Preprint Frataxin Deficiency Drives Shift from Mitochondrial Metabolism to Glucose Catabolism, Triggering Inflammatory Phenotype in Microglia,2023,Sciarretta+

[SNT Gatchaman]

Frataxin Deficiency Drives a Shift from Mitochondrial Metabolism to Glucose Catabolism, Triggering an Inflammatory Phenotype in Microglia
Francesca Sciarretta; Fabio Zaccaria; Andrea Ninni; Veronica Ceci; Riccardo Turchi; Savina Apolloni; Valerio Chiurchiu; Marta Tiberi; Nadia D'Ambrosi; Silvia Pedretti; Nico Mitro; KATIA AQUILANO; Daniele Lettieri Barbato; Ilaria Della Valle; Martina Milani

Immunometabolism investigates the complex interplay between the immune system and cellular metabolism. This study highlights the effects of mitochondrial frataxin (FXN) depletion, which causes Friedreich’s ataxia (FRDA), a neurodegenerative condition characterized by coordination and muscle control deficiencies.

Using single-cell RNA sequencing, we identified specific cell groups in the cerebellum of a FRDA mouse model, emphasizing a notable inflammatory microglial response. These FXN-deficient microglia cells exhibited enhanced inflammatory reactions. Furthermore, our metabolomic analyses revealed increased glycolysis and itaconate production in these cells, possibly driving the inflammation. Remarkably, butyrate treatment counteracted these immunometabolic changes, triggered an antioxidant response via the itaconate-Nrf2-GSH pathways, and dampened inflammation. The study also pinpointed Hcar2 (GPR109A) as a potential agent for butyrate anti-inflammatory impact on microglia. Tests on FRDA mice highlighted the neuroprotective attributes of butyrate intake, bolstering neuromotor performance.

In essence, our findings shed light on how cerebellar microglia activation contributes to FRDA and highlight butyrate potential to alleviate neuroinflammation, rectify metabolic imbalances, and boost neuromotor capabilities in FRDA and similar conditions.


Link | PDF (Preprint: BioRxiv)

 

[SNT Gatchaman]

Herein we demonstrated that the loss of FXN forces glycolytic catabolism promoting inflammatory phenotype in microglial cells. FXN is a mitochondrial protein and its dysfunction causes mitochondrial failure, thus recruiting glycolysis as the main source of ATP. This is consistent with the increased glycolysis flux occurring in M1 macrophages and microglial cells.

Krebs cycle breaks were also described in M1 macrophages and microglia, which cause an overproduction of itaconic acid. This mitochondrial metabolite has been shown to participate in the inflammatory response restraining IL1ß production and glycolysis. Itaconate and its derivatives showed antiinflammatory effects in preclinical models [...] pointing to possible itaconate-based therapeutics for a range of inflammatory diseases. Consistently, itaconate improved the immunometabolic profile in microglia downregulating FXN through Nrf2-mediated mechanism, highlighting itaconate as novel therapeutical option to improve FRDA-related inflammatory symptoms. [...] Nrf2 controls the antioxidant responses counteracting the production of oxidatively damaged molecules through GSH synthesis.

Mounting evidence reports that gut microbiota releases immunomodulatory molecules and counteracts neuroinflammatory conditions. To this end targeting gut microbiota has been proposed to alleviate neuroinflammation. [...] Dietary butyrate ameliorates microglia-mediated neuroinflammation in several inflammatory mouse models and improves cognitive decline following neuroinflammatory neurotoxin injection.

In accordance with these data, KIKO mice treated with butyrate show reduced neuroinflammation and improvement of neurobehavioral abilities. In microglial cells downregulating FXN, we observed that butyrate improves the immunometabolic profile via itaconate/Nrf2/GSH pathway. Butyrate shows a strong chemical similarity to β-hydroxybutyrate, a ketone body increased in a FRDA mouse model. However, comparative analyses revealed that butyrate exerts higher impact in terms of induction of the mitochondrial anti-oxidant genes and inhibition of pro-inflammatory genes. It has been suggested that the Nrf2-mediated antioxidant responses induced by butyrate are mediated by Hcar2 (also called as GPR109A), which is strongly expressed by CD11b microglial cells.

The current study provides compelling evidence that the loss of FXN is associated with a disruption in mitochondrial activity, rendering microglial cells highly susceptible to inflammatory responses. Furthermore, our research indicates that itaconate plays a pivotal role in mitigating this inflammatory cascade through a Nrf2-mediated mechanism.

 

[Hutan]

I'm not sure I understand that.

A loss of FXN results in glycolysis which promotes an inflammatory phenotype in microglial cells.

Whereas itaconate has anti-inflammatory properties, but it's reducing FXN, which is the same direction as a loss of FXN which supposedly prompted the inflammatory phenotype?

itaconate improved the immunometabolic profile in microglia downregulating FXN through Nrf2-mediated mechanism, highlighting itaconate as novel therapeutical option to improve FRDA-related inflammatory symptoms.

Maybe I'll look closer tomorrow. NRF-2 seems to come up a bit.

Whatever, dietary fibre = a good thing. I'm prepared to believe that.

 

[Creekside]

Whatever, dietary fibre = a good thing.

... unless you have a strong negative response to a metabolic product of fibre fermentation. I developed that earlier this year, and had to avoid fermentable fibre. Oral acetate had no effect; probably absorbed/used before reaching the colon. I seem to have a stronger response to pectin, which produces 80% acetate, and the weakest response to oats, which produce 43/31/26 acetate/propionate/butyrate.

FWIW, after months of minimal butyrate-producing fibre, I haven't noticed any significant worsening of any symptoms. Eating a significant amount of butter doesn't have noticeable effects either.

 

[SNT Gatchaman]

Whereas itaconate has anti-inflammatory properties, but it's reducing FXN, which is the same direction as a loss of FXN which supposedly prompted the inflammatory phenotype?

itaconate improved the immunometabolic profile in microglia downregulating FXN through Nrf2-mediated mechanism, highlighting itaconate as novel therapeutical option to improve FRDA-related inflammatory symptoms.

Perhaps expanded more clearly as:

"itaconate improved the immunometabolic profile in microglia [that were] downregulating FXN[,] through Nrf2-mediated mechanism"

FXN deficiency has been shown to increase the production of pro-inflammatory cytokines, suggesting that FXN might be involved in regulating microglial activity. FXN is a mitochondrial protein, playing an essential role in the intricate process of iron-sulfur cluster assembly regulating mitochondrial electron transport chain (ETC) and aconitase activity. Loss of FXN has been suggested to disrupt mitochondrial oxidative capacity and cause mitochondrial ROS production. Aberrant mitochondrial metabolism and increased glycolytic flux are metabolic hallmarks of inflammatory macrophage/microglia activation. Although it is now well established that FXN takes center place in mitochondrial metabolism, the consequence of FXN loss in microglia cells has never been explored.

To give more insight to the molecular mechanisms leading to inflammatory activation observed in KIKO-derived microglia cells, we generated a [Friedreich's ataxia] cell model by stably downregulating FXN in a microglia cell line (BV2FXN-).

In microglial cells downregulating FXN, we observed that butyrate improves the immunometabolic profile via itaconate/Nrf2/GSH pathway.

 

[Hutan]

Ah, ok, thanks SNT

 

[Samuel]

i eat a low fiber diet because when i tried taking capsules of fiber they caused gastroparesis attacks.

 

[Ash]

... unless you have a strong negative response to a metabolic product of fibre fermentation. I developed that earlier this year, and had to avoid fermentable fibre. Oral acetate had no effect; probably absorbed/used before reaching the colon. I seem to have a stronger response to pectin, which produces 80% acetate, and the weakest response to oats, which produce 43/31/26 acetate/propionate/butyrate.

FWIW, after months of minimal butyrate-producing fibre, I haven't noticed any significant worsening of any symptoms. Eating a significant amount of butter doesn't have noticeable effects either.

What is Oral acetate?

I googled but got an avalanche that I couldn’t understand.

 

[Creekside]

What is Oral acetate?

Orally taken acetate. In my case, I added some baking soda to vinegar, which results in sodium acetate. Fizzy drink; needs flavouring. Pectin, which generates lots of acetate in the colon, is really nasty for me (or was, not really eager to retest that).

Update: I tried probiotics (14 strains), and it's increased my tolerance for oats. I'm testing 4 tsps of oats this morning, and will try 5 tonight, trying to find my new limit, since the old one was just 1. I also tried wheat flour and chocolate, but one or both of those resulted in the same symptoms, so the probiotics weren't a complete fix.

 

[Ash]

Orally taken acetate. In my case, I added some baking soda to vinegar, which results in sodium acetate. Fizzy drink; needs flavouring. Pectin, which generates lots of acetate in the colon, is really nasty for me (or was, not really eager to retest that).

Update: I tried probiotics (14 strains), and it's increased my tolerance for oats. I'm testing 4 tsps of oats this morning, and will try 5 tonight, trying to find my new limit, since the old one was just 1. I also tried wheat flour and chocolate, but one or both of those resulted in the same symptoms, so the probiotics weren't a complete fix.

Ahh thanks, I was imagining you could buy acetate tablets of some kind.

Pretty sure I am not brave enough to try the vinegar baking soda drink. What symptoms does it help with, or is supposed to help with in theory?

 

[Creekside]

Pretty sure I am not brave enough to try the vinegar baking soda drink.

It doesn't have the unpleasantness of either ingredient. It's just a fizzy drink. If you wait for the fizz to stop, it's probably not worse tasting than some mineral waters. I expect acetate tablets are available, but I had these ingredients, so that's cheap and convenient.

What symptoms does it help with, or is supposed to help with in theory?

For acetate? I took it to see whether that was the metabolite that was causing my worsening of symptoms (brainfog, aches, lethargy). Butyrate is supposed to be helpful for some things. Propionate is harmful if you take too much. I didn't come across anything about effects of acetate supplementation. I couldn't find a cheap source for propionate (just a $70 sack), so I couldn't test that on its own. I would have needed slow-dissolving capsules too, or apply it as an enema. However, since I couldn't think of any way to apply the knowledge of which metabolite was responsible, I wasn't willing to go to extremes (or mess/discomfort) to test it.

 

[Ash]

It doesn't have the unpleasantness of either ingredient. It's just a fizzy drink. If you wait for the fizz to stop, it's probably not worse tasting than some mineral waters. I expect acetate tablets are available, but I had these ingredients, so that's cheap and convenient.


For acetate? I took it to see whether that was the metabolite that was causing my worsening of symptoms (brainfog, aches, lethargy). Butyrate is supposed to be helpful for some things. Propionate is harmful if you take too much. I didn't come across anything about effects of acetate supplementation. I couldn't find a cheap source for propionate (just a $70 sack), so I couldn't test that on its own. I would have needed slow-dissolving capsules too, or apply it as an enema. However, since I couldn't think of any way to apply the knowledge of which metabolite was responsible, I wasn't willing to go to extremes (or mess/discomfort) to test it.

You took acetate to see if it would make your symptoms worse?

 

[Creekside]

You took acetate to see if it would make your symptoms worse?

Yes, quite a few of my ME experiments are done expecting to make my symptoms worse. I like the black box approach: poke the box and see if anything changes. If it makes me feel worse, I know to avoid that factor in the future. I've had a number of surprises, where the factors I expected to make me feel worse failed to do so. Then there were experiments like the sodium acetate, which was a failure as an experiment because I didn't take into account the likelihood of it reaching my colon. Still valuable, since I now know that acetate at the start of the digestive tract (and I assume in the blood) does not cause the symptoms, but acetate in the colon seems to. That changes how I set up future experiments.