Lysosomal gene Hexb displays haploinsufficiency in a knock-in mouse model of Alzheimer's disease.

Lysosomal network abnormalities are an increasingly recognised feature of Alzheimer's disease (AD), which appear early and are progressive in nature. Sandhoff disease and Tay-Sachs disease (neurological lysosomal storage diseases caused by mutations in genes that code for critical subunits of ß-hexosaminidase) result in accumulation of amyloid-ß (Aß) and related proteolytic fragments in the brain. However, experiments that determine whether mutations in genes that code for ß-hexosaminidase are risk factors for AD are currently lacking. To determine the relationship between ß-hexosaminidase and AD, we investigated whether a heterozygous deletion of Hexb, the gene that encodes the beta subunit of ß-hexosaminidase, modifies the behavioural phenotype and appearance of disease lesions in App NL-G-F/NL-G-F (App KI/KI ) mice. App KI/KI and Hexb +/- mice were crossed and evaluated in a behavioural test battery. Neuropathological hallmarks of AD and ganglioside levels in the brain were also examined. Heterozygosity of Hexb in App KI/KI mice reduced learning flexibility during the Reversal Phase of the Morris water maze. Contrary to expectation, heterozygosity of Hexb caused a small but significant decrease in amyloid beta deposition and an increase in the microglial marker IBA1 that was region- and age-specific. Hexb heterozygosity caused detectable changes in the brain and in the behaviour of an AD model mouse, consistent with previous reports that described a biochemical relationship between HEXB and AD. This study reveals that the lysosomal enzyme gene Hexb is not haplosufficient in the mouse AD brain.

Lysosomal Dysregulation in the Murine AppNL-G-F/NL-G-F Model of Alzheimer's Disease.

Lysosomal network dysfunction is a prominent feature of Alzheimer's disease (AD). Although transgenic mouse models of AD are known to model some aspects of lysosomal network dysfunction, the lysosomal network has not yet been examined in the knock-in AppNL-G-F/NL-G-F mouse. We aimed to determine whether AppNL-G-F/NL-G-F mice exhibit disruptions to the lysosomal network in the brain. Lysosome-associated membrane protein 1 (LAMP1) and cathepsins B, L and D accumulated at amyloid beta plaques in the AppNL-G-F/NL-G-F mice, as occurs in human Alzheimer's patients. The accumulation of these lysosomal proteins occurred early in the development of neuropathology, presenting at the earliest and smallest amyloid beta plaques observed. AppNL-G-F/NL-G-F mice also exhibited elevated activity of ß-hexosaminidase and cathepsins D/E and elevated levels of selected lysosomal network proteins, namely LAMP1, cathepsin D and microtubule-associated protein light chain 3 (LC3-II) in the cerebral cortex, as determined by western blot. Elevation of cathepsin D did not change the extent of co-localisation between cathepsin D and LAMP1 in the AppNL-G-F/NL-G-F mice. These findings demonstrate that perturbations of the lysosomal network occur in the AppNL-G-F/NL-G-F mouse model, further validating its use an animal model of pre-symptomatic AD.

Reduction in open field activity in the absence of memory deficits in the AppNL-G-F knock-in mouse model of Alzheimer's disease.

The recent development of knock-in mouse models of Alzheimer's disease provides distinct advantages over traditional transgenic mouse models that rely on over-expression of amyloid precursor protein. Two such knock-in models that have recently been widely adopted by Alzheimer's researchers are the AppNL-F and AppNL-G-F mice. This study aimed to further characterise the behavioural phenotype and amyloid plaque distribution of AppNL-G-F/NL-G-F (C57BL/6J background) mice at six-months of age. An attempt to replicate a previous study that observed deficits in working memory in the Y-maze, showed no difference between AppNL-G-F/NL-G-F and wild-type mice. Further assessment of these mice using the novel object recognition test and Morris water maze also revealed no differences between AppNL-G-F/NL-G-F and wild-type mice. Despite a lack of demonstrated cognitive deficits, we report a reduction in locomotor/exploratory activity in an open field. Histological examination of AppNL-G-F/NL-G-F mice showed widespread distribution of amyloid plaques at this age. We conclude that whilst at six-months of age, memory deficits are not sufficiently robust to be replicated in varying environments, amyloid plaque burden is significant in AppNL-G-F/NL-G-F knock-in brain.

A novel conditional Sgsh knockout mouse model recapitulates phenotypic and neuropathic deficits of Sanfilippo syndrome.

Mucopolysaccharidosis (MPS) type IIIA, or Sanfilippo syndrome, is a neurodegenerative lysosomal storage disorder caused by a deficiency of the lysosomal enzyme N-sulfoglucosamine sulfohydrolase (SGSH), involved in the catabolism of heparan sulfate. The clinical spectrum is broad and the age of symptom onset and the degree of preservation of cognitive and motor functions appears greatly influenced by genotype. To explore this further, we generated a conditional knockout (Sgsh KO ) mouse model with ubiquitous Sgsh deletion, and compared the clinical and pathological phenotype with that of the spontaneous Sgsh D31N MPS-IIIA mouse model. Phenotypic deficits were noted in Sgsh KO mice prior to Sgsh D31N mice, however these outcomes did not correlate with any shift in the time of appearance nor rate of accumulation of primary (heparan sulfate) or secondary substrates (GM2/GM3 gangliosides). Other disease lesions (elevations in lysosomal integral membrane protein-II expression, reactive astrocytosis and appearance of ubiquitin-positive inclusions) were also comparable between affected mouse strains. This suggests that gross substrate storage and these neuropathological markers are neither primary determinants, nor good biomarkers/indicators of symptom generation, confirming similar observations made recently in MPS-IIIA patients. The Sgsh KO mouse will be a useful tool for elucidation of the neurological basis of disease and assessment of the clinical efficacy of new treatments for Sanfilippo syndrome.

Endo-lysosomal and autophagic dysfunction: a driving factor in Alzheimer's disease?

Alzheimer's disease (AD) is the most common cause of dementia, and its prevalence will increase significantly in the coming decades. Although important progress has been made, fundamental pathogenic mechanisms as well as most hereditary contributions to the sporadic form of the disease remain unknown. In this review, we examine the now substantial links between AD pathogenesis and lysosomal biology. The lysosome hydrolyses and processes cargo delivered by multiple pathways, including endocytosis and autophagy. The endo-lysosomal and autophagic networks are central to clearance of cellular macromolecules, which is important given there is a deficit in clearance of amyloid-ß in AD. Numerous studies show prominent lysosomal dysfunction in AD, including perturbed trafficking of lysosomal enzymes and accumulation of the same substrates that accumulate in lysosomal storage disorders. Examination of the brain in lysosomal storage disorders shows the accumulation of amyloid precursor protein metabolites, which further links lysosomal dysfunction with AD. This and other evidence leads us to hypothesise that genetic variation in lysosomal genes modifies the disease course of sporadic AD.

Identification of Novel GPR55 Modulators Using Cell-Impedance-Based Label-Free Technology.

The orphan G protein-coupled receptor GPR55 has been proposed as a novel receptor of the endocannabinoid system. However, the validity of this categorization is still under debate mainly because of the lack of potent and selective agonists and antagonists of GPR55. Binding assays are not yet available for GPR55 screening, and discrepancies in GPR55 mediated signaling pathways have been reported. In this context, we have designed and synthesized novel GPR55 ligands based on a chromenopyrazole scaffold. Appraisal of GPR55 activity was accomplished using a label-free cell-impedance-based assay in hGPR55-HEK293 cells. The real-time impedance responses provided an integrative assessment of the cellular consequence to GPR55 stimulation taking into account the different possible signaling pathways. Potent GPR55 partial agonists (14b, 18b, 19b, 20b, and 21-24) have been identified; one of them (14b) being selective versus classical cannabinoid receptors. Upon antagonist treatment, chromenopyrazoles 21-24 inhibited lysophosphatidylinositol (LPI) effect. One of these GPR55 antagonists (21) is fully selective versus classic cannabinoid receptors. Compared to LPI, the predicted physicochemical parameters of the new compounds suggest a clear pharmacokinetic improvement.

Variables influencing fluorimetric N-sulfoglucosamine sulfohydrolase (SGSH) activity measurement in brain homogenates.

Deficient N-sulfoglucosamine sulfohydrolase (SGSH) enzyme activity causes mucopolysaccharidosis (MPS) type IIIA. A fluorimetric SGSH activity assay is commonly used to examine patient cells. Here, we modified this method for brain homogenates and define the parameters for assay linearity. SGSH activity was suppressed outside of these parameters. This method will enable the accurate measurement of SGSH activity in MPS IIIA tissues to examine disease pathogenesis and evaluate therapies.

The putative cannabinoid receptor GPR55 affects osteoclast function in vitro and bone mass in vivo.

GPR55 is a G protein-coupled receptor recently shown to be activated by certain cannabinoids and by lysophosphatidylinositol (LPI). However, the physiological role of GPR55 remains unknown. Given the recent finding that the cannabinoid receptors CB(1) and CB(2) affect bone metabolism, we examined the role of GPR55 in bone biology. GPR55 was expressed in human and mouse osteoclasts and osteoblasts; expression was higher in human osteoclasts than in macrophage progenitors. Although the GPR55 agonists O-1602 and LPI inhibited mouse osteoclast formation in vitro, these ligands stimulated mouse and human osteoclast polarization and resorption in vitro and caused activation of Rho and ERK1/2. These stimulatory effects on osteoclast function were attenuated in osteoclasts generated from GPR55(-/-) macrophages and by the GPR55 antagonist cannabidiol (CBD). Furthermore, treatment of mice with this non-psychoactive constituent of cannabis significantly reduced bone resorption in vivo. Consistent with the ability of GPR55 to suppress osteoclast formation but stimulate osteoclast function, histomorphometric and microcomputed tomographic analysis of the long bones from male GPR55(-/-) mice revealed increased numbers of morphologically inactive osteoclasts but a significant increase in the volume and thickness of trabecular bone and the presence of unresorbed cartilage. These data reveal a role of GPR55 in bone physiology by regulating osteoclast number and function. In addition, this study also brings to light an effect of both the endogenous ligand, LPI, on osteoclasts and of the cannabis constituent, CBD, on osteoclasts and bone turnover in vivo.