Identification of novel proteins differentially expressed in pluripotent embryonic stem cells and differentiated cells.

Mammalian pluripotent stem cells possess properties of self-renewal and pluripotency. These abilities are maintained by the strict regulation of pluripotent stem cell-specific transcription factor network and unique properties of chromatin in the stem cells. Although these major signaling pathways robustly control the characteristics of stem cells, other regulatory factors, such as metabolic pathways, are also known to modulate stem cell proliferation and differentiation. In this study, we fractionated protein samples from mouse embryonic stem (ES) cells cultured with or without the leukemia inhibitory factor (LIF). Protein expression was quantified by 2-dimensional differential gel electrophoresis (2D-DIGE). In total, 44 proteins were identified as being differentially expressed in the pluripotent stem cells and the differentiated cells. Surprisingly, half of the identified proteins were the proteins localized in mitochondria, which supply cellular energy and regulate cell cycle, development, and cell death. Some of these identified proteins are involved in the metabolic function and the regulation of pluripotency. Further analysis of the identified proteins could provide new information for the manipulation of pluripotency in ES cells.

Prohibitin 2 regulates the proliferation and lineage-specific differentiation of mouse embryonic stem cells in mitochondria.

BACKGROUND: The pluripotent state of embryonic stem (ES) cells is controlled by a network of specific transcription factors. Recent studies also suggested the significant contribution of mitochondria on the regulation of pluripotent stem cells. However, the molecules involved in these regulations are still unknown. METHODOLOGY/PRINCIPAL FINDINGS: In this study, we found that prohibitin 2 (PHB2), a pleiotrophic factor mainly localized in mitochondria, is a crucial regulatory factor for the homeostasis and differentiation of ES cells. PHB2 was highly expressed in undifferentiated mouse ES cells, and the expression was decreased during the differentiation of ES cells. Knockdown of PHB2 induced significant apoptosis in pluripotent ES cells, whereas enhanced expression of PHB2 contributed to the proliferation of ES cells. However, enhanced expression of PHB2 strongly inhibited ES cell differentiation into neuronal and endodermal cells. Interestingly, only PHB2 with intact mitochondrial targeting signal showed these specific effects on ES cells. Moreover, overexpression of PHB2 enhanced the processing of a dynamin-like GTPase (OPA1) that regulates mitochondrial fusion and cristae remodeling, which could induce partial dysfunction of mitochondria. CONCLUSIONS/SIGNIFICANCE: Our results suggest that PHB2 is a crucial mitochondrial regulator for homeostasis and lineage-specific differentiation of ES cells.