Hereditary spastic paraplegia (HSP) gene 11 (Spg11) attenuates lipid accumulation in myeloid cells and neuroinflammation in the midbrain without affecting α-synuclein pathology.

Hereditary spastic paraplegia type 11 (SPG11-HSP) is a neurodegenerative disorder caused by mutations in SPG11, which encodes the large scaffolding protein spatacsin, involved in lysosomal and autophagosomal trafficking. A portion of patients with SPG11 mutations present with parkinsonism features. While spatacsin dysfunction is linked to neurodegeneration, the underlying cellular mechanisms, especially in the midbrain, remain largely unclear. Here, we demonstrate that loss of Spg11 in mice results in neuroinflammation and lipid accumulation in myeloid cells. Bulk RNA sequencing revealed a strong upregulation of microglial genes in the midbrain of Spg11 knockouts, supported by increased CD68 and CLEC7A expression and morphological changes consistent with microglial activation. Spg11 depletion in two in vivo models of synucleinopathy revealed no enhancement of phosphorylated α-synuclein-positive inclusions or dopaminergic neuron loss; however, the mice did exhibit Spg11-dependent microglial reactivity. Further in vitro studies using primary bone-derived macrophages revealed increased phagocytic capacity and neutral lipid accumulation under basal and stress conditions. These findings support a model where SPG11 is a critical regulator of microglial activation and myeloid lipid metabolism, contributing to neurodegeneration through pathways distinct from α-synuclein-mediated pathology.