RESUMO
Inadequate functional ß cell mass underlies both type 1 and type 2 diabetes. ß Cell growth and regeneration also decrease with age through mechanisms that are not fully understood. Age-dependent loss of enhancer of zeste homolog 2 (EZH2) prevents adult ß cell replication through derepression of the gene encoding cyclin-dependent kinase inhibitor 2a (INK4a). We investigated whether replenishing EZH2 could reverse the age-dependent increase of Ink4a transcription. We generated an inducible pancreatic ß cell-specific Ezh2 transgenic mouse model and showed that transgene expression of Ezh2 was sufficient to increase ß cell replication and regeneration in young adult mice. In mice older than 8 months, induction of Ezh2 was unable to repress Ink4a. Older mice had an enrichment of a trithorax group (TrxG) protein complex at the Ink4a locus. Knockdown of TrxG complex components, in conjunction with expression of Ezh2, resulted in Ink4a repression and increased replication of ß cells in aged mice. These results indicate that combined modulation of polycomb group proteins, such as EZH2, along with TrxG proteins to repress Ink4a can rejuvenate the replication capacity of aged ß cells. This study provides potential therapeutic targets for expansion of adult ß cell mass.
Assuntos
Inibidor p16 de Quinase Dependente de Ciclina/genética , Células Secretoras de Insulina/citologia , Células Secretoras de Insulina/metabolismo , Complexo Repressor Polycomb 2/genética , Proteínas do Grupo Polycomb/genética , Envelhecimento/genética , Envelhecimento/metabolismo , Envelhecimento/patologia , Animais , Proliferação de Células , Diabetes Mellitus/genética , Diabetes Mellitus/metabolismo , Diabetes Mellitus/patologia , Proteína Potenciadora do Homólogo 2 de Zeste , Expressão Gênica , Técnicas de Silenciamento de Genes , Histona-Lisina N-Metiltransferase/genética , Humanos , Histona Desmetilases com o Domínio Jumonji/antagonistas & inibidores , Histona Desmetilases com o Domínio Jumonji/genética , Histona Desmetilases com o Domínio Jumonji/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos DBA , Camundongos Transgênicos , Proteína de Leucina Linfoide-Mieloide/genética , Complexo Repressor Polycomb 2/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
Stem cell differentiation depends on transcriptional activation driven by lineage-specific regulators as well as changes in chromatin organization. However, the coordination of these events is poorly understood. Here, we show that T-box proteins team up with chromatin modifying enzymes to drive the expression of the key lineage regulator, Eomes during endodermal differentiation of embryonic stem (ES) cells. The Eomes locus is maintained in a transcriptionally poised configuration in ES cells. During early differentiation steps, the ES cell factor Tbx3 associates with the histone demethylase Jmjd3 at the enhancer element of the Eomes locus to allow enhancer-promoter interactions. This spatial reorganization of the chromatin primes the cells to respond to Activin signalling, which promotes the binding of Jmjd3 and Eomes to its own bivalent promoter region to further stimulate Eomes expression in a positive feedback loop. In addition, Eomes activates a transcriptional network of core regulators of endodermal differentiation. Our results demonstrate that Jmjd3 sequentially associates with two T-box factors, Tbx3 and Eomes to drive stem cell differentiation towards the definitive endoderm lineage.
