Correlation Between Anti-Myelin Proteolipid Protein (PLP) Antibodies and Disease Severity in Multiple Sclerosis Patients With PLP Response-Permissive HLA Types.

The most prominent pathological features of multiple sclerosis (MS) are demyelination and neurodegeneration. The exact pathogenesis of MS is unknown, but it is generally regarded as a T cell-mediated autoimmune disease. Increasing evidence, however, suggests that other components of the immune system, particularly B cells and antibodies, contribute to the cumulative CNS damage and worsening disability that characterize the disease course in many patients. We have previously described strongly elevated T cell reactivity to an extracellular domain of the most abundant CNS myelin protein, myelin proteolipid protein (PLP) in people with MS. The current paper addresses the question of whether this region of PLP is also a target of autoantibodies in MS. Here we show that serum levels of isotype-switched anti-PLP181-230 specific antibodies are significantly elevated in patients with MS compared to healthy individuals and patients with other neurological diseases. These anti-PLP181-230 antibodies can also live-label PLP-transfected cells, confirming that they can recognize native PLP expressed at the cell surface. Importantly, the antibodies are only elevated in patients who carry HLA molecules that allow strong T cell responses to PLP. In that subgroup of patients, there is a positive correlation between the levels of anti-PLP181-230 antibodies and the severity of MS. These results demonstrate that anti-PLP antibodies have potentially important roles to play in the pathogenesis of MS.

FTY720 controls disease severity and attenuates sciatic nerve damage in chronic experimental autoimmune neuritis.

BACKGROUND: Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is an autoimmune-mediated inflammatory disease of the peripheral nervous system characterized by a response directed against certain myelin proteins and for which therapies are limited. Previous studies have suggested a beneficial role of FTY720, a sphingosine 1-phosphate (S1P) receptor agonist, known to deplete lymphocytes from the peripheral blood by sequestering them into lymph nodes, in the treatment of experimental autoimmune neuritis (EAN). Therefore, we investigated whether FTY720 is also beneficial in chronic experimental autoimmune neuritis (c-EAN), a recently developed rat model mimicking human CIDP. METHODS: c-EAN was induced in Lewis rats by immunization with S-palm P0(180-199) peptide. Rats were treated with FTY720 (1 mg/kg) or vehicle intraperitoneally once daily from the onset of clinical signs for 18 days; clinical signs were assessed daily until 60 days post-immunization (dpi). Electrophysiological and histological features were examined at different time points. We also evaluated the serum levels of different pro- and anti-inflammatory cytokines by ELISA or flow cytometry at 18, 40, and 60 dpi. RESULTS: Our data demonstrate that FTY720 decreased the severity and abolished the chronicity of the disease in c-EAN rats. Therapeutic FTY720 treatment reversed electrophysiological and histological anomalies, suggesting that myelinated fibers were subsequently preserved, it inhibited macrophage and IL-17+ cell infiltration in PNS, and it significantly reduced circulating pro-inflammatory cytokines. CONCLUSIONS: FTY720 treatment has beneficial effects on c-EAN, a new animal model mimicking human CIDP. We have shown that FTY720 is an effective immunomodulatory agent, improving the disease course of c-EAN, preserving the myelinated fibers, attenuating the axonal degeneration, and decreasing the number of infiltrated inflammatory cells in peripheral nerves. These data confirm the interest of testing FTY720 or molecules targeting S1P in human peripheral neuropathies.

Predicting the effects of potentially therapeutic modified peptides on polyclonal T cell populations in a mouse model of multiple sclerosis.

Altered peptide ligands (APLs) have routinely been studied in clonal populations of Th cells that express a single T cell receptor (TCR), but results generated in this manner poorly predict the effects of APLs on polyclonal Th cells in vivo, contributing to the failure of phase II clinical trials of APLs in autoimmune diseases such as multiple sclerosis (MS). We have used a panel of APLs derived from an encephalitogenic epitope of myelin proteolipid protein to investigate the relationship between antigen cross-reactivity in a polyclonal environment, encephalitogenicity, and the capacity of an APL to provide protection against experimental autoimmune encephalomyelitis (EAE) in SJL mice. In general, polyclonal Th cell lines specific for encephalitogenic APLs cross-reacted with other encephalitogenic APLs, but not with non-encephalitogenic APLs, and vice versa. This, alongside analysis of TCR Vß usage, suggested that encephalitogenic and non-encephalitogenic subgroups of APLs expand largely non-cross-reactive Th cell populations. As an exception to the rule, one non-encephalitogenic APL, L188, induced proliferation in polyclonal CD4+ T cells specific for the native encephalitogen, with minimal induction of cytokine production. Co-immunization of L188 alongside the native encephalitogen slightly enhanced disease development. In contrast, another APL, A188, which induced IL-10 production without proliferation in CD4+ T cells specific for the native encephalitogen, was able to protect against development of EAE in a dose-dependent fashion when co-immunized alongside the native encephalitogen. These results suggest that testing against polyclonal Th cell lines in vitro may be an effective strategy for distinguishing between potentially therapeutic and non-therapeutic APLs.

Characterization of a new rat model for chronic inflammatory demyelinating polyneuropathies.

Our objective was to develop a chronic model of EAN which could be used as a tool to test treatment strategies for CIDP. Lewis rats injected with S-palmitoylated P0(180-199) peptide developed a chronic, sometimes relapsing-remitting type of disease. Our model fulfills electrophysiological criteria of demyelination with axonal degeneration, confirmed by immunohistopathology. The late phase of the chronic disease was characterized by accumulation of IL-17(+) cells and macrophages in sciatic nerves and by high serum IL-17 levels. In conclusion, we have developed a reliable and reproducible animal model resembling CIDP that can now be used for translational drug studies.

The major myelin-resident protein PLP is transported to myelin membranes via a transcytotic mechanism: involvement of sulfatide.

Myelin membranes are sheet-like extensions of oligodendrocytes that can be considered membrane domains distinct from the cell's plasma membrane. Consistent with the polarized nature of oligodendrocytes, we demonstrate that transcytotic transport of the major myelin-resident protein proteolipid protein (PLP) is a key element in the mechanism of myelin assembly. Upon biosynthesis, PLP traffics to myelin membranes via syntaxin 3-mediated docking at the apical-surface-like cell body plasma membrane, which is followed by subsequent internalization and transport to the basolateral-surface-like myelin sheet. Pulse-chase experiments, in conjunction with surface biotinylation and organelle fractionation, reveal that following biosynthesis, PLP is transported to the cell body surface in Triton X-100 (TX-100)-resistant microdomains. At the plasma membrane, PLP transiently resides within these microdomains and its lateral dissipation is followed by segregation into 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS)-resistant domains, internalization, and subsequent transport toward the myelin membrane. Sulfatide triggers PLP's reallocation from TX-100- into CHAPS-resistant membrane domains, while inhibition of sulfatide biosynthesis inhibits transcytotic PLP transport. Taking these findings together, we propose a model in which PLP transport to the myelin membrane proceeds via a transcytotic mechanism mediated by sulfatide and characterized by a conformational alteration and dynamic, i.e., transient, partitioning of PLP into distinct membrane microdomains involved in biosynthetic and transcytotic transport.

Thiopalmitoylation of altered peptide ligands enhances their protective effects in an animal model of multiple sclerosis.

Previously, we have shown that conjugation of a palmitic chain via a thioester bond to a cysteine residue in weakly or nonencephalitogenic or neuritogenic peptides markedly enhances their ability to induce autoimmune disease in an MHC class II-restricted manner. From those studies, however, it was not clear whether thiopalmitoylation of the peptides was merely enhancing their disease-inducing potential or whether the lipid was itself playing a pathogenic role. To investigate this further, we have now tested the effects of thiopalmitoylation on MHC class II-restricted altered peptide ligands (APLs), which are normally protective in experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis. We hypothesized that if thiopalmitoylation of a peptide merely enhances its innate potential, then thiopalmitoylated APLs (S-palmAPLs) should show enhanced protective effects. Alternatively, if thiopalmitoylation itself can make a peptide pathogenic, then S-palmAPLs should have decreased therapeutic potential. We synthesized APLs and corresponding S-palmAPLs and showed that the S-palmAPLs were much more effective than the nonconjugated APL at inhibiting the development of experimental autoimmune encephalomyelitis. This was due to several features of the S-palmAPL:S-palmAPL-primed cells show an enhanced ability to proliferate and produce the anti-inflammatory cytokine, IL-10, in vitro. Furthermore, the bioavailability of S-palmAPL was greatly enhanced, compared with the nonpalmitoylated APL, and S-palm APL was taken up more rapidly into dendritic cells and channeled into the MHC class II processing pathway. These results show that thiopalmitoylation of MHC class II-restricted peptides is a simple way to enhance their effects in vivo and could have wide therapeutic application.

Evaluation of new immunological targets in neuromyelitis optica.

The detection of reactivity against autoantigens plays a crucial role in the diagnosis of autoimmune diseases. However, only a few autoantibodies are known in each disease, and their precise targets are often not precisely defined. In neuromyelitis optica (NMO), an autoimmune disease of the central nervous system, anti-aquaporin 4 antibodies are currently the only available immunological markers, although they are not detected in 10-50% of patients. Using enzyme-linked immunosorbent assays, we evaluated the reactivity against 19 structurally defined peptides in 26 NMO sera compared with 21 healthy subjects. We observed increased levels of IgG against myelin basic protein sequence MBP(156-175), pyruvate dehydrogenase sequence PDH(167-186) and CSF114(Glc), the last of these having a possible correlation with onset of inflammatory relapse. These preliminary results may suggest that the aquaporin 4 is not the unique target in NMO and that the study of reactivity against these peptides would be helpful for the diagnosis and follow-up of the disease. Complementary studies are however warranted to confirm these results.

Thiopalmitoylated peptides from the peripheral nervous system myelin p0 protein: synthesis, characterization, and neuritogenic properties.

Thiopalmitoylation (i.e., the covalent attachment of palmitic acid via a thioester linkage to cysteine residues in the polypeptide backbone) is a common post-translational modification of proteins. Several proteins that have been identified as putative autoantigens in a variety of T-cell mediated autoimmune diseases are thiopalmitoylated, and thus, we have hypothesized that endogenous thiopalmitoylated peptides released during tissue breakdown may play a role in the development and chronicity of autoimmune diseases. To investigate this, we have studied the effect of thiopalmitoylation on the immunogenic and neuritogenic properties of P0, the major peripheral nervous system (PNS) myelin protein, which is thiopalmitoylated at cysteine 153, and described as a candidate autoantigen in Guillain-Barre syndrome (GBS), a human inflammatory demyelinating disease of the PNS. This paper describes the synthesis of palmitoylated peptide P0(180-199) and P0(152-171) by on-resin acylation using specific cysteine side-chain protecting groups: Mmt (labile in diluted acid) and StBu (labile in the presence of tributylphosphine). Our results show that the thiol protecting group had to be adjusted to the peptide sequence: Mmt was efficiently used for P0(180-199) thioacylation, but it was not suitable for thiopalmitoylation of P0(152-171) because of a premature deprotection of the Boc protecting group on the epsilon-NH(2) Lys in the presence of 2% TFA, leading to dipalmitoylation. Palmitoylated P0(152-171) was successfully obtained by using StBu as the thiol protecting group. We could show by circular dichroism that palmitoylation has no influence on the structuration of the peptide in solution but palmitoylation increased the stability of the peptide in the presence of serum. Using EAN (experimental autoimmune neuritis), the rat model of GBS, we have compared the immunological properties of palm and non-palm P0 peptides and showed that thiopalmitoylation has indeed a great influence on their neuritogenic and immunogenic properties. This study provides further support for our hypothesis concerning the role of thiopalmitoylation in the development and chronicity of inflammatory demyelinating diseases and confirms that thiopalmitoylation of peptides may provide a simple means to increase MHC class II restricted responses.

Route of uptake of palmitoylated encephalitogenic peptides of myelin proteolipid protein by antigen-presenting cells: importance of the type of bond between lipid chain and peptide and relevance to autoimmunity.

Previously, we have shown that thiopalmitoylation of peptides of myelin proteolipid protein, as occurs naturally in vivo, increases their ability to induce experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis, and skews the autoimmune response toward a CD4(+)-mediated response. In contrast, the same peptide, when synthesized with a stable amide bond between peptide and lipid, inhibits experimental autoimmune encephalomyelitis and skews the response toward a CD8(+) response. The aim of the current study was to determine the mechanisms responsible for these observations. We show that proteolipid protein lipopeptides, when synthesized with a thioester bond between the lipid and the peptide, are taken up into APCs via an actin-independent endocytic route, the thioester bond is cleaved in the endosome, and the peptide is subsequently displayed on the surface of the APC in the context of MHC class II. The same peptide, when synthesized with the lipid attached via a stable amide bond, rapidly enters into the cytoplasm of the APC and forms micelles; however, the bond between peptide and lipid is not cleaved, and the micelles travel via the endoplasmic reticulum to complex with MHC class I. These findings have implications for vaccine development and for the development of MHC class II-restricted autoimmune diseases, as many human autoantigens thus far identified are thioacylated.

Identification of two proteins associated with mammalian ATP synthase.

Bovine mitochondrial ATP synthase commonly is isolated as a monomeric complex that contains 16 protein subunits and the natural IF(1) inhibitor protein in substoichiometric amounts. Alternatively ATP synthase can be isolated in dimeric and higher oligomeric states using digitonin for membrane solubilization and blue native or clear native electrophoresis for separation of the native mitochondrial complexes. Using blue native electrophoresis we could identify two ATP synthase-associated membrane proteins with masses smaller than 7 kDa and isoelectric points close to 10 that previously had been removed during purification. We show that in the mitochondrial membrane both proteins are almost quantitatively bound to ATP synthase. Both proteins had been identified earlier in a different context, but their association with ATP synthase was unknown. The first one had been named 6.8-kDa mitochondrial proteolipid because it can be isolated by chloroform/methanol extraction from mitochondrial membranes. The second one had been denoted as diabetes-associated protein in insulin-sensitive tissue (DAPIT), which may provide a clue for further functional and clinical investigations.