Anti-heat shock protein 90β antibodies decrease pre-oligodendrocyte population in perinatal and adult cell cultures. Implications for remyelination in multiple sclerosis

The interaction of heat shock proteins with cellular membranes: a historical perspective

The interaction of heat shock proteins (HSP) with cellular membranes has been an enigmatic process, initially observed by morphological studies, inferred during the purification of HSP70s, and confirmed after the detection of these proteins on the surface of cancer cells and their insertion into artificial lipid bilayers. Today, the association of several HSP with lipid membranes is well established. However, the mechanisms for membrane insertion have been elusive. There is conclusive evidence indicating that HSP70s have a great selectivity for negatively charged phospholipids, whereas other HSP have a broader spectrum of lipid specificity. HSP70 also oligomerizes upon membrane insertion, forming ion conductance channels. The functional role of HSP70 lipid interactions appears related to membrane stabilization that may play a role during cell membrane biogenesis. They could also play a role as membrane chaperones as well as during endocytosis, microautophagy, and signal transduction. Moreover, HSP membrane association is a key component in the extracellular export of these proteins. The presence of HSP70 on the surface of cancer cells and its interaction with lysosome membranes have been envisioned as potential therapeutic targets. Thus, the biology and function of HSP membrane association are reaching a new level of excitement. This review is an attempt to preserve the recollection of the pioneering contributions of many investigators that have participated in this endeavor.

Target-Mediated Brain Tissue Binding for Small Molecule Inhibitors of Heat Shock Protein 90

Drug distribution in the brain is generally associated with an affinity for fatty brain tissues and therefore known to be species- and concentration-independent. We report here the effect of target affinity on brain tissue binding for 10 small molecules designed to inhibit brain heat shock protein 90 (HSP90), a widespread protein whose expression is 1–2% of total cytosolic proteins in eucaryotes. Our results show that increasing the test item concentrations from 0.3 to 100 µM increased the unbound fraction 32-fold for the most potent molecules, with no change for the inactive one (1.1 fold change). Saturation of HSP90 led to normal concentration-independent brain tissue binding. In vivo pharmacokinetics performed in rats showed that the overall volume of distribution of compounds is correlated with their affinity for HSP90. The in vitro binding and in vivo pharmacokinetics (PK) performed in rats showed that small molecule HSP90 inhibitors followed the principle of target-mediated drug disposition. We demonstrate that assessing unbound fractions in brain homogenate was subject to HSP90 target interference; this may challenge the process of linking systemic-free drug concentrations to central nervous system unbound concentrations necessary to establish the proper pharmacokinetics/pharmacodynamics (PK/PD) relation needed for human dose prediction.

Identification of common key genes and pathways between type 1 diabetes and multiple sclerosis using transcriptome and interactome analysis

PURPOSE

Type 1 diabetes (T1D) and multiple sclerosis (MS) are classified as T cell-mediated autoimmune diseases. Although convergent evidence proposed common genetic architecture for autoimmune diseases, it remains a challenge to identify them. This study aimed to determine common gene signature and pathways in T1D and MS via systems biology approach.

METHODS

Gene expression profiles of peripheral blood mononuclear cells (PBMCs) and pancreatic-β cells in T1D as well as PBMCs and cerebrospinal fluid (CSF) in MS were analyzed in our previous published data, and differential expressed genes were integrated with protein-protein interactions data to construct Query-Query PPI (QQPPI) networks. In this study, QQPPI networks were further analyzed to investigate more central genes, functional modules and complexes shared in T1D and MS progression. Lastly, the interaction of common genes with drugs was also explored.

RESULTS

Several cytokines such as IL-23A, IL-32, IL-34, and IL-37 tend to be differentially expressed in both diseases. In addition, PSMA1, MYC, SRPK1, YBX1, HNRNPM, NF-κB2, IKBKE, RAC1, FN1, ARRB2, ESR1, HSP90AB1, and PPP1CA were common high central genes in QQPPI networks corresponding to each disease. Proteasome, spliceosome, immune responses, apoptosis, cellular communication/signaling transduction mechanism, interaction with environment, and activity of intercellular mediators were shared biological processes in T1D and MS. Finally, azathioprine, melatonin, resveratrol, and geldanamycin identified as prioritized drugs for the treatment of patients with T1D and MS.

CONCLUSIONS

This study represented novel key genes and pathways shared between T1D and MS, which may facilitate the identification of potential therapeutic targets in these diseases.

Identification of biomarkers in cerebrospinal fluid and serum of multiple sclerosis patients by immunoproteomics approach

Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the central nervous system. At present, the molecular mechanisms causing the initiation, development and progression of MS are poorly understood, and no reliable proteinaceous disease markers are available. In this study, we used an immunoproteomics approach to identify autoreactive antibodies in the cerebrospinal fluid of MS patients to use as candidate markers with potential diagnostic value. We identified an autoreactive anti-transferrin antibody that may have a potential link with the development and progression of MS. We found this antibody at high levels also in the serum of MS patients and created an immunoenzymatic assay to detect it. Because of the complexity and heterogeneity of multiple sclerosis, it is difficult to find a single marker for all of the processes involved in the origin and progression of the disease, so the development of a panel of biomarkers is desirable, and anti-transferrin antibody could be one of these.

Expression of heat shock protein 90 at the cell surface in human neuroblastoma cells

In addition to the activity of heat shock protein 90 (Hsp90/HSPC) as a chaperone, some recent studies have reported expression of Hsp90 at the cell surface in certain types of cancer and nervous system cells. We study the expression of Hsp90 at the cell surface in human neuroblastoma (NB69) cells. Immunofluorescence experiments labeling with anti-Hsp90 antibodies on both nonpermeabilized cells and live cells detected Hsp90 at the cell surface. Hsp90 was also identified in a membrane fraction from subcellular fractionation. Cell-surface Hsp90 was significantly more expressed in undifferentiated proliferative spherical neuroblastoma cells than in differentiated flattened cells. In addition, spherical cells were significantly more sensitive to Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin compared to flattened cells. This paper describes the first evidence of cell-surface Hsp90 expression in a cancer cell line from nervous tissue and may indicate a novel target for anti-tumoral agents.

High cytotoxic sensitivity of the oligodendrocyte precursor cells to HSP90 inhibitors in cell cultures

Oligodendrocyte precursor cells (OPCs) are able to proliferate, and most differentiate into post-mitotic oligodendrocytes that contribute to remyelination. We have previously studied the expression of heat shock protein90 (HSP90) in OPCs. The ansamycins, such as geldanamycin and 17-allylamino-17-demethoxygeldanamycin (17-AAG) act as specific HSP90 inhibitors, are potent anti-tumor agents and are currently undergoing clinical trials. This work investigated the effect of HSP90 inhibitors on cultured OPCs. Geldanamycin, 17-AAG and another chemically unrelated HSP90 inhibitor, radicicol, were extremely cytotoxic for OPCs. The IC50 values of geldanamycin, 17-AAG and radicicol for OPCs were 7.1, 10.7 and 137 nM, respectively, compared to 1000-2000 nM for preoligodendrocytes, astrocytes and neurons. Adult OPCs were found to be susceptible to HSP90 inhibitors in a similar fashion to perinatal cells. OPC death induced by these HSP90 inhibitors led to a significant decrease in the oligodendrocyte population. The present results highlight that OPCs are uniquely sensitive to HSP90 inhibitors. Geldanamycin and 17-AAG, which penetrate the blood-brain barrier, are novel cancer chemotherapeutic agents and we noted that, in anti-cancer therapy with these drugs, the OPCs may be compromised.

Maturation-dependent sensitivity of oligodendrocyte lineage cells to apoptosis: implications for normal development and disease

Apoptosis plays a crucial role in brain development by ensuring that only appropriately growing, migrating, and synapse-forming neurons and their associated glial cells survive. This process involves an intimate relationship between cell-cell interactions and developmental cues and is further impacted by environmental stress during neurogenesis and disease. Oligodendrocytes (OLs), the major myelin-forming cells in the central nervous system, largely form after this wave of neurogenesis but also show a selective vulnerability to cell death stimuli depending on their stage of development. This can affect not only embryonic and early postnatal brain formation but also the response to demyelinating pathologies. In the present review, we discuss the stage-specific sensitivity of OL lineage cells to damage-induced death and how this might impact myelin survival and regeneration during injury or disease.

Multiple sclerosis: Disease biomarkers as indicated by pathophysiology

Multiple sclerosis (MS), the most important human inflammatory demyelinating disease of the central nervous system, is characterized by heterogenous genetic backgrounds and immunopathogenetic subtypes, various clinical disease courses, and inhomogeneous and unpredictable therapeutic effects. Because of this heterogeneity, subtyping of our MS patients by genetical, clinical, neuroradiological, and neuroimmunological parameters will be an urgent need in the near future. Therefore the importance of identifying biological markers for MS has evolved over the past years. Evidence for a possible role of antibodies as biological markers for MS comes from several studies indicating that intrathecal antibody production and the dominance of B-cells are associated with a more progressive disease course. This review summarizes the current status and potential applicability of antibodies as biological markers for the diagnosis, classification, disease activity and prediction of clinical courses in MS. Antibodies (and other molecules) serving as biomarkers will help to establish a differential therapeutic concept in MS, which should allow to treat individuals selectively according to their pathogenetic subtype and disease status.

[Promoting myelin repair in disorders such as multiple sclerosis and some types of leukodystrophy: current studies]

Several ways of promoting myelin repair in myelin disorders such as multiple sclerosis and certain types of leukodystrophies are currently being investigated. Numerous studies suggest that it is possible to repair the central nervous system (CNS) by cell transplantation or by enhancing endogenous remyelination. Investigations in animal models indicate that cell therapy results in robust anatomical and functional recovery of acute myelin lesions. These models are also used to explore and validate the role of candidate molecules to stimulate endogenous remyelination by activating the myelin competent population or providing neuroprotection. However, in view of the heterogeneity of the lesion environment in MS, it seems more likely that cell therapy alone will not be able to contribute efficiently to the repair of the lesion. Further developments should indicate whether combining multiple approaches will be more powerful to achieve global myelin repair in the CNS than applying these strategies alone.

Detection of anti-heat shock protein 90 beta (Hsp90beta) antibodies in cerebrospinal fluid

Antibodies against heat shock protein 90 beta (Hsp90beta) recognize the antigen on the cell surface of the oligodendrocyte precursor cells and cause a decrease of oligodendrocyte population in cell cultures. These antibodies have been found in patients with multiple sclerosis (MS). This report describes an original and sensitive method to detect anti-Hsp90beta antibodies in cerebrospinal fluid (CSF) using a western blot procedure. We have developed the method for autoantibody detection using Hsp90beta from cell membrane fraction instead of commercial Hsp90beta as antigen. The presence of anti-Hsp90beta antibodies in CSF of MS patients may play a pathogenic role in MS, and a large-scale study is needed to establish a possible diagnostic value of these antibodies in MS patients.

Antibodies as biological markers for pathophysiological processes in MS

Multiple sclerosis (MS), the most important human inflammatory demyelinating disease of the central nervous system, is characterized by various clinical disease courses, inhomogeneous and unpredictable therapeutic effects, heterogenous genetic backgrounds and immunopathogenetic subtypes as demonstrated by neuropathology. Because of this heterogeneity of MS, a subtyping of our patients by genetical, clinical, neuroradiological, and neuroimmunological parameters will be necessary in the future. Therefore the importance of identifying biological markers for MS has evolved over the past years. Evidence for a possible role of antibodies as biological markers for MS comes from several studies indicating that intrathecal antibody production and the dominance of B cells are associated with a more progressive disease course. In this review we will give an overview on the current status and potential applicability of antibodies as biological markers for the diagnosis, classification, disease activity and prediction of clinical courses in MS. We will therefore summarize the findings on autoantibodies to myelin and nonmyelin antigens and on viral antigens in MS. We believe that antibodies serving as biomarkers will help to establish a differential therapeutic concept in MS, which will allow to treat individuals selectively according to their pathogenetic subtype and disease status.