MINPP1 prevents intracellular accumulation of the chelator inositol hexakisphosphate and is mutated in Pontocerebellar Hypoplasia

Inositol polyphosphates are vital metabolic and secondary messengers, involved in diverse cellular functions. Therefore, tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, we describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the multiple inositol-polyphosphate phosphatase 1 gene (MINPP1). Patients are found to have a distinct type of Pontocerebellar Hypoplasia with typical basal ganglia involvement on neuroimaging. We find that patient-derived and genome edited MINPP1−/− induced stem cells exhibit an inefficient neuronal differentiation combined with an increased cell death. MINPP1 deficiency results in an intracellular imbalance of the inositol polyphosphate metabolism. This metabolic defect is characterized by an accumulation of highly phosphorylated inositols, mostly inositol hexakisphosphate (IP6), detected in HEK293 cells, fibroblasts, iPSCs and differentiating neurons lacking MINPP1. In mutant cells, higher IP6 level is expected to be associated with an increased chelation of intracellular cations, such as iron or calcium, resulting in decreased levels of available ions. These data suggest the involvement of IP6-mediated chelation on Pontocerebellar Hypoplasia disease pathology and thereby highlight the critical role of MINPP1 in the regulation of human brain development and homeostasis

Purification and activity determination of ADAMTS-4 and ADAMTS-5 and their domain deleted mutants

AA disintegrin-like and metalloproteinase with thrombospondin type-1 motifs-4 (ADAMTS-4) and ADAMTS-5 are zinc-dependent metalloproteinases that are involved in the maintenance of cartilage extracellular matrix (ECM) and are currently considered the major aggrecanases in the development of osteoarthritis. In this chapter we describe the establishment and cultivation of cell lines expressing ADAMTS-4,-5 and their domain deletion mutants; the collection of medium containing expressed ADAMTS-4,-5; the subsequent purification of this medium through anti-FLAG affinity chromatography; and the characterization of ADAMTS-4,-5 activity using synthetic Förster resonance energy transfer (FRET) peptide substrates