Superoxide Dismutase 1 Knock-down Induces Senescence in Human Fibroblasts

Abstract

Reactive oxygen species (ROS) such as superoxide radicals are responsible for the pathogenesis of various human diseases. ROS are generated during normal metabolic process in all of the oxygen-utilizing organisms. The copper-zinc-containing SOD (SOD1) acts as a major defense against ROS by detoxifying the superoxide anion. In model organisms, SOD1 has been shown to play a role in the aging process. However, the exact role of the SOD1 protein in the human aging process remains to be resolved. We show that SOD1 RNA interference (RNAi) induces senescence in normal human fibroblasts. This premature senescence depends on p53 induction. In contrast, in human fibroblastic cells with inactivated p53, the SOD1 RNAi is without effect. Surprisingly, in cancer cells (HeLa), the SOD1 RNAi induces cell death rather then senescence. Together, these findings support the notion that in normal human cells the SOD1 protein may play a role in the regulation of cellular lifespan by p53 and may also regulate the death signals in cancer cells. ROS1 are generated by normal metabolic processes in all of the oxygen-utilizing organisms. It is estimated that around 1% of the total oxygen consumed in the mitochondria becomes the superoxide anion (1). Damage induced by ROS includes DNA mutation, protein oxidation, and lipid peroxidation. ROS may contribute to the development of various diseases, such as cancer, diabetes, atherosclerosis, inflammation, and premature aging (2, 3).The superoxide dismutases (SODs) constitute a family of antioxidant enzymes that catalyzes the conversion of superoxide anions to oxygen and hydrogen peroxide (for recent review on SODs, see Ref. 4). They include the manganese-containing SOD (SOD2) in the mitochondria (5) and the copper-zinc-containing SOD (SOD1) in the cytoplasm (5) with a small fraction in the mitochondria intermembrane space (6). Ͼ90 different mutations in the SOD1 gene have been found to associate with amyotrophic lateral sclerosis, a disease that causes the degradation of motor neurons (7).The free radical theory of aging states that ROS generation during metabolism can cause damage to cellular constituents (8). During the life of a cell or an organism, SODs and catalase detoxify ROS. However this process is not perfect and ROS species can cause cumulative damage, which causes the physiological decline characteristic of aging (for review, see Ref. 9). In yeast survival, the stationary phase appears to be limited by ROS because deletion of either SOD1 or SOD2 shortens survival time (10). In Drosophila, overexpression of the human SOD1 extends the fly life span by 40% over controls (11).After a finite number of divisions, primary human cells in culture enter into a state of replicative senescence in which they are growth-arrested and resistant to mitogenic stimulation. Senescence is considered a mechanism to suppress tumorigenesis because it inhibits cell proliferation (12). Oxidants appear to be important in the development of the senescent phenotype. Cells grown in low oxygen tension exhibit a pr...

The DNA Damage Signaling Pathway Connects Oncogenic Stress to Cellular Senescence

“…In agreement, direct ablation of SOD by RNA interference induced cellular senescence. 45 Together, the available data support a model where both replication stress and ROS contribute to OIS perhaps converging on the DNA (Fig. 2).…”

Mitochondria are required for pro‐ageing features of the senescent phenotype

“…While pharmacological interventions reducing ROS generation have been proven to be beneficial, it is unclear whether mitochondria are required for senescence. ROS derived from non‐mitochondrial sources (Takahashi et al , 2006) and imbalances in antioxidant defence (Blander et al , 2003) have equally been implicated in the process. Chemical and genetic interventions impacting on the mitochondrial electron transport chain have been shown to enhance OIS (Moiseeva et al , 2009); however, to date, no study has effectively evaluated the necessity of mitochondria for the induction of the senescent phenotype.…”

“…ROS have been shown to play important roles in senescence by inducing genomic damage (Parrinello et al , 2003), accelerating telomere shortening (von Zglinicki, 2002) and acting as drivers of signalling networks important for the maintenance of the senescent phenotype (Passos et al , 2010). However, other reports have also highlighted the importance of non‐mitochondrial ROS sources (Takahashi et al , 2006), redox stress (Kaplon et al , 2013) or deficits in antioxidant defence (Blander et al , 2003) in the development of senescence. Therefore, it remains unknown whether mitochondria are truly necessary for senescence.…”

Kaempferol induces apoptosis in glioblastoma cells through oxidative stress

“…SOD-1 acts as a major defense against ROS by detoxifying the superoxide anion, and knockdown of SOD-1 expression induces cell death in malignant cells (38). Increased levels of TRX-1 in a variety of malignant tumors may contribute to the resistance of cancers to therapy by scavenging ROS, which are generated by various anticancer agents (39).…”