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A. D'Alessandro et al.
phan metabolism) have been reported in RBC from aging mice and mouse models of parabiosis, raising the possibili- ty of a role for PIMT-associated dysregulation of trypto- phan metabolism in the aging process. On the other hand, dopamine – whose metabolism is dependent on NADPH – has been shown to accumulate in RBC from individuals with G6PD deficiency,32 as well as in response to exercise- induced oxidant stress.36 These hypotheses will need to be rigorously assessed by subsequent studies, but the pattern that emerges from the current findings are consistent with a possible role of PIMT in these processes.
An important implication of the findings in this report is that there are widespread metabolic effects of deleting PCMT1, far beyond the predicted decrease in methionine consumption as a PIMT substrate. Rather, general shifts were seen in PPP activity, both at baseline as well as in response to oxidative stress. Moreover, as above, alter- ations in other metabolic pathways were likewise
observed. This raises the important question of how PIMT contributes to widespread metabolic effects, since the known activity of PIMT is with regards to repairing oxida- tive damage once it has occurred and not altering the metabolism of oxidative pathways. The most likely hypothesis is that aspartate and asparagine residues are critically important in a wide range of metabolic enzymes and failure of PIMT to repair them when they are oxidized, results in alterations of these pathways through alteration of enzymatic activity or even inactivation. As isoaspartyl damage would impact protein backbone orientation, while methylation of isoaspartyl groups would affect the charge of side chains, one could speculate that PIMT activity (or lack thereof) could play a role in enzymatic function37 and RBC structural/function homeostasis through regulation of protein-protein interactions, in like fashion to phosphory- lation.38 A related, but distinct hypothesis is that lack of PCMT1 results in functional alteration of proteins involved
ABC
D
Figure 5. Metabolomics of bone marrow-transplanted wild-type and PCMT1-/- knockout x Ubi-GFP.B6 chimerae. (A) Metabolomics of bone marrow-transplanted wild-type and PCMT1-/- knockout ((PCMT1 KO) x Ubi-GFP.B6 chimerae; (B) no significant changes in the time necessary to reconstitute the bone marrow of non- green fluorescence protein (GFP)-labeled red blood cells (RBC) were noted between the two groups, however, significant changes in RBC metabolism was noted between WT→GFP-WT and PCMT1→GFP WT mouse RBC; (C and D) show the top 50 significant metabolites (t-test) and variable importance in projection from these analyses.
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haematologica | 2021; 106(10)