SCRT1 is a novel beta cell transcription factor with insulin regulatory properties

Biological characteristics of microRNAs secreted by exosomes of periodontal ligament stem cells due to mechanical force

BACKGROUND

Orthodontic tooth movement (OTM) has previously been considered an inflammatory process. However, recent studies suggest that exosomes may play an important role in the cellular microenvironment of OTM. microRNAs (miRNAs) are one of the major constituents of exosomes. This study aims to investigate the biological characteristics of miRNAs secreted by exosomes of periodontal ligament stem cells (PDLSCs) due to mechanical forces.

MATERIALS AND METHODS

First, we established a mechanical stress model. The PDLSCs were loaded under different force values and exosomes were extracted after 48 h. High-throughput sequencing of exosomal miRNAs was performed to further evaluate their biological functions and underlying mechanisms.

RESULTS

The morphology and functions of exosomes were not significantly different between the loading and non-loading PDLSC groups. The optimal loading time and force were 48 h and 1 g/cm2, respectively. After sequencing, gene ontology (GO) and Kyoto encyclopaedia of genes and genomes (KEGG) pathway and network analyses were performed and 10 differentially expressed miRNAs were identified according to a literature search. These are miR-99a-5p, miR-485-3P, miR-29a-3p,miR-21-5p, miR-146a-5p, miR140-3p, miR-1306-5p, miR-126-5p, miR-125a-5p, and miR-23a-3p.

LIMITATIONS

Extracting exosomes needs a large amount of PDLSCs. More functional experiments need to be done to confirm the exact mechanism of exosomal miRNAs of PDLSCs due to mechanical force.

CONCLUSIONS

The expression levels of miRNAs secreted by PDLSC-derived exosomes due to mechanical force were very different compared to PDLSC-derived exosomes under nonmechanical stress. The function of many of the identified exosomal miRNAs was found to be related to osteoblasts and osteoclasts. Further validation is required. A functional investigation of these miRNA could provide novel insights into their mechanism.

Functional, metabolic and transcriptional maturation of human pancreatic islets derived from stem cells

Transplantation of pancreatic islet cells derived from human pluripotent stem cells is a promising treatment for diabetes. Despite progress in the generation of stem-cell-derived islets (SC-islets), no detailed characterization of their functional properties has been conducted. Here, we generated functionally mature SC-islets using an optimized protocol and benchmarked them comprehensively against primary adult islets. Biphasic glucose-stimulated insulin secretion developed during in vitro maturation, associated with cytoarchitectural reorganization and the increasing presence of alpha cells. Electrophysiology, signaling and exocytosis of SC-islets were similar to those of adult islets. Glucose-responsive insulin secretion was achieved despite differences in glycolytic and mitochondrial glucose metabolism. Single-cell transcriptomics of SC-islets in vitro and throughout 6 months of engraftment in mice revealed a continuous maturation trajectory culminating in a transcriptional landscape closely resembling that of primary islets. Our thorough evaluation of SC-islet maturation highlights their advanced degree of functionality and supports their use in further efforts to understand and combat diabetes.

Pancreatic islets derived from stem cells are benchmarked against primary cells.

Scrt1, a transcriptional regulator of β-cell proliferation identified by differential chromatin accessibility during islet maturation

Glucose-induced insulin secretion, a hallmark of mature β-cells, is achieved after birth and is preceded by a phase of intense proliferation. These events occurring in the neonatal period are decisive for establishing an appropriate functional β-cell mass that provides the required insulin throughout life. However, key regulators of gene expression involved in functional maturation of β-cells remain to be elucidated. Here, we addressed this issue by mapping open chromatin regions in newborn versus adult rat islets using the ATAC-seq assay. We obtained a genome-wide picture of chromatin accessible sites (~ 100,000) among which 20% were differentially accessible during maturation. An enrichment analysis of transcription factor binding sites identified a group of transcription factors that could explain these changes. Among them, Scrt1 was found to act as a transcriptional repressor and to control β-cell proliferation. Interestingly, Scrt1 expression was controlled by the transcriptional repressor RE-1 silencing transcription factor (REST) and was increased in an in vitro reprogramming system of pancreatic exocrine cells to β-like cells. Overall, this study led to the identification of several known and unforeseen key transcriptional events occurring during β-cell maturation. These findings will help defining new strategies to induce the functional maturation of surrogate insulin-producing cells.