GNMT & Folate - the guardians of methylation potential

Valve-role to reduce SAMe/SAH ratio

The primary role of GNMT is to methylate glycine, to produce sarcosine. GNMT enzyme serves a role of pressure-release valve that reduces the level of SAMe and it’s controlled by the level of pentaglutamated 5-MTHF.

S-adenosylmethionine was decreased significantly (GNMT– versus GNMT+ cells = 3,195.8 ± 114.1 versus 2,313.4 ± 134.0 [pmol/mg protein], P < 0.001) and S-adenosylhomocysteine increased (GNMT– versus GNMT+ cells = 18.2 ± 1.2 versus 36.1 ± 0.8 [pmol/mg protein], P = 0.003) by GNMT expression. (R1)

Glycine N-methyltransferase is a regulatory enzyme mediating the availability of methyl groups by virtue of being inhibited by folate. (R2)

GNMT may increase folate retention

Taken together, we proved that GNMT expression increases cellular methyl-folate retention, and the retained folates are used effectively for the only biochemical reaction in which 5-methyl-THF participates. (R1)

In the present study, we demonstrated numerous findings. (a) Restoring GNMT in cells with diminished GNMT can improve intracellular folate status. (b) GNMT expression can increase 5-methylTHF-dependent metabolic fluxes in GNMT–deficient cells. (R1)

In vivo GNMT expression improves folate status presumably owing to increased retention and bioavailability in the liver. (f) Destruction of GNMT in vivo specifically reduces hepatic folate and decreases methylfolate-dependent methionine synthase expression in the liver. (R1)

GNMT may donate 5-MTHF to other enzymes

GNMT is a widely known folate binding protein that is sensitive to inhibition by 5-methyl-THF polyglutamates (40). Here we provide novel in vivo and in vitro evidence that, by binding to 5-methyl-THF, GNMT may serve as a reservoir for intracellular folate that can be further utilized for folate-dependent reaction including homocysteine remethylation. We provide evidence that GNMT expression retains the folate in the liver. (R1)

GNMT prefers pentaglutamate

Binding of both the mono- and pentaglutamate forms of 5-methyltetrahydrofolate is the same for the acetylated and non-acetylated forms of the enzyme, however the pentaglutamate form is bound more tightly than the monoglutamate form in both cases. (R2)

Acetylation increases inhibition by folate

Although binding of the folates is similar for the acetylated and non-acetylated forms of the enzyme, inhibition of enzyme activity differs significantly. The native, N-acetylated form of the enzyme shows 50% inhibition at 1.3 microM concentration of the pentaglutamate while the recombinant non-acetylated form shows 50% inhibition at 590 microM.(R2)

Acetylation seems to increase inhibition of the enzyme by folates 453-fold (that’s significant), making it very sensitive to 5-MTHF.

Folate level may affect expression of MS (MTR)

A recent study demonstrated that low dietary folate led to higher betaine demand and reduced MTR expression in mice (32). Our unpublished work also indicated that folate restriction causes low hepatic folate concentrations, decreased MTR protein and reduced folate dependent homocysteine remethylation fluxes in mice livers. (R1)

Mitochondrial GNMT regulates complex II activity in the ETC

GNMT was found to interact with mitochondrial complex II and expression of GNMT directly affects Fatty Acid Oxidation:

indicating that GNMT recovery by anti-miR-873-5p therapy is sufficient to restore methionine and one-carbon metabolism in the liver. Globally, these results indicate an enhanced flux within the one-carbon metabolism particularly in those steps occurring in the mitochondria, after mitochondrial GNMT recovery.

Overall, these results together with the localization of GNMT in the CII suggest a new association between mitochondrial one-carbon metabolism and ETC functionality regulated by GNMT. (R4)

Connection to FAO is described as following:

Different metabolites of one-carbon metabolism, including sarcosine and dimethylglycine (DMG) can be metabolized by sarcosine dehydrogenase (SARDH) and dimethylglycine dehydrogenase (DMGDH), respectively, in reactions producing FADH2, in which two e− are transferred to ubiquinone within the ETC.

These reactions are known as the electron transfer flavoprotein: ubiquinone reductase system (ETF:QO) and occur in the mitochondria, connecting FAO, ETC, and one-carbon metabolism. (R4)

Questionable claims

Nuclear GNMT might inhibit Nrf2 expression (misunderstood)

One paper contains a rather questionable statement that GNMT inhibits Nrf2:

Interestingly, nuclear GNMT interacts with the promoter region of the genes encoding NRF2 ⁽⁷⁹⁾ (R3)

While the referred article only suggests further research if GNMT and Nrf2 have any interaction at all:

Thus, it is interesting to test whether these gallotannins can inhibit NRF2 activity in HCC cells. Surprisingly, we found that Compounds 40 and 43, the two most potent GNMT inducers, also suppressed NRF2 activity in Huh7 cells. These results indicated that the sensitization ability of PGG could be attributed to its inhibitory effect on NRF2 activity. However, further investigations are needed to delineate the underlying mechanisms. (R)

Although the coumarinolignans in this study did not show biological effects on GNMT-promoter and NRF2 activity, this indicated that the coumarinolignans might exert its activity via mechanisms not involving these two proteins. To our knowledge, this is the first report on the GNMT-promoter-enhancing and NRF2 suppressing activities of this plant in Huh 7 cells. Further evidence is needed to support whether E. formosana is helpful to HCC patients. (R)

The referred article is about the plant that has dual effect on GNMT and Nrf2. It’s it not about GNMT interacting with Nrf2.

Therefore the claim that GNMT interacts with the promoter region of Nrf2 is made up and not based on the content of the referred article.