Oxidative damage to RNA: mechanisms, consequences, and diseases

Abstract

Overproduction of free radicals can damage cellular components resulting in progressive physiological dysfunction, which has been implicated in many human diseases. Oxidative damage to RNA received little attention until the past decade. Recent studies indicate that RNA, such as messenger RNA and ribosomal RNA, is very vulnerable to oxidative damage. RNA oxidation is not a consequence of dying cells but an early event involved in pathogenesis. Oxidative modification to RNA results in disturbance of the translational process and impairment of protein synthesis, which can cause cell deterioration or even cell death. In this review, we discuss the mechanisms of oxidative damage to RNA and the possible biological consequences of damaged RNA. Furthermore, we review recent evidence suggesting that oxidative damage to RNA may contribute to progression of many human diseases.

Fig. 1

The most prevalent oxidized base in RNA is 8-hydroxyguanosine (8-OHG). Guanosine (a RNA nucleoside) can be oxidized by highly reactive hydroxyl radicals to form a C8-OH adduct radical, which then loses an electron (e⁻) and a proton (H⁺) to form 8-OHG (an oxidized RNA nucleoside)

Fig. 2

Significant amounts of mRNAs are oxidized in the frontal cortices of AD patients. a Southern blot analysis of oxidized (O) and non-oxidized (N) mRNA pools prepared from the frontal cortices from AD patients or normal controls (n = 6 per group). Oxidized mRNAs were separated from non-oxidized mRNAs by immunoprecipitation with 15A3 antibodies. Both oxidized and non-oxidized mRNA pools were then reverse transcribed to cDNAs. DIG-labeled dUTPs were incorporated into cDNAs to facilitate analysis by Southern blotting. b Densitometric analysis of the Southern blot results reveals that 52.3 ± 6.15% of total mRNA is oxidized in the brains of AD patients while only 1.78 ± 0.56% of total mRNA is oxidized in those of normal controls. Values are means ± SEM; **P < 0.001. Details are provided in reference [37]

Fig. 3

RNA oxidation is an early event in the process of motor neuron degeneration in SOD1^G93A mice. Oxidative RNA damage was examined by immunohistochemistry with 15A3 antibodies in lumbar spinal cord sections of SOD1^G93A mice at the indicated ages (G93A; b, d–j) and nontransgenic littermates (WT; a, c). Increased 15A3 immunofluorescence is apparent in the motor neurons of SOD1^G93A lumbar spinal cord of mice as young as 45 days (d), is further enhanced at 60 days of age (b, e), and then starts to diminish during the symptomatic stage (f–h). The immunoreactivity was diminished greatly by RNase treatment (j) and when the antibody was preincubated with 8-OHG (i). Scale bars 50 μm. Details are provided in reference [38]

Fig. 4

Proteins corresponding to oxidized mRNA species are decreased in SOD1^G93A mice. a Immunofluorescent staining of lumbar spinal cord sections prepared from 60-day-old SOD1^G93A mice (G93A) and nontransgenic littermates (WT) (n = 3). Mouse anti-NADH-ubiquinol oxidoreductase antibodies and rabbit anti-EAAT3 antibodies were used. A decrease in protein levels in SOD1^G93A mice was found in NADH-ubiquinol oxidoreductase subunit 39 kDa (NADH oxi), whose mRNAs were highly oxidized, but not in EAAT3 protein, whose mRNAs were not oxidized. Scale bar 25 μm. b Statistical analysis of immunoreactivity within motor neurons (n = 20). Values are means ± SEM; *P < 0.0001. Details are provided in reference [38]