Treating KCC2 Down-Regulation in Autism, Rett/Down Syndromes, Epilepsy and Neuronal Trauma ?

In this composite image, a human nerve cell derived from a patient with Rett syndrome shows significantly decreased levels of KCC2 compared to a control cell.  This will be equally true of about 50% people with classic autism, people with Down syndrome, many with TBI and many with epilepsy

In a recent post I highlighted an idea from the epilepsy research to treat a common phenomenon also found in much classic autism.  Neurons are in an immature state with too much intracellular chloride, the transporter that brings it in, called NKCC1, is over-expressed and the one that takes it out, KCC2, is under-expressed.  The net result is high levels of intracellular chloride and this leaves the brain in an over-excited state (GABA working in reverse) reducing cognitive function and with a reduced threshold to seizures.

The epilepsy research noted that increased BDNF is one factor that down regulates KCC2, which would have taken chloride out of the cells.  So it was suggested to block BDNF, or something closely related called trkB.

Unfortunately there is no easy way to this.  But I did some more digging and found various other ways to upregulate KCC2.

There is indeed a clever safe way that may achieve this and it is a therapy that I have already suggested for other reasons, intranasal insulin.

BDNF is a neurotrophin and other neurothrophins also have the ability to regulate KCC2. IGF-1 is another such neurotrophin and we even have very recent experimental data showing its effect on KCC2.

Regular readers will know that several trials with IGF-1, or analogs thereof, are underway.

I actually am rather biased against IGF-1 as a therapy, since in my son’s case the level of IGF-1 in blood is already high.  So I do not want to inject him with IGF-1 or even give him an oral analog.

However by using intranasal insulin the effect would be just within the CNS and insulin binds at the same receptors as IGF-1. So if IGF-1 upregulates KCC2 so will insulin.

We know from extensive existing trial data and direct feedback from one researcher that intranasal insulin is well tolerated and has no effect outside the CNS.

So rather to my surprise there seems to be a safe, cheap way to treat KCC2 down-regulation and this would also be applicable in epilepsy, traumatic brain injury (TBI) and any other condition involving immature neurons or neuronal trauma. 

The Science

There is a very thorough recent review paper that looks at all the ways that KCC2 expression is regulated.

Current view on the functional regulation of the neuronal K⁺-Cl⁻ cotransporter KCC2

The epilepsy researchers consider trkB, top left in the figure below.  But just next to it is IGFR which can be activated by both insulin and IGF-1.

In Rett syndrome they are already using IGF-1 to modulate KCC2.  The research is done at Penn State.

As you can see in the figure the mechanism for IGF-1 and insulin is not the same as BNDF/trkb, but Penn State have already shown that IGF-1 works in vitro.

We saw in early posts regarding intranasal insulin that this was a safe way to deliver insulin to the brain without effects in the rest of the body.

So we know it is safe and in theory it should achieve the same thing that the Penn State researchers are trying to achieve.

Signaling pathways controlling KCC2 function. The regulation of KCC2 activity is mediated by many proteins including kinases and phosphatases. It affects either the steady state protein expression at the plasma membrane or the KCC2 protein recycling. All the different pathways are explained and discussed in the main text. The schematic drawings of KCC2 as well as other membrane molecules do not reflect their oligomeric structure. GRFα2, GDNF family receptor α2; BDNF, Brain-derived neurotrophic factor; TrKB, Tropomyosin receptor kinase B; Insulin, Insulin-like growth factor 1 (IGF-1); IGFR, Insulin-like growth factor 1 receptor; mGluR1, Group I metabotropic glutamate receptor; 5-HT-2A, 5-hydroxytryptamine (5-HT) type 2A receptor; mAChR, Muscarinic acetylcholine receptor; NMDAR, N-methyl-D-aspartate receptor; mZnR, Metabotropic zinc-sensing receptor (mZnR); GPR39, G-protein-coupled receptor (GPR39); ERK-1,2, Extracellular signal-regulated kinases 1, 2; PKC, Protein kinase C; Src-TK, cytosolic Scr tyrosine kinase; WNKs1–4, with-no-lysine [K] kinase 1–4; SPAK, Ste20p-related proline/alanine-rich kinase; OSR1, oxidative stress-responsive kinase -1; Tph, Tyrosine phosphatase; PP1, protein phosphatase 1; Egr4, Early growth response transcription factor 4; USF 1/2, Upstream stimulating factor 1, 2.

The Penn State research on using IGF-1 to increase KCC2 in Rett Syndrome

Discovery of a new drug target could lead to novel treatment for severe autism

The researchers also showed that treating diseased nerve cells with insulin-like growth factor 1 (IGF1) elevated the level of KCC2 and corrected the function of the GABA neurotransmitter. IGF1 is a molecule that has been shown to alleviate symptoms in a mouse model of Rett Syndrome and is the subject of an ongoing phase-2 clinical trial for the treatment of the disease in humans.

"The finding that IGF1 can rescue the impaired KCC2 level in Rett neurons is important not only because it provides an explanation for the action of IGF1," said Xin Tang, a graduate student in Chen's Lab and the first-listed author of the paper, "but also because it opens the possibility of finding more small molecules that can act on KCC2 to treat Rett syndrome and other autism spectrum disorders."

More Melatonin?

As Agnieszka pointed out in the previous post it appears that extremely high doses of melatonin can increase KCC2 in traumatic brain injury (TBI). In this example BDNF was increased by the therapy, so I think TBI may be a specific case.  In most autism BDNF starts out elevated and in epilepsy, seizures are known to increase BDNF and that process is seen as down regulating KCC2 expression.  So in much autism and epilepsy you want less BDNF.

Melatonin attenuates neuronal apoptosis through up-regulation of K+ -Cl- cotransporter KCC2 expression following traumatic brain injury in rats

Compared with the vehicle group, melatonin treatment altered the down-regulation of KCC2 expression in both mRNA and protein levels after TBI. Also, melatonin treatment increased the protein levels of brain-derived neurotrophic factor (BDNF) and phosphorylated extracellular signal-regulated kinase (p-ERK). Simultaneously, melatonin administration ameliorated cortical neuronal apoptosis, reduced brain edema, and attenuated neurological deficits after TBI. In conclusion, our findings suggested that melatonin restores KCC2 expression, inhibits neuronal apoptosis and attenuates secondary brain injury after TBI, partially through activation of BDNF/ERK pathway.

More Science

There is plenty more science on this subject.

It is suggested that in addition to IGF-1/insulin it may be necessary to involve Protein tyrosine kinase (PTK).

Insulin-Like Growth Factor 1 and a Cytosolic Tyrosine Kinase Activate Chloride Outward Transport during Maturation of Hippocampal Neurons

Protein tyrosine kinase (PTK) phosphorylation is considered a key biochemical event in numerous cellular processes, including proliferation, growth, and differentiation, and has also been implicated in synaptogenesis. Protein tyrosine kinases are subdivided into the cytosolic nonreceptor family and the transmembrane growth factor receptor family, which includes receptors for insulin and insulin-like growth factor (IGF-1). The maturation of postsynaptic inhibition may require both a cytoplasmic PTK, which increases GABA_A receptor-mediated currents, and insulin, which was shown to induce a rapid translocation of GABA_A receptors from intracellular compartments to the plasma membrane. KCC2 is also known to have a C-terminal PTK consensus site. Therefore, the maturation of postsynaptic inhibition may, in addition to other mechanisms, also involve the effects of PTK and insulin acting on KCC2.

Development and regulation of chloride homeostasis in the central nervous system

Conclusion

I would infer from all this science that intranasal insulin is likely to increase KCC2 expression in the brain, certainly worthy of investigation.

Protein tyrosine kinase (PTK) phosphorylation is considered a key biochemical event in numerous cellular processes.  This might be a limiting factor on the effectiveness of insulin in raising KCC2.  This would then add yet more complexity.

Protein kinases are enzymes that add a phosphate(PO₄) group to a protein, and can modulate its function.  A protein kinase inhibitor is a type of enzyme inhibitor that blocks the action of one or more protein kinases.

Abnormal protein tyrosine kinases (PTKs) cause many human leukaemias, so there is research into PTK inhibitors (PTK-Is).

As we know from Abha Chauhan’s mammoth book, oxidative stress controls the activities of PTK.