Reversing Epidermal Stem Cell Aging: Role of Bmi-1 and the Stem Cell Niche

描述(由申请人提供)：在美国，伤口愈合受损、皮肤破裂和皮肤脆弱会导致皮肤感染和相当大的发病率和死亡率。我们最近的研究表明，虽然随着年龄的增长，表皮干细胞的频率没有明显的差异，但单个表皮干细胞的增殖能力降低了。老年传代扩增细胞频率较高，细胞周期时程延长，并可观察到祖细胞提前分化。我们的假设是，Bmi-1在老年EpiSCs的分化、增殖和对称分裂的改变中起关键作用，内源性(Bmi-1)和/或外源性(小生境)的改变可以部分或完全恢复Bmi-1的表达、分化、增殖和对称分裂的改变。该项目的长期目标是了解表皮干细胞及其随年龄变化的生态位变化的机制。这些知识将被用来改善老年人的伤口愈合和组织工程应用。具体目的：在这项建议中，我们将研究内在(Bmi-1/p16)和外在/环境影响在表皮干细胞老化中的作用。在目标1中，我们将优化和完成老年和年轻EpiSCs之间的差异分析，然后研究Bmi-1基因敲除小鼠的表皮干细胞是否表现出过早衰老的皮肤表型(过早分化、增殖减少、细胞周期延长、对称分裂增加和p16表达增加)。然后，我们将在衰老的表皮干细胞中过表达Bmi-1，以确定是否可以通过过表达Bmi-1来恢复衰老的表型。在目标2中，我们将确定局部和系统的外部因素对表皮干细胞老化的影响，以及年轻的局部和/或系统环境是否可以逆转过早分化、增殖能力下降、细胞周期增加、对称分裂增加和Bmi-1减少的情况。这些研究将在移植试验中进行，使我们能够观察局部和全身因素对单个祖细胞的影响。意义：通过改变Bmi-1/p16状态来改变EpiSCs的增龄相关功能变化，可能有助于保留增殖潜能和抑制终末分化。此外，更好地了解环境对EpiSCs的影响将决定改善老年表皮功能的潜在疗法。对老年人的巨大好处将包括防止皮肤破裂/脆弱(例如褥疮、瘀伤、撕裂)和改进伤口的治疗(腿部溃疡和缓慢愈合的外科伤口)。 公共卫生相关性：在美国，伤口愈合受损、皮肤破裂和皮肤脆弱会导致皮肤感染和相当大的发病率和死亡率。在这项建议中，我们将研究内在(Bmi-1/p16)和环境影响在表皮干细胞老化中的作用。通过改变Bmi-1/p16的状态来改变EpiSCs的增龄相关功能变化，可能有助于保留增殖潜能和抑制终末分化。此外，更好地了解环境对EpiSCs的影响将决定改善老年表皮功能的潜在疗法。对老年人的好处包括防止皮肤破裂/脆弱(如褥疮、瘀伤、撕裂)和改进伤口(腿部溃疡和外科伤口)的治疗。

DESCRIPTION (provided by applicant): Impaired wound healing, susceptibility to skin breakdown and skin fragility lead to skin infections and considerable morbidity and mortality in the US. Our recent study shows that while no significant difference in epidermal stem cell frequency could be detected with aging, the proliferative capacity of individual epidermal stem cells was reduced. Also, transit amplifying cell frequency was greater in the aged, cell cycle duration was increased, and premature progenitor differentiation was observed. Our HYPOTHESIS is that Bmi-1 has a key role in the altered differentiation, proliferation, and symmetric divisions of aged EpiSCs and that intrinsic (Bmi-1) and/or extrinsic (niche) alterations can partially or completely restore the alterations in Bmi-1 expression, differentiation, proliferation, and symmetric division. The long-term goal of this project is to understand the mechanisms that underlie the alterations in epidermal stem cells and their niche with aging. This knowledge will be used to improve wound healing in the aged and for tissue engineering applications. SPECIFIC AIMS: In this proposal we will study the roles of both intrinsic (Bmi-1/p16) and extrinsic/environmental influences on epidermal stem cell aging. In Aim 1 we will optimize and complete our assay of the differences between aged and young EpiSCs and then investigate whether the epidermal stem cells of Bmi-1 knockout mice show a premature aging skin phenotype, (premature differentiation, decreased proliferation, extended cell cycle, increased symmetric division and increased p16 expression). We will then overexpress Bmi-1 in aged epidermal stem cells to determine whether the aging phenotype can be rejuvenated with Bmi-1 overexpression. In Aim 2 we will determine the effects of extrinsic factors, both local and systemic, on the aging of epidermal stem cells, and whether the premature differentiation, decreased proliferative capacity, increased cell cycle, increased symmetric division and decreased Bmi-1 can be reversed with a young local and/or systemic environment. These studies will be performed in a transplantation assay that allows us to look at the effects of local and systemic factors on individual progenitor cells. SIGNIFICANCE: Modifying age-related functional changes in EpiSCs through alteration of Bmi-1/p16 status could be used for retention of proliferative potential and suppression of terminal differentiation. Also better understanding environmental influences on EpiSCs would determine potential therapies to improve aged epidermal function. Great benefits for the elderly would include preventing skin breakdown/fragility (e.g. bedsores, bruising, tearing) and improved treatment of wounds (leg ulcers and slow healing surgical wounds). PUBLIC HEALTH RELEVANCE: Impaired wound healing, susceptibility to skin breakdown and skin fragility lead to skin infections and considerable morbidity and mortality in the US. In this proposal we will study the roles of both intrinsic (Bmi- 1/p16) and environmental influences on epidermal stem cell aging. Modifying age-related functional changes in EpiSCs through alteration of Bmi-1/p16 status could be used for retention of proliferative potential and suppression of terminal differentiation. Also better understanding environmental influences on EpiSCs would determine potential therapies to improve aged epidermal function. Benefits for the elderly would include preventing skin breakdown/fragility (e.g. bedsores, bruising, tearing) and improved treatment of wounds (leg ulcers and surgical wounds).