Rational re-design of Monoamine Oxidase A into a dehydrogenase to probe ROS in cardiac ageing

Cardiac senescence is a typical frailty chronic condition in elderly population and cellular ageing is often associated with oxidative stress. The mitochondrial-membrane flavoenzyme monoamine oxidase A (MAO A) catalyzes the oxidative deamination of neurotransmitters and its expression increases in aged hearts. We produced recombinant human MAO A variants at Lys305 that plays a key role in O2 reactivity leading to H2O2 production. The K305Q variant is as active as the wild-type enzyme, whereas K305M and K305S have 200-fold and 100-fold lower kcat values and similar Km. Under anaerobic conditions K305M MAO A was normally reduced by substrate, whereas reoxidation by O2 was much slower but could be accomplished by quinone electron acceptors. When overexpressed in cardiomyoblasts by adenoviral vectors, the K305M variant showed enzymatic turnover similar to wild-type but displayed decreased ROS levels and senescence markers. These results might translate into pharmacological treatments as MAO inhibitors may attenuate cardiomyocytes ageing.