Age-related changes in regiospecific expression of Lipolysis Stimulated Receptor (LSR) in mice brain

Overexpression of LSR suppresses glioma proliferation and invasion via regulating FOXO3a

PURPOSE

Gliomas, the most prevalent type of central nervous system tumors, currently lack effective therapeutic options. Lipolysis-stimulated lipoprotein receptors (LSR) have been implicated in tumor development and progression. This study aims to investigate the influence of LSR on gliomas and elucidate the underlying mechanisms.

METHODS

We analyze LSR expression in gliomas and its association with patient prognosis using bioinformatics tools. Western blotting and immunohistochemistry revealed differential expression of LSR across different grades of glioma. The effects of LSR on glioma cell proliferation and invasion are evaluated through a series of cellular assays. Subcutaneous xenografts in nude mice are utilized to assess the impact of LSR on gliomas in vivo. Additionally, western blotting is employed to detect changes in protein levels related to the FOXO3a signaling pathway following LSR overexpression.

RESULTS

LSR expression is higher in tissues from low-grade gliomas compared to those from glioblastomas. Patients with low LSR expression exhibit poorer prognoses. Overexpression of LSR inhibit glioma cell proliferation and invasion. The protein levels of PCNA, Cyclin D1, MMP2, and MMP9 are significantly decreased in the OE-LSR group. Tumor volume is reduced in nude mice injected subcutaneously with LSR-overexpressing glioma cells. Overexpression of LSR increases nuclear FOXO3a level while reduces p-FOXO3a and p-14-3-3 levels. Knockdown of FOXO3a reverse the inhibitory effects of LSR overexpression on glioma cell proliferation and invasion.

CONCLUSION

Low LSR expression is associated with adverse prognosis in glioma patients. By modulating FOXO3a, LSR overexpression suppresses glioma cell proliferation and invasion.

Aging, Neurodegenerative Disorders, and Cerebellum

An important part of the central nervous system (CNS), the cerebellum is involved in motor control, learning, reflex adaptation, and cognition. Diminished cerebellar function results in the motor and cognitive impairment observed in patients with neurodegenerative disorders such as Alzheimer's disease (AD), vascular dementia (VD), Parkinson's disease (PD), Huntington's disease (HD), spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS), Friedreich's ataxia (FRDA), and multiple sclerosis (MS), and even during the normal aging process. In most neurodegenerative disorders, impairment mainly occurs as a result of morphological changes over time, although during the early stages of some disorders such as AD, the cerebellum also serves a compensatory function. Biological aging is accompanied by changes in cerebellar circuits, which are predominantly involved in motor control. Despite decades of research, the functional contributions of the cerebellum and the underlying molecular mechanisms in aging and neurodegenerative disorders remain largely unknown. Therefore, this review will highlight the molecular and cellular events in the cerebellum that are disrupted during the process of aging and the development of neurodegenerative disorders. We believe that deeper insights into the pathophysiological mechanisms of the cerebellum during aging and the development of neurodegenerative disorders will be essential for the design of new effective strategies for neuroprotection and the alleviation of some neurodegenerative disorders.

Mechanisms of 3-Hydroxyl 3-Methylglutaryl CoA Reductase in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide and has a high incidence in the elderly. Unfortunately, there is no effective therapy for AD owing to its complicated pathogenesis. However, the development of lipid-lowering anti-inflammatory drugs has heralded a new era in the treatment of Alzheimer's disease. Several studies in recent years have shown that lipid metabolic dysregulation and neuroinflammation are associated with the pathogenesis of AD. 3-Hydroxyl 3-methylglutaryl CoA reductase (HMGCR) is a rate-limiting enzyme in cholesterol synthesis that plays a key role in cholesterol metabolism. HMGCR inhibitors, known as statins, have changed from being solely lipid-lowering agents to neuroprotective compounds because of their effects on lipid levels and inflammation. In this review, we first summarize the main regulatory mechanism of HMGCR affecting cholesterol biosynthesis. We also discuss the pathogenesis of AD induced by HMGCR, including disordered lipid metabolism, oxidative stress, inflammation, microglial proliferation, and amyloid-β (Aβ) deposition. Subsequently, we explain the possibility of HMGCR as a potential target for AD treatment. Statins-based AD treatment is an ascent field and currently quite controversial; therefore, we also elaborate on the current application prospects and limitations of statins in AD treatment.

Lipolysis-Stimulated Lipoprotein Receptor Acts as Sensor to Regulate ApoE Release in Astrocytes

Astroglia play an important role, providing de novo synthesized cholesterol to neurons in the form of ApoE-lipidated particles; disruption of this process can increase the risk of Alzheimer’s disease. We recently reported that glia-specific suppression of the lipolysis-stimulated lipoprotein receptor (LSR) gene leads to Alzheimer’s disease-like memory deficits. Since LSR is an Apo-E lipoprotein receptor, our objective of this study was to determine the effect of LSR expression modulation on cholesterol and ApoE output in mouse astrocytes expressing human ApoE3. qPCR analysis showed that siRNA-mediated lsr knockdown significantly increased expression of the genes involved in cholesterol synthesis, secretion, and metabolism. Analysis of media and lipoprotein fractions showed increased cholesterol and lipidated ApoE output in HDL-like particles. Further, lsr expression could be upregulated when astrocytes were incubated 5 days in media containing high levels (two-fold) of lipoprotein, or after 8 h treatment with 1 µM LXR agonist T0901317 in lipoprotein-deficient media. In both conditions of increased lsr expression, the ApoE output was repressed or unchanged despite increased abca1 mRNA levels and cholesterol production. We conclude that LSR acts as a sensor of lipoprotein content in the medium and repressor of ApoE release, while ABCA1 drives cholesterol efflux, thereby potentially affecting cholesterol load, ApoE lipidation, and limiting cholesterol trafficking towards the neuron.

Targeted Suppression of Lipoprotein Receptor LSR in Astrocytes Leads to Olfactory and Memory Deficits in Mice

Perturbations of cholesterol metabolism have been linked to neurodegenerative diseases. Glia–neuron crosstalk is essential to achieve a tight regulation of brain cholesterol trafficking. Adequate cholesterol supply from glia via apolipoprotein E-containing lipoproteins ensures neuronal development and function. The lipolysis-stimulated lipoprotein receptor (LSR), plays an important role in brain cholesterol homeostasis. Aged heterozygote Lsr+/− mice show altered brain cholesterol distribution and increased susceptibility to amyloid stress. Since LSR expression is higher in astroglia as compared to neurons, we sought to determine if astroglial LSR deficiency could lead to cognitive defects similar to those of Alzheimer’s disease (AD). Cre recombinase was activated in adult Glast-CreERT/lsrfl/fl mice by tamoxifen to induce astroglial Lsr deletion. Behavioral phenotyping of young and old astroglial Lsr KO animals revealed hyperactivity during the nocturnal period, deficits in olfactory function affecting social memory and causing possible apathy, as well as visual memory and short-term working memory problems, and deficits similar to those reported in neurodegenerative diseases, such as AD. Furthermore, GFAP staining revealed astroglial activation in the olfactory bulb. Therefore, astroglial LSR is important for working, spatial, and social memory related to sensory input, and represents a novel pathway for the study of brain aging and neurodegeneration.

Leptin Downregulates Angulin-1 in Active Crohn's Disease via STAT3

Crohn’s disease (CD) has an altered intestinal barrier function, yet the underlying mechanisms remain to be disclosed. The tricellular tight junction protein tricellulin is involved in the maintenance of the paracellular macromolecule barrier and features an unchanged expression level in CD but a shifted localization. As angulins are known to regulate the localization of tricellulin, we hypothesized the involvement of angulins in CD. Using human biopsies, we found angulin-1 was downregulated in active CD compared with both controls and CD in remission. In T84 and Caco-2 monolayers, leptin, a cytokine secreted by fat tissue and affected in CD, decreased angulin-1 expression. This effect was completely blocked by STAT3 inhibitors, Stattic and WP1066, but only partially by JAK2 inhibitor AG490. The effect of leptin was also seen at a functional level as we observed in Caco-2 cells an increased permeability for FITC-dextran 4 kDa indicating an impaired barrier against macromolecule uptake. In conclusion, we were able to show that in active CD angulin-1 expression is downregulated, which leads to increased macromolecule permeability and is inducible by leptin via STAT3. This suggests that angulin-1 and leptin secretion are potential targets for intervention in CD to restore the impaired intestinal barrier.

Impact of Sex and Age on the Mevalonate Pathway in the Brain: A Focus on Effects Induced by Maternal Exposure to Exogenous Compounds

The mevalonate pathway produces cholesterol and other compounds crucial for numerous cellular processes. It is well known that age and sex modulate this pathway in the liver. Recently, similar effects were also noted in different brain areas, suggesting that alterations of the mevalonate pathway are at the root of marked sex-specific disparities in some neurodevelopmental disorders related to disturbed cholesterol homeostasis. Here, we show how the mevalonate pathway is modulated in a sex-, age- and region-specific manner, and how maternal exposure to exogenous compounds can disturb the regulation of this pathway in the brain, possibly inducing functional alterations.