Translating Single-cell Vulnerability Into Novel ALS Biomarkers and Therapeutic Targets: Towards a Liquid Nerve Biopsy

Overview

The progress of ALS research and clinical practice is hampered by lack of effective biomarkers to monitor disease onset and progression. In response to this urgent need, we will integrate single-cell system biology approaches, histopathological and clinical data from precious human nerve biopsies collected from living ALS patients during the diagnostic workup and findings from innovative preclinical mouse models to unmask cell-specific molecular alterations that arise in the PNS tissue during the course of ALS pathology. This information will be used to select protein biomarkers of dysfunctional states associated with pre-manifest or early symptomatic stages of the disease, which will be further screened and validated in patient biofluids. Altogether, this project will lead to the discovery of novel, reliable and specific ALS biomarkers while providing insights into ALS mechanisms by leveraging an original "PNS perspective" on disease pathogenesis.

The absence of specific biomarkers poses a significant impediment to the advancement of new treatments for amyotrophic lateral sclerosis (ALS), a severe and rapidly fatal neurodegenerative disease with no cure to date, defined by degeneration of motor neurons. Early pathological events, such as the selective damage of motor axons and the loss of neuromuscular connections, precede complete neurodegeneration and the manifestation of clinical symptoms. Therefore, we argue that understanding disease-related changes occurring in peripheral nerves is crucial for defining the underlying pathogenetic mechanisms. Preliminary data from our research team suggest that phosphorylated TDP-43, the pathological hallmark of ALS, forms aggregates in motor axons and Schwann cells of living ALS patients before the onset of axonal degeneration. However, peripheral nerves constitute complex multicellular tissues, and the specific contributions of individual cellular components to ALS pathology remain poorly understood. The overarching concept of this proposal is that distinct cell types within the nerve tissue (e.g., Schwann cells, endothelial cells, fibroblasts, macrophages) function as exquisite early detectors of motor neuron damage and initiate secondary responses that amplify neuropathology. These studies will steer the analysis of minimally invasive skin biopsies to uncover deregulated PNS signatures in ALS patients. Finally, candidate molecular targets reflecting cell-type-specific deregulation in the diseased nerve microenvironment will be screened in the biofluids of ALS patients and at-risk individuals from genetic ALS families, enabling the discovery of novel diagnostic and prognostic biomarkers. The integrative approach proposed in this study will elucidate the pathogenic mechanisms of ALS and establish a roadmap towards identifying potential therapeutic targets.