A proteomic analysis of pediatric seizure cases associated with astrocytic inclusions

Hyaline protoplasmic astrocytopathy in epilepsy

Hyaline protoplasmic astrocytopathy (HPA) describes a rare histologic finding of eosinophilic, hyaline cytoplasmic inclusions in astrocytes, predominantly in the cerebral cortex. It has mainly been observed in children and adults with a history of developmental delay and epilepsy, frequently with focal cortical dysplasia (FCD), but the nature and significance of these inclusions are unclear. In this study, we review the clinical and pathologic features of HPA and characterize the inclusions and brain tissue in which they are seen in surgical resection specimens from five patients with intractable epilepsy and HPA compared to five patients with intractable epilepsy without HPA using immunohistochemistry for filamin A, previously shown to label these inclusions, and a variety of astrocytic markers including aldehyde dehydrogenase 1 family member L1 (ALDH1L1), SRY-Box Transcription Factor 9 (SOX9), and glutamate transporter 1/excitatory amino acid transporter 2 (GLT-1/EAAT2) proteins. The inclusions were positive for ALDH1L1 with increased ALDH1L1 expression in areas of gliosis. SOX9 was also positive in the inclusions, although to a lesser intensity than the astrocyte nuclei. Filamin A labeled the inclusions but also labeled reactive astrocytes in a subset of patients. The immunoreactivity of the inclusions for various astrocytic markers and filamin A as well as the positivity of filamin A in reactive astrocytes raise the possibility that these astrocytic inclusions may be the result of an uncommon reactive or degenerative phenomenon.

GPR37L1 controls maturation and organization of cortical astrocytes during development

Astrocyte maturation is crucial to proper brain development and function. This maturation process includes the ramification of astrocytic morphology and the establishment of astrocytic domains. While this process has been well-studied, the mechanisms by which astrocyte maturation is initiated are not well understood. GPR37L1 is an astrocyte-specific G protein-coupled receptor (GPCR) that is predominantly expressed in mature astrocytes and has been linked to the modulation of seizure susceptibility in both humans and mice. To investigate the role of GPR37L1 in astrocyte biology, RNA-seq analyses were performed on astrocytes immunopanned from P7 Gpr37L1-/- knockout (L1KO) mouse cortex and compared to those from wild-type (WT) mouse cortex. These RNA-seq studies revealed that pathways involved in central nervous system development were altered and that L1KO cortical astrocytes express lower amounts of mature astrocytic genes compared to WT astrocytes. Immunohistochemical studies of astrocytes from L1KO mouse brain revealed that these astrocytes exhibit overall shorter total process length, and are also less complex and spaced further apart from each other in the mouse cortex. This work sheds light on how GPR37L1 regulates cellular processes involved in the control of astrocyte biology and maturation.

Hyaline Protoplasmic Astrocytopathy in the Setting of Epilepsy

OBJECTIVES

Cerebral hyaline protoplasmic astrocytopathy (HPA) is a clinicopathologic entity characterized by eosinophilic cytoplasmic inclusions within astrocytes. It has been observed in a subset of patients with early-onset epilepsy, brain malformations, and developmental delay. The exact association of this entity with epilepsy is still unknown. This report, with its review of the literature, aims to summarize HPA features to raise awareness regarding this entity.

METHODS

We report on 2 HPA cases and critically review the literature.

RESULTS

Approximately 42 cases of HPA have been reported, including the 2 cases presented here, consisting of 23 female and 19 male patients. Patient age ranged from 3 to 39 years. All patients had early-onset seizures (3-20 months of age), ranging from partial to generalized, that were refractory despite treatment with antiepileptic drugs. Postoperative follow-up intervals ranged from 2 to 93 months, and the clinical outcome was graded according to the Engel classification, showing variable results.

CONCLUSIONS

Clinicians should consider HPA in differential diagnosis in patients with intractable seizures, especially when they are associated with developmental delay and brain malformations. Increasing awareness of this entity among pathologists may promote better understanding of this condition as well as better diagnosis and treatment for these patients.

Neuroproteomics in Epilepsy: What Do We Know so Far?

Epilepsies are chronic neurological diseases that affect approximately 2% of the world population. In addition to being one of the most frequent neurological disorders, treatment for patients with epilepsy remains a challenge, because a proportion of patients do not respond to the antiseizure medications that are currently available. This results in a severe economic and social burden for patients, families, and the healthcare system. A characteristic common to all forms of epilepsy is the occurrence of epileptic seizures that are caused by abnormal neuronal discharges, leading to a clinical manifestation that is dependent on the affected brain region. It is generally accepted that an imbalance between neuronal excitation and inhibition generates the synchronic electrical activity leading to seizures. However, it is still unclear how a normal neural circuit becomes susceptible to the generation of seizures or how epileptogenesis is induced. Herein, we review the results of recent proteomic studies applied to investigate the underlying mechanisms leading to epilepsies and how these findings may impact research and treatment for these disorders.

Filamin A-negative hyaline astrocytic inclusions in pediatric patients with intractable epilepsy: report of 2 cases

Although rare, hyaline cytoplasmic inclusions isolated to astrocytes of the cerebral cortex have been identified in a spectrum of diseases ranging from intractable epilepsy in pediatric patients with only mild to moderate developmental delays to Aicardi syndrome. These inclusions classically stain positive for filamin A, giving rise to the term "filaminopathies." The authors report on 2 pediatric patients with intractable epilepsy and developmental delay who uniquely displayed filamin A-negative hyaline astrocytic inclusions in resected brain tissues. Additionally, these inclusions stained positive for S100 and negative for glial fibrillary acidic protein, chromogranin, neurofilament, CD34, vimentin, periodic acid-Schiff (PAS), and Alcian blue. These are the first reported cases of filamin A-negative hyaline astrocytic inclusions, providing a novel variation on a previously reported entity and justification to further investigate the pathogenesis of these inclusions. The authors compare their findings with previously reported cases and review the literature on hyaline astrocytic inclusions in intractable pediatric epilepsy.

Proteomic analysis of human epileptic neocortex predicts vascular and glial changes in epileptic regions

Epilepsy is a common neurological disorder, which is not well understood at the molecular level. Exactly why some brain regions produce epileptic discharges and others do not is not known. Patients who fail to respond to antiseizure medication (refractory epilepsy) can benefit from surgical removal of brain regions to reduce seizure frequency. The tissue removed in these surgeries offers an invaluable resource to uncover the molecular and cellular basis of human epilepsy. Here, we report a proteomic study to determine whether there are common proteomic patterns in human brain regions that produce epileptic discharges. We analyzed human brain samples, as part of the Systems Biology of Epilepsy Project (SBEP). These brain pieces are in vivo electrophysiologically characterized human brain samples withdrawn from the neocortex of six patients with refractory epilepsy. This study is unique in that for each of these six patients the comparison of protein expression was made within the same patient: a more epileptic region was compared to a less epileptic brain region. The amount of epileptic activity was defined for each patient as the frequency of their interictal spikes (electric activity between seizures that is a parameter strongly linked to epilepsy). Proteins were resolved from three subcellular fractions, using a 2D differential gel electrophoresis (2D-DIGE), revealing 31 identified protein spots that changed significantly. Interestingly, glial fibrillary acidic protein (GFAP) was found to be consistently down regulated in high spiking brain tissue and showed a strong negative correlation with spike frequency. We also developed a two-step analysis method to select for protein species that changed frequently among the patients and identified these proteins. A total of 397 protein spots of interest (SOI) were clustered by protein expression patterns across all samples. These clusters were used as markers and this analysis predicted proteomic changes due to both histological differences and molecular pathways, revealed by examination of gene ontology clusters. Our experimental design and proteomic data analysis predicts novel glial changes, increased angiogenesis, and changes in cytoskeleton and neuronal projections between high and low interictal spiking regions. Quantitative histological staining of these same tissues for both the vascular and glial changes confirmed these findings, which provide new insights into the structural and functional basis of neocortical epilepsy.

Variations in the cerebrospinal fluid proteome following traumatic brain injury and subarachnoid hemorrhage

BACKGROUND

Proteomic analysis of cerebrospinal fluid (CSF) has shown great promise in identifying potential markers of injury in neurodegenerative diseases [1-13]. Here we compared CSF proteomes in healthy individuals, with patients diagnosed with traumatic brain injury (TBI) and subarachnoid hemorrhage (SAH) in order to characterize molecular biomarkers which might identify these different clinical states and describe different molecular mechanisms active in each disease state.

METHODS

Patients presenting to the Neurosurgery service at the Louisiana State University Hospital-Shreveport with an admitting diagnosis of TBI or SAH were prospectively enrolled. Patients undergoing CSF sampling for diagnostic procedures were also enrolled as controls. CSF aliquots were subjected to 2-dimensional gel electrophoresis (2D GE) and spot percentage densities analyzed. Increased or decreased spot expression (compared to controls) was defined in terms of in spot percentages, with spots showing consistent expression change across TBI or SAH specimens being followed up by Matrix-Assisted Laser Desorption/Ionization mass spectrometry (MALDI-MS). Polypeptide masses generated were matched to known standards using a search of the NCBI and/or GenPept databases for protein matches. Eight hundred fifteen separately identifiable polypeptide migration spots were identified on 2D GE gels. MALDI-MS successfully identified 13 of 22 selected 2D GE spots as recognizable polypeptides.

RESULTS

Statistically significant changes were noted in the expression of fibrinogen, carbonic anhydrase-I (CA-I), peroxiredoxin-2 (Prx-2), both α and β chains of hemoglobin, serotransferrin (Tf) and N-terminal haptoglobin (Hp) in TBI and SAH specimens, as compared to controls. The greatest mean fold change among all specimens was seen in CA-I and Hp at 30.7 and -25.7, respectively. TBI specimens trended toward greater mean increases in CA-I and Prx-2 and greater mean decreases in Hp and Tf.

CONCLUSIONS

Consistent CSF elevation of CA-I and Prx-2 with concurrent depletion of Hp and Tf may represent a useful combination of biomarkers for the prediction of severity and prognosis following brain injury.

The Fault in Their Stars-Accumulating Astrocytic Inclusions Associated With Clusters of Epileptic Spasms in Children With Global Developmental Delay

BACKGROUND

The presence of cerebral astrocytic inclusions recently has been described in a subset of children with early-onset refractory epilepsy, with or without structural brain malformations, and varying degrees of developmental delay.

METHODS

We describe two new individuals with epilepsy with astrocytic inclusions and suggest that in some children this disorder may represent a unique hemispheric epilepsy. We review previously reported individuals with epilepsy with astrocytic inclusions.

RESULTS

Two children with early onset epilepsy with astrocytic inclusions had refractory clusters of epileptic spasms, developmental delay, abnormal neuroimaging, and hemispheric or diffuse interictal epileptiform discharges. In both children, the initial focal resection of the putative epileptogenic zone was unsuccessful and pathology failed to show astrocytic inclusions. Subsequently, both children underwent functional hemispherectomy due to ongoing clusters of epileptic spasms, and the presence of multilobar astrocytic inclusions was demonstrated. Postoperatively, both children have remained seizure free in the short-term with improved development.

CONCLUSIONS

We highlight that functional hemispherectomy may be required for seizure control in a select subset of children with clusters of epileptic spasms, astrocytic inclusions, and global developmental delay. Given the small number of documented patients, however, ongoing collaboration is needed to better understand the pathophysiology of this condition and determine the optimal way to diagnose and manage these children.

Expression of Carbonic Anhydrase I in Motor Neurons and Alterations in ALS

Carbonic anhydrase I (CA1) is the cytosolic isoform of mammalian α-CA family members which are responsible for maintaining pH homeostasis in the physiology and pathology of organisms. A subset of CA isoforms are known to be expressed and function in the central nervous system (CNS). CA1 has not been extensively characterized in the CNS. In this study, we demonstrate that CA1 is expressed in the motor neurons in human spinal cord. Unexpectedly, a subpopulation of CA1 appears to be associated with endoplasmic reticulum (ER) membranes. In addition, the membrane-associated CA1s are preferentially upregulated in amyotrophic lateral sclerosis (ALS) and exhibit altered distribution in motor neurons. Furthermore, long-term expression of CA1 in mammalian cells activates apoptosis. Our results suggest a previously unknown role for CA1 function in the CNS and its potential involvement in motor neuron degeneration in ALS.

Hyaline Protoplasmic Astrocytopathy: A Clinicopathologic Study

OBJECTIVES

Hyaline protoplasmic astrocytopathy is a rare condition marked by the accumulation of various proteins in the cytoplasm of protoplasmic astrocytes.

METHODS

This study retrospectively reviews the clinicopathologic features of 14 patients (nine females; mean age, 9.1 years) with hyaline protoplasmic astrocytopathy.

RESULTS

Patients had chronic seizures (mean duration, 101.1 months); mean age at seizure onset was 6.9 months. Three patients had Aicardi syndrome, and one patient had tuberous sclerosis. Associated focal cortical dysplasia was noted in all 14 cases. Patterns of dysplasia observed included International League Against Epilepsy (ILAE) type I Ib (n = 7), ILAE type Ib (n = 4), ILAE type Ic (n = 2), and ILAE type IIa (n = 1). Additional pathologic findings included evidence of contusional damage (n = 5), gray matter nodular heterotopias (n = 3), polymicrogygria (n = 2), hemimegalencephaly (n = 2), and hippocampal sclerosis (ILAE type II, CA1 sclerosis) (n = 1). Postoperative follow-up intervals ranged from two to 93 months (mean, 31.2 months). Seven patients were free of seizures or had only rare disabling seizures (Engel I/II) at most recent follow-up. Two patients had recurrent seizures with no worthwhile improvement (Engel IV) at follow-up.

CONCLUSIONS

The current series supports an association of Aicardi syndrome (21% of cases) and focal cortical dysplasia (100% of cases) and hyaline protoplasmic astrocytopathy.

Hyaline protoplasmic astrocytopathy in the setting of tuberous sclerosis

Hyaline protoplasmic astrocytopathy is a rare disorder marked by an accumulation of protein material in the cytoplasm of astrocytic cells, mostly in the cortex. The finding has been described in Aicardi syndrome (agenesis of the corpus callosum, chorioretinal lacunae and infantile spasms) as well as in patients with pharmacoresistant epilepsy and in association with focal cortical dysplasia, polymicrogyria and nodular heterotopia. This report describes the first case of this entity described in a patient with tuberous sclerosis. The patient was a 3-year-old boy who presented at age 2months with medically intractable seizures. Has mother has a tuberous sclerosis 2 (TSC 2) gene abnormality and a diagnosis of tuberous sclerosis. On imaging, he was noted to have multiple lesions in the left parietal and temporal lobes consistent with focal cortical dysplasia and a subependymal nodule. He additionally had two hypopigmented lesions on the skin. He underwent resection of the left parietal lobe 32months after seizure onset. Histopathologic examination showed eosinophilic cytoplasmic inclusions within astrocytes in the cortex and superficial white matter focally accompanied by a disordered cortical architecture with dysmorphic neurons and balloon cells, consistent with focal cortical dysplasia classified as type IIb according to International League Against Epilepsy classification criteria (ILAE type IIb). At the time of most recent follow-up, 93months postoperatively, he is still experiencing seizures with overall worthwhile improvement while on seizure medication.

Clinical, EEG, MRI, MEG, and surgical outcomes of pediatric epilepsy with astrocytic inclusions versus focal cortical dysplasia

OBJECTIVE

Astrocytic inclusions (AIs) have been identified on histologic specimens of patients with early onset seizures, and the proteomic contents have been described. The aim of this study was to compare the clinical, electroencephalography (EEG), magnetoencephalography (MEG), magnetic resonance imaging (MRI), and surgical outcomes of AIs relative to focal cortical dysplasia (FCD).

METHODS

We assessed the clinical manifestations, semiology, ictal and interictal features on video-EEG, MEG, MRI features, and surgical outcomes of children with histologically proven AIs compared to FCD.

RESULTS

Six children had AIs and 27 had FCD. Children with AIs had an earlier age at seizure onset, periodic spasms (all children), and interictal epileptiform discharges consisting of a mixture of generalized or diffuse hemispheric slow waves, sharp waves, spikes and polyspikes. Children with FCD were less likely to have spasms (4/27 [15%]), and the morphology of the diffuse hemispheric or generalized discharges were different from those of AI, consisting of spike-and-waves, polyspike-and-waves, sharp-and-slow waves, and paroxysmal fast activity. Patients with AIs were less likely to have tightly clustered MEG spike sources (3/6 [50%] vs. 23/27 [85%]), and more likely to demonstrate abnormal sulcation and gyration pattern (4/6 [67%] vs. 2/27 [7%]) and gray matter heterotopia (2/6 [33%] vs. 0/27 [0%]) than patients with FCD. Four children with AIs had resection and two had biopsy but did not undergo resection. Children with AIs had lower rates of seizure freedom after surgery compared to FCD (1/4 [25%] vs. 15/27 [56%], respectively).

SIGNIFICANCE

Although there were some similarities between AIs and FCD, patients with AIs were more likely to present with early onset periodic spasms, have unusual interictal epileptiform discharges, abnormal sulcation, gyration pattern, and gray matter heterotopia, and were less likely to be seizure free following surgical resection relative to FCD. Further study with a larger sample size is needed to validate our findings.

Astrocytes and disease: a neurodevelopmental perspective

Astrocytes are no longer seen as a homogenous population of cells. In fact, recent studies indicate that astrocytes are morphologically and functionally diverse and play critical roles in neurodevelopmental diseases such as Rett syndrome and fragile X mental retardation. This review summarizes recent advances in astrocyte development, including the role of neural tube patterning in specification and developmental functions of astrocytes during synaptogenesis. We propose here that a precise understanding of astrocyte development is critical to defining heterogeneity and could lead advances in understanding and treating a variety of neuropsychiatric diseases.