Lysosomal abnormalities in hereditary spastic paraplegia types SPG 15 and SPG 11

Abstract

ObjectiveHereditary spastic paraplegias (HSPs) are among the most genetically diverse inherited neurological disorders, with over 70 disease loci identified (SPG1-71) to date. SPG15 and SPG11 are clinically similar, autosomal recessive disorders characterized by progressive spastic paraplegia along with thin corpus callosum, white matter abnormalities, cognitive impairment, and ophthalmologic abnormalities. Furthermore, both have been linked to early-onset parkinsonism.MethodsWe describe two new cases of SPG15 and investigate cellular changes in SPG15 and SPG11 patient-derived fibroblasts, seeking to identify shared pathogenic themes. Cells were evaluated for any abnormalities in cell division, DNA repair, endoplasmic reticulum, endosomes, and lysosomes.ResultsFibroblasts prepared from patients with SPG15 have selective enlargement of LAMP1-positive structures, and they consistently exhibited abnormal lysosomal storage by electron microscopy. A similar enlargement of LAMP1-positive structures was also observed in cells from multiple SPG11 patients, though prominent abnormal lysosomal storage was not evident. The stabilities of the SPG15 protein spastizin/ZFYVE26 and the SPG11 protein spatacsin were interdependent.InterpretationEmerging studies implicating these two proteins in interactions with the late endosomal/lysosomal adaptor protein complex AP-5 are consistent with shared abnormalities in lysosomes, supporting a converging mechanism for these two disorders. Recent work with Zfyve26−/− mice revealed a similar phenotype to human SPG15, and cells in these mice had endolysosomal abnormalities. SPG15 and SPG11 are particularly notable among HSPs because they can also present with juvenile parkinsonism, and this lysosomal trafficking or storage defect may be relevant for other forms of parkinsonism associated with lysosomal dysfunction.

Spastic paraplegia proteins spastizin and spatacsin mediate autophagic lysosome reformation

“…The accumulation of enlarged LPOs in spastizin-or spatacsin-depleted cells led us to investigate any impairment in lysosome-dependent autophagy. Indeed, accumulation of autophagosomes has been observed in fibroblasts derived from patients with SPG15 and SPG11 (12,13). Furthermore, mature autophagosomes, as visualized by immunostaining for p62 or and autophagic defects in spastizin-and spatacsin-depleted HeLa cells as well as fibroblasts from patients with AR-HSP-TCC.…”

“…In contrast, endogenous spastizin immunolabeling overlapped minimally with the early endosomal marker early endosomal antigen 1 (EEA1) and only partially with the late endosomal marker cation-independent mannose-6-phosphate receptor (CI-MPR) ( Figure 1E). To confirm the specificity of endogenous spastizin labeling, we compared spastizin immunostaining in control fibroblasts with that in cells from a patient with SPG15 lacking spastizin protein (13). Lysosomal labeling in wild-type fibroblasts was similar to that in HeLa cells, but the immunoreactive signal was nearly undetectable in SPG15 patient cells, indicating that the robust staining represents bona fide spastizin ( Figure 1F).…”

“…Among these, recent studies in cells from patients SPG15 and SPG11 have favored pathogenic alterations in lysosomes or autophagy (12,13). Furthermore, AP-5 coprecipitates with spastizin and spatacsin while also colocalizing with the lysosomal protein LAMP1 in cells (7,8,14).…”

“…We recently reported that fibroblasts from patients with SPG15 or SPG11 contain enlarged LAMP1-positive organelles (LPOs) (13). The lysosomal localization of spastizin and enlarged LPOs in patient cells prompted us to examine this phenotype.…”

GSK3ß‐dependent dysregulation of neurodevelopment in SPG11‐patient induced pluripotent stem cell model

“…Because of the lack of relevant disease models, the underlying molecular mechanisms and, in particular, the neuronal functions of spatacsin are still unclear. Previous studies employing non‐neuronal cellular models suggested stress‐related impairments within the lysosomal‐autophagy pathway attributed to loss of function of spatacsin in HeLa cells and patient‐derived fibroblasts 10, 11. We recently reported that SPG11‐iPSC‐derived patient neurites exhibited neurodegenerative changes on a functional and ultrastructural level 12…”