealed by Heterotopic Grafting in the Adult Brain.

The neural stem cells (NSCs) residing in the olfactory epithelium (OE) regenerate damaged olfactory sensory neurons throughout adulthood. The accessibility and availability of these NSCs in living individuals, including humans, makes them a promising candidate for harvesting their potential for cell replacement therapies. However, this requires an in-depth understanding of their developmental potential after grafting. Here, we investigated the developmental potential and plasticity of mouse OE-derived NSCs after grafting into the adult subventricular zone (SVZ) neurogenic niche. Our results showed that OE-derived NSCs integrate and proliferate just like endogenous SVZ stem cells, migrate with similar dynamics as endogenous neuroblasts toward the olfactory bulb, and mature and acquire similar electrophysiological properties as endogenous adult-born bulbar interneurons. These results reveal the developmental potential and plasticity of OE-derived NSCs in vivo and show that they can respond to heterotopic neurogenic cues to adapt their phenotype and become functional neurons in ectopic brain regions.

Intrinsic Mechanisms Regulating Neuronal Migration in the Postnatal Brain.

Neuronal migration is a fundamental brain development process that allows cells to move from their birthplaces to their sites of integration. Although neuronal migration largely ceases during embryonic and early postnatal development, neuroblasts continue to be produced and to migrate to a few regions of the adult brain such as the dentate gyrus and the subventricular zone (SVZ). In the SVZ, a large number of neuroblasts migrate into the olfactory bulb (OB) along the rostral migratory stream (RMS). Neuroblasts migrate in chains in a tightly organized micro-environment composed of astrocytes that ensheath the chains of neuroblasts and regulate their migration; the blood vessels that are used by neuroblasts as a physical scaffold and a source of molecular factors; and axons that modulate neuronal migration. In addition to diverse sets of extrinsic micro-environmental cues, long-distance neuronal migration involves a number of intrinsic mechanisms, including membrane and cytoskeleton remodeling, Ca2+ signaling, mitochondria dynamics, energy consumption, and autophagy. All these mechanisms are required to cope with the different micro-environment signals and maintain cellular homeostasis in order to sustain the proper dynamics of migrating neuroblasts and their faithful arrival in the target regions. Neuroblasts in the postnatal brain not only migrate into the OB but may also deviate from their normal path to migrate to a site of injury induced by a stroke or by certain neurodegenerative disorders. In this review, we will focus on the intrinsic mechanisms that regulate long-distance neuroblast migration in the adult brain and on how these pathways may be modulated to control the recruitment of neuroblasts to damaged/diseased brain areas.

Expression of young HERV-H loci in the course of colorectal carcinoma and correlation with molecular subtypes.

BACKGROUND: Expression of the human endogenous retrovirus (HERV)-H family has been associated with colorectal carcinomas (CRC), yet no individual HERV-H locus expression has been thoroughly correlated with clinical data.Here, we characterized HERV-H reactivations in clinical CRC samples by integrating expression profiles, molecular patterns and clinical data. Expression of relevant HERV-H sequences was analyzed by qRT-PCR on two well-defined clinical cohorts (n = 139 pairs of tumor and adjacent normal colon tissue) including samples from adenomas (n = 21) and liver metastases (n = 16). Correlations with clinical and molecular data were assessed. RESULTS: CRC specific HERV-H sequences were validated and found expressed throughout CRC disease progression. Correlations between HERV-H expression and lymph node invasion of tumor cells (p = 0.0006) as well as microsatellite instable tumors (p < 0.0001) were established. No association with regard to age, tumor localization, grading or common mutations became apparent. Interestingly, CRC expressed elements belonged to specific young HERV-H subfamilies and their 5' LTR often presented active histone marks. CONCLUSION: These results suggest a functional role of HERV-H sequences in colorectal carcinogenesis. The pronounced connection with microsatellite instability warrants a more detailed investigation. Thus, HERV-H sequences in addition to tumor specific mutations may represent clinically relevant, truly CRC specific markers for diagnostic, prognostic and therapeutic purposes.