Phosphoinositides and ME

Germain et al:

"Another hypothesis that could be drawn from the pathway analysis concerns the glycerophospholipid metabolism, as we observed five altered metabolites involved in biological membrane composition. Phosphoinositides are phospholipids that play critical roles in the brain and the spinal cord and peripheral nerves, by being involved in cell regulation and membrane dynamics."

I believe this hypothesis is true and very important.

Phosphoinositides (PIs) are generated in the PI-cycle. The first step in the PI-cycle is the conversion of diacylglycerol (DAG) to phosphatidic acid (PA) via the enzyme diacylglycerol kinase (DGK).

The last step is genration of PIP2. PIP2 is involved in cell signaling, fx regulation of TRPs.

Glycerol-3-phosphate can be converted to lysophosphatidic acid, which can be converted to PA. Lipin (gene: LPIN) can convert PA to DAG.

Epigenetic changed genes in ME:

• DGKA (DGK-alpha) hypomethylated (2)
• DGKQ (DGK-theta) hypermethylated, with a negative foldchange (3)
• LPIN1 hypermethylated (2)

References:

1. Germain et al: Metabolic profiling of a ME/CFS discovery cohort reveals disturbances in fatty acid and lipid metabolism. Mol. BioSyst. 2017, 13, 371
2. Vega et al. DNA methylation Modifications associated with CFS. Plos One, aug 2014, vol 9, Issue 8, e104757
3. Brenu et al: Methylation profile of CD4+ T cells in CFS/ME. J. Clin Cell Immunol 5, 228

GPD2, the glycerophosphate-shuttle and ME

Glucose/pyruvate and lipid metabolism have been found dysregulated in ME (1, 2, 3)

Glycero-3-phosphate has been found up-regulated in ME (3).

The gene GPD2 codes mithochondrial glycerol-3-phosphate dehydrogenase (mGPDH).

mGPDH oxidizes glycerol-3-phosphate to dihydroxyacetone phosphate.

mGPDH is a very important enzyme of intermediary metabolism and as a component of glycerophosphate shuttle at the crossroads of glycolysis, oxidative phosphorylation and fatty acid metabolism (4).

These genes have been found epigenetic changed (hypermethylated) in ME (5):

• GPD2, glycerol-3-phosphate dehydrogenase 2
• SLC37A3, solute carrier family 37, glycerol-3-phosphate transporter
• DAK, dihydroxyacetone kinase 2 homolog

References:

1. Fluge et al: Metabolic profiling indicates impaired pyruvate dehydrogenase function in myalgic encephalopathy / chronic fatigue syndrome. JCI Insight. 2016; 1(21):e89376. Doi 10.1172/jci.insight.89276
2. Naviaux et al: Metabolic features of CFS. www.pnas.org/cgi/doi/10.1073/pnas.1607571113
3. Germain et al: Metabolic profiling of a ME/CFS discovery cohort reveals disturbances in fatty acid and lipid metabolism. Mol. BioSyst. 2017, 13, 371
4. Mracek et al: The function and the role of the mitochondrial glycerol-3-phosphate dehydrogenase in mammalian tissue. Biochimica et Biophysica Acta 1827, 2013, 401-410.
5. Vega et al. DNA methylation Modifications associated with CFS. Plos One, aug 2014, vol 9, Issue 8, e104757

IDH, GOT and ME

Fluge, Mella et al. have shown that ME is associated with defective oxidative metabolism - most likely involving impaired pyruvate dehydrogenase (PDH) function (1).

A study showed that PDH suppression shifted the source of lipogenic acetyl-CoA from glucose to glutamine, and this compensatory pathway required a net reductive isocitrate dehydrogenase (IDH) flux to produce a source of glutamine-derived acetyl-CoA for fatty acid. Levels of intra- and extracellular aspartate and alanine were enhanced (2).

Another study showed that inhibition of the mitochondrial pyruvate carrier in the retina caused accumulation of aspartate at the expense of glutamate. The mitochondrial glutamate oxoglutarate transaminase (GOT2) - also knowns as aspartate aminotransferase - became upregulated (3).

Expression of IDH-proteins (IDH3A, IDH3B and IDHP) and of GOT2 have been found upregulated in ME (4).

A proteomic study on cerebrospinal fluid from ME/CFS patients has shown (5):

• IDH1, CFS:2, normal value 4
• GOT1, CFS:39, normal value 29
• GOT2, CFS:1, normal value 6

Armstrong et al have shown increased aspartate, decreased glutamate and a potentially reduced provision of acetyl-CoA for the TCA-cycle (6).

Glutamate is important as a neurotransmitter and as a substrate for glutathione synthesis. Depletion of glutamate correlates with cell death in the retina (3).

Shungu et al. have found elevated ventricular lactate and decreased glutathione in CFS patients (7).

I have noticed that some ME patients develop an early age-related degeneration of the retina. Could dysregulated metabolism be involved?

The aspartate aminotransferase blood test (ASAT) is usually normal in ME patients. Could there be a local tissue-specific dysregulayion?

If glutamate decreases, what happens to the glutamate-NO-cGMP pathway in the brain?

References:

1. Fluge et al: Metabolic profiling indicates impaired pyruvate dehydrogenase function in myalgic encephalopathy / chronic fatigue syndrome. JCI Insight. 2016; 1(21):e89376. Doi 10.1172/jci.insight.89276
2. Rajagopalan et al. Metabolic plasticity maintains proliferation in pyruvate dehydrogenase deficient cells. Cancer & Metabolism (2015) 3:7
3. Du et al. Inhibition of mitochondrial pyruvate transport by Zaprinast couses massive accumulation of aspartate at the expence of glutamate in the retina. Journal of Biological Chemistry 288,50,dec 2013
4. Ciregia et al.
   Translational Psychiatry (2016), 6, e904
   doi:10.1038/tp.2016.184
5. Schutzer et al: Distinct Cerebrospinal Fluid Proteomes Differentiate Post- Treatment Lyme Disease from Chronic Fatigue Syndrome. PLOS One February 2011, volume 6, Issue 2
6. Armstrong et al. Metabolic profiling reveals anomalous energy metabolism and oxidative stress pathways in CFS. Metabolomics, 2015, 11:1626-1639.
7. Dikoma C Shungu et al. Increased Ventricular lactate in chronic fatigue syndrome. III. Relationships to cortical glutathione and clinical symptoms implicate oxidative stress in disorder oathophysiology. NMR Biomed (2012)

nAChR, agrin, rapsyn and ME

Nicotinic acatylcholine receptors (nAChRs) are suspected to be involved in the ME pathomechanism (1).

ME patients have dysregulated lipid metabolism (2). This could have an impact on lipid rafts?

Lipid rafts serve as signaling platforms for nAChRs clustering. The clustering is induced by the heparan sulphate proteoglyan, agrin. The nAChRs are anchored into the lipid rafts by rapsyn (3).

A proteomic study on cerebrospinal fluid from ME patients has shown an upregulation of the arin precursor and of the heparan sulfate proteoglyan core protein precursor (4).

The gene RAPSN (protein: rapsyn) has been found epigenetic changed (hypermethylated) in ME (5).

References:

1. Griffith University. https://www.griffith.edu.au/health/national-centre-neuroimmunology-emerging-diseases
2. Naviaux et al: Metabolic features of CFS. www.pnas.org/cgi/doi/10.1073/pnas.1607571113
3. Allen et al: Lipid raft microdomains and neurotransmitter signalling. Nature Reviews, feb 2007, vol 8.
4. Schutzer et al: Distinct Cerebrospinal Fluid Proteomes Differentiate Post- Treatment Lyme Disease from Chronic Fatigue Syndrome. PLOS One February 2011, volume 6, Issue 
5. Vega et al. DNA methylation Modifications associated with CFS. Plos One, aug 2014, vol 9, Issue 8, e104757

Pyruvate and ME/POTS

Fluge, Mella et al. have shown that ME is associated with defective oxidative metabolism - most likely involving impaired pyruvate dehydrogenase function (1).

Expression of the protein mitochondrial pyruvate carrier 2 (MCC2) has been found downregulated in ME (2)

The gene similar to pyruvate kinase-isozymes M1/M2 (PKM2) has been found epigenetic changed (hypermethylated) in ME (3).

Immunoreactive proteins against IgGs from POTS patients (4, 5):

• ODPB, pyruvate dehydrogenase E1 component subunit beta.
• KPYM, pyruvate kinase isoenzyme M1.
• PDHX, pyruvate dehydrogenase protein X component.
• PKM2, pyruvate kinase isozymes M1/M2

References:

1.  Fluge et al: Metabolic profiling indicates impaired pyruvate dehydrogenase function in myalgic encephalopathy / chronic fatigue syndrome. JCI Insight. 2016; 1(21):e89376. Doi 10.1172/jci.insight.89276
2. Ciregia et al.
   Translational Psychiatry (2016), 6, e904
   doi:10.1038/tp.2016.184
3. Vega et al. DNA methylation Modifications associated with CFS. Plos One, aug 2014, vol 9, Issue 8, e104757
4. Wang et al: Autoimmunoreactive IgGs from patients with POTS. Prot. Clin. Appl. 2012, 6, 1-11.
5. Wang et al: Autoimmunoreactive IgGs against cardiac lipid raft-associated proteins in patients with POTS. doi: 10.1016/j.trsl.2013.03.002

T-celler og lipid rafts

Forskning viser, at ME patienter har dysreguleret metabolisme, der påvirker sphingolipider (især ceramider) og kolesterol.

Disse lipider er særligt koncentrerede i områder i cellemembranen, der kaldes lipid rafts. Områderne er vigtige for mange forskellige cellesignaler.

Der sker en samling (eng: clustering) af receptorer i lipid rafts. Her kan receptorer bindes til deres ligand, og en celleproces udløses.

En lipid raft skal have den korrekte sammensætning af lipider for normal og optimal funktion af T-celle receptoren.

I den autoimmune sygdom, lupus, bidrager dysreguleret ceramid sammensætning til dysreguleret T-celle receptor.

Er ME patienters T-celle funktion påvirket af dysregulerede lipid rafts, som følge af dysreguleret lipidomsætning?

T-celler og apoptose

Apoptose er programmeret celledød. For at holde immunsystemet i balance skal der være ligevægt mellem pro-apoptopic og anti-apoptopic signalering. Det foregår ud fra lipid rafts.

Der indgår mange gener og hermed proteiner i apoptose-stivejene.

CD95/CD95L også kaldet Fas og Fasligand kan igangsætte apoptose i T-celler. Mus der mangler dette system udvikler en lupus-ligende autoimmun sygdom.

Ceramid dannet i cellemembranen er vigtig for at kunne medføre clustering af CD95 og efterfølgende apoptose.

Hvordan og om systemet er dysreguleret hos ME patienter ved jeg ikke. Men et studie har vist epigenetiske ændringer i gener, der er involveret i sphingolipid, ceramide og apoptose stiveje. Her er nogle ad dem:

Hypomethylerede gener: FASLG, FAIM3, DIABLO, PDCD1, TNFSF10 (TRAIL), S1PR1, PRKCQ (PKC.theta er vigtig for TCR/CD3 medieret T-celle aktivering og induktion af FASLG ekspression).

Hypermethylerede gener: AATK, ACIN1, BMF, PDCD11, S1PR2, SGMS2 (=sphingomyelinsynthase 2), LASS6 (=ceramide synthase 6), PRKCZ (PKC zeta aktiveres af ceramid og er involveret i pro-apoptolic funktion).

ME puslespilsbrikkerne er der. Vi skal bare have forskere med tung biokemisk og immunologisk viden til at samle dem.

Reference:
Vega et al. DNA methylation Modifications associated with CFS. Plos One, aug 2014, vol 9, Issue 8, e104757

Find et autoantistof - og læs i Wikipedia!

ME/CFS, POTS og MCS er sygdomme med stor symptomoverlap, og er måske endda forskellige sider af samme sygdom.

ME/CFS er især karakteriseret ved motionsintolerance. POTS er en form for ortostatisk intolerance. MCS er reaktion på dufte under enhver toksikologisk grænseværdi.

Der er påvist autoantistoffer mod den adrenerge receptor alfa1AR hos POTS patienter. Det forstyrrer receptorens funktion. (1)

Wikipedia oplyser, at alfa1AR:

• påvirker muskler under motion.
• påvirkes af nogle typer medicin, så der udløses ortostatisk hypotension.
• øger inhibering i lugte-systemet.

Interessant sammenhæng!

Interessant er det også, at ME/CFS patienter har genetiske variationer (SNPs) i generne for alfa1AR, muscarinM3 og TRPC4 receptor. Alle receptorer er både involveret i regulering af blodkarsammentrækning / udvidelse og i regulering af inhibering af lugtsystemet (2 og 3).

Referencer:

1. Fedorowski et al: Antiadrenergic aytoimmunity in POTS. doi: 10.1093/europace/euw 154
2. Griffith University https://www.griffith.edu.au/health/national-centre-neuroimmunology-emerging-diseases
3. Mammalian Transient Receptor Potential (TRP) Cation Channels. Handbook of Experimental Pharmacology www.springer.com/series/164 volumen1,222 Editors: Bernd Nilius, Veit Flockerzi.