Balance between autophagy and cell death is maintained by Polycomb-mediated regulation during stem cell differentiation.

Autophagy is a conserved cytoprotective process, aberrations in which lead to numerous degenerative disorders. While the cytoplasmic components of autophagy have been extensively studied, the epigenetic regulation of autophagy genes, especially in stem cells, is less understood. Deciphering the epigenetic regulation of autophagy genes becomes increasingly relevant given the therapeutic benefits of small-molecule epigenetic inhibitors in novel treatment modalities. We observe that, during retinoic acid-mediated differentiation of mouse embryonic stem cells (mESCs), autophagy is induced, and identify the Polycomb group histone methyl transferase EZH2 as a regulator of this process. In mESCs, EZH2 represses several autophagy genes, including the autophagy regulator DNA damage-regulated autophagy modulator protein 1 (Dram1). EZH2 facilitates the formation of a bivalent chromatin domain at the Dram1 promoter, allowing gene expression and autophagy induction during differentiation while retaining the repressive H3K27me3 mark. EZH2 inhibition leads to loss of the bivalent domain, with consequent 'hyper-expression' of Dram1, accompanied by extensive cell death. This study shows that Polycomb group proteins help maintain a balance between autophagy and cell death during stem cell differentiation, in part, by regulating the expression of the Dram1 gene.

Recent technological advancements in stem cell research for targeted therapeutics.

Stem cells have characteristic features of self-renewal, pluripotency and differentiation, which are responsible for replenishment of tissue or organ. Stem cells are potentiated as therapeutic tool in drug targeting and regenerative medicine-from curing various neurological diseases and malignancies to congenital diseases. These technological advancements have established stem cells as future of medicine. However, due to ethico-social limitations, the use of embryonic stem cells (ESCs) has been avoided, while physiological availability of adult stem cells (ASCs) and induced pluripotent stem cells (iPSCs) has gained appropriate preference. These iPSCs are very much similar to ESCs in terms of their self-renewal and pluripotency. Here, we have summarized the technologies that have established stem cells isolation, their molecular marker and factors responsible for their maintenance. Different cellular (transcription factors, regulatory proteins, miRNA like miRNA-296, miRNA-145, etc.) and extracellular components transcend stem cell fate. Their identification and characterization involve development and efficient utilization of tools like magnetic activated cell sorting (MACS) and fluorescence activated cell sorting (FACS). Some of the technologies have been patented and spin-off's based on them have been commercialized. In conclusion, we present the future scope and possibilities that stem cell technologies behold for us. Graphical abstract Pictorial representation of therapeutic approaches for disease treatment using stem cell technology. Disease-specific adult stem cells are isolated along with niche cells by utilizing tools like FACS/MACS/LCM, etc. Thereafter, cells are reprogrammed through introduction of Yamanaka factors (Oct3/4, Sox2, c-myc, Klf4) to make induced pluripotent stem cell (iPSCs). The disease-specific iPSCs undergo genetic modification after delivery of therapeutic gene through retroviral vehicle. The genetically modified cells are introduced back in person with disease for therapeutic effects. FACS, fluorescence activated cell sorting; MACS, magnetic-activated cell sorting; LCM, laser capture microdissection; Oct3/4, octamer-binding transcription factor 3/4; Sox2, sex determining region Y-box 2; Klf4, Kruppel-like factor 4.