Early in the course of infection, human immunodeficiency virus (HIV) is able to enter the central nervous system where it stablishes a permanent reservoir. Current antiretroviral therapies do not efficiently cross the blood-brain barrier and therefore do not reach the HIV located in the central nervous system. Consequently, HIV infection can often be associated with neurocognitive impairment and HIV-associated dementia. The purpose of this review is to brief the reader into the world of neurological complications arising from HIV infection. Mechanisms by which HIV directly or indirectly impairs the central nervous system are discussed, as well as other factors influencing or contributing to the impairment, and the animal models currently used to perform research on the topic.

The autism spectrum disorder (ASD) comprises a series of neurological diseases that share serious alterations of the development of the central nervous system. The degree of disability may vary so that Asperger’s may have a relatively normal life and get positions of responsibility in corporations and even in Governments, whereas other ASD sufferers are fully dependent on caregivers and have serious cognitive deficits. Although the first cases of autism were detected by looking at failures in metabolism, e.g., phenylketonuria, to later identify the faulty gene, today the trend is the opposite, first obtaining the exome and minimizing the look for altered parameters in blood, urine, etc. Cholesterol is key for neural development as it is not able to cross the blood brain barrier. Therefore, any gene or environmental factor that affects cholesterol synthesis will impact early developmental stages eventually leading to a disease within the autism spectrum and/or schizophrenia. This review provides data of the relevance of cholesterol dyshomeostasis in autism spectrum disorders. Determining biochemical parameters in body fluids should help to provide new therapeutic approaches in some cases of autism.

Peroxisomes are actively involved in the metabolism of various lipids including fatty acids, ether phospholipids, bile acids as well as the processing of reactive oxygen and nitrogen species. Recent studies show that peroxisomes can regulate cholesterol homeostasis by mediating cholesterol transport from the lysosomes to the endoplasmic reticulum and towards primary cilium as well. Disruptions of peroxisome biogenesis or functions lead to peroxisomal disorders that usually involve neurological deficits. Peroxisomal dysfunction is also linked to several neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. In many peroxisomal disorders and neurodegenerative diseases, aberrant cholesterol accumulation is frequently encountered yet largely neglected. This review discusses the current understanding of the mechanisms by which peroxisomes facilitate cholesterol trafficking within the cell and the pathological conditions related to impaired cholesterol transport by peroxisomes, with the hope to inspire future development of the treatments for peroxisomal disorders and neurodegenerative diseases.

Phosphoinositides are membrane phospholipids involved in a variety of cellular processes like growth, development, metabolism, and transport. This review focuses on the maintenance of cellular homeostasis of phosphatidylinositol 4,5-bisphosphate (PIP₂), and phosphatidylinositol 3,4,5-trisphosphate (PIP₃). The critical balance of these PIPs is crucial for regulation of neuronal form and function. The activity of PIP₂ and PIP₃ can be regulated through kinases, phosphatases, phospholipases and cholesterol microdomains. PIP₂ and PIP₃ carry out their functions either indirectly through their effectors activating integral signaling pathways, or through direct regulation of membrane channels, transporters, and cytoskeletal proteins. Any perturbations to the balance between PIP₂ and PIP₃ signaling result in neurodevelopmental and neurodegenerative disorders. This review will discuss the upstream modulators and downstream effectors of the PIP₂ and PIP₃ signaling, in the context of neuronal health and disease.

Niemann-Pick C disease is a rare neurodegenerative, lysosomal storage disease caused by accumulation of unesterified cholesterol. Diagnosis of the disease is often delayed due to its rarity, the heterogeneous presentation, and the early non-specific symptoms. The discovery of disease-specific biomarkers—cholestane-3β,5α,6β-triol (C-triol), trihydroxycholanic acid glycinate (TCG) and N-palmitoyl-O-phosphocholineserine [PPCS, initially referred to as lysosphingomyelin-509 (lysoSM-509)]—has led to development of non-invasive, blood-based diagnostics. Dissemination of these rapid, sensitive, and specific clinical assays has accelerated diagnosis. Moreover, the superior receiver operating characteristic of the TCG bile acid biomarker and its detection in dried blood spots has also facilitated development of a newborn screen for NPC, which is currently being piloted in New York state. The C-triol, TCG and PPCS biomarkers have also been proved useful for monitoring treatment response in peripheral tissues, but are uninformative with respect to treatment efficacy in the central nervous system (CNS). A major gap for the field is the lack of a validated, non-invasive biomarker to monitor the course of disease and CNS response to therapy.

The pathogenic basis behind some of the most prevalent neurodegenerative diseases in advanced societies, known as proteinopathies, deals with alterations in protein homeostasis. Despite the broad diversity of clinical symptoms, they share a remarkably common feature that is the serious neuronal loss in several disease-specific brain regions due to the presence of toxic aggregations of misfolded proteins. So far, research efforts have been insufficient to decipher the exact molecular mechanisms that trigger the conformational change from a functional healthy protein to its pathological version. This is a sine qua non condition to progress in developing new approaches and treatments for these diseases for which there is no cure. Currently, it is well accepted that perturbations in gut microbiota composition negatively impact a wide range of brain processes via the gut-brain axis which increases host susceptibility to neurodegenerative disorders. In this context, modulate the microbial ecosystem colonizing the gastrointestinal tract may be a promising therapeutic approach in the management of proteinopathies. This review aims to provide an updated view of the role that gut microbiota poses in the pathogenesis of Parkinson’s disease, Alzheimer’s disease and Huntington’s disease, the most common neurodegenerative proteinopathies, and of the possibility of translating this knowledge into effective and safe clinical microbiota-based interventions, especially those designed to afford neuroprotection.

Spinal cord injury (SCI) induces several destructive events that develop immediately after the primary insult. These phenomena increase tissue damage; that is why, numerous therapeutic approaches are studied in order to neutralize these destructive mechanisms. In line with this, several studies indicate that after injury, neural tissue could be protected by an adaptive immune response directed against self-antigens. Immunization with neural-derived peptides (INDP) reduces secondary degeneration of neurons after spinal cord insult and promotes a significant motor recovery. The combination of antioxidants or other immunomodulatory peptides after SCI can improve the protective effect induced by INDP. INDP in acute SCI is a promising strategy, so further studies should be addressed to be able to formulate the best strategy.

Current evidence indicates that neurodegeneration of dopaminergic neurons of the substantia nigra associated to Parkinson’s disease is a consequence of a neuroinflammatory process in which microglial cells play a central role. The initial activation of microglial cells is triggered by pathogenic protein inclusions, which are mainly composed by α-synuclein. Importantly, these pathogenic forms of α-synuclein subsequently induce a T-cell-mediated autoimmune response to dopaminergic neurons. Depending on their functional phenotype, these autoreactive T-cells might shape the functional features of activated microglia. T-cells bearing pro-inflammatory phenotypes such as T-helper (Th)1 or Th17 promote a chronic inflammatory behaviour on microglia, whilst anti-inflammatory T-cells, such as regulatory T-cells (Treg) favour the acquisition of neuroprotective features by microglia. Thus, T-cells play a fundamental role in the development of neuroinflammation and neurodegeneration involved in Parkinson’s disease. This review summarizes the evidence indicating that not only CD4⁺ T-cells, but also CD8⁺ T-cells play an important role in the physiopathology of Parkinson’s disease. Next, this review analyses the different T-cell epitopes derived from the pathogenic forms of α-synuclein involved in the autoimmune response associated to Parkinson’s disease in animal models and humans. It also summarizes the requirement of specific alleles of major histocompatibility complexes (MHC) class I and class II necessaries for the presentation of CD8⁺ and CD4⁺ T-cell epitopes from the pathogenic forms of α-synuclein in both humans and animal models. Finally, this work summarizes and discusses a number of experimental immunotherapies that aim to strengthen the Treg response or to dampen the inflammatory T-cell response as a therapeutic approach in animal models of Parkinson’s disease.

Since the identification and cloning of the cannabinoid receptor 2 (CB₂R), several studies focused on the characterization of its physiological and pathological role. Initially, CB₂R was considered as the peripheral cannabinoid receptor due to its detection in the rat spleen and leukocyte subpopulation in humans. Later, CB₂R was identified in different brain regions significantly modifying the landscape and pointing out its role in a wide variety of central physiological functions and pathological conditions. Additional research also detected the expression of CB₂R in neurons, microglia, and astroglia in different brain regions. Indeed, the findings collected to date support a significant function of CB₂R in anxiety, depression, schizophrenia, and additional neuropsychiatric disorders. This review gathers the most relevant literature regarding new advances about the role of CB₂R in a variety of neuropsychiatric conditions, with special emphasis on its potential as a new therapeutic target for the treatment of different psychiatric disorders.

The brain cholesterol content is determined by the balance between the pathways of in situ biosynthesis and cholesterol elimination via 24-hydroxylation catalyzed by cytochrome P450 46A1 (CYP46A1). Both pathways are tightly coupled and determine the rate of brain cholesterol turnover. Evidence is accumulating that modulation of CYP46A1 activity by gene therapy or pharmacologic means could be beneficial in the case of neurodegenerative and other brain diseases and affect brain processes other than cholesterol biosynthesis and elimination. This minireview summarizes these other processes, most common of which include abnormal protein accumulation, memory, and cognition, motor behavior, gene transcription, protein phosphorylation as well as autophagy and lysosomal processing. The unifying mechanisms, by which these processes could be affected by CYP46A targeting are also discussed.

Familial early-onset Alzheimer’s disease (AD) is more probable in individuals coming from mothers diagnosed with AD than from fathers diagnosed with AD. Studies in animal models have shown maternal imprinting due to the transmission to the embryo of altered material in the ovum. In the case of transgenic animals harboring a mutated form of the human amyloid precursor protein (APP), offspring from crosses with wild-type (WT) fathers and transgenic mothers display more abnormalities than offspring from crosses with transgenic fathers and WT mothers. Expression of the mutated APP in the ovum may lead to alterations that may be genetic and/or epigenetic in the nuclear and/or the mitochondrial DNA. These modifications that are transmitted to the new living beings affect more mitochondrial proteins and, therefore, the mitochondrial function may be affected in adulthood by trends present in the ovum.

Cholesterol serves as an essential lipid molecule in various membrane organelles of mammalian cells. The metabolites of cholesterol also play important functions. Acyl-coenzyme A: cholesterol acyltransferase 1 (ACAT1), also named as sterol O-acyltransferase 1, is a membrane-bound enzyme residing at the endoplasmic reticulum (ER). It converts cholesterol to cholesteryl esters (CEs) for storage, and is expressed in all cells. CEs cannot partition in membranes; they can only coalesce as cytosolic lipid droplets. Excess CEs are found in the vulnerable region of the brains of patients with late-onset Alzheimer’s disease (AD), and in cell and mouse models for AD. Reducing CE contents by genetic inactivation of ACAT1, or by pharmacological inhibition of ACAT is shown to reduce amyloidopathy and other hallmarks for AD. To account for the various beneficial actions of the ACAT1 blockade (A1B), a working hypothesis is proposed here: the increase in CE contents observed in the AD brain is caused by damages of cholesterol-rich lipid rafts that are known to occur in neurons affected by AD. These damages cause cholesterol to release from lipid rafts and move to the ER where it will be converted to CEs by ACAT1. In addition, the increase in CE contents may also be caused by overloading with cholesterol-rich substances, or through activation of ACAT1 gene expression by various pro-inflammatory agents. Both scenarios may occur in microglia of the chronically inflamed brain. A1B ameliorates AD by diverting the cholesterol pool destined for CE biosynthesis such that it can be utilized more efficiently to repair membrane damage in various organelles, and to exert regulatory actions more effectively to defend against AD. To test the validity of the A1B hypothesis in cell culture and in vivo, the current status of various anti-ACAT1 agents that could be further developed is briefly discussed.