I just want to be sure that everyone is agreed on the definition of mitochondrial fission/fragmentation. Neither fission nor fragmentation implies the destruction of the mitochondrial membranes. Fission and fragmentation are used to describe the transition from long tubular mitochondrial networks to short ovoid mitochondria, like the ones in old biology textbooks. These short mitochondria still have completely intact inner and outer mitochondrial membranes. Agreed?
To Serg1942's point:
The purinergic response is upstream of the IFN response in the Naviaux-Prusty model. In the IFNa-itaconate-shunt model, what's upstream is the normal innate immune response to infection or trauma, namely, the cellular pattern recognition receptors (PRRs) detect PAMPs (infections) or DAMPs (damage). PRRs detect many pathogen or damage signals and the sensing of purines in places they shouldn't be is one of them.
When a cell detects any of these signals it initiates two responses: 1) the acute inflammatory response, and 2) the antiviral state. If you have access to a copy of the textbook titled Cellular and Molecular Immunology (Abbas, Lichtman, and Pillai, 10th edition, 2022), there is a nice diagram of this in Figure 4.3. I think this figure is the most interesting one in the book.
Pathway 1 (acute inflammation) paves the way for the adaptive immune system to take over the body's defense. You follow pathway 1 if you are interested in chemokines, T cells, and B cells.
Pathway 2, on the other hand, is a local warning and defense system that begins with the induction of Type I interferon genes, translation of their mRNAs on bound ribosomes, and secretion of Type I interferons into the extracellular space. It's here that the two theories converge. Dr. Naviaux independently conceived the CDR and the healing cycle and they turned out to have much in common with the innate immune system. I'm still working to understand whether/the two theories diverge after this point of convergence.
I am interested in pathway 2 because it leads to the induction of ACOD1 and therefore to the itaconate shunt. This can happen in any cell type because the secreted type I interferons can initiate JAK-STAT signaling by binding to the universally expressed IFNa receptor, consisting of two proteins: IFNAR1 and IFNAR2. This is the warning/defense signal. It says, "Prepare your defenses, there is danger nearby."
IFNa signaling via the JAK-STAT pathway (worked out in the 1980s by a legendary East-coast-West-coast collaboration) induces ~300 genes. Some are antiviral, some antibacterial, some are repair proteins, and one is ACOD1, which drives the itaconate shunt in mitochondria.
This is all part of the innate immune system. There is no mention of T cells or B cells in pathway 2. Normally, the innate immune system is turned off about 4 days after the initial PRR signal. Our hypothesis is that the innate immune system failed to turn off when it was supposed to. We think PWME are sick because a small percentage of body cells are chronically running the itaconate shunt and consequently are not producing sufficient ATP to do their jobs. We're looking for molecular mechanisms that keep ACOD1 up-regulated long after the triggering infection/trauma is gone. One of those mechanisms is chronically elevated IFNa caused by the inherent positive feedback in IFNa signaling.
Thank you so much Dr Phair for your magnificent and detailed response!
I understand that your theory puts the focus on the stimulation of pattern recognition receptors, where the high purines are only one of the many different signals that stimulate these receptors.
Please, let me however highlight a few points that make me conceive the purinergic signal as, at least, a key part. I would really appreciate if you could let us know how you could explain the following facts in the light of your theory.
The studies done by Dr Naviaux showed how a genetic and an acquired murine model of autism could be mostly reversed by just one dose of suramin. Specifically, the acquired model showed a 94% normalization of the metabolites of 18 biochemical pathways, and the genetic model showed significant improvement of the metabolome and the synaptosome. Most importantly, in both models the autistic-like behaviors were normalized.
Among the corrected metabolites by suramin, I think that we can find an indirect sign of normalization of the innate immunity as well as normalization of the itaconate and the Krebs cycle pathway.
For example, most intermediaries of the Krebs cycle increased, including fumaric acid, malic acid, succinil-CoA, 2-oxoglutarate or citramalic acid.
The coenzyme-A and the CoA-containing metabolites also increased, including acetyl-coA and malonyl-CoA. So perhaps this means that the Coenzyme A is not longer sequestered by the itaconate metabolites.
On the contrary, NH3 and glutamate don't increase, in relative terms.
Oxidative stress seems to improve as well. For example, the ratio GSH/GSSG increases . The ratio NADH/NAD+ increased. Coq10 and lipoic acid increased as well.
In addition, and this really amazes me, the microbiome abnormalities showed a generalized normalization.
Finally, the C1q complement decreases significantly, what I understand could mean a concomitant decrease of the complete innate response (given that, for example, LPS stimulate both IFNa and the complement system).
After carefully studying your great lecture on the itaconate pathway, it seems to me that these changes fit with a temporary reversal of the itaconate pathway activation and a restoration of the normal mitochondrial and overall metabolic function.
Would you please let us know how these changes induced by suramin could be explained from the itaconate hypothesis, where the IFNa signal would be central?
Thank you very much for your fantastic work and for your willingness to teach us and to let us discuss with you all these points!
Sergio
PS. the Naviaux's studies I am referring to are:
https://pubmed.ncbi.nlm.nih.gov/25705365/
https://pubmed.ncbi.nlm.nih.gov/24937094/