FGF10 regulates thalamocortical axon guidance in the developing thalamus

Fibroblast growth factor 10 ameliorates neurodegeneration in mouse and cellular models of Alzheimer's disease via reducing tau hyperphosphorylation and neuronal apoptosis

Alzheimer's disease (AD) is characterized with senile plaques formed by Aβ deposition, and neurofibrillary tangles composed of hyperphosphorylated tau protein, which ultimately lead to cognitive impairment. Despite the heavy economic and life burdens faced by the patients with AD, effective treatments are still lacking. Previous studies have reported the neuroprotective effects of FGF10 in CNS diseases, but its role in AD remains unclear. In this study, we demonstrated that FGF10 levels were reduced in the serum of AD patients, as well as in the brains of 3xTg-AD mice and APPswe-transfected HT22 cells, suggesting a close relationship between FGF10 and AD. Further investigations revealed that intranasal delivery of FGF10 improved cognitive functions in 3xTg-AD mice. Additionally, FGF10 treatment reduced tau hyperphosphorylation and neuronal apoptosis, thereby mitigating neuronal cell damage and synaptic deficits in the cortex and hippocampus of 3xTg-AD mice, as well as APPswe-transfected HT22 cells. Furthermore, we evaluated the therapeutic potential of FGF10 gene delivery for treating AD symptoms and pathologies. Tail vein delivery of the FGF10 gene using AAV9 improved cognitive and neuronal functions in 3xTg-AD mice. Similarly, endogenous FGF10 overexpression ameliorated tau hyperphosphorylation and neuronal apoptosis in the cortex and hippocampus of 3xTg-AD mice. Importantly, we confirmed that the FGFR2/PI3K/AKT signaling pathway was activated following intranasal FGF10 delivery and AAV9-mediated FGF10 gene delivery in 3xTg-AD mice and APPswe-transfected HT22 cells. Knockdown of FGFR2 attenuated the protective effect of FGF10. Collectively, these findings suggest that intranasal delivery of FGF10 and AAV9-mediated FGF10 gene delivery could be a promising disease-modifying therapy for AD.

Transcriptome and methylome of the supraoptic nucleus provides insights into the age-dependent loss of neuronal plasticity

The age-dependent loss of neuronal plasticity is a well-known phenomenon that is poorly understood. The loss of this capacity for axonal regeneration is emphasized following traumatic brain injury, which is a major cause of disability and death among adults in the US. We have previously shown the intrinsic capacity of magnocellular neurons within the supraoptic nucleus to undergo axonal regeneration following unilateral axotomization in an age-dependent manner. The aim of this research was to determine the age-dependent molecular mechanisms that may underlie this phenomenon. As such, we characterized the transcriptome and DNA methylome of the supraoptic nucleus in uninjured 35-day old rats and 125-day old rats. Our data indicates the downregulation of a large number of axonogenesis related transcripts in 125-day old rats compared to 35-day old rats. Specifically, several semaphorin and ephrin genes were downregulated, as well as growth factors including FGF's, insulin-like growth factors (IGFs), and brain-derived neurotrophic factor (BDNF). Differential methylation analysis indicates enrichment of biological processes involved in axonogenesis and axon guidance. Conversely, we observed a robust and specific upregulation of MHCI related transcripts. This may involve the activator protein 1 (AP-1) transcription factor complex as motif analysis of differentially methylated regions indicate enrichment of AP-1 binding sites in hypomethylated regions. Together, our data suggests a loss of pro-regenerative capabilities with age which would prevent axonal growth and appropriate innervation following injury.

Roles of Fibroblast Growth Factors in the Axon Guidance

Fibroblast growth factors (FGFs) have been widely studied by virtue of their ability to regulate many essential cellular activities, including proliferation, survival, migration, differentiation and metabolism. Recently, these molecules have emerged as the key components in forming the intricate connections within the nervous system. FGF and FGF receptor (FGFR) signaling pathways play important roles in axon guidance as axons navigate toward their synaptic targets. This review offers a current account of axonal navigation functions performed by FGFs, which operate as chemoattractants and/or chemorepellents in different circumstances. Meanwhile, detailed mechanisms behind the axon guidance process are elaborated, which are related to intracellular signaling integration and cytoskeleton dynamics.

Gli2-Mediated Shh Signaling Is Required for Thalamocortical Projection Guidance

The thalamocortical projections are part of the most important higher level processing connections in the vertebrates and follow a highly ordered pathway from their origin in the thalamus to the cerebral cortex. Their functional complexities are not only due to an extremely elaborate axon guidance process but also due to activity-dependent mechanisms. Gli2 is an intermediary transcription factor in the Sonic hedgehog (Shh) pathway. During neural early development, Shh has an important role in dorsoventral patterning, diencephalic anteroposterior patterning, and many later developmental processes, such as axon guidance and cell migration. Using a Gli2 knockout mouse line, we have studied the role of Shh signaling mediated by Gli2 in the development of the thalamocortical projections during embryonic development. In wild-type brains, we have described the normal trajectory of the thalamocortical axons into the context of the prosomeric model. Then, we have compared it with the altered thalamocortical axons course in Gli2 homozygous embryos. The thalamocortical axons followed different trajectories and were misdirected to other territories probably due to alterations in the Robo/Slit signaling mechanism. In conclusion, the alteration of Gli2-mediated Shh signaling produces an erroneous specification of several territories related with the thalamocortical axons. This is translated into a huge modification in the pathfinding signaling mechanisms needed for the correct wiring of the thalamocortical axons.

FGF3 from the Hypothalamus Regulates the Guidance of Thalamocortical Axons

Thalamus is an important sensory relay station: afferent sensory information, except olfactory signals, is transmitted by thalamocortical axons (TCAs) to the cerebral cortex. The pathway choice of TCAs depends on diverse diffusible or substrate-bound guidance cues in the environment. Not only classical guidance cues (ephrins, slits, semaphorins, and netrins), morphogens, which exerts patterning effects during early embryonic development, can also help axons navigate to their targets at later development stages. Here, expression analyses reveal that morphogen Fibroblast growth factor (FGF)-3 is expressed in the chick ventral diencephalon, hypothalamus, during the pathfinding of TCAs. Then, using in vitro analyses in chick explants, we identify a concentration-dependent effect of FGF3 on thalamic axons: attractant 100 ng/mL FGF3 transforms to a repellent at high concentration 500 ng/mL. Moreover, inhibition of FGF3 guidance functions indicates that FGF3 signaling is necessary for the correct navigation of thalamic axons. Together, these studies demonstrate a direct effect for the member of FGF7 subfamily, FGF3, in the axonal pathfinding of TCAs.

Sequencing analysis of matrix metalloproteinase 7-induced genetic changes in Schwann cells

Previous research revealed the positive activity of matrix metalloproteinase 7 (MMP7) on migration and myelin regeneration of Schwann cells (SCs). However, understanding of the molecular changes and biological activities induced by increased amounts of MMP7 in SCs remains limited. To better understand the underlying molecular events, primary SCs were isolated from the sciatic nerve stump of newborn rats and cultured with 10 nM human MMP7 for 24 hours. The results of genetic testing were analyzed at a relatively relaxed threshold value (fold change ≥ 1.5 and P-value < 0.05). Upon MMP7 exposure, 149 genes were found to be upregulated in SCs, whereas 133 genes were downregulated. Gene Ontology analysis suggested that many differentially expressed molecules were related to cellular processes, single-organism processes, and metabolic processes. Kyoto Enrichment of Genes and Genomes pathway analysis further indicated the critical involvement of cell signaling and metabolism in MMP7-induced molecular regulation of SCs. Results of Ingenuity Pathway Analysis (IPA) also revealed that MMP7 regulates biological processes, molecular functions, cellular components, diseases and functions, biosynthesis, material metabolism, cell movement, and axon guidance. The outcomes of further analysis will deepen our comprehension of MMP7-induced biological changes in SCs. This study was approved by the Laboratory Animal Ethics Committee of Nantong University, China (approval No. 20190225-004) on February 27, 2019.