MedNous June 2023
The following article text is as published in the June 2023 edition of MedNous, a publication of Evernow Publishing Ltd. You can download the original PDF version here.
The accelerated approvals in the US of Alzheimer’s disease treatments Aduhelm (aducanumab) and Leqembi (lecanemab) in June 2021 and early 2023 have energised the field of neuroscience. Of the two drugs, Leqembi will come up for a Food and Drug Administration decision on full approval in early July. These are examples of disease-modifying immunotherapies built around the ‘amyloid hypothesis’, where toxic proteins are considered to trigger a pathologic cascade that ultimately destroys neurons in the brain. Whilst these treatments have been very good at clearing the brain of amyloid deposits, their clinical significance remains controversial.
Other strategies are also under investigation including regenerative medicine therapies. This article describes a new version of one of these: an autologous cell therapy comprised of neuroprecursors derived from the human hair follicle targeted at the hippocampus, the memory centre of the brain.
Whilst at the University of Sydney, I led a research team on this project for several years and now the concept is being taken forward by our new biotech company. At all times our focus has been the same – to replace and restore the hippocampal brain cells devastated by Alzheimer’s disease and thereby recover peoples’ memories and brain function.
Through successive laboratory studies and a landmark veterinary trial in dogs with a canine analogue of Alzheimer’s, we have been able to show that these cells can indeed restore neurons and their synapses in the hippocampus, and we hope in humans as well. In 2019 we founded the company Skin2Neuron Pty Ltd to translate this science into an actual new treatment. Earlier this year, we were granted a patent by IP Australia, the country’s patent authority, for this discovery and is under examination in several jurisdictions around the world.
The near-term goal of our company is to prepare for a human clinical trial of our cell therapy in patients with Alzheimer’s disease in 2025. The Australian regulator, the Therapeutics Goods Administration, has streamlined our path to trial by classifying our cells as below high risk. This is because production of these cells does not involve the induction or modification of pluripotency genes.
Background to our discovery
Our approach to Alzheimer’s disease starts with recognising the distinction between Alzheimer’s disease and Alzheimer’s dementia. Two pathologies define the disease: amyloid plaques that form between and around neurons, or tangled up tau proteins inside the neurons themselves. For the longest time, a formal diagnosis of Alzheimer’s disease was only possible post mortem, by looking at sections of the brain under a microscope. Now, using specialised positron emission tomography, it is possible to see the accumulation of these pathognomonic proteins in the living brain.
We now understand that Alzheimer’s disease can be silent for many years – if not decades – before manifesting itself as a clinical problem. In fact, 20-30% of people with the disease will die without ever knowing anything about it. But for those who develop dementia, it is devastating. Dementia simply refers to a noticeable decline in a person’s cognitive function, to the point where he or she can no longer carry out day-to-day tasks.
Dementia can be caused by several different pathologies, but when Alzheimer’s disease is the culprit it generally starts as subtle and then more obvious memory problems. These impairments widen to affect other areas of thinking, planning, speaking, and then even simple things like getting dressed or making a meal. But perhaps the cruellest aspect of Alzheimer’s dementia is that it robs us of meaning, an untethering of those long-term memories of events, experiences and relationships that anchor us to a personal narrative.
Alzheimer’s disease progresses to dementia when at least 10 million neurons have been destroyed in the hippocampus (1). Without these neurons, and more specifically the synapses between them, the brain loses the capacity to handle information including laying down new memories or accessing old ones. Replacing these lost hippocampal neurons is the raison d’être of Skin2Neuron.
My research team discovered that a rare cell within the human hair follicle was exceptionally neurogenic, meaning that these cells naturally and exclusively develop into brain cells. This finding is described in our patent. To be specific, we report that “the adult human hair follicle contains both unipotent precursor cells as well as multipotent stem cells. Unipotent precursors are fundamentally different from multipotent stem cells by virtue of fate restriction to only one cell lineage, and being incapable of indefinite cell replication in vitro.”
This surprising finding leverages developmental biology because at the earliest stages of foetal growth an outer layer of cells organises to form the ectoderm. Normally, ectodermal cells end up facing a choice: continue developing the primitive brain, or begin filling out nascent skin. For this reason, precursor cells in the hair follicle and the brain are remarkably interchangeable. For example, a Korean research group has shown that neural stem cells extracted from the human brain’s ventricular zone, injected just below the skin of experimental animals, stimulated new hair production (2).
Incredibly, the opposite is also possible. Over several years, we have shown that delivery of canine hair follicle cells into the hippocampus of aged rodents produce ‘showcase’ engraftment. Donor cells migrate towards local neuronal signals, position themselves appropriately into anatomical layers, mature into arborised neurons, and integrate into the animal’s memory circuits. Not only did overall synapses spring back up to healthy numbers, but spatial memory was corrected from chance performance before treatment, to levels only seen in youthful animals.
How is this possible? We now understand that there are a vast number of shared biological pathways, receptors and markers between stem cells in the hair follicle and the brain. Two examples illustrate this point.
First, the mammalian hair follicle continuously cycles between phases of quiescence (telogen), growth (anagen) and shrinkage (catagen). Where an individual hair follicle sits in the cycle is a fine balance between competing signals – the most powerful being bone morphogenetic proteins that are pro-telogen and Wnt proteins that are pro-anagen. This has been understood for decades but only recently was it appreciated that the same dynamic tension, based on the same regulatory factors, applies to neural stem cells in the brain (3).
Second, there is arguably no more potent or well-known chemical signal for neural stem cells to stop proliferating and start maturing into elaborate neurons, in the brain or in a dish, than the appropriately named brain-derived neurotrophic factor (BDNF). BDNF is pumped out by individual neurons and is inducible. Increases in neuronal activity trigger BDNF release in the local microenvironment, helping neurons create synapses to keep up with the extra demand. Remarkably, the same system is active in the hair follicle. BDNF is a pro-catagen signal, in effect helping the follicle switch out of the cell proliferation phase (4).
Given all this, and the lack of translation between rodent studies and humans when it comes to therapies for the central nervous system, the next major challenge for our research was to put the idea to the test in an ecologically-valid large animal model.
We now understand that about 10-15% of older pet dogs can develop both Alzheimer’s disease (5), including amyloid plaques and tau tangles, and a dementia-like syndrome(6). These older dogs become confused, disoriented and fail to recognise their carers, spending endless hours restless, pacing, circling or staring robotically at walls. In later stages they lose continence and become too hard for their carers to manage. Canine cognitive dysfunction was most recently documented in the Dog Aging Project a study of more than 15,000 dogs. The results of this study were published in the journal Scientific Reports in August 2022.
But could an autologous skin-derived neural precursor cell therapy actually reverse Alzheimer’s dementia in dogs and serve as a model for a treatment in humans? We tested the first part of this question in a Phase 1/2a veterinary trial in six older companion dogs with a diagnosis of canine cognitive dysfunction. The DOGS+CELLS veterinary trial (7) took place over a period of eight years. It involved the direct microinjection of 250,000 autologous canine skin-derived neuroprecursors into the bilateral hippocampus of the animals. Safety was evaluated clinically, and efficacy was assessed using a validated clinical scale at baseline and three months after treatment.
Results from the trial showed that four out of five dogs improved in a clinically meaningful way, and for three patients in the trial, the dementia syndrome was completely reversed. In addition, microscopic examination of the dogs’ brains years after treatment revealed fold-wise increases in synapses only in the hippocampus, the therapeutic target. Evidently, the personalised donor cells not only persisted in the face of proven Alzheimer pathology, but developed into neurons packed with synaptic connections, enabling memory function to return. The results of the trial were published in the journal Stem Cell Research & Therapy on 17 June 2022.
The applicability of this model and therapeutic strategy to humans remains to be seen. As noted in the discussion of the article, a human trial will need to select correspondent early-stage Alzheimer’s disease patients. Choice of starting dose will also need to be careful, as the veterinary trial did not compare different therapeutic doses. At the same time, this unique study suggests that it may be possible to introduce a new class of neurorestorative cell therapy for Alzheimer’s disease. For the first time, a prospective therapy is under development to target neuronal and synaptic loss in the hippocampus based on neuroprecursor cells derived from a patient’s own hair follicles.
References
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2. Hwang I, Choi KA, Park HS, Jeong H, Kim JO, Seol KC, Kwon HJ, Park IH, Hong S. Neural Stem Cells Restore Hair Growth Through Activation of the Hair Follicle Niche. Cell Transplant. 2016;25(8):1439-51. doi: 10.3727/096368916X691466. Epub 2016 Apr 22. PMID: 27110030.
3. Jensen et al. Bone morphogenetic proteins (BMPs) in the central regulation of energy balance and adult neural plasticity. Metabolism. 2021 Oct;123:154837
4. Peters EM, Hansen MG, Overall RW, Nakamura M, Pertile P, Klapp BF, Arck PC, Paus R. Control of human hair growth by neurotrophins: brain-derived neurotrophic factor inhibits hair shaft elongation, induces catagen, and stimulates follicular transforming growth factor beta2 expression. J Invest Dermatol. 2005 Apr;124(4):675-85. doi: 10.1111/j.0022-202X.2005.23648.x. PMID: 15816823.
5. Abey A, Davies D, Goldsbury C, Buckland M, Valenzuela M, Duncan T. Distribution of tau hyperphosphorylation in canine dementia resembles early Alzheimer's disease and other tauopathies. Brain Pathol. 2021 Jan;31(1):144-162. doi: 10.1111/bpa.12893. Epub 2020 Sep 10. PMID: 32810333; PMCID: PMC8018065
6. Salvin HE, McGreevy PD, Sachdev PS, Valenzuela MJ. The canine cognitive dysfunction rating scale (CCDR): a data-driven and ecologically relevant assessment tool. Vet J. 2011 Jun;188(3):331-6. doi: 10.1016/j.tvjl.2010.05.014. Epub 2010 Jun 12. PMID: 20542455.
7. Valenzuela M, Duncan T, Abey A, Johnson A, Boulamatsis C, Dalton MA, Jacobson E, Brunel L, Child G, Simpson D, Buckland M, Lowe A, Siette J, Westbrook F, McGreevy P. Autologous skin-derived neural precursor cell therapy reverses canine Alzheimer dementia-like syndrome in a proof of concept veterinary trial. Stem Cell Res Ther. 2022 Jun 17;13(1):261. doi: 10.1186/s13287-022-02933-w. PMID: 35715872; PMCID: PMC9205057.
Author’s box: This article was written by Michael Valenzuela, scientific co-founder and chief executive officer of Skin2Neuron Pty Ltd, a visiting professor at the Centre for Healthy Brain Ageing at the University of New South Wales, Australia.