Hi Amna,

You can view the hypoxia as a trigger to a dynamic system so even if you have local O2 decline you can trigger something that increases O2 for ROS production. For instance erythropoietin can increase O2 (http://www.mdpi.com/1422-0067/15/6/10296) that complex 3 can use to produce ROS (http://www.jbc.org/content/275/33/25130.full). Hope these help!

-ED

Hi Amna,

actually, the overproduction of ROS initiates during the reperfusion and not during ischemia. However, activation and upregulated expression of enzymes capable of producing reactive oxygen species (ROS) and electron transport chain (ETC) dysfunction are initiated during ischemia, beyond decreased ATP production, which in

turn, disrupts ion pump function, leading to accumulation of Na + , Ca2 + , and H +.

The HIF-1a is not stabilized by ROS. It is constantly produced and degraded in a normal cell. However, its degradation depends on oxygen. So, during ischemia HIF-1a builds up in the cell.

Here is a nice and short review:

Mitochondrial reactive oxygen species: A double edged sword in ischemia/reperfusion vs preconditioning

Theodore Kalogeris, Yimin Bao, Ronald J. Korthuis*

Redox Biology 2 (2014) 702–714

Hi Amna,

This is a great question, so thanks for asking - it is something which generated considerable curiosity in my mind also.

It is true that mitochondria are the major source of ROS and under hypoxia, ROS production gets enhanced in several cell lines/animals. It is well known that O2(.-)  in mitochondria originate from complexes I, II, & III, and the possible explanation to your question lies in these complexes as also indicated by Dr Emmanuel Datan. Inner membrane of the mitochondrial house complexes I & II which generate O2(.-) that follows its release into the matrix. Complex III is a transmembrane protein complex which generate O2(.-) in the matrix as well as the inter-membrane space from where O2(.-) get carried to the cytoplasm also wherein it implicates in cell signaling (including HIF induction). Studies have now established that hypoxic conditions lead to a conformational change in complex III which aids the interaction between O2 and ubisemiquinone ultimately resulting in an enhanced generation of O2(∙−) . Upon hypoxia, complex II also switches its activity from succinate dehydrogenase to fumarate reductase which is a known O2 (∙−) generator. I hope this sheds some light on the mechanisms involved in the induction of ROS generation under hypoxic conditions and for more details, you can see research articles with PMIDs- 16054089; 12200425; 25383517; 26408245

Also, for answers to more than 25 frequently asked questions on hypoxia/HIFs, I would suggest reviewing: FAQs - Hypoxia and HIFs at http://www.novusbio.com/support/hypoxia-and-hif-faqs

Best Wishes

Subhash

Thanks all for sharing your knowledge! :)

Sir Subhash, your detailed answer is quite helpful. I will surely look into the referred articles! 

You're very welcome Amna :-)

I am glad that you found the answer useful at your end. Yes, the resources which I suggested are great and hopefully you will enjoy reading them all. 

I noticed that you are interested in Autophagy also and from Novus, we published troubleshooting tips/answers to more than 20 frequently asked questions on autophagy/LC3 analysis at: http://www.novusbio.com/support/faqs-autophagy-and-lc3

Best Wishes 

Subhash

Thank you sir! Ans yes, "Autophagy" is actually my topic of interest.