Amnionless, essential for mouse gastrulation, is mutated in recessive hereditary megaloblastic anemia.

The amnionless gene, Amn, on mouse chromosome 12 encodes a type I transmembrane protein that is expressed in the extraembryonic visceral layer during gastrulation. Mice homozygous with respect to the amn mutation generated by a transgene insertion have no amnion. The embryos are severely compromised, surviving to the tenth day of gestation but seem to lack the mesodermal layers that normally produce the trunk. The Amn protein has one transmembrane domain separating a larger, N-terminal extracellular region and a smaller, C-terminal cytoplasmic region. The extracellular region harbors a cysteine-rich domain resembling those occurring in Chordin, found in Xenopus laevis embryos, and Sog, found in Drosophila melanogaster. As these cysteine-rich domains bind bone morphogenetic proteins (Bmps), it has been speculated that the cysteine-rich domain in Amn also binds Bmps. We show that homozygous mutations affecting exons 1-4 of human AMN lead to selective malabsorption of vitamin B12 (a phenotype associated with megaloblastic anemia 1, MGA1; OMIM 261100; refs. 5,6) in otherwise normal individuals, suggesting that the 5' end of AMN is dispensable for embryonic development but necessary for absorption of vitamin B12. When the 5' end of AMN is truncated by mutations, translation is initiated from alternative downstream start codons.

Selective spatiotemporal patterns of glial activation and neuron loss in the sensory thalamocortical pathways of neuronal ceroid lipofuscinosis 8 mice.

The neuronal ceroid lipofuscinoses constitute the most common group of childhood neurodegenerative disorders. These devastating disorders still remain without effective treatment. The use of animal models has provided significant information about NCL pathogenesis, highlighting early glial activation and neuron loss in specific brain regions of affected animals. Here, we have characterized the timing and regional-specificity of the pathological events of CLN8 disease utilizing the Cln8 deficient mouse model, Cln8(mnd). We have studied the progression of neuron loss, astrocytosis and microglial activation from early to moderately symptomatic (1, 3 and 5 months) and late symptomatic (8 months) mice. In Cln8 deficiency, the somatosensory pathway comprising the thalamic ventral posterior nucleus (VPM/VPL) and the primary somatosensory cortex (S1BF) was found to be the most affected relay system. Scattered microglia that appeared partially activated were already present at 3 months of age, followed by astrocytosis and the loss of thalamic relay neurons at 5 months of age, with all these phenotypes and glial activation becoming more pronounced with disease progression. Reactive changes followed a similar pattern in the corresponding cortical target regions, but only moderate neuron loss was detected. Compared to the somatosensory system, in the visual thalamocortical pathway, neuron loss appeared relatively late in the disease, at 8 months. Neuron loss was preceded by glial activation in the dorsal lateral geniculate nucleus (LGNd) and in the primary visual cortex (V1). Taken together these data highlight the pathological targeting of the somatosensory thalamocortical pathway in Cln8 deficiency, in common with other forms of NCL. However, in contrast to other previously characterized NCL models, the Cln8(mnd) mouse shows relatively mild and late appearing pathology within the thalamocortical visual pathway.

Cln5-deficiency in mice leads to microglial activation, defective myelination and changes in lipid metabolism.

CLN5 disease, late infantile variant phenotype neuronal ceroid lipofuscinosis, is a severe neurodegenerative disease caused by mutations in the CLN5 gene, which encodes a lysosomal protein of unknown function. Cln5-deficiency in mice leads to loss of thalamocortical neurons, and glial activation, but the underlying mechanisms are poorly understood. We have now studied the gene expression of Cln5 in the mouse brain and show that it increases gradually with age and differs between neurons and glia, with the highest expression in microglia. In Cln5(-/-) mice, we documented early and significant microglial activation that was already evident at 3 months of age. Loss of Cln5 also leads to defective myelination in vitro and in the developing mouse brain. This was accompanied by early alterations in serum lipid profiles, dysfunctional cellular metabolism and lipid transport in Cln5(-/-) mice. Taken together, these data provide significant new information about events associated with Cln5-deficiency, revealing altered myelination and disturbances in lipid metabolism, together with an early neuroimmune response.

Outcomes of progranulin gene therapy in the retina are dependent on time and route of delivery.

Neuronal ceroid lipofuscinosis (NCL) is a family of neurodegenerative diseases caused by mutations to genes related to lysosomal function. One variant, CNL11, is caused by mutations to the gene encoding the protein progranulin, which regulates neuronal lysosomal function. Absence of progranulin causes cerebellar atrophy, seizures, dementia, and vision loss. As progranulin gene therapies targeting the brain are developed, it is advantageous to focus on the retina, as its characteristics are beneficial for gene therapy development: the retina is easily visible through direct imaging, can be assessed through quantitative methods in vivo, and requires smaller amounts of adeno-associated virus (AAV). In this study we characterize the retinal degeneration in a progranulin knockout mouse model of CLN11 and study the effects of gene replacement at different time points. Mice heterologously expressing progranulin showed a reduction in lipofuscin deposits and microglia infiltration. While mice that receive systemic AAV92YF-scCAG-PGRN at post-natal day 3 or 4 show a reduction in retina thinning, mice injected intravitreally at months 1 and 6 with AAV2.7m8-scCAG-PGRN exhibit no improvement, and mice injected at 12 months of age have thinner retinas than do their controls. Thus, delivery of progranulin proves to be time sensitive and dependent on route of administration, requiring early delivery for optimal therapeutic benefit.

Genetic modifiers of degeneration in the cathepsin D deficient Drosophila model for neuronal ceroid lipofuscinosis.

Neuronal ceroid lipofuscinoses (NCLs) are pediatric, neurodegenerative, lysosomal storage disorders. Mutations in cathepsin D result in the most severe, congenital form of NCLs. We have previously generated a cathepsin D deficient Drosophila model, which exhibits the key features of NCLs: progressive intracellular accumulation of autofluorescent storage material and modest neurodegeneration in the brain areas related to visual functions. Here we extend the phenotypic characterization of cathepsin D deficient Drosophila and report that modest degenerative changes are also present in their retinae. Furthermore, by utilizing this phenotype, we examined the possible effect of 17 candidate modifiers, selected based on the results from other cathepsin D deficiency models. We found enhancers of this phenotype that support the involvement of endocytosis-, lipid metabolism- and oxidation-related factors in the cathepsin D deficiency induced degeneration. Our results warrant further investigation of these mechanisms in the pathogenesis of cathepsin D deficiency.

Fibroblast Growth Factor 21 Drives Dynamics of Local and Systemic Stress Responses in Mitochondrial Myopathy with mtDNA Deletions.

Mitochondrial dysfunction elicits stress responses that safeguard cellular homeostasis against metabolic insults. Mitochondrial integrated stress response (ISRmt) is a major response to mitochondrial (mt)DNA expression stress (mtDNA maintenance, translation defects), but the knowledge of dynamics or interdependence of components is lacking. We report that in mitochondrial myopathy, ISRmt progresses in temporal stages and development from early to chronic and is regulated by autocrine and endocrine effects of FGF21, a metabolic hormone with pleiotropic effects. Initial disease signs induce transcriptional ISRmt (ATF5, mitochondrial one-carbon cycle, FGF21, and GDF15). The local progression to 2nd metabolic ISRmt stage (ATF3, ATF4, glucose uptake, serine biosynthesis, and transsulfuration) is FGF21 dependent. Mitochondrial unfolded protein response marks the 3rd ISRmt stage of failing tissue. Systemically, FGF21 drives weight loss and glucose preference, and modifies metabolism and respiratory chain deficiency in a specific hippocampal brain region. Our evidence indicates that FGF21 is a local and systemic messenger of mtDNA stress in mice and humans with mitochondrial disease.

Cystatin B: mutation detection, alternative splicing and expression in progressive myclonus epilepsy of Unverricht-Lundborg type (EPM1) patients.

Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) is an autosomal recessive neurodegenerative disorder caused by mutations in the cystatin B gene (CSTB) that encodes an inhibitor of several lysosomal cathepsins. An unstable expansion of a dodecamer repeat in the CSTB promoter accounts for the majority of EPM1 disease alleles worldwide. We here describe a novel PCR protocol for detection of the dodecamer repeat expansion. We describe two novel EPM1-associated mutations, c.149G > A leading to the p.G50E missense change and an intronic 18-bp deletion (c.168+1_18del), which affects splicing of CSTB. The p.G50E mutation that affects the conserved QVVAG amino acid sequence critical for cathepsin binding fails to associate with lysosomes. This further supports the previously implicated physiological importance of the CSTB-lysosome association. Expression of CSTB mRNA and protein was markedly reduced in lymphoblastoid cells of the patients irrespective of the mutation type. Patients homozygous for the dodecamer expansion mutation showed 5-10% expression compared to controls. By combining database searches with RT-PCR we identified several alternatively spliced CSTB isoforms. One of these, CSTB2, was also present in mouse and was analyzed in more detail. In real-time PCR quantification, CSTB2 expression was less than 5% of total CSTB expression in all human adult and fetal tissues analyzed. In patients homozygous for the minisatellite mutation, the level of CSTB2 was reduced similarly to that of CSTB implicating regulation from the same promoter. The physiological significance of CSTB2 remains to be determined.

The neuronal ceroid lipofuscinosis Cln8 gene expression is developmentally regulated in mouse brain and up-regulated in the hippocampal kindling model of epilepsy.

BACKGROUND: The neuronal ceroid lipofuscinoses (NCLs) are a group of inherited neurodegenerative disorders characterized by accumulation of autofluorescent material in many tissues, especially in neurons. Mutations in the CLN8 gene, encoding an endoplasmic reticulum (ER) transmembrane protein of unknown function, underlie NCL phenotypes in humans and mice. The human phenotype is characterized by epilepsy, progressive psychomotor deterioration and visual loss, while motor neuron degeneration (mnd) mice with a Cln8 mutation show progressive motor neuron dysfunction and retinal degeneration. RESULTS: We investigated spatial and temporal expression of Cln8 messenger ribonucleic acid (mRNA) using in situ hybridization, reverse transcriptase polymerase chain reaction (RT-PCR) and northern blotting. Cln8 is ubiquitously expressed at low levels in embryonic and adult tissues. In prenatal embryos Cln8 is most prominently expressed in the developing gastrointestinal tract, dorsal root ganglia (DRG) and brain. In postnatal brain the highest expression is in the cortex and hippocampus. Expression of Cln8 mRNA in the central nervous system (CNS) was also analyzed in the hippocampal electrical kindling model of epilepsy, in which Cln8 expression was rapidly up-regulated in hippocampal pyramidal and granular neurons. CONCLUSION: Expression of Cln8 in the developing and mature brain suggests roles for Cln8 in maturation, differentiation and supporting the survival of different neuronal populations. The relevance of Cln8 up-regulation in hippocampal neurons of kindled mice should be further explored.