Increasing involvement of CAPN1 variants in spastic ataxias and phenotype-genotype correlations

Revisiting the calpain hypothesis of learning and memory 40 years later

In 1984, Gary Lynch and Michel Baudry published in Science a novel biochemical hypothesis for learning and memory, in which they postulated that the calcium-dependent protease, calpain, played a critical role in regulating synaptic properties and the distribution of glutamate receptors, thereby participating in memory formation in hippocampus. Over the following 40 years, much work has been done to refine this hypothesis and to provide convincing arguments supporting what was viewed at the time as a simplistic view of synaptic biochemistry. We have now demonstrated that the two major calpain isoforms in the brain, calpain-1 and calpain-2, execute opposite functions in both synaptic plasticity/learning and memory and in neuroprotection/neurodegeneration. Thus, calpain-1 activation is required for triggering long-term potentiation (LTP) of synaptic transmission and learning of episodic memory, while calpain-2 activation limits the magnitude of LTP and the extent of learning. On the other hand, calpain-1 is neuroprotective while calpain-2 is neurodegenerative, and its prolonged activation following various types of brain insults leads to neurodegeneration. The signaling pathways responsible for these functions have been identified and involve local protein synthesis, cytoskeletal regulation, and regulation of glutamate receptors. Human families with mutations in calpain-1 have been reported to have impairment in motor and cognitive functions. Selective calpain-2 inhibitors have been synthesized and clinical studies to test their potential use to treat disorders associated with acute neuronal damage, such as traumatic brain injury, are being planned. This review will illustrate the long and difficult journey to validate a bold hypothesis.

White matter abnormalities in 15 subjects with SPG76

BACKGROUND AND OBJECTIVES

Hereditary spastic paraplegias (HSPs) are heterogenous genetic disorders characterized by progressive pyramidal tract involvement. SPG76 is a recently identified form of HSP, caused by biallelic calpain-1 (CAPN1) variants. The most frequently described MRI abnormality in SPG76 is mild cerebellar atrophy and non-specific white matter abnormalities were reported in only one case. Following the identification of prominent white matter abnormalities in a subject with CAPN1 variants, which delayed the diagnosis, we aimed to verify the presence of MRI patterns of white matter involvement specific to this HSP.

METHODS

We performed a retrospective radiological qualitative analysis of 15 subjects with SPG76 (4 previously unreported) initially screened for white matter involvement. Moreover, we performed quantitative analyses in our proband with available longitudinal studies.

RESULTS

We observed bilateral, periventricular white matter involvement in 12 subjects (80%), associated with multifocal subcortical abnormalities in 5 of them (33.3%). Three subjects (20%) presented only multifocal subcortical involvement. Longitudinal quantitative analyses of our proband revealed increase in multifocal white matter lesion count and increased area of periventricular white matter involvement over time.

DISCUSSION

SPG76 should be added to the list of HSPs with associated white matter abnormalities. We identified periventricular white matter involvement in subjects with SPG76, variably associated with multifocal subcortical white matter abnormalities. These findings, in the presence of progressive spastic paraparesis, can mislead the diagnostic process towards an acquired white matter disorder.

Spastic paraplegia type 76 due to novel CAPN1 mutations: three case reports with literature review

Spastic paraplegia type 76 (SPG76) is a subtype of hereditary spastic paraplegia (HSP) caused by calpain-1 (CAPN1) mutations. Our study described the phenotypic and genetic characteristics of three families with spastic ataxia due to various CAPN1 mutations and further explored the pathogenesis of the two novel mutations. The three patients were 48, 39, and 48 years old, respectively. Patients 1 and 3 were from consanguineous families, while patient 2 was sporadic. Physical examination showed hypertonia, hyperreflexia, and Babinski signs in the lower limbs. Patients 2 and 3 additionally had dysarthria and depression. CAPN1 mutations were identified by whole-exome sequencing, followed by Sanger sequencing and co-segregation analysis within the family. Functional examination of the newly identified mutations was further explored. Two homozygous mutations were detected in patient 1 (c.213dupG, p.D72Gfs*95) and patient 3 (c.1729+1G>A) with HSP, respectively. Patient 2 had compound heterozygous mutations c.853C>T (p.R285X) and c.1324G>A (p.G442S). Western blotting revealed the p.D72Gfs*95 with a smaller molecular weight than WT and p.G442S. In vitro, the wild-type calpain-1 is mostly located in the cytoplasm and colocalized with tubulin by immunostaining. However, p.D72Gfs*95 and p.G442S abnormally formed intracellular aggregation, with little colocalization with tubulin. In this study, we identified three cases with SPG76, due to four various CAPN1 mutations, presenting lower limb spasticity and ataxia, with or without bulbar involvement and emotional disorder. Among these, c.213dupG and c.1324G>A are first identified in this paper. The genotype-phenotype correlation of the SPG76 cases reported worldwide was further summarized.

The hereditary spastic paraplegias

The hereditary spastic paraplegias (HSPs) are a group of more than 90 genetic disorders in which lower extremity spasticity and weakness are either the primary neurologic impairments ("uncomplicated HSP") or when accompanied by other neurologic deficits ("complicated HSP"), important features of the clinical syndrome. Various genetic types of HSP are inherited such as autosomal dominant, autosomal recessive, X-linked, and maternal (mitochondrial) traits. Symptoms that begin in early childhood may be nonprogressive and resemble spastic diplegic cerebral palsy. Symptoms that begin later, typically progress insidiously over a number of years. Genetic testing is able to confirm the diagnosis for many subjects. Insights from gene discovery indicate that abnormalities in diverse molecular processes underlie various forms of HSP, including disturbance in axon transport, endoplasmic reticulum morphogenesis, vesicle transport, lipid metabolism, and mitochondrial function. Pathologic studies in "uncomplicated" HSP have shown axon degeneration particularly involving the distal ends of corticospinal tracts and dorsal column fibers. Treatment is limited to symptom reduction including amelioration of spasticity, reducing urinary urgency, proactive physical therapy including strengthening, stretching, balance, and agility exercise.

Fear extinction induced by activation of PKA ameliorates anxiety-like behavior in PTSD mice

Prolonged exposure (PE) therapy aiming to promote fear extinction is a useful treatment for post-traumatic stress disorder (PTSD). However, the mechanisms underlying fear extinction and effective methods used to promote fear extinction in PTSD are still lacking. In this study, we displayed dysfunctions of cyclic adenosine 3,5-monophosphate (cAMP)-protein kinase A (PKA), protein kinase B (Akt)/mammalian target of rapamycin (mTOR) and calcium signaling in peripheral serum of PTSD patients using bioinformatics analysis. Later, we confirmed the dysfunctions of cAMP-PKA, AKT/mTOR and calcium signaling in the hippocampus of PTSD mice. Moreover, the reduction of calpain1 in the hippocampus enhanced fear memory acquisition. Single activation of PKA by systemic application of rolipram (ROL) or meglumine cyclic adenylate (M-cAMP) before re-exposure promoted fear extinction and improved anxiety-like behavior in PTSD mice. Moreover, systemic application of ROL before re-exposure improved hippocampal brain-derived neurotrophic factor (BDNF)/tyrosine kinase receptor B (TrkB) signaling and calpain1/AKT/mTOR signaling. Interestingly, the effects of activation of PKA could be partially blocked by TrkB antagonist, ANA-12 and mTOR inhibitor, RAPA. Finally, intranasal administration of ROL could also adjust the abnormality of fear memory and improve anxiety-like behaviors in PTSD mice. Collectively, activation of PKA could promote fear extinction, which correlated with the reduction of anxiety-like behavior. The mechanisms were related to the BDNF/TrkB and calpain1/AKT/mTOR signaling pathways. PKA activation might be a useful complementary therapy for PE in the symptom elimination of PTSD.

Anshen Dingzhi prescription in the treatment of PTSD in mice: Investigation of the underlying mechanism from the perspective of hippocampal synaptic function

BACKGROUND

Anshen Dingzhi prescription (ADP) is an important prescription for the treatment of mental diseases in traditional Chinese medicine and is widely used to treat neuropsychiatric disorders.

PURPOSE

To explore the ameliorative effect of ADP on post-traumatic stress disorder (PTSD)-like behaviors in mice and determine the underlying mechanism.

METHODS

The constituents of ADP were analyzed by UPLC-Q-TOF/MS. The PTSD-like behaviors of mice subjected to single prolonged stress (SPS) were evaluated using behavioral tests. Potential pathological changes in the hippocampus were assessed by hematoxylin and eosin (H&E) staining. Western blotting and immunohistochemistry (IHC) were employed to detect the expression of proteins involved in relevant signaling pathways.

RESULTS

Five quality control markers (ginsenoside Rg1, ginsenoside Rb1, tenuifolin, poricoic acid B, and α-asarone) were detected in the ADP solution. The ginsenoside Rg1 content in ADP was found to be 0.114 mg/g. Mice subjected to SPS showed obvious fear generalization and anxiety-like behaviors. ADP treatment prevented the behavioral changes caused by exposure to SPS. Compared with control animals, the number of normal pyramidal cells in the hippocampal CA1 region of mice exposed to SPS was decreased and the number of degenerating pyramidal cells was increased; however, ADP administration could counteract these effects. Furthermore, the protein expression of BDNF, p-TrkB, μ-calpain, PSD95, GluN2A, GluA1, p-AKT, p-mTOR, and ARC was decreased, while that of PTEN and GluN2B was increased in the hippocampus of mice subjected to SPS compared with that in control animals; however, these changes in protein expression were reversed following ADP treatment. Importantly, the ameliorative effect of ADP on PTSD-like behaviors and synaptic protein expression were inhibited by rapamycin administration.

CONCLUSIONS

ADP administration improves PTSD-like behaviors in mice and this effect may be mediated through an mTOR-dependent improvement in synaptic function in the hippocampus.

Novel CAPN1 missense variants in complex hereditary spastic paraplegia with early-onset psychosis

CAPN1-associated hereditary spastic paraplegia (SPG76) is a rare and clinically heterogenous syndrome due to loss of calpain-1 function. Here we illustrate a translational approach to the case of an 18-year-old patient who first presented with psychiatric symptoms followed by spastic gait, intention tremor, and neurogenic bladder dysfunction, consistent with a complex form of HSP. Exome sequencing showed compound-heterozygous missense variants in CAPN1 (NM_001198868.2: c.1712A>G (p.Asn571Ser)/c.1991C>T (p.Ser664Leu)) and a previously reported heterozygous stop-gain variant in RCL1. In silico analyses of the CAPN1 variants predicted a deleterious effect and in vitro functional studies confirmed reduced calpain-1 activity and dysregulated downstream signaling. These findings support a diagnosis of SPG76 and highlight that the psychiatric symptoms can precede the motor symptoms in HSP. Our results also suggest that multiple genes can potentially contribute to complex neuropsychiatric diseases.

Utility of 7,8-dihydroxyflavone in preventing astrocytic and synaptic deficits in the hippocampus elicited by PTSD

Astrocytic functions and brain-derived neurotrophic factor (BDNF)-tyrosine kinase receptor B (TrkB) signaling pathways are impaired in stress-related neuropsychiatric diseases. Previous studies have reported neuroprotective effects of 7,8-dihydroxyflavone (7,8-DHF), a TrkB activator. Here, we investigated the molecular mechanisms underlying pathogenesis of post-traumatic stress disorder (PTSD) using a modified single-prolonged stress (SPS&S) model and the potential beneficial effects of 7,8-DHF. SPS&S reduced the hippocampal expression of glial fibrillary acidic protein (GFAP), a marker of astrocytes, and induced morphological changes in astrocytes. From the perspective of synaptic function, the SPS&S model displayed reduced expression of BDNF, p-TrkB, postsynaptic density protein 95 (PSD95), AMPA receptor subunit GluR1 (GluA1), NMDA receptor subunit N2A/N2B ratio, calpain-1, phosphorylated protein kinase B (Akt) and phosphorylated mammalian target of rapamycin (mTOR) and conversely, higher phosphatase and tension homolog (PTEN) expression in the hippocampus. Acute or continuous intraperitoneal administration of 7,8-DHF (5 mg/kg) after SPS&S procedures prevented SPS&S-induced fear memory generalization and anxiety-like behaviors as well as abnormalities of hippocampal oscillations. Most importantly, 7,8-DHF attenuated SPS&S-induced abnormal BDNF-TrkB signaling and calpain-1-dependent cascade of synaptic deficits. Furthermore, treatment with a TrkB inhibitor completely blocked while an mTOR inhibitor partially blocked the effects of 7,8-DHF on behavioral changes of SPS&S model mice. Our collective findings suggest that 7,8-DHF effectively alleviates PTSD-like symptoms, including fear generalization and anxiety-like behavior, potentially by preventing astrocytic and synaptic deficits in the hippocampus through targeting of TrkB.

A Compound Heterozygous Mutation in Calpain 1 Identifies a New Genetic Cause for Spinal Muscular Atrophy Type 4 (SMA4)

Spinal Muscular Atrophy (SMA) is a heterogeneous group of neuromuscular diseases characterized by degeneration of anterior horn cells of the spinal cord, leading to muscular atrophy and weakness. Although the major cause of SMA is autosomal recessive exon deletions or loss-of-function mutations of survival motor neuron 1 (SMN1) gene, next generation sequencing technologies are increasing the genetic heterogeneity of SMA. SMA type 4 (SMA4) is an adult onset, less severe form of SMA for which genetic and pathogenic causes remain elusive.Whole exome sequencing in a 30-year-old brother and sister with SMA4 identified a compound heterozygous mutation (p. G492R/p. F610C) in calpain-1 (CAPN1). Mutations in CAPN1 have been previously associated with cerebellar ataxia and hereditary spastic paraplegia. Using skin fibroblasts from a patient bearing the p. G492R/p. F610C mutation, we demonstrate reduced levels of CAPN1 protein and protease activity. Functional characterization of the SMA4 fibroblasts revealed no changes in SMN protein levels and subcellular distribution. Additional cellular pathways associated with SMA remain unaffected in the patient fibroblasts, highlighting the tissue specificity of CAPN1 dysfunction in SMA4 pathophysiology. This study provides genetic and functional evidence of CAPN1 as a novel gene for the SMA4 phenotype and expands the phenotype of CAPN1 mutation disorders.

Clinical and genetic spectra of 1550 index patients with hereditary spastic paraplegia

Hereditary spastic paraplegia refers to rare genetic neurodevelopmental and/or neurodegenerative disorders in which spasticity due to length-dependent damage to the upper motor neuron is a core sign. Their high clinical and genetic heterogeneity makes their diagnosis challenging. Multigene panels allow a high-throughput targeted analysis of the increasing number of genes involved using next-generation sequencing. We report here the clinical and genetic results of 1550 index cases tested for variants in a panel of hereditary spastic paraplegia related genes analyzed in routine diagnosis. A causative variant was found in 475 patients (30.7%) in 35/65 screened genes. SPAST and SPG7 were the most frequently mutated genes, representing 142 (9.2%) and 75 (4.8%) index cases of the whole series, respectively. KIF1A, ATL1, SPG11, KIF5A and REEP1 represented more than 1% (> 17 cases) each. There were 661 causative variants (382 different ones) and 30 of them were structural variants. This large cohort allowed us obtaining an overview of the clinical and genetic spectrum of hereditary spastic paraplegia in clinical practice. Because of the wide phenotypic variability, there was no very specific sign that could predict the causative gene but there were some constellations of symptoms that were found often related to specific subtypes. Finally, we confirmed the diagnostic effectiveness of a targeted sequencing panel as a first-line genetic test in hereditary spastic paraplegia. This is a pertinent strategy because of the relative frequency of several known genes (i.e.: SPAST, KIF1A) and it allows identifying variants in the rarest involved genes and to detect structural rearrangements via coverage analysis, which is less efficient in exome data sets. It is crucial because these structural variants represent a significant proportion of the pathogenic hereditary spastic paraplegia variants (∼6% of patients), notably for SPAST and REEP1. In a subset of 42 index cases negative for the targeted multigene panel, subsequent whole exome sequencing allowed to reach a theoretical diagnosis yield of ∼50%. We then propose a two-step strategy combining the use of a panel of genes followed by whole exome sequencing in negative cases.

Insights into Clinical, Genetic, and Pathological Aspects of Hereditary Spastic Paraplegias: A Comprehensive Overview

Hereditary spastic paraplegias (HSP) are a heterogeneous group of motor neurodegenerative disorders that have the core clinical presentation of pyramidal syndrome which starts typically in the lower limbs. They can present as pure or complex forms with all classical modes of monogenic inheritance reported. To date, there are more than 100 loci/88 spastic paraplegia genes (SPG) involved in the pathogenesis of HSP. New patterns of inheritance are being increasingly identified in this era of huge advances in genetic and functional studies. A wide range of clinical symptoms and signs are now reported to complicate HSP with increasing overall complexity of the clinical presentations considered as HSP. This is especially true with the emergence of multiple HSP phenotypes that are situated in the borderline zone with other neurogenetic disorders. The genetic diagnostic approaches and the utilized techniques leave a diagnostic gap of 25% in the best studies. In this review, we summarize the known types of HSP with special focus on those in which spasticity is the principal clinical phenotype ("SPGn" designation). We discuss their modes of inheritance, clinical phenotypes, underlying genetics, and molecular pathways, providing some observations about therapeutic opportunities gained from animal models and functional studies. This review may pave the way for more analytic approaches that take into consideration the overall picture of HSP. It will shed light on subtle associations that can explain the occurrence of the disease and allow a better understanding of its observed variations. This should help in the identification of future biomarkers, predictors of disease onset and progression, and treatments for both better functional outcomes and quality of life.