Defense Date

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Pathology

First Advisor

Youngman Oh

Abstract

Normal somatic cells have a limited proliferative capacity in vivo and in vitro, termed senescence and later, thought to contribute to molecular and cellular organismal aging. There are several studies that demonstrate the importance of the GH/IGF axis in longevity, aging and cellular senescence. One primary component of the IGF signaling involves IGFBP-3. It is well documented that IGFBP-3 levels are significantly increased in senescent human diploid fibroblasts however IGFBP-3 function is not known in this system. Interestingly, Werner syndrome fibroblasts, commonly used as a model of cellular aging, have upregulated IGFBP-3 levels in young and late passage cells compared to age matched normal fibroblasts. It is known that suppression of p38 MAPK activity in WS fibroblasts can reverse the senescence and promotes cell proliferation. As increased IGFBP-3 expression is associated with cellular senescence, and suppression of p38 MAPK can reverse senescence in WS fibroblasts, it is hypothesized that “IGFBP-3 can induce senescence, by activating the p38 MAPK signaling pathway.” Our studies demonstrate IGFBP-3 and novel IGFBP-3R can induce senescence in young fibroblasts, while suppression of IGFBP-3 in pre-senescent fibroblasts, can delay the onset of replicative senescence. We identified ROS accumulation in IGFBP-3/IGFBP-R-induced senescent cells which we speculated may be signaling p38 MAPK activation. Inhibition of ROS accumulation suppressed p38 signaling and prevented IGFBP-3/IGFBP-3R-induced senescence. To evaluate the sequence of activation we inhibited p38 activity prior to senescence induction. Interestingly, p38 inhibition prevented IGFBP-3/IGFBP-3R-induced senescence, suggesting IGFBP-3 signals ROS induction which activates p38 signaling. We next examined the significance of IGFBP-3R in IGFBP-3-induced senescence. Suppression of endogenous IGFBP-3R inhibits IGFBP-3-induced senescence. We aimed to identify a possible regulatory mechanism for IGFBP-3 upregulation. Using sequence analysis software we identified 3 possible highly conserved miRNA sequences aligned to IGFBP-3. miR-19a appeared to have the most significant downregulated expression in late passage fibroblasts compared to early passage. Furthermore, overexpression miR-19a in late passage cells, significantly decreased IGFBP-3 expression, suggesting miR-19a may silence IGFBP-3 expression in senescence. Making a direct mechanistic connection between senescence and aging is significant and unraveling how IGFBP-3/IGFBP-3R can induce senescence could prove beneficial in understanding the aging process.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

May 2010

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