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Severe disturbance in the Ca2+ signaling in astrocytes from mouse models of human infantile neuroaxonal dystrophy with mutated Pla2g6.

ABSTRACT: Infantile neuroaxonal dystrophy (INAD; OMIM #no. 256600) is an inherited degenerative nervous system disorder characterized by nerve abnormalities in brain, spinal cord and peripheral nerves. About 85% of INAD patients carry mutations in the PLA2G6 gene that encodes for a Ca(2+)-independent phospholipase A(2) (VIA iPLA(2)), but how these mutations lead to disease is unknown. Besides regulating phospholipid homeostasis, VIA iPLA(2) is emerging with additional non-canonical functions, such as modulating store-regulated Ca(2+) entry into cells, and mitochondrial functions. In turn, defective Ca(2+) regulation could contribute to the development of INAD. Here, we studied possible changes in ATP-induced Ca(2+) signaling in astrocytes derived from two mutant strains of mice. The first strain carries a hypomorphic allele of the Pla2g6 that reduces transcript levels to 5-10% of that observed in wild-type mice. The second strain carries a point mutation in Pla2g6 that results in inactive VIA iPLA(2) protein with postulated gain in toxicity. Homozygous mice from both strains develop pathology analogous to that observed in INAD patients. The nucleotide ATP is the most important transmitter inducing Ca(2+) signals in astroglial networks. We demonstrate here a severe disturbance in Ca(2+) responses to ATP in astrocytes derived from both mutant mouse strains. The duration of the Ca(2+) responses in mutant astrocytes was significantly reduced when compared with values observed in control cells. We also show that the reduced Ca(2+) responses are probably due to a reduction in capacitative Ca(2+) entry (2.3-fold). Results suggest that altered Ca(2+) signaling could be a central mechanism in the development of INAD pathology.

SUBMITTER: Strokin M

PROVIDER: S-EPMC3363330 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Severe disturbance in the Ca2+ signaling in astrocytes from mouse models of human infantile neuroaxonal dystrophy with mutated Pla2g6.

Strokin Mikhail M Seburn Kevin L KL Cox Gregory A GA Martens Kimberly A KA Reiser Georg G

Human molecular genetics 20120322 12

Infantile neuroaxonal dystrophy (INAD; OMIM #no. 256600) is an inherited degenerative nervous system disorder characterized by nerve abnormalities in brain, spinal cord and peripheral nerves. About 85% of INAD patients carry mutations in the PLA2G6 gene that encodes for a Ca(2+)-independent phospholipase A(2) (VIA iPLA(2)), but how these mutations lead to disease is unknown. Besides regulating phospholipid homeostasis, VIA iPLA(2) is emerging with additional non-canonical functions, such as modu ...[more]

PMID: 22442204

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Project description:BackgroundMutations in the PLA2G6 gene have been identified in autosomal recessive neurodegenerative diseases classified as infantile neuroaxonal dystrophy (INAD), neurodegeneration with brain iron accumulation (NBIA), and dystonia-parkinsonism. These clinical syndromes display two significantly different disease phenotypes. NBIA and INAD are very similar, involving widespread neurodegeneration that begins within the first 1-2 years of life. In contrast, patients with dystonia-parkinsonism present with a parkinsonian movement disorder beginning at 15 to 30 years of age. The PLA2G6 gene encodes the PLA2G6 enzyme, also known as group VIA calcium-independent phospholipase A(2), which has previously been shown to hydrolyze the sn-2 acyl chain of phospholipids, generating free fatty acids and lysophospholipids.Methodology/principal findingsWe produced purified recombinant wildtype (WT) and mutant human PLA2G6 proteins and examined their catalytic function using in vitro assays with radiolabeled lipid substrates. We find that human PLA2G6 enzyme hydrolyzes both phospholipids and lysophospholipids, releasing free fatty acids. Mutations associated with different disease phenotypes have different effects on catalytic activity. Mutations associated with INAD/NBIA cause loss of enzyme activity, with mutant proteins exhibiting less than 20% of the specific activity of WT protein in both lysophospholipase and phospholipase assays. In contrast, mutations associated with dystonia-parkinsonism do not impair catalytic activity, and two mutations produce a significant increase in specific activity for phospholipid but not lysophospholipid substrates.Conclusions/significanceThese results indicate that different alterations in PLA2G6 function produce the different disease phenotypes of NBIA/INAD and dystonia-parkinsonism. INAD/NBIA is caused by loss of the ability of PLA2G6 to catalyze fatty acid release from phospholipids, which predicts accumulation of PLA2G6 phospholipid substrates and provides a mechanistic explanation for the accumulation of membranes in neuroaxonal spheroids previously observed in histopathological studies of INAD/NBIA. In contrast, dystonia-parkinsonism mutations do not appear to directly impair catalytic function, but may modify substrate preferences or regulatory mechanisms for PLA2G6.

Project description:BACKGROUND:Infantile neuroaxonal dystrophy (INAD) is a rapidly progressive neurodegenerative disorder of early onset causing premature death. It results from biallelic pathogenic variants in PLA2G6, which encodes a calcium-independent phospholipase A2. OBJECTIVE:We aim to outline the natural history of INAD and provide a comprehensive description of its clinical, radiological, laboratory, and molecular findings. MATERIALS AND METHODS:We comprehensively analyzed the charts of 28 patients: 16 patients from Riyadh, Saudi Arabia, 8 patients from North and South America and 4 patients from Europe with a molecularly confirmed diagnosis of PLA2G6-associated neurodegeneration (PLAN) and a clinical history consistent with INAD. RESULTS:In our cohort, speech impairment and loss of gross motor milestones were the earliest signs of the disease. As the disease progressed, loss of fine motor milestones and bulbar dysfunction were observed. Temporo-frontal function was among the last of the milestones to be lost. Appendicular spastic hypertonia, axial hypotonia, and hyperreflexia were common neurological findings. Other common clinical findings include nystagmus (60.7%), seizures (42.9%), gastrointestinal disease (42.9%), skeletal deformities (35.7%), and strabismus (28.6%). Cerebellar atrophy and elevations in serum AST and LDH levels were consistent features of INAD. There was a statistically significant difference when comparing patients with non-sense/truncating variants compared with missense/in-frame deletions in the time of initial concern (p?=?0.04), initial loss of language (p?=?0.001), initial loss of fine motor skills (p?=?0.009), and initial loss of bulbar skills (p?=?0.007). CONCLUSION:INAD is an ultra-rare neurodegenerative disorder that presents in early childhood, with a relentlessly progressive clinical course. Knowledge of the natural history of INAD may serve as a resource for healthcare providers to develop a targeted care plan and may facilitate the design of clinical trials to treat this disease.

Project description:BACKGROUND:INAD is an autosomal recessive neurogenetic disorder caused by biallelic pathogenic variants in PLA2G6. The downstream enzyme, iPLA2, plays a critical role in cell membrane homeostasis by helping to regulate levels of phospholipids. The clinical presentation occurs between 6?months and 3?years with global developmental regression, hypotonia, and progressive spastic tetraparesis. Progression is often rapid, resulting in severe spasticity, visual impairment, and cognitive decline, with many children not surviving past the first decade of life. To date, no accepted tool for assessing the severity of INAD exists; other commonly used scales (e.g. CHOP-INTEND, Modified Ashworth, Hammersmith Functional Motor Scale) do not accurately gauge the current severity of INAD, nor are they sensitive/specific enough to monitor disease progression. Finally, these other scales are not appropriate, because they do not address the combination of CNS, peripheral nerve, and visual pathology that occurs in children with INAD. METHODS:We have developed and validated a structured neurological examination for INAD (scored out of 80). The examination includes six main categories of pediatric developmental evaluation: 1) gross motor-and-truncal-stability skills, 2) fine motor skills, 3) bulbar function, 4) ocular function, 5) temporo-frontal function, and, 6) Functional evaluation of the autonomic nervous system. A cohort of patients diagnosed with INAD were followed prospectively to validate the score against disease severity and disease progression. RESULTS:We show significant correlation between the total neurological assessment score and months since symptom onset with a statistically significant (p?=?6.7?×?10-?07) correlation between assessment score and disease onset. As hypothesized, the coefficient of months-since-symptom-onset is strongly negative, indicating a negative correlation between total score and months since symptom onset. CONCLUSION:We have developed and validated a novel neurological assessment score in INAD that demonstrates strong correlation with disease severity and disease progression.

Dataset Information

Severe disturbance in the Ca2+ signaling in astrocytes from mouse models of human infantile neuroaxonal dystrophy with mutated Pla2g6.

Publications

Severe disturbance in the Ca2+ signaling in astrocytes from mouse models of human infantile neuroaxonal dystrophy with mutated Pla2g6.

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