Category Archives: Medicine in general

Good luck, RBG

Once again the press seems to dancing around a serious health problem of major public figure without saying just what it is.  Just about everyone admires RBG, but saying “The tumor was treated definitively and there is no evidence of disease elsewhere in the body” as the Supreme Court announced yesterday sounds wonderful doesn’t it?  Except that it isn’t.  8 months ago she had two metastatic tumors removed from her lung.  Sometimes it is possible to tell the tissue of origin from slides made from the tumors, but, as far as I can tell, this information was never released.  Now they say there is no sign of tumor elsewhere in her body (just as they said 8 months ago).

One hopes for the best for her.  Agree or disagree with her political philosophy, she is an admirable, brilliant and likable individual who has overcome a lot over the years.

Unfortunately Justice Ginsburg has metastatic cancer.  Her prognosis is not good.  As President Trump said “I’m hoping she’s going to be fine. She’s pulled through a lot. She’s strong, very tough.”

She had better be.

Addendum 28 August ’19

We’ll see how the right responds when RBG passes.  Here’s leftist folk hero Bill Maher on the death of one of the Koch brothers.  There are other similar responses.

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What can dogs tell us about cancer, and (wait for it) sexually transmitted disease

What can 546 dogs tell us about cancer, and STDs (sexually transmitted diseases)?  An enormous amount ! [ Science vol 365 pp. 440 – 441, 464 3aau9923 1 –> 7 ’19 ].  You may have heard about the transmissible tumor that has reduced the Tasmanian Devil population from its appearance in ’96 by 80%.  The animals bite each other transmitting the tumor.  Only 10 – 100 cells are transferred, but death occurs within a year.  The cells survive because Tasmanian devels have low genetic diversity.

The work concerns a much older transmissible tumor (Canine Transmissible Venereal Tumor — aka CTVT) which appeared in Asia an estimated 6,000 year ago, and began dispersing worldwide 2,000 years ago.   Unlike the Tasmanian devil tumor, the tumor is usually cleared by the immune system.

The Science paper has 80+ authors from all over the world, who sequenced the protein coding part of the dog genome (the exome) to a > 100fold depth.   The exome contains 43.6 megabases.   The tumor is transmitted by sex, and the authors note that this mode of transmission nearly requires a rather indolent clinical course, as the animal must survive long enough to transmit the organism again.  This fits with syphilis, AIDs, gonorrhea.  Contrast this with anthrax, cholera, plague which spread differently and kill much faster.

So what does CTVT tell us about cancer?   Quite a bit.  First some background.  The Cancer Genome Atlas (CGA) was criticized as being a boondoggle, but it at least gave us an idea of how many mutations are present in various cancers– around 100 in colon and breast cancers.

Viewed across all dogs, the CTVT genome is riddled with somatic mutations (as compared to the genome of the dog carrying the tumor) –148,030 single nucleotide variants (3.4/1000 !) 12,177 insertion/deletions.  Of the 20,000 dog genes only 2,000 didn’t contain a mutation.   This implies that most genes in the mammalian genome aren’t needed by the cancer cells.  The CTVTs also show no signs of the high rates of chromosomal instability seen in human tumors.

The work provides evidence that cancer isn’t inherently progressive.  This gives hope that some relatively indolent human cancers (say cancer of the prostate) can be controlled.  This calls for ‘adaptive therapy’  — something that limits tumor  growth rather than trying to kill every cancer cell with curative therapy which, if it fails, essentially selects for more aggressive cancer cells.

Some 14,412 genes have 1 mutation changing the amino acid sequence (nonSynonymous) and 5,704 have protein truncating mutations.  The ratio of synonymous to non synonymous mutations is about 3 implying that the mutations which have arisen haven’t been selected for (after all the triplet code for 20 amino acids and 1 stop codon has 64 possibilities), so the average amino acid has 3 codons for it.  This is called neutral genetic drift.

They also found 5 mutated genes present in all 541 tumors — these are the driver mutations, 3 are well known, MYC, PTEN, and retinoblastoma1.

Tons to think about here.  I’ll be away for a few weeks traveling and playing music, but this work should keep you busy thinking about its implications.

 

 

Antioxidants — the dark side

There was (and probably still is) quite a vogue for antioxidants.  They were supposed to counteract aging, vascular disease, and prevent cancer.  So much so that 25 years ago, they were given in a trial to prevent lung cancer.  It didn’t work.  Here are the gory details

[ New England J. Med. vol. 330 pp. 1029 – 1035 ’94 ] The Alpha-Tocopherol, Beta-Carotene Trial (ATBC trial)  randomized double blind placebo controlled of daily supplementation with alpha-tocopherol (a form of vitamin E), beta carotene or both to see if it reduced the incidence of lung cancer was done in 29000 Finnish male smokers ages 50 – 69 (when most of the damage had been done).  They received either alpha tocopherol 50 mg/day, beta carotene 20 mg/day or both.   There was a high incidence of lung cancer (876/29000) during the 5 – 8 year period of followup.  Alpha tocopherol didn’t decrease the incidence of lung cancer, and there was a higher incidence among the men receiving beta carotene (by 18%).    Alpha tocopherol had no benefit on mortality (although there were more deaths from hemorrhagic stroke among the men receiving the supplement).   Total mortality was 8% higher among the participants on beta carotene (more deaths from lung cancer and ischemic heart disease).  It is unlikely that the dose was too low, since it was much higher than the estimated intake thought to be protective in the uncontrolled dietaryt studies.   The trial organizers were so baffled by the results that they even wondered whether the beta-carotene pills used in the study had become contaminated with some known carcinogen during the manufacturing process.  However, tests have ruled out that possibility.

Needless to say investigators in other beta carotene clinical trials (the Women’s Health Study, the Carotene and Retinoid Efficacy Trial) are upset.  [ Science vol. 264 pp. 501 – 502 ’94 ]  “In our heart of hearts, we don’t believe [ beta carotene is ] toxic”  says one researcher.

This is not science.

On to the present [ Cell vol. 178 pp. 265 – 267, 316 – 329, 330 – 345 ’19 ] in which the following appears “Recent evidence ‘suggests’ that antioxidants can also promote tumor formation”

The work concerns an animal model of nonsmallcell lung cancer (NSCLC).  I’m always wary of animal models, as they have been so useless in pointing to a useful therapy for stroke.  But the model is worth studying as it provides a mechanism by which antioxidants promote metastases of the primary tumor.  It is also worth studying because it shows the fiendish complexity of cellular biochemistry and physiology.

The only way you can appreciate complexity is by being buried in details. So let’s begin.  The actual details aren’t that important, just the number and the intricacy of them.

30% of humans with NSCLC have mutations in two genes (NFEL2L2, KEAP1).  The mutation in NFEL2L2 produces mutated NRF2 (a transcriptional activator of the antioxidant response gene set). The mutation doesn’t inactivate NRF2, but leaves it in a hyperactivated state.  KEAP1 normally inactivates NRF2, but not the mutated forms found in NSCLC.

One gene turned on by activated NRF2 is HO1 (heme oxidase).  During oxidative stress heme is released from heme containing resulting elevated intracellular heme lever resulting in the creation of free radicals which are inherently oxidative.  HO1 destroys heme. So this is one mechanisms of NRF2’s antioxidative activity.

Heme isn’t all bad, as it destabilizes BACH1 (not the composer)which is a prometastatic transcription factor.  Antioxidants (N-acetyl-cysteine, tocopherol [ vitamin E to you ] reduce heme levels stabilizing BACH1 (hence promoting metastasis).  Genes activated by BACH1 include glycolytic enzymes (hexokinase2, GAPDH).  So what?  Cancer cells use a lot of glycolytic enzymes even when oxygen is available — this is called aerobic glycolysis.  This is the Warburg effect.

I’m sure there’s far more to discover, but this should be enough to convince you that things are pretty complicated inside us.

The wages of inbreeding

Saguenay Lac St. Jean is a beautiful region of Quebec. It’s fairly isolated. Once you get to the top of the lake there is no way that you can drive farther north (no road).  We spent part of our 25th anniversary there.  The population bears a heavy load of genetic disease (through no fault of their own).

The reason is historical. Only 8,000 people emigrated from France to Quebec between 1608 and 1763. After the English victory that year  only 1,000 emigrated in the next 90 years.  In 1992, the population of the Saguenay  region was around 300,000 and Quebec itself 2,000,000.

This means that once the population began expanding with relatively little outside input, recessive genes began to meet each other, as in a large population there are so many more ways to make this happen than in a small one.

To keep the the nonBiologists reading this aboard, here is what recessive means. Our genome has 46 chromosomes.  We all have two sex chromosomes (either X and Y or X and X).  The other 44 chromosomes come in pairs.  This gives you two copies of each gene.  The classic recessive gene is that for sickle cell anemia.  If just one of the pair has the Sickle trait you are OK, if both have it, you have sickle cell anemia (which you definitely don’t want to have).  Actually if you live in Africa it is better if you have one gene with the trait as it makes you more resistant to Malaria.  This is why the trait became so common in Africans.  It’s natural selection in action (and in a human population to boot).  Just one good sickle gene (not carrying the trait) is enough to mask the effects of the bad gene, so the carrier is normal.   This is why sickle cell trait is called a recessive gene.

Here is one example.  The incidence of a muscle disease (myotonic dystrophy) worldwide is 2 – 14/100,000.  In the Saguenay region it is 189/100,000.

Even 20 years ago, the carrier frequency of many genetic disorders up there was quite high [ Proc. Natl. Acad. Sci. vol. 95 pp. 15140 – 15144 ’98 ]

Spastic ataxia 1/21

Type I tyrosinemia 1/22

Sensorimotor polyneuropathy 1/23

Pseudovitamin D deficient rickets 1/26

Cytochrome C oxidase deficiency 1/26

Cystinosis 1/39

Histidase 1/32

Lipoprotein lipase 1/43

Pyruvic kinase 1/64

Then again, there are all sorts of genetic diseases found only in this region.

Similar conditions may apply to the ancestors of today’s native Americans — for details see the previous post — https://luysii.wordpress.com/2019/07/16/the-initial-native-americans-were-quite-inbred/.  Incredible as it may sound, the rape and pillage of the conquistadores may have actually been good from a genetic point of view.  Similar considerations may apply to any pair of populations meeting each other for the first time.  Hard stuff indeed, but you can’t repeal biology.

So, from a genetic point of view, it’s good if you reproduce with someone from a different group.  It’s why I’m glad to have a Chinese daughter in law, 2 grand-nephews whose father is Hindu, and a Russian woman about to marry our nephew.

 

 

How general anesthesia works

People have been theorizing how general anesthesia works since there has been general anesthesia.  The first useful one was diethyl ether (by definition what lipids dissolve in).  Since the brain has the one of the highest fat contents of any organ, the mechanism was obvious to all.  Anesthetics dissolve membranes.  Even the newer anesthetics look quite lipophilic — isoflurane CF3CHCL O CF2H screams (to the chemist) find me a lipid to swim in.  One can show effects of lipids on artificial membranes but the concentrations to do so are so high they would be lethal.

Attention shifted to the GABA[A] receptor, because anesthetics are effective in potentiating responses to GABA  — all the benzodiazepines (valium, librium) which bind to it are sedating.  Further evidence that a protein is involved, is that the optical isomers of enflurane vary in anesthetic potency (but not by very much — only 60%).  Lipids (except cholesterol) just aren’t optically active.  Interestingly, alfaxolone is a steroid and a general anesthetic as well.

Well GABA[A] is an ion channel, meaning that its amino acids form alpha helices which span the membrane (and create a channel for ion flow).  It would be devilishly hard to distinguish binding to the transmembrane part from binding to the membrane near it. [ Science vol. 322 pp. 876 – 880 2008 ] Studied 4 IV anesthetics (propofol, ketamine, etomidate, barbiturate) and 4 gasses (nitrous  oxide, isoflurance, devoflurane, desflurane) and their effects on 11 ion channels — unsurprisingly all sorts of effects were found — but which ones are the relevant.

All this sort of stuff could be irrelevant, if a new paper is actually correct [ Neuron vol. 102 pp. 1053 – 1065 ’19 ].  The following general anesthetics (isoflurane, propofol, ketamine and desmedtomidine) all activate cells in the hypothalamus (before this anesthetics were thought to work by ultimately inhibiting neurons).  They authors call these cells AANs (Anesthesia Activated Neurons).

They are found in the hypothalamus and contain ADH.  Time for some anatomy.  The pituitary gland is really two glands — the adenohypophysis which secretes things like ACTH, TSH, FSH, LH etc. etc, and the neurohypophysis which secretes oxytocin and vasopressin (ADH) directly into the blood (and also into the spinal fluid where it can reach other parts of the brain.  ADH release is actually from the axons of the hypothalamic neurons.  The AANs activated by the anesthetics release ADH.

Of course the workers didn’t stop there — they stimulated the neurons optogenetically and put the animals to sleep. Inhibition of these neurons shortened the duration of general anesthesia.

Fascinating (if true).  The next question is how such chemically disparate molecules can activate the AANs.  Is there a common receptor for them, and if so what is it?

Happy fiscal new year !

A sad (but brilliant) paper about autophagy

Over the past several decades I’ve accumulated a lot of notes on autophagy (> 125,000 characters).  It’s obviously important, but in a given cell or disease (cancer, neurodegeneration) whether it helps a cell die gracefully or is an executioner is far from clear.  Ditto for whether enhancing or inhibiting it in a given situation would be helpful (or hurtful).

A major reason for the lack of clarity despite all the work that’s been done can be found in the following excellent paper [ Cell vol. 177 pp.1682 – 1699 ’19 ].  Some 41 proteins are involved in autophagy in yeast and more in man.  Many are described as ATGnn (AuTophagy Gene nn).

Autophagy is a complicated business: forming a membrane, then engulfing various things, then forming a vacuole,  then fusing with the lysosome so that the engulfees are destroyed.

The problem with previous work is that if a protein was found to be important in autophagy, it was assumed to have that function and that function only.   The paper shows that core autophagy proteins are involved in (at least) 5 other processes (endocytosis, melanocyte formation, cytokinesis, LC3 assisted phagocytosis and translocation of vesicles from the Golgi to the endoplasmic reticulum).

Experiments deleting or  increasing a given ATGnn were assumed to produce their biological effects by affecting autophagy.

The names are unimportant.  Here is a diagram of 6 autophagy proteins forming a complex producing autophagy

1 2 3

4 5 6

So 2 binds to 1, 3 and 5

But in endocytosis

1 2 3

5

form an important complex

In cytokinesis the complex formed by

2 3

5

is important.

Well you get the idea.  Knocking out 2 has cellular effects on far more than autophagy.  So a lot of work has to be re-thought and probably repeated.

Notice that all 6 functions involve movement of membranes.  So just regard the 6 proteins as gears of different diameters which can form the guts of different machines as they combine with each other (and proteins specific to the other 5 processes mentioned) to move things around in the cell.

Set points, a mechanism for one at last.

Human biology is full of set points.  Despite our best efforts few can lose weight and keep it off.  Yet few count calories and try to eat so their weight is constant.  Average body temperature is pretty constant (despite daily fluctuations).  Neuroscientists are quite aware of synaptic homeostasis.

And yet until now, despite their obvious existence, all we could do is describe setpoints, not explain the mechanisms behind them.  Most ‘explanations’ of them were really descriptions.

Here is an example:

Endocrinology was pretty simple in med school back in the 60s. All the target endocrine glands (ovary, adrenal, thyroid, etc.) were controlled by the pituitary; a gland about the size of a marble sitting an inch or so directly behind the bridge of your nose. The pituitary released a variety of hormones into the blood (one or more for each target gland) telling the target glands to secrete, and secrete they did. That’s why the pituitary was called the master gland back then.  The master gland ruled.

Things became a bit more complicated when it was found that a small (4 grams or so out of 1500) part of the brain called the hypothalamus sitting just above the pituitary was really in control, telling the pituitary what and when to secrete. Subsequently it was found that the hormones secreted by the target glands (thyroid, ovary, etc.) were getting into the hypothalamus and altering its effects on the pituitary. Estrogen is one example. Any notion of simple control vanished into an ambiguous miasma of setpoints, influences and equilibria. Goodbye linearity and simple notions of causation.

As soon as feedback (or simultaneous influence) enters the picture it becomes like the three body problem in physics, where 3 objects influence each other’s motion at the same time by the gravitational force. As John Gribbin (former science writer at Nature and now prolific author) said in his book ‘Deep Simplicity’, “It’s important to appreciate, though, that the lack of solutions to the three-body problem is not caused by our human deficiencies as mathematicians; it is built into the laws of mathematics.” The physics problem is actually much easier than endocrinology, because we know the exact strength and form of the gravitational force.

A recent paper [ Neuron vol. 102 pp. 908 – 910, 1009 – 1024 ’19 ] is the first to describe a mechanism behind any setpoint and one of particular importance to the brain (and possibly to epilepsy as well).

The work was done at significant remove from the brain — hippocampal neurons grown in culture.  They synapse with each other, action potentials are fired and postsynaptic responses occur.  The firing rate is pretty constant.  Block a neurotransmitter receptor, and the firing rate increases to keep postsynaptic responses the same.  Increase the amount of neurotransmitter released by an action potential (neuronal firing) and the firing rate descreases.  This is what synaptic homeostasis is all about.  It’s back to baseline transmission across the synapse regardless of what we do, but we had no idea how this happened.

Well we still don’t but at least we know what controls the rate at which hippocampal neurons fire in culture (e.g. the setpoint).  It has to do with an enzyme (DHODH) and mitochondrial calcium levels.

DHODH stands for Di Hydro Orotate DeHydrogenase, an enzyme in mitochondria involved in electron transfer (and ultimately energy production).   Inhibit the enzyme (or decrease the amount of DHODH around) and the neurons fire less.  What is interesting about this, that all that is changed is the neuronal firing rate (e.g. the setpoint is changed).  However, there is no change in the intrinsic excitability of the neurons (to external electrical stimulation), the postsynaptic response to transmitter, the number of mitochondria, presynaptic ATP levels etc.

Even better, synaptic homeostasis is preserved.  Manipulations increasing or decreasing the firing rate are never permanent, so that changes back to the baseline rate occur.

Aside from its intrinsic intellectual interest, this work is potentially quite useful.  The firing rate of neurons in people with epilepsy is increased.  It is conceivable that drugs inhibiting DHODH would treat epilepsy.  Such drugs (teriflunomide) are available for the treatment of multiple sclerosis.

The paper has some speculation of how DHODH inhibition would lead to decreased neuronal firing (changes in mitochondrial calcium levels etc. etc) which I won’t go into here as it’s just speculation (but at least plausible spectulation).

Will flickering light treat Alzheimer’s disease ? — Take II

30 months ago, a fascinating paper appeared in which flickering light improved a mouse model of Alzheimer’s disease.  The authors (MIT mostly) have continued to extend their work.   Here is a copy of the post back then.  Their new work is summarized after the ****

Big pharma has spent zillions trying to rid the brain of senile plaques, to no avail. A recent paper shows that light flickering at 40 cycles/second (40 Hertz) can do it — this is not a misprint [ Nature vol. 540 pp. 207 – 208, 230 – 235 ’16 ]. As most know the main component of the senile plaque of Alzheimer’s disease is a fragment (called the aBeta peptide) of the amyloid precursor protein (APP).

The most interesting part of the paper showed that just an hour or so of light flickering at 40 Hertz temporarily reduced the amount of Abeta peptide in visual cortex of aged mice. Nothing invasive about that.

Should we try this in people? How harmful could it be? Unfortunately the visual cortex is relatively unaffected in Alzheimer’s disease — the disease starts deep inside the head in the medial temporal lobe, particularly the hippocampus — the link shows just how deep it is -https://en.wikipedia.org/wiki/Hippocampus#/media/File:MRI_Location_Hippocampus_up..png

You might be able to do this through the squamous portion of the temporal bone which is just in front of and above the ear. It’s very thin, and ultrasound probes placed here can ‘see’ blood flowing in arteries in this region. Another way to do it might be a light source placed in the mouth.

The technical aspects of the paper are fascinating and will be described later.

First, what could go wrong?

The work shows that the flickering light activates the scavenger cells of the brain (microglia) and then eat the extracellular plaques. However that may not be a good thing as microglia could attack normal cells. In particular they are important in the remodeling of the dendritic tree (notably dendritic spines) that occurs during experience and learning.

Second, why wouldn’t it work? So much has been spent on trying to remove abeta, that serious doubt exists as to whether excessive extracellular Abeta causes Alzheimer’s and even if it does, would removing it be helpful.

Now for some fascinating detail on the paper (for the cognoscenti)

They used a mouse model of Alzheimer’s disease (the 5XFAD mouse). This poor creature has 3 different mutations associated with Alzheimer’s disease in the amyloid precursor protein (APP) — these are the Swedish (K670B), Florida (I716V) and London (V717I). If that wasn’t enough there are two Alzheimer associated mutations in one of the enzymes that processes the APP into Abeta (M146L, L286V) — using the single letter amino acid code –http://www.biochem.ucl.ac.uk/bsm/dbbrowser/c32/aacode.html.hy1. Then the whole mess is put under control of a promoter particularly active in mice (the Thy1 promoter). This results in high expression of the two mutant proteins.

So the poor mice get lots of senile plaques (particularly in the hippocampus) at an early age.

The first experiment was even more complicated, as a way was found to put channelrhodopsin into a set of hippocampal interneurons (this is optogenetics and hardly simple). Exposing the channel to light causes it to open the membrane to depolarize and the neuron to fire. Then fiberoptics were used to stimulate these neurons at 40 Hertz and the effects on the plaques were noted. Clearly a lot of work and the authors (and grad students) deserve our thanks.

Light at 8 Hertz did nothing to the plaques. I couldn’t find what other stimulation frequencies were used (assuming they were tried).

It would be wonderful if something so simple could help these people.

For other ideas about Alzheimer’s using physics rather than chemistry please see — https://luysii.wordpress.com/2014/11/30/could-alzheimers-disease-be-a-problem-in-physics-rather-than-chemistry/

****

The new work appears in two papers.

First [ Cell vol. 1777 pp. 256 – 271 ’19 ] 7 days of auditory tone stimuli at 40 cycles/second (40 Hertz) for just one hour a day reduced amyloid in the auditory cortex of the same pathetic mice described above (the 5XFAD mice).  They call this GENUS (Gamma ENtrainment Using sensory Stimuli).  Neurologists love to name frequencies in the EEG, and the 40 Hertz is in the gamma range.

The second paper [ Neuron vol. 102 pp. 929 – 943 ’19 ] is even better.  Alzheimer’s disease is characterized by two types of pathology — neurofibrillary tangles inside the remaining neurons and the senile plaque outside them.  The tangles are made of the tau protein, the plaques mostly of fragments of the amyloid precursor protein (APP).  The 5XFAD mouse had 3 separate mutations in the APP and two more in the enzyme that chops it up.

The present work looked at the other half of Alzheimer’s the neurofibrillary tangle.  They had mice with the P301S mutation in the tau protein found in a hereditary form of dementia (not Alzheimer’s) and also with excessive levels of CK-p25 which also results in tangles.

Again chronic visual GENUS worked in this (completely different) model of neurodegeneration.

This is very exciting stuff, but I’d love to see a different group of researchers reproduce it.  Also billions have been spent and lost on promising treatments of Alzheimer’s (all based on animal work).

Probably someone is trying it out on themselves or their spouse.  A EE friend notes that engineers have been trying homebrew transcranial magnetic and current stimulation using themselves or someone close as guineapigs for years.

What is legionella trying to tell us?

10 years out of Med School, a classmate in the Public Health service had to deal with the first recognized outbreak of Legionnaire’s disease, at the Bellevue Stratford hotel in Philly, about one air mile from Penn Med where we went.   The organism wasn’t known at the time and caused 182 cases with 29 deaths.  We’ve learned a lot more about Legionella Pneumophila since 1976 and the organism continues to instruct us.

The most recent lesson concerns one of the 300 or so proteins Legionella injects into a cell it attacks.  This is remarkable in itself.  The organism uses them to hijack various cellular mechanisms to build a home for itself in the cell (the LCV — Legionella Containing Vacuole).  Contrast this with diphtheria which basically uses one protein (diphtheria toxin) to kill the cell.

One of the 300 proteins is called SidJ and looks like a protein kinase (of which our genome has over 500).  However [ Science vol. 364 pp. 787 – 792 ’19 ] shows that SidJ carries out a different different reaction.SidJ is activated by host-cell calmodulin to polyglutamylate the SidE family of ubiquitin (Ub) ligases inhibiting them. Crystal structures of the SidJ-calmodulin complex reveal a protein kinase fold that catalyzes ATP-dependent isopeptide bond formation between the amino group of free glutamate and the gamma carboxyl group in the catalytic center of SidE a ubiquitin ligase.   This, instead of just esterifying the hydroxyl group of serine or threonine or tyrosine with the terminal phosphate of ATP as a kinase is supposed to do.

Why is this important? The only protein known to have polyglutamic acid added to it is tubulin, the protein from which microtubules (neurotubules to the neurologist).  The work is important because some of the 500+ protein kinases in our genome might be doing something else.  Has the chemistry each and every member of the group been studied?  Probably not..

The authors close with “In summary, our results underscore the diversity and catalytic versatility of the protein kinase superfamily. We propose that ATP-dependent ligation reactions may be a common feature among the vast diversity of eukaryotic protein kinase–like enzymes found in nature (25). There are more than 500 protein kinases in humans and our results suggest that they should be ex- amined for alternative activities.”

I couldn’t agree more.

RIPK1

The innate immune system is intrinsically fascinating, dealing with invaders long before antibodies or cytotoxic cells are on the scene.  It is even more fascinating to a chemist because it works in part by forming amyloid inside the cell.  And you thought amyloid was bad.

The system becomes even more fascinating because blocking one part of it (RIPK1) may be a way to treat a variety of neurologic diseases (ALS, MS,Alzheimer’s, Parkinsonism) whose treatment could be improved to put it mildly.

One way to deal with an invader which has made it inside the cell, is for the cell to purposely die.  More and more it appears that many forms of cell death are elaborately programmed (like taking down a stage set).

Necroptosis is one such, distinct from the better known and studied apoptosis.   It is programmed and occurs when a cytokine such as tumor necrosis factor binds to its receptor, or when an invader binds to members of the innate immune system (TLR3, TLR4).

The system is insanely complicated.  Here is a taste from a superb review — unfortunately probably behind a paywall — https://www.pnas.org/content/116/20/9714 — PNAS vol. 116 pp. 9714 – 9722 ’19.

“RIPK1 is a multidomain protein comprising an N-terminal kinase domain, an intermediate domain, and a C-terminal death domain (DD). The intermediate domain of RIPK1 contains an RHIM [receptor interacting protein (rip) homotypic interaction motif] domain which is important for interacting with other RHIM-containing proteins such as RIPK3, TRIF, and ZBP1. The C-terminal DD mediates its recruitment by interacting with other DD-containing proteins, such as TNFR1 and FADD, and its homodimerization to promote the activation of the N-terminal kinase domain. In the case of TNF-α signaling, ligand-induced TNFR1 trimerization leads to the assembly of a large receptor-bound signaling complex, termed Complex I, which includes multiple adaptors (TRADD, TRAF2, and RIPK1), and E3 ubiquitin ligases (cIAP1/2, LUBAC complex).”

Got that?  Here’s a bit more

“RIPK1 is regulated by multiple posttranslational modifications, but one of the most critical regulatory mechanisms is via ubiquitination. The E3 ubiquitin ligases cIAP1/2 are recruited into Complex I with the help of TRAF2 to mediate RIPK1 K63 ubiquitination. K63 ubiquitination of RIPK1 by cIAP1/2 promotes the recruitment and activation of TAK1 kinase through the polyubiquitin binding adaptors TAB2/TAB3. K63 ubiquitination also facilitates the recruitment of the LUBAC complex, which in turn performs M1- type ubiquitination of RIPK1 and TNFR1. M1 ubiquitination of Complex I is important for the recruitment of the trimeric IκB kinase complex (IKK) through a polyubuiquitin-binding adaptor subunit IKKγ/NEMO . The activation of RIPK1 is inhibited by direct phosphorylation by TAK1, IKKα/β, MK2, and TBK1. cIAP1 was also found to mediate K48 ubiquitination of RIPK1, inhibiting its catalytic activity and promoting degradation.”

So why should you plow through all this?  Because inhibiting RIPK1 reduces oxygen/glucose deprivation induced cell death in neurons, and reduced infarct size in experimental middle cerebral artery occlusion.

RIPK1 is elevated in MS brain, and inhibition of it helps an animal model (EAE).  Mutations in optineurin, and TBK1 leading to familial ALS promote the onset of RIPK1 necroptosis

Inflammation is seen in a variety of neurologic diseases (Alzheimer’s, MS) and RIPK1 is elevated in them.

Inhibitors of RIPK1 are available and do get into the brain.  As of now two RIPK1 inhibitors have made it through phase I human safety trials.

So it’s time to try RIPK1 inhibitors in these diseases.  It is an entirely new approach to them.  Even if it works only in one disease it would be worth it.

Now a dose of cynicism.  Diseased cells have to die one way or another.  RIPK1 may help this along, but it tells us nothing about what caused RIPK1 to become activated.  It may be a biomarker of a diseased cell.  The animal models are suggestive (as they always are) but few of them have panned out when applied to man.