Targeting p75NTR activity alleviates the neurotoxic effect of high glucose on iPSC-derived dopaminergic neurons

Abstract

Background: Hyperglycemia, a hallmark of diabetes mellitus, is a metabolic condition that highly affects the nervous system. While evidence from epidemiological and animal studies links diabetes to dopaminergic dysfunction and an increased risk of Parkinson’s disease, the underlying mechanisms remain unclear. Here, we examined the effects of high glucose on human iPSC-derived dopaminergic neurons and glial cells to better understand the pathogenic alterations that lead to neurotoxicity. Previous implication of neurotrophins in the neurological manifestations of diabetes prompted us to focus on the role of p75NTR neurotrophin receptor (p75NTR) in dopaminergic neurodegeneration under hyperglycemic conditions. Methods: iPSC-derived dopaminergic neurons, astrocytes and microglia were treated with high glucose (50mM, 100mM) for 48 h to simulate hyperglycemia. Cytotoxicity assays, RNA sequencing and DNA damage assessments were employed to investigate the pathological alterations induced by high glucose exposure in neurons. Pharmacological targeting of p75NTR activity allowed investigation of its involvement in glucose neurotoxicity. Glial-mediated neurotoxicity was evaluated using conditioned media and inflammatory marker analysis. Results: High glucose treatment led to DNA damage, activation of JNK signaling and cell death in neurons. Importantly, we observed upregulation of p75NTR and its pro-apoptotic ligand pro-NGF, suggesting activation of the pro-NGF/p75NTR axis in high glucose-treated neurons. Inhibition of p75NTR activity rescued neuronal cell death, identifying p75NTR as a central mediator of glucose neurotoxicity. Furthermore, glucose overload sensitized neurons to 6-hydroxydopamine (6-OHDA), increasing their vulnerability to neurotoxic insults—an effect reversed by p75NTR blockade. Treatment with BNN27, a synthetic NGF mimetic, prevented neuronal loss through p75NTR and TrkA receptors, suggesting neurotrophin signaling as a potential therapeutic target for combating high glucose-induced neuronal damage. Finally, we demonstrated the contribution of glial cells to neurodegeneration since high glucose treatment of iPSC-derived astrocytes and microglia enhanced their inflammatory potential and triggered the release of neurotoxic factors, causing pro-apoptotic effects on neurons. Conclusions: Our findings show that high glucose impairs human dopaminergic neuron survival through activation of the pro-NGF/p75NTR axis and indirect glia-mediated mechanisms. Targeting p75NTR signaling may offer neuroprotective benefits in diabetes-related neurodegeneration, particularly for patients at risk of Parkinson’s disease.

1. Introduction

Hyperglycemia, a defining feature of diabetes mellitus (DM), is a metabolic condition that highly affects the nervous system accelerating neurodegeneration. Although the connection between DM and Alzheimer’s disease is well documented [9], its association with Parkinson’s Disease (PD) is still largely unclear. Growing evidence links DM to dopaminergic neurodegeneration and increased risk of PD [10, 21, 46, 89]. Animal models and patients with DM show striatal dopaminergic dysfunction, altered dopamine neurotransmission and have increased risk for parkinsonian symptoms [23, 47, 68]. However, the mechanistic interlink between the two disorders remains unclear impairing the development of neuroprotective therapies.

Glucose is the main source of energy for the brain. Both preclinical and clinical evidence suggest that elevated glucose levels can have detrimental effects on neurons. Preclinical studies have demonstrated that high glucose leads to neuronal injury, synaptic dysfunction and changes in the brain [58, 77, 92]. These findings are supported by clinical studies linking hyperglycemia and DM with brain atrophy, reduced cortical thickness and increased risk of dementia [22, 59, 63]. Glucose neurotoxicity has been linked to mitochondrial dysfunction, oxidative stress and accumulation of AGEs [84], mechanisms that are also common with many neurodegenerative disorders. Additionally, diabetes leads to systemic inflammation, changes in blood brain barrier (BBB) integrity and gliosis in the brain [50]. Streptozotocin (STZ)-treated mice display increased brain sensitivity to peripheral LPS-induced inflammation [50] while STZ treatment in the rotenone model of PD activates microglia and eventually worsens neurodegeneration and motor symptoms [90].