THE CELL CHANGES IN AMAUROTIC FAMILY IDIOCY

A Compendium of Information on the Lysosome

For a long time, lysosomes were considered as mere waste bags for cellular constituents. Thankfully, studies carried out in the past 15 years were brimming with elegant and crucial breakthroughs in lysosome research, uncovering their complex roles as nutrient sensors and characterizing them as crucial multifaceted signaling organelles. This review presents the scientific knowledge on lysosome physiology and functions, starting with their discovery and reviewing up to date ground-breaking discoveries highlighting their heterogeneous functions as well as pending questions that remain to be answered. We also review the roles of lysosomes in anti-cancer drug resistance and how they undergo a series of molecular and functional changes during malignant transformation which lead to tumor aggression, angiogenesis, and metastases. Finally, we discuss the strategy of targeting lysosomes in cancer which could lead to the development of new and effective targeted therapies.

Diagnostic Tips from a Video Series and Literature Review of Patients with Late-Onset Tay-Sachs Disease

Background

Late-Onset Tay-Sachs (LOTS) disease is a rare, progressive neurological condition that can dramatically affect the life of these patients. The diagnosis of LOTS is easily missed because of the multifaced presentation of these patients, who can initially be assessed by neuromuscular or movement disorder specialists, or psychiatrists. Clinical trials are now becoming available for LOTS. Therefore, early diagnosis can be detrimental for these patients and for insuring informative research outcomes.

Methods

We characterized a cohort of nine patients with LOTS through a detailed clinical and video description. We then reviewed the available literature regarding the clinical description of patients with LOTS. Our findings were summarized based on the predominant phenotype of presentation to highlight diagnostic clues to guide the diagnosis of LOTS for different neurology specialists (neuromuscular, movement disorders) and psychiatrist.

Results

We described a cohort of 9 new patients with LOTS seen at our clinic. Our literature review identified 76 patients mainly presenting with a neuromuscular, cerebellar, psychiatric, stuttering, or movement disorder phenotype. Diagnostic tips, such as the triceps sign, distinct speech patterns, early psychiatric presentation and impulsivity, as well as neurological symptoms (cerebellar or neuromuscular) in patients with a prominent psychiatric presentation, are described.

Discussion

Specific diagnostics clues can help neurologists and psychiatrists in the early diagnosis of LOTS disease. Our work also represent the first video presentation of a cohort of patients with LOTS that can help different specialists to familiarize with these features and improve diagnostic outcomes.

Highlights

Late-Onset Tay-Sachs (LOTS) disease, a severe progressive neurological condition, has multifaced presentations causing diagnostic delays that can significantly affect research outcomes now that clinical trials are available. We highlight useful diagnostic clues from our cohort (including the first video representation of a LOTS cohort) and comprehensive literature review.

Lysosomal Diseases and Neuropsychiatry: Opportunities to Rebalance the Mind

The brain is the physical organ of the mind but efforts to understand mental illness within a neurobiological context have hitherto been unavailing. Mental disorders (anxiety, depression, bipolar disorder, and schizophrenia) affect about one fifth of the population and present an almost endless societal challenge at the frontier of human sciences. Prodigious technological advances in functional neuroimaging and large-scale genetics have not yet delivered the prospect of refined molecular understanding of mental illness beyond early anatomical descriptions of brain metabolism. However, intensive clinical phenotyping and quantitative metabolic studies using sophisticated radio-ligands in positron-emission tomography, persistently favor the neurobiological approach. This Perspective pursues a familiar maxim in Medicine, aptly summarized in the words of Arthur Koestler: “Nature is generous in her senseless experiments on mankind.” Hitherto, studies in neuropsychiatry have largely ignored rare genetic disorders but derangements of specific components within the cerebral laboratory offer rich opportunities for mechanistic exploration. Aberrant psychic behavior is characteristic of many inborn errors of metabolism and although each disorder represents a universe of its own, we are at a threshold for understanding, since contemporary genetics and cell biology furnish abundant materials to take on the perturbing enigma of mental derangement. A further development relates to orphan drugs with actions on defined molecular targets: these represent new ways to study the pathogenesis of psychiatric phenomena associated with rare diseases and in a manner not formerly possible. Here we introduce the frontier of schizophrenia and its strong association with late-onset Tay-Sachs disease as a paradigm to explore.

Cellular pathology of lysosomal storage disorders

Lysosomal storage disorders are rare, inborn errors of metabolism characterized by intralysosomal accumulation of unmetabolized compounds. The brain is commonly a central focus of the disease process and children and animals affected by these disorders often exhibit progressively severe neurological abnormalities. Although most storage diseases result from loss of activity of a single enzyme responsible for a single catabolic step in a single organelle, the lysosome, the overall features of the resulting disease belies this simple beginning. These are enormously complex disorders with metabolic and functional consequences that go far beyond the lysosome and impact both soma-dendritic and axonal domains of neurons in highly neuron type-specific ways. Cellular pathological changes include growth of ectopic dendrites and new synaptic connections and formation of enlargements in axons far distant from the lysosomal defect. Other storage diseases exhibit neuron death, also occurring in a cell-selective manner. The functional links between known molecular genetic and enzyme defects and changes in neuronal integrity remain largely unknown. Future studies on the biology of lysosomal storage diseases affecting the brain can be anticipated to provide insights not only into these pathogenic mechanisms, but also into the role of lysosomes and related organelles in normal neuron function.

Further studies on ectopic dendrite growth and other geometrical distortions of neurons in feline GM1 gangliosidosis

Systematic Golgi studies have been performed on major subcortical, diencephalic, brain stem and spinal cord regions from cats with the inherited neuronal storage disease, GM1 gangliosidosis. Resulting data have been compared with other Golgi studies of neuronal storage disorders in man and animals, including an earlier, more limited examination of this same disease model. These previous studies have shown that in human and feline gangliosidoses cortical pyramidal neurons undergo remarkable changes in soma-dendritic geometry. The latter include the formation of conspicuous cellular enlargements between somata and axonal initial segments (meganeurites) and the sprouting of secondary neuritic processes from this same region of the cell. Further, ultrastructural studies have revealed normal appearing synapses on the surface of this ectopically placed dendritic-like membrane. Results of the present study indicate that the distribution of meganeurites, secondary neurites and other geometrical distortions of neurons in GM1 gangliosidosis varies with cell type and brain region. This cell type-specific response to the metabolic error and subsequent storage could be categorized in three ways. Firstly, certain types of cells (e.g. multipolar neurons of the amygdala and claustrum) exhibited changes similar to those reported for cortical pyramidal neurons. That is, cells of these regions either displayed spine or neurite-bearing meganeurites, or enlarged axon hillocks which were covered with similar processes. Other types of neurons did not demonstrate ectopic neurite growth or spine-covered meganeurites, but did display prominent aspiny meganeurites (e.g. neurons of the superior colliculus, periaqueductal gray, hypothalamus and basal forebrain nuclei). A third category of neurons did not possess meganeurites or neurite growth but instead demonstrated massive somatic expansion which exceeded that observed in meganeurite-bearing cell types (e.g. certain brain stem and spinal cord neurons). These data have been compared with the more limited Golgi studies of other types of neuronal storage disorders and the same types of neurons appeared to respond in similar fashion across this spectrum of diseases. The data presented and discussed in this paper demonstrate three significant morphological events which occur in neurons as a result of lysosomal hydrolase deficiency. These are storage, which occurs in all neurons but manifests as meganeurite formation or somatic enlargement depending on the cell type, axon hillock or meganeurite-associated spine and neurite growth, and new synapse formation on spine-covered meganeurites and on neurites.(ABSTRACT TRUNCATED AT 250 WORDS)

Ferric ion-ferrocyanide staining in ganglioside storage disease establishes that meganeurites are of axon hillock origin and distinct from axonal spheroids

Ferric ion-ferrocyanide staining and safranin-0-counterstaining of neocortical tissue from cats with GM1 gangliosidosis have established that pyramidal neuron meganeurites occur proximal to axonal initial segments and that they are distinct from axonal spheroids. The latter, which were found to be widely distributed throughout cerebral cortex, were located distal to axonal initial segments and could be differentiated from meganeurites at both light and electron microscopic levels. This report confirms an earlier electron microscopic study which suggested that meganeurites are of axon hillock origin, and illustrates the striking distinction between abnormalities in the soma-dendritic and axonal domains of neurons in a lysosomal storage disease.

Sphingomyelin lipidosis in a cat: Golgi studies

Alterations in neuronal geometry in a feline model of sphingomyelin lipidosis were evaluated using Golgi staining. Neurons in cerebral cortex, basal ganglia, amygdala, thalamus, and cerebellum were impregnated and many were found to possess conspicuous enlargements at the axon hillock-initial segment region (meganeurites) and/or to sprout secondary neuritic processes from this same area. The latter were sometimes well developed and resembled small dendrites. These changes were cell type specific with distribution limited to certain types of neurons in select brain regions, while others remained normal, or underwent only simple somatic enlargement or generalized degenerative changes. Occasional cortical pyramidal neurons also displayed thinning of dendrites and extensive loss of dendritic spines. These observations add sphingomyelin lipidosis to other neuronal storage disorders in which aberrant neurite growth and meganeurite formation accompany lysosomal enzyme deficiency and the associated metabolic alterations and storage. Although meganeurite-like expansions have been reported to occur in many storage disorders, the appearance of axon hillock-associated neurite growth on morphologically mature neurons has been identified heretofore only in the gangliosidoses, and in feline models of alpha-mannosidosis and mucopolysaccharidosis type 1.