NEW PROJECTS

PROJECT ONE

Role of microRNAs in cellular senescence and aging (Supported by the Dept of Pathology and Laboratory Medicine, MUSC, PI: Wang):

MicroRNAs (miRNAs) are small ~22 nucleotide non-coding RNA molecules that regulate a myriad of biological processes, including the regulation of aging and lifespan in C. elegans. However, it remains to be determined whether miRNAs contribute to mammalian aging, particularly at the level of cellular senescence. Through miRNA microarray assays, we have identified a set of 8 miRNAs that are differentially expressed in senescent fibroblasts. Interestingly, one of the senescence-associated miRNAs (SA-miRNAs) we identified is miR-155, which is significantly down-regulated in senescent fibroblasts but over-expressed in many different types of immortalized tumor cells that escape from cellular senescence. Given that miRNAs play a critical role in developmental timing as well as the aging process of C. elegans, we hypothesize that selective SA-miRNAs can be used as novel biomarkers of organismal aging and that SA-miRNAs, particularly miR-155, play an important role in regulation of cellular senescence. Three specific aims will test this hypothesis: 1) to determine which SA-miRNAs can be used as novel biomarkers of organismal aging; 2) to identify the targets of SA-miRNAs; and 3) to elucidate the mechanisms by which SA-miRNAs regulate cellular senescence.This study will provide novel information on how SA-miRNAs regulate aging process and advance our understanding of the molecular mechanisms of aging and age-related diseases. 

PROJECT TWO

DNA damage and repair in Hematopoietic stem cells (Supported by the Dept of Pathology and Laboratory Medicine, MUSC, PI: Pazhanisamy):

Our research focuses on deciphering the underlying mechanisms of the genetic instability in the stem cells under various genotoxic stress. One of the most important long-term consequences of exposure of the hematopoietic system to ionizing radiation (IR) is the induction of genetic instability. This is particularly detrimental to hematopoietic stem cells (HSCs), because it can lead to the impairment of HSC self-renewal and HSC transformation to cause long-term bone marrow suppression and leukemia, respectively. However, the mechanisms underlying HSC susceptibility to IR-induced genetic instability are unknown, and thus, were investigated in the present study using a mouse model. First, we compared the responses of HSCs (LKS+ cells) to IR-induced DNA damage with those of hematopoietic progenitor cells (HPCs or LKS- cells) in vivo and in vitro. We found that two months after a sublethal dose (6.5 Gy) of total body irradiation (TBI), HSCs, but not HPCs, from irradiated C57BL/6 mice exhibited significantly more DNA double-strained breaks (DSBs) detected by g-H2AX immunostaining than the cells from control animals. The increase in HSC DSBs was associated with a selective induction of reactive oxygen species (ROS) in HSCs and could be attenuated by the treatment with N-acetyl-cysteine (NAC), indicating that HSCs are more susceptible to IR-induced genetic instability at least in part due to a selective induction of oxidative stress in HSCs by IR. In addition, HSCs are less capable of repairing IR-induced DNA damage than HPCs in vitro, which can also contribute to the high susceptibility of HSCs to IR-induced genetic instability. Interestingly, quiescent HSCs (G0; PYlow-LKS+) are more susceptible to IR-induced DSBs and less proficient in repairing the damage than HSCs in cell cycle (PYhigh-LKS+) and proliferating HPCs. This finding suggests that cell cycle status of HSCs play a vital role in DNA damage response against radiation exposure. Therefore, these results highlight the significant difference between HSCs and HPCs in response to IR-induced DNA damage and could have a major impact on our understanding of induction of hematological genetic instability and malignancies by IR.