瀬原 吉英

BACKGROUND: Fabry disease is a hereditary disorder caused by a deficiency of α-galactosidase A, leading to the accumulation of globotriaosylceramide (GL-3) in multiple cell types throughout the body. Terminally differentiated non-dividing cells, such as podocytes, are particularly susceptible to such accumulation and therefore require effective therapeutic intervention. Gene therapy is an ideal therapeutic intervention for replacing the deficient enzyme; however, one of the major challenges is maintaining long-term expression of episomal transgenes during cell division. In this regard, podocytes, as non-dividing cells, represent an ideal target for gene therapy in Fabry disease. Nevertheless, it has not been confirmed yet whether gene therapy vectors can transduce podocytes and reduce GL-3 accumulation especially in podocytes. METHODS: Male Fabry disease model mice (TgG3S/GLA knockout mice) received an intravenous injection of 2 × 1012 vector genomes of AAV9 encoding human GLA at 6 weeks of age. Kidney tissues were analyzed 8 weeks after administration by electron microscopy (EM) and immunogold EM. RESULTS: In AAV9/hGLA-treated mice, GL-3 accumulation was markedly reduced in most podocytes, endothelial cells, and tubular epithelial cells, whereas it was evident in untreated mice. Virus-like particles were detected only in treated mice. Furthermore, immunogold EM confirmed the presence of AAV9 particles in the podocytes of treated mice. CONCLUSIONS: AAV9/hGLA gene therapy may reduce podocyte GL-3 accumulation in a Fabry disease mouse model, potentially through AAV9 transduction of podocytes; however, given the technical limitations of our approach, the precise cellular mechanisms remain to be determined.

Neurogenesis and oligodendrogenesis occur throughout life under both physiological and pathophysiological conditions. Brain insults such as ischemia, trauma, epilepsy, or Alzheimer disease result in the promotion of neurogenesis and oligodendrogenesis; however, the mechanisms and the roles of this promotion are not well elucidated. Neurogenesis occurs in two distinct regions in the brain, namely, the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus. Neural stem cells (NSCs) have the potential to self-renew, proliferate, and differentiate into various cell types. NSCs in the SVZ migrate toward the site of injury, and those in the SGZ migrate toward the granule cell layer after ischemic insult. Numerous animal experiments have shown that inhibition of post-ischemic neurogenesis both in the SVZ and the dentate gyrus impairs functional recovery. Oligodendrogenesis regenerates myelin around demyelinated axons after white matter injury, thus promoting functional recovery after ischemia. Oligodendrocyte progenitor cells derived from NSCs and progenitor cells of the SVZ and from intrinsic cells from other brain regions proliferate at the demyelinated lesions. However, deposition of extracellular matrices, including chondroitin sulfate proteoglycans, hyaluronan, fibronectin, and fibrinogen, have been reported to inhibit remyelination. Furthermore, our data showed that type I collagen was deposited in the white matter lesions of stroke patients, and that it may inhibit oligodendrocyte differentiation in these lesions. In this review, we focus on the mechanisms and the roles of post-ischemic neurogenesis and oligodendrogenesis based on recently published data of mainly rodent models.

Gene therapy using adeno-associated virus (AAV) vectors is currently expanding to broad clinical applications. As the presence of a neutralizing antibody (NAb) against AAV capsids significantly restrains their efficacy, an accurate evaluation of NAb status is crucial for selecting appropriate candidates for gene therapy. Notably, cell-based NAb assays may not be sufficiently sensitive for detecting low-titer NAb, and few assays can evaluate multiple AAV serotypes using a commonly available cell. In this study, we developed a sensitive NAb assay against various AAV serotypes using commonly available HEK293 and Huh-7 cells. We found that adding glucose efficiently enhanced transgene expression across various AAV serotypes without causing cell damage. In addition, by combining a highly sensitive reporter gene, NanoLuc, the necessary dose of AAV vector was significantly reduced. The reduction of AAV dose resulted in the increased sensitivity of NAb detection as low as 100 vector genomes/cell. At the lower vector doses, sensitivity improvement was not observed regardless of serotypes, suggesting the limit of assay sensitivity of the cell-based NAb assay. These findings provide a highly sensitive methodology for assessing NAb titers and offer insights into conditions to attain maximal sensitivity in the cell-based NAb assay.

It is established that neurogenesis of dentate gyrus is increased after ischemic insult, although the regulatory mechanisms have not yet been elucidated. In this study, we focused on Ezh2 which suppresses gene expression through catalyzing trimethylation of lysine 27 of histone 3. Male gerbils were injected with adeno-associated virus (AAV) carrying shRNA targeting to Ezh2 into right dentate gyrus 2 weeks prior to forebrain ischemia. One week after ischemia, animals were injected with thymidine analogue to label proliferating cells. Three weeks after ischemia, animals were killed for histological analysis. AAV-mediated knockdown of Ezh2 significantly decreased the ischemia-induced increment of proliferating cells, and the proliferated cells after ischemia showed significantly longer migration from subgranular zone (SGZ), compared to the control group. Furthermore, the number of neural stem cells in SGZ significantly decreased after ischemia with Ezh2 knockdown group. Of note, Ezh2 knockdown did not affect the number of proliferating cells or the migration from SGZ in the non-ischemic condition. Our data showed that, specifically after ischemia, Ezh2 knockdown shifted the balance between self-renewal and differentiation toward differentiation in adult dentate gyrus.