Neuropathy Cell Models for Research

Neuropathy encompasses a wide range of disorders affecting peripheral nerves, with a global prevalence estimated at 2-8% of the general population, rising to over 50% in diabetic patients (WHO, 2023). The most common form, diabetic peripheral neuropathy, affects approximately 50% of individuals with diabetes, leading to significant morbidity, including pain, sensory loss, and increased risk of foot ulcers and amputations. Other major causes include chemotherapy-induced peripheral neuropathy (CIPN), affecting 30-40% of cancer patients receiving neurotoxic agents, and inherited neuropathies such as Charcot-Marie-Tooth disease (CMT), with a prevalence of 1 in 2,500. The clinical impact is profound, with reduced quality of life and substantial healthcare costs. Research into neuropathy mechanisms is critical for developing effective therapies, as current treatments are largely symptomatic and do not halt disease progression.

Neuropathy is an ideal model for mechanistic studies due to its well-defined subtypes, including axonal, demyelinating, and small fiber neuropathies, each with distinct genetic and molecular underpinnings. Public datasets, such as the NCBI Gene Expression Omnibus (GEO), provide extensive transcriptomic and proteomic data from patient nerve biopsies and animal models. Open questions include the precise role of Schwann cell-axon interactions, mitochondrial dysfunction, and neuroinflammation in disease progression. Gene-edited cell models offer a powerful approach to dissect these pathways, enabling the study of specific genetic mutations in a controlled in vitro environment.

While neuropathy is not a cancer, the term 'carcinogenic' is not applicable. Instead, we focus on pathogenic pathways. Key pathways involved in neuropathy include:

• • Schwann Cell Signaling: Schwann cells are critical for myelination and axonal support. Disruption of signaling pathways such as neuregulin-1/ErbB, which regulates myelination, leads to demyelinating neuropathies.
• • Axonal Transport and Mitochondrial Function: Impaired axonal transport and mitochondrial dysfunction are common in axonal neuropathies. Mutations in genes like MFN2 (mitofusin 2) affect mitochondrial fusion and transport, leading to CMT2A.
• • Inflammatory and Immune Pathways: Inflammatory neuropathies, such as Guillain-Barré syndrome, involve autoimmune attack on peripheral nerves, with cytokines and complement playing key roles.
• • Metabolic Pathways: In diabetic neuropathy, hyperglycemia activates the polyol pathway, increases oxidative stress, and promotes advanced glycation end-product (AGE) formation, damaging neurons and Schwann cells.

Data from TCGA and COSMIC for cancer-related mutations, but for neuropathy, sources include NCBI Gene and ClinVar.

Key signaling networks in neuropathy include:

• • Neuregulin-1/ErbB Signaling: Essential for Schwann cell development and myelination. Dysregulation leads to demyelinating neuropathies.
• • PI3K/AKT Pathway: Regulates Schwann cell survival and proliferation. Aberrant signaling contributes to neuropathy progression.
• • MAPK/ERK Pathway: Involved in Schwann cell differentiation and response to injury. Overactivation can lead to neuropathic pain.
• • Mitochondrial Dynamics: MFN2 and OPA1 regulate mitochondrial fusion, while DRP1 controls fission. Imbalance leads to axonal degeneration.
• • Wallerian Degeneration Pathway: SARM1 is a key executioner of axonal degeneration. Its activation triggers NAD+ depletion and energy failure.

Organoids, such as dorsal root ganglion (DRG) organoids, provide a more physiologically relevant 3D model that recapitulates neuron-Schwann cell interactions and can be derived from patient iPSCs.

• • Patient-Derived Xenografts (PDX): Not commonly used for neuropathy, but xenografts of human Schwann cell tumors (e.g., schwannomas) can be established in immunodeficient mice.
• • Genetically Engineered Mouse Models (GEMM): Include PMP22 transgenic mice (CMT1A), MPZ knockout mice (CMT1B), and MFN2 mutant mice (CMT2A).
• • Induced Models: For diabetic neuropathy, streptozotocin (STZ) injection in mice induces type 1 diabetes and subsequent neuropathy. Chemotherapy-induced neuropathy is modeled by administration of paclitaxel or cisplatin.

CRISPR-based gene editing has revolutionized neuropathy research by enabling the creation of isogenic cell lines with precise genetic modifications. These models are essential for studying the functional consequences of specific mutations in a controlled genetic background. For example:

• • PMP22 Knockout Schwann Cells: Generated by CRISPR-mediated deletion of PMP22, these cells exhibit impaired myelination and can be used to study CMT1A mechanisms.
• • MFN2 Knock-In Lines: Introduction of the MFN2 R94Q mutation (associated with CMT2A) into a wild-type Schwann cell line allows investigation of mitochondrial dysfunction.
• • SARM1 Knockout Neurons: SARM1 deletion protects against axonal degeneration, making these cells valuable for studying Wallerian degeneration and developing neuroprotective drugs.

Commercially available, sequence-verified gene-edited cell lines accelerate research by providing reliable and reproducible models. These are available from commercial sources and can be custom-generated to meet specific research needs.

Gene-edited cell lines are instrumental in functional genomics, allowing researchers to validate the role of candidate genes in neuropathy. For example, knocking out SARM1 in neurons confirms its role in axonal degeneration, while overexpressing PMP22 in Schwann cells recapitulates the myelination defects seen in CMT1A. These models enable high-throughput screening to identify modifiers of disease phenotypes.

Isogenic pairs (wild-type vs. mutant) are powerful tools for drug screening. For instance, a Schwann cell line with a specific MPZ mutation can be used to screen for compounds that restore myelination. Similarly, chemotherapy-induced neuropathy can be modeled by treating neurons with paclitaxel, and gene-edited lines with altered SARM1 expression can be used to test neuroprotective agents. Resistance mechanisms can also be studied by exposing cells to increasing drug concentrations and selecting for resistant clones.

CRISPR-based synthetic lethality screens can identify genes that, when knocked out, are lethal only in the presence of a specific neuropathy-associated mutation. This approach can uncover novel therapeutic targets and biomarkers. For example, a screen in MFN2-mutant cells might identify genes essential for mitochondrial function that could be targeted to selectively kill dysfunctional cells.