An investigation into the transcriptional control of the Schwann cell during differentiation, demyelization and disease.

The generation of mature myelinating and non-myelinating Schwann cells from immature Schwann cells is regulated by signals from the axon. In the absence of axonal signals, for example during nerve injury, Schwann cells will return to an immature-like phenotype. However, Schwann cells retain the ability to re-differentiate after injury, demonstrating remarkable plasticity throughout adult life. Although these cellular transformations are normally beneficial, during diseases of the peripheral nervous system, they are often disrupted producing negative consequences. In this thesis, I have demonstrated a synergistic relationship between two signals, cyclic adenosine monophosphate (cyclic AMP) and p-neuregulin-1 (NRG1) in inducing myelin differentiation in cultured mouse Schwann cells. Furthermore, I found that the cyclic-AMP response element binding protein (CREB) family of transcription factors are required for this differentiation. Second, I have investigated the role of the transcription factor c-Jun in controlling Schwann cell responses after nerve injury. Using in vivo and in vitro approaches, I have found that c-Jun is an axonal-regulated injury factor that controls Schwann cell demyelination and dedifferentiation. Furthermore, Schwann cell derived c-Jun is crucial for adequate nerve regeneration and repair after injury. Finally, I investigated the functional properties of a mutant form of the my el in-related transcription factor Egr2 (Krox-20), which leads to severe congenital hypomyelinating neuropathy in humans. I found that mutant Egr2 is not transcriptionally inactive but retains residual wild-type Egr2 functions. More importantly, mutant Egr2 also demonstrates aberrant effects in Schwann cells, enhancing DNA synthesis, both in the presence and absence of the putative axonal mitogen, p-neuregulin 1. This is in stark contrast to wild-type Egr2, which causes withdrawal from the cell cycle

Lessons from Injury: How Nerve Injury Studies Reveal Basic Biological Mechanisms and Therapeutic Opportunities for Peripheral Nerve Diseases.

Funder: john and lucille van geest foundationSince Waller and Cajal in the nineteenth and early twentieth centuries, laboratory traumatic peripheral nerve injury studies have provided great insight into cellular and molecular mechanisms governing axon degeneration and the responses of Schwann cells, the major glial cell type of peripheral nerves. It is now evident that pathways underlying injury-induced axon degeneration and the Schwann cell injury-specific state, the repair Schwann cell, are relevant to many inherited and acquired disorders of peripheral nerves. This review provides a timely update on the molecular understanding of axon degeneration and formation of the repair Schwann cell. We discuss how nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) and sterile alpha TIR motif containing protein 1 (SARM1) are required for axon survival and degeneration, respectively, how transcription factor c-JUN is essential for the Schwann cell response to nerve injury and what each tells us about disease mechanisms and potential therapies. Human genetic association with NMNAT2 and SARM1 strongly suggests aberrant activation of programmed axon death in polyneuropathies and motor neuron disorders, respectively, and animal studies suggest wider involvement including in chemotherapy-induced and diabetic neuropathies. In repair Schwann cells, cJUN is aberrantly expressed in a wide variety of human acquired and inherited neuropathies. Animal models suggest it limits axon loss in both genetic and traumatic neuropathies, whereas in contrast, Schwann cell secreted Neuregulin-1 type 1 drives onion bulb pathology in CMT1A. Finally, we discuss opportunities for drug-based and gene therapies to prevent axon loss or manipulate the repair Schwann cell state to treat acquired and inherited neuropathies and neuronopathies

Neurotoxin-mediated potent activation of the axon degeneration regulator SARM1

Axon loss underlies symptom onset and progression in many neurodegenerative disorders. Axon degeneration in injury and disease is promoted by activation of the nicotinamide adenine dinucleotide (NAD)-consuming enzyme SARM1. Here, we report a novel activator of SARM1, a metabolite of the pesticide and neurotoxin vacor. Removal of SARM1 completely rescues mouse neurons from vacor-induced neuron and axon death in vitro and in vivo. We present the crystal structure the Drosophila SARM1 regulatory domain complexed with this activator, the vacor metabolite VMN, which as the most potent activator yet know is likely to support drug development for human SARM1 and NMNAT2 disorders. This study indicates the mechanism of neurotoxicity and pesticide action by vacor, raises important questions about other pyridines in wider use today, provides important new tools for drug discovery, and demonstrates that removing SARM1 can robustly block programmed axon death induced by toxicity as well as genetic mutation

Cerebral venous thrombosis after vaccination against COVID-19 in the UK: a multicentre cohort study

BACKGROUND: A new syndrome of vaccine-induced immune thrombotic thrombocytopenia (VITT) has emerged as a rare side-effect of vaccination against COVID-19. Cerebral venous thrombosis is the most common manifestation of this syndrome but, to our knowledge, has not previously been described in detail. We aimed to document the features of post-vaccination cerebral venous thrombosis with and without VITT and to assess whether VITT is associated with poorer outcomes. METHODS: For this multicentre cohort study, clinicians were asked to submit all cases in which COVID-19 vaccination preceded the onset of cerebral venous thrombosis, regardless of the type of vaccine, interval between vaccine and onset of cerebral venous thrombosis symptoms, or blood test results. We collected clinical characteristics, laboratory results (including the results of tests for anti-platelet factor 4 antibodies where available), and radiological features at hospital admission of patients with cerebral venous thrombosis after vaccination against COVID-19, with no exclusion criteria. We defined cerebral venous thrombosis cases as VITT-associated if the lowest platelet count recorded during admission was below 150 × 109 per L and, if the D-dimer was measured, the highest value recorded was greater than 2000 μg/L. We compared the VITT and non-VITT groups for the proportion of patients who had died or were dependent on others to help them with their activities of daily living (modified Rankin score 3–6) at the end of hospital admission (the primary outcome of the study). The VITT group were also compared with a large cohort of patients with cerebral venous thrombosis described in the International Study on Cerebral Vein and Dural Sinus Thrombosis. FINDINGS: Between April 1 and May 20, 2021, we received data on 99 patients from collaborators in 43 hospitals across the UK. Four patients were excluded because they did not have definitive evidence of cerebral venous thrombosis on imaging. Of the remaining 95 patients, 70 had VITT and 25 did not. The median age of the VITT group (47 years, IQR 32–55) was lower than in the non-VITT group (57 years; 41–62; p=0·0045). Patients with VITT-associated cerebral venous thrombosis had more intracranial veins thrombosed (median three, IQR 2–4) than non-VITT patients (two, 2–3; p=0·041) and more frequently had extracranial thrombosis (31 [44%] of 70 patients) compared with non-VITT patients (one [4%] of 25 patients; p=0·0003). The primary outcome of death or dependency occurred more frequently in patients with VITT-associated cerebral venous thrombosis (33 [47%] of 70 patients) compared with the non-VITT control group (four [16%] of 25 patients; p=0·0061). This adverse outcome was less frequent in patients with VITT who received non-heparin anticoagulants (18 [36%] of 50 patients) compared with those who did not (15 [75%] of 20 patients; p=0·0031), and in those who received intravenous immunoglobulin (22 [40%] of 55 patients) compared with those who did not (11 [73%] of 15 patients; p=0·022). INTERPRETATION: Cerebral venous thrombosis is more severe in the context of VITT. Non-heparin anticoagulants and immunoglobulin treatment might improve outcomes of VITT-associated cerebral venous thrombosis. Since existing criteria excluded some patients with otherwise typical VITT-associated cerebral venous thrombosis, we propose new diagnostic criteria that are more appropriate. FUNDING: None

SARM1 detection in myelinating glia: sarm1/Sarm1 is dispensable for PNS and CNS myelination in zebrafish and mice

Since SARM1 mutations have been identified in human neurological disease, SARM1 inhibition has become an attractive therapeutic strategy to preserve axons in a variety of disorders of the peripheral (PNS) and central nervous system (CNS). While SARM1 has been extensively studied in neurons, it remains unknown whether SARM1 is present and functional in myelinating glia? This is an important question to address. Firstly, to identify whether SARM1 dysfunction in other cell types in the nervous system may contribute to neuropathology in SARM1 dependent diseases? Secondly, to ascertain whether therapies altering SARM1 function may have unintended deleterious impacts on PNS or CNS myelination? Surprisingly, we find that oligodendrocytes express sarm1 mRNA in the zebrafish spinal cord and that SARM1 protein is readily detectable in rodent oligodendrocytes in vitro and in vivo. Furthermore, activation of endogenous SARM1 in cultured oligodendrocytes induces rapid cell death. In contrast, in peripheral glia, SARM1 protein is not detectable in Schwann cells and satellite glia in vivo and sarm1/Sarm1 mRNA is detected at very low levels in Schwann cells, in vivo, in zebrafish and mouse. Application of specific SARM1 activators to cultured mouse Schwann cells does not induce cell death and nicotinamide adenine dinucleotide (NAD) levels remain unaltered suggesting Schwann cells likely contain no functionally relevant levels of SARM1. Finally, we address the question of whether SARM1 is required for myelination or myelin maintenance. In the zebrafish and mouse PNS and CNS, we show that SARM1 is not required for initiation of myelination and myelin sheath maintenance is unaffected in the adult mouse nervous system. Thus, strategies to inhibit SARM1 function to treat neurological disease are unlikely to perturb myelination in humans.CM was funded by a Medical Research Council (UK) studentship (2251399). PA-F (206634/Z/17/Z), AL (210904/Z/18/Z), CC (220027/Z/19/Z), RB (203151/Z/16/Z) and MC (220906/Z/20/Z) were funded by the Wellcome Trust (UK). BS was supported by a Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (109408/Z/15/Z). KM was funded by the National Institute of Neurological Disorders and Stroke Awards (R01NS079445). JG-S was funded by a Miguel Servet Fellowship (CP22/00078) from the Instituto de Salud Carlos III and the Millennium Nucleus for the Study of Pain (MiNuSPain), Santiago, Chile. HC was funded by the Spanish “Ministerio de Economía y Competitividad” (BFU2016-75864R and PID2019-109762RB-I00), ISABIAL (UGP18-257 and UGP-2019-128), and Generalitat Valenciana (PROMETEO 2018/114). Y-PH and C-YC were funded by Academia Sinica, AS-IA-106-L04 to Y-PH.Peer reviewe

Zeb2 is essential for Schwann cell differentiation, myelination and nerve repair

Schwann cell development and peripheral nerve myelination require the serial expression of transcriptional activators, such as Sox10, Oct6 (also called Scip or Pou3f1) and Krox20 (also called Egr2). Here we show that transcriptional repression, mediated by the zinc-finger protein Zeb2 (also known as Sip1), is essential for differentiation and myelination. Mice lacking Zeb2 in Schwann cells develop a severe peripheral neuropathy, caused by failure of axonal sorting and virtual absence of myelin membranes. Zeb2-deficient Schwann cells continuously express repressors of lineage progression. Moreover, genes for negative regulators of maturation such as Sox2 and Ednrb emerge as Zeb2 target genes, supporting its function as an inhibitor of inhibitors in myelination control. When Zeb2 is deleted in adult mice, Schwann cells readily dedifferentiate following peripheral nerve injury and become repair cells. However, nerve regeneration and remyelination are both perturbed, demonstrating that Zeb2, although undetectable in adult Schwann cells, has a latent function throughout life

Schwann cells are axo-protective after injury irrespective of myelination status in mouse Schwann cell/neuron cocultures.

Myelinating Schwann cell (SC)- dorsal root ganglion (DRG) neuron cocultures are an important technique for understanding cell-cell signalling and interactions during peripheral nervous system (PNS) myelination, injury, and regeneration. While methods using rat SCs and neurons or mouse DRG explants are commonplace, there are no established protocols for compartmentalised myelinating cocultures with dissociated mouse cells. There consequently is a need for a coculture protocol that allows separate genetic manipulation of mouse SCs or neurons, or use of cells from different transgenic animals to complement in vivo mouse experiments. However, inducing myelination of dissociated mouse SCs in culture is challenging. Here we describe a new method to coculture dissociated mouse SCs and DRG neurons in microfluidic chambers and induce robust myelination. Cocultures can be axotomised to study injury, used for drug treatments, and cells can be lentivirally transduced for live imaging. We used this model to investigate axon degeneration after traumatic axotomy and find that SCs, irrespective of myelination status, are axo-protective. At later timepoints after injury, live imaging of cocultures shows that SCs break up, ingest, and clear axonal debris