Metabolomic investigation of CLN6 neuronal ceroid lipofuscinosis in affected South Hampshire sheep

Metabolomics-a powerful tool in livestock research

Advancements in the Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS) along with recent developments in omics sciences have resulted in a better understanding of molecular mechanisms and pathways associated with the physio-pathological state of the animal. Metabolomics is a post-genomics tool that deals with small molecular metabolites in a given set of time which provides clear information about the status of an organism. Recently many researchers mainly focus their research on metabolomics studies due to its valuable information in the various fields of livestock management and precision dairying. The main aim of the present review is to provide an insight into the current research output from different sources and application of metabolomics in various areas of livestock including nutri-metabolomics, disease diagnosis advancements, reproductive disorders, pharmaco-metabolomics, genomics studies, and dairy production studies. The present review would be helpful in understanding the metabolomics methodologies and use of livestock metabolomics in various areas in a brief way.

Neuronal progenitor cells-based metabolomics study reveals dysregulated lipid metabolism and identifies putative biomarkers for CLN6 disease

Neuronal ceroid lipofuscinosis 6 (CLN6) is a rare and fatal autosomal recessive disease primarily affecting the nervous system in children. It is caused by a pathogenic mutation in the CLN6 gene for which no therapy is available. Employing an untargeted metabolomics approach, we analyzed the metabolic changes in CLN6 subjects to see if this system could potentially yield biomarkers for diagnosis and monitoring disease progression. Neuronal-like cells were derived from human fibroblast lines from CLN6-affected subjects (n = 3) and controls (wild type, n = 3). These were used to assess the potential of a neuronal-like cell-based metabolomics approach to identify CLN6 distinctive and specific biomarkers. The most impacted metabolic profile is associated with sphingolipids, glycerophospholipids metabolism, and calcium signaling. Over 2700 spectral features were screened, and fifteen metabolites were identified that differed significantly between both groups, including the sphingolipids C16 GlcCer, C24 GlcCer, C24:1 GlcCer and glycerophospholipids PG 40:6 and PG 40:7. Of note, these fifteen metabolites were downregulated in the CLN6 disease group. This study is the first to analyze the metabolome of neuronal-like cells with a pathogenic mutation in the CLN6 gene and to provide insights into their metabolomic alterations. This could allow for the development of novel biomarkers for monitoring CLN6 disease.

Loss of Cln5 causes altered neurogenesis in a mouse model of a childhood neurodegenerative disorder

Neural stem/progenitor cells (NPCs) generate new neurons in the brain throughout an individual's lifetime in an intricate process called neurogenesis. Neurogenic alterations are a common feature of several adult-onset neurodegenerative diseases. The neuronal ceroid lipofuscinoses (NCLs) are the most common group of inherited neurodegenerative diseases that mainly affect children. Pathological features of the NCLs include accumulation of lysosomal storage material, neuroinflammation and neuronal degeneration, yet the exact cause of this group of diseases remains poorly understood. The function of the CLN5 protein, causative of the CLN5 disease form of NCL, is unknown. In the present study, we sought to examine neurogenesis in the neurodegenerative disorder caused by loss of Cln5 Our findings demonstrate a newly identified crucial role for CLN5 in neurogenesis. We report for the first time that neurogenesis is increased in Cln5-deficient mice, which model the childhood neurodegenerative disorder caused by loss of Cln5 Our results demonstrate that, in Cln5 deficiency, proliferation of NPCs is increased, NPC migration is reduced and NPC differentiation towards the neuronal lineage is increased concomitantly with functional alterations in the NPCs. Moreover, the observed impairment in neurogenesis is correlated with increased expression of the pro-inflammatory cytokine IL-1β. A full understanding of the pathological mechanisms that lead to disease and the function of the NCL proteins are critical for designing effective therapeutic approaches for this devastating neurodegenerative disorder.

Progress in the Development of Small Molecule Therapeutics for the Treatment of Neuronal Ceroid Lipofuscinoses (NCLs)

The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited and incurable neurodegenerative disorders primarily afflicting the pediatric population. Current treatment regimens offer only symptomatic relief and do not target the underlying cause of the disease. Although the underlying pathophysiology that drives disease progression is unknown, several small molecules have been identified with diverse mechanisms of action that provide promise for the treatment of this devastating disease. This review aims to summarize the current cellular and animal models available for the identification of potential therapeutics and presents the current state of knowledge on small molecule compounds that demonstrate in vitro and/or in vivo efficacy across the NCLs with an emphasis on targets of action.

Neuroinflammatory paradigms in lysosomal storage diseases

Lysosomal storage diseases (LSDs) include approximately 70 distinct disorders that collectively account for 14% of all inherited metabolic diseases. LSDs are caused by mutations in various enzymes/proteins that disrupt lysosomal function, which impairs macromolecule degradation following endosome-lysosome and phagosome-lysosome fusion and autophagy, ultimately disrupting cellular homeostasis. LSDs are pathologically typified by lysosomal inclusions composed of a heterogeneous mixture of various proteins and lipids that can be found throughout the body. However, in many cases the CNS is dramatically affected, which may result from heightened neuronal vulnerability based on their post-mitotic state. Besides intrinsic neuronal defects, another emerging factor common to many LSDs is neuroinflammation, which may negatively impact neuronal survival and contribute to neurodegeneration. Microglial and astrocyte activation is a hallmark of many LSDs that affect the CNS, which often precedes and predicts regions where eventual neuron loss will occur. However, the timing, intensity, and duration of neuroinflammation may ultimately dictate the impact on CNS homeostasis. For example, a transient inflammatory response following CNS insult/injury can be neuroprotective, as glial cells attempt to remove the insult and provide trophic support to neurons. However, chronic inflammation, as seen in several LSDs, can promote neurodegeneration by creating a neurotoxic environment due to elevated levels of cytokines, chemokines, and pro-apoptotic molecules. Although neuroinflammation has been reported in several LSDs, the cellular basis and mechanisms responsible for eliciting neuroinflammatory pathways are just beginning to be defined. This review highlights the role of neuroinflammation in select LSDs and its potential contribution to neuron loss.

A murine model of variant late infantile ceroid lipofuscinosis recapitulates behavioral and pathological phenotypes of human disease

Neuronal ceroid lipofuscinoses (NCLs; also known collectively as Batten Disease) are a family of autosomal recessive lysosomal storage disorders. Mutations in as many as 13 genes give rise to ∼10 variants of NCL, all with overlapping clinical symptomatology including visual impairment, motor and cognitive dysfunction, seizures, and premature death. Mutations in CLN6 result in both a variant late infantile onset neuronal ceroid lipofuscinosis (vLINCL) as well as an adult-onset form of the disease called Type A Kufs. CLN6 is a non-glycosylated membrane protein of unknown function localized to the endoplasmic reticulum (ER). In this study, we perform a detailed characterization of a naturally occurring Cln6 mutant (Cln6^nclf) mouse line to validate its utility for translational research. We demonstrate that this Cln6^nclf mutation leads to deficits in motor coordination, vision, memory, and learning. Pathologically, we demonstrate loss of neurons within specific subregions and lamina of the cortex that correlate to behavioral phenotypes. As in other NCL models, this model displays selective loss of GABAergic interneuron sub-populations in the cortex and the hippocampus with profound, early-onset glial activation. Finally, we demonstrate a novel deficit in memory and learning, including a dramatic reduction in dendritic spine density in the cerebral cortex, which suggests a reduction in synaptic strength following disruption in CLN6. Together, these findings highlight the behavioral and pathological similarities between the Cln6^nclf mouse model and human NCL patients, validating this model as a reliable format for screening potential therapeutics.

Age-dependent therapeutic effect of memantine in a mouse model of juvenile Batten disease

Currently there is no treatment for juvenile Batten disease, a fatal childhood neurodegenerative disorder caused by mutations in the CLN3 gene. The Cln3-knockout (Cln3(Δex1-6)) mouse model recapitulates several features of the human disorder. Cln3(Δex1-6) mice, similarly to juvenile Batten disease patients, have a motor coordination deficit detectable as early as postnatal day 14. Previous studies demonstrated that acute attenuation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamate receptor activity by the non-competitive AMPA antagonist, EGIS-8332, in both 1- and 6-7-month-old Cln3(Δex1-6) mice results in improvement in motor coordination. Here we show that acute inhibition of N-methyl-D-aspartate (NMDA)-type glutamate receptors by memantine (1 and 5 mg/kg i.p.) had no effect on the impaired motor coordination of one-month-old Cln3(Δex1-6) mice. At a later stage of the disease, in 6-7-month-old Cln3(Δex1-6) mice, memantine induced a delayed but extended (8 days) improvement of motor skills similarly to that observed previously with EGIS-8332 treatment. An age-dependent therapeutic effect of memantine implies that the pathomechanism in juvenile Batten disease changes during disease progression. In contrast to acute treatment, repeated administration of memantine or EGIS-8332 (1 mg/kg, once a week for 4 weeks) to 6-month-old Cln3(Δex1-6) mice had no beneficial effect on motor coordination. Moreover, repeated treatments did not impact microglial activation or the survival of vulnerable neuron populations. Memantine did not affect astrocytosis in the cortex. EGIS-8332, however, decreased astrocytic activation in the somatosensory barrelfield cortex. Acute inhibition of NMDA receptors can induce a prolonged therapeutic effect, identifying NMDA receptors as a new therapeutic target for juvenile Batten disease.

Late infantile neuronal ceroid lipofuscinosis and dopamine deficiency

Neuronal ceroid lipofuscinosis is a severe neurodegenerative lysosomal storage disorder. Gamma-aminobutyric acid and glutamate deficiency have been reported with CLN1, CLN3, and CLN6. Isolated biopterin/neopterin without dopamine deficiency has been reported in 1 patient with a CLN2 mutation. This report describes a patient with a CLN2 mutation with symptomatic biopterin and dopamine deficiency. A 4-year-old boy presented with intractable epilepsy and developmental regression starting 1 year previously. His exam showed retinopathy, scanning speech, dysmetria, and ataxic fenestrating gait with stooped posture. Electroencephalogram showed generalized spikes with occipital spikes on slow photic stimulation. Brain magnetic resonance images 1 year apart showed significant diffuse atrophy. CLN2 gene sequencing showed pathogenic compound heterozygous mutations. Cerebrospinal fluid neurotransmitters showed low homovanillic acid and tetrahydrobiopterin. Levodopa-carbidopa resulted in dramatic improvement of gait. Dopamine/biopterin deficiency is a possible secondary manifestation of CLN2 mutations. Levodopa and dopamine agonists might be useful in treating these secondary abnormalities and improving quality of life in these patients.

Deletion of btn1, an orthologue of CLN3, increases glycolysis and perturbs amino acid metabolism in the fission yeast model of Batten disease

The neuronal ceroid lipofuscinoses (NCLs) constitute a group of autosomal recessive neurodegenerative diseases affecting children. To date, the disease pathogenesis remains unknown, although the role of lysosomal impairment is widely recognized across the different diseases. Recently, the creation of simple models of juvenile NCL (Batten disease) has provided additional insights into the disease mechanism at the molecular level. We report defects in metabolism identified in the Schizosacchromyces pombe yeast model, where btn1, the orthologue of CLN3, has been deleted, using a metabolomics approach based on high resolution 1H and 13C NMR spectroscopy. Such changes represent the first documented metabolic changes associated with deletion of btn1. A decrease in extracellular glucose and increases in the concentration of extracellular ethanol and alanine labelling demonstrate increased glycolytic flux that may arise from vacuolar impairment, whilst amino acid changes were detected which were also in accordance with defective vacuolar functionality. That these changes were detected using a metabolomic based approach advocates its use to further analyse other yeast models of human disease to better understand the function of orthologue genes.

Effects of pentylenetetrazole-induced seizures on metabolomic profiles of rat brain

Epilepsy is one of the most common neurological disorders and approximately one-third of patients with epilepsy are resistant to treatment. In order to develop our understanding of the metabolic changes occurring during seizure a metabolomic approach was employed. Using a pentylenetetrazole (PTZ) kindling model of epilepsy metabolomic analysis of brain extracts from the cerebellum, brain stem, prefrontal cortex and hippocampus was performed. Principal component analysis (PCA) of the (1)H NMR derived data revealed a distinct metabolic profile for each brain region. In order to assess the changes occurring following seizure partial least square discriminant analysis (PLS-DA) models for each brain region for PTZ-kindled and control animals were constructed. For all the brain regions good predictive models were built and the discriminating metabolites were identified. Results following one injection of PTZ indicated that the changes observed in the cerebellum and hippocampus were mainly due to seizure. In the hippocampus of PTZ-kindled animals the metabolites changing included lactate, succinate, GABA, NAA, choline and taurine. Analysis of the cerebellum of PTZ-kindled animals revealed changes in lactate, myo-inositol, choline, GABA, creatine, succinate, phosphocholine and GPC. Overall, the results indicate that seizure may be associated with an increase in energy demand, altered neurotransmitter balance and an increase in neuronal loss and gliosis.

Neuropeptide changes and neuroactive amino acids in CSF from humans and sheep with neuronal ceroid lipofuscinoses (NCLs, Batten disease)

Anomalies in neuropeptides and neuroactive amino acids have been postulated to play a role in neurodegeneration in a variety of diseases including the inherited neuronal ceroid lipofuscinoses (NCLs, Batten disease). These are often indicated by concentration changes in cerebrospinal fluid (CSF). Here we compare CSF neuropeptide concentrations in patients with the classical juvenile CLN3 form of NCL and the classical late infantile CLN2 form with neuropeptide and neuroactive amino acid concentrations in CSF from sheep with the late infantile variant CLN6 form. A marked disease related increase in CSF concentrations of neuron specific enolase and tau protein was noted in the juvenile CLN3 patients but this was not observed in an advanced CLN2 patient nor CLN6 affected sheep. No changes were noted in S-100b, GFAP or MBP in patients or of S-100b, GFAP or IGF-1 in affected sheep. There were no disease related changes in CSF concentrations of the neuroactive amino acids, aspartate, glutamate, serine, glutamine, glycine, taurine and GABA in these sheep. The changes observed in the CLN3 patients may be progressive markers of neurodegeneration, or of underlying metabolic changes perhaps associated with CLN3 specific changes in neuroactive amino acids, as have been postulated. The lack of changes in the CLN2 and CLN6 subjects indicate that these changes are not shared by the CLN2 or CLN6 forms and changes in CSF concentrations of these compounds are unreliable as biomarkers of neurodegeneration in the NCLs in general.

Location and connectivity determine GABAergic interneuron survival in the brains of South Hampshire sheep with CLN6 neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs, Batten disease) are fatal inherited neurodegenerative diseases. Sheep affected with the CLN6 form provide a valuable model to investigate underlying disease mechanisms from preclinical stages. Excitatory neuron loss in these sheep is markedly regional, localized early reactive changes accurately predicting neuron loss and subsequent symptom development. This investigation of GABAergic interneuron loss revealed similar regional effects that correlate with symptoms. Loss of parvalbumin positive neurons from the affected cortex was apparent at four months and became profound by 19 months, as was somatostatin positive neuron loss to a lesser extent. Conversely calbindin and neuropeptide Y positive neurons were relatively preserved and calretinin staining temporarily increased. Staining of subcortical regions was more intense but subcortical architecture remained relatively intact. Discrete subcortical changes followed from cortical changes in interconnected regions. These data highlight cellular location and interconnectivity as the major determinants of neuron survival, rather than phenotype.

The human cerebrospinal fluid metabolome

With continuing improvements in analytical technology and an increased interest in comprehensive metabolic profiling of biofluids and tissues, there is a growing need to develop comprehensive reference resources for certain clinically important biofluids, such as blood, urine and cerebrospinal fluid (CSF). As part of our effort to systematically characterize the human metabolome we have chosen to characterize CSF as the first biofluid to be intensively scrutinized. In doing so, we combined comprehensive NMR, gas chromatography-mass spectrometry (GC-MS) and liquid chromatography (LC) Fourier transform-mass spectrometry (FTMS) methods with computer-aided literature mining to identify and quantify essentially all of the metabolites that can be commonly detected (with today's technology) in the human CSF metabolome. Tables containing the compounds, concentrations, spectra, protocols and links to disease associations that we have found for the human CSF metabolome are freely available at http://www.csfmetabolome.ca.