Yes. And no. It is a proxy and will therefore always be open to discussion or doubt. On the other hand, many people use it, there is no good way of directly measuring DNA damage. My advice would be use other (indirect) measures as well. If they all point in the same direction it will be hard for people to argue it is an artefact of PARP.

I agree with the previous answer, the "traditional" role of PARP1 and the formation of PAR polymers was always associated with DNA damage and then if not kept in check cell death by Parthanatos, however there are studies to suggest that an increase in PARylation may not necessarily indicate damage but rather transcription. I would suggest looking for phosphor y-H2AX or other markers in conjunction to see if you really have damage.

The short answer is: Yes, but... As the others already pointed out PARylation may be related to DNA transcription/replication and so is DNA oxidation. Hence if you see a little DNA oxidation and PARylation of proteins, then things are probably still within the physiological ranges. If you see a lot of it, then there is little doubt that you are looking at a pathological process.

BTW, an easy test for DNA oxidation is to incubate cells/sections with fluorescently labelled avidin. Avidin binds 8-Oxo-Guanosine (and biotin, which can be blocked) and cells with high amounts of oxidized DNA will show lots of nuclear avidin binding. Alternatively - or for confirmation - you can use an antibody directed against 8-Oxo-Guanosine which should give a similar picture.

...and if you are at it already, you could check for 8-Oxo-Guanosine-Glycosidase (OGG1) activity/localization. This is the enzyme that moves in once PARP has detected DNA oxidation, and which then excises 8-OG for subsequent replacement with G.

A short answer is NO! Although PARP-1 is definitely involved in DNA damage and repair, the relationship of PARP-1 with stress comes from stroke research where several proteins are elevated. The involvement of PARP1 with NAD+ and energy usage then becomes a theory that PARP1 is a stress protein. The brain itself is constantly repair damage to nucleic acids (DNA and RNA) as only a few cells are capable of replication, and most neurons are replication silence. The energy theory works well in male mice, but it dies when female mice were used. Can one say female mice does not need energy or the stroke model did not induce stress in female mice?

On the other hand, OGG1 and AP1 proteins may be better candidates (J Neurochem, 2000;74(3):1098-105; FASEB J. 2000;14(2):407-17).

I would say yes only if you refer to genetic stress that induces directly or indirectly DNA damage. So far, PARP1 requires to bind DNA nick, gap or end to become activated as a polymerase. Therefore presence of polymers means that at a time there were such DNA structures in the cells. If you do not activate PARG (which remove the polymers) you can detect polymers even when the "activator" DNA damage have deseappeared. In these conditions looking for oxydative damage (8-oxoG) or doube-strand breaks (gammaH2AX) might not be completely informative. I would suggest to check PARG status and test for replicative stress (cell cycle defect) in the cells first.

I believe that monitoring the level of cellular PAR polymer in a cell is the surest way of assessing effect of any kind of cellular stress. I have worked on it for a very long time and I have experimental evidences to conclusively show it. In fact, I developed an immuno-probe assay to quantitatively and sensitively assay the level of the ADP-ribose polymer (and not PARP-1 or any of its very large number of sub-types) in a cell. This correlates very well with stress caused by carcinogens. In principle, the PAR polymer level in a cell is an outcome of PAR metabolism, which comprises a bio-synthetic (anabolic) process, catalyzed by PARP-1 and others, as well as a bio-degradative (catabolic) process, catalyzed by PARG and others. So, only assessing the PARP enzyme level does not tell anything about its influence on the level of the PAR polymer, the level of which actually controls the chromatic superstructure and, therefore, its biological functions.

I sully subscribe to the view that detection of PAR polymer is the best way to assess DNA stress.

My opinion is that high PAR levels in cells will reflect DNA breaks, as these are the most powerful activators, but you could introduce such stress by rough handling of the cells as well so be careful. I would also be inclined to go for a direct measure, such as Comet assay

I would say Yes PAR polymers are an indicator for DNA stress. Breaks in DNA result in rapid activation of poly(ADP-ribose) (PAR) polymerases, PARP1 and PARP2, which catalyze the assembly of poly(ADP-ribose) (PAR) chains onto chromatin substrates. PAR modification at DNA damage sites facilitates repair by attracting PAR-binding DNA repair factors and promoting chromatin relaxation at the damage site. PARP-1 as an indicator of other molecular processes is less defined as far as I know.

Yes, but it is difficult. PARP is still rather a matter of basic research and not a routine tool for DNA-Stress detections.

I agree with "Yes & No". With the traditional visualization method like western or IF you will only see PAR induced by DNA damage - and only this. There is no antibody that picks up the very low levels of PAR constantly present in cells or induced very locally for gene regulation. And I doubt if some of the newer antibodies are sufficent specific/sensitive enough (we are currently testing this). If you see "massive" (detectable) PAR, you can assume that it was induced by DNA damage. Of course you have to have identically handled controls to assure not to have PARP activation by the processing the samples. Be aware, fixation itself can induce DNA stress and subsequent damage signaling. 1% formaldehyde for 10 minutes induces massive PAR and gammaH2AX, for example (PLoS Biology 2012, Beneke et al.). So, either use precipitating agents (methanol) or higher formaldehyde concentrations (3.7%, 4% PFA) for 20 minutes. But not all damaging agents show standard PARP activation (UV is only very weakly inducing it).

If you use more sensitive methods (IP, MS), you will also detect PAR induced by other pathways (i.e. transcription, UV) or even background levels.

In addition: PAR-synthesis is a very short-lived cell response to genotoxic stress. Even at sites of persistent damage/breaks, there is no significant PAR detectable. This is not well understood (or investigated), but probably other damage markers such as gammaH2AX take over and shield the break from activating PARP1/2. So, PAR levels can only be used as a surrogate for newly formed DNA breaks, and most likely not for persistent breaks.