Interaction of TPPP/p25 protein with glyceraldehyde-3-phosphate dehydrogenase and their co-localization in Lewy bodies

SNCA and TPPP transcripts increase in oligodendroglial cytoplasmic inclusions in multiple system atrophy

Multiple system atrophy (MSA) is characterized by glial cytoplasmic inclusions (GCIs) containing aggregated α-synuclein (α-syn) in oligodendrocytes. The origin of α-syn accumulation in GCIs is unclear, in particular whether abnormal α-syn aggregates result from the abnormal elevation of endogenous α-syn expression in MSA or ingested from the neuronal source. Tubulin polymerization promoting protein (TPPP) has been reported to play a crucial role in developing GCI pathology. Here, the total cell body, nucleus, and cytoplasmic area density of SNCA and TPPP transcripts in neurons and oligodendrocytes with and without various α-syn pathologies in the pontine base in autopsy cases of MSA (n = 4) and controls (n = 2) were evaluated using RNAscope with immunofluorescence. Single-nucleus RNA-sequencing data for TPPP was evaluated using control frontal cortex (n = 3). SNCA and TPPP transcripts were present in the nucleus and cytoplasm of oligodendrocytes in both controls and diseased, with higher area density in GCIs and glial nuclear inclusions in MSA. Area densities of SNCA and TPPP transcripts were lower in neurons showing cytoplasmic inclusions in MSA. Indeed, TPPP transcripts were unexpectedly found in neurons, while the anti-TPPP antibody failed to detect immunoreactivity. Single-nucleus RNA-sequencing revealed significant TPPP transcript expression predominantly in oligodendrocytes, but also in excitatory and inhibitory neurons. This study addressed the unclear origin of accumulated α-syn in GCIs, proposing that the elevation of SNCA transcripts may supply templates for misfolded α-syn. In addition, the parallel behavior of TPPP and SNCA transcripts in GCI development highlights their potential synergistic contribution to inclusion formation. In conclusion, this study advances our understanding of MSA pathogenesis, offers insights into the dynamics of SNCA and TPPP transcripts in inclusion formation, and proposes regulating their transcripts for future molecular therapy to MSA.

The Role of Tubulin Polymerization-Promoting Protein2 (TPPP2) in Spermatogenesis: A Narrative Review

Tubulin polymerization-promoting protein2 (TPPP2) is one of the three paralogs of mammalian TPPP proteins. Its possible role in spermatogenesis is described in this narrative review. TPPP2 is expressed specifically in the male reproductive system, mainly in testes and sperm, and also in the epididymis. In testes, TPPP2 is exclusively expressed in elongating spermatids; in the epididymis, it is located in the middle piece of the sperm tail. TPPP2 is involved in spermiogenesis, in steps which are determinative for the formation and morphology of spermatids. The inhibition of TPPP2 decreases sperm motility (the curvilinear velocity of sperms), probably due to influencing mitochondrial energy production since TPPP2 knockout mice possess an impaired mitochondrial structure. There are data on the role of TPPP2 in various mammalian species: human, mouse, swine, and various ruminants; there is a significant homology among TPPP2s from different species. Experiments with Tppp2-/--mice show that the absence of TPPP2 results in decreased sperm count and serious dysfunction of sperm, including decreased motility; however, the in vitro capacitation and acrosome reaction are not influenced. The symptoms show that Tppp2-/--mice may be considered as a model for oligoasthenozoospermia.

Acute inhibition of OGA sex-dependently alters the networks associated with bioenergetics, autophagy, and neurodegeneration

The accumulation of neurotoxic proteins characteristic of age-related neurodegenerative pathologies such as Alzheimer's and Parkinson's diseases is associated with the perturbation of metabolism, bioenergetics, and mitochondrial quality control. One approach to exploit these interactions therapeutically is to target the pathways that regulate metabolism. In this respect, the nutrient-sensing hexosamine biosynthesis pathway is of particular interest since it introduces a protein post-translational modification known as O-GlcNAcylation, which modifies different proteins in control versus neurodegenerative disease postmortem brains. A potent inhibitor of the O-GlcNAcase enzyme that removes the modification from proteins, Thiamet G (TG), has been proposed to have potential benefits in Alzheimer's disease. We tested whether key factors in the O-GlcNAcylation are correlated with mitochondrial electron transport and proteins related to the autophagy/lysosomal pathways in the cortex of male and female mice with and without exposure to TG (10 mg/kg i.p.). Mitochondrial complex activities were measured in the protein homogenates, and a panel of metabolic, autophagy/lysosomal proteins and O-GlcNAcylation enzymes were assessed by either enzyme activity assay or by western blot analysis. We found that the networks associated with O-GlcNAcylation enzymes and activities with mitochondrial parameters, autophagy-related proteins as well as neurodegenerative disease-related proteins exhibited sex and TG dependent differences. Taken together, these studies provide a framework of interconnectivity for multiple O-GlcNAc-dependent pathways in mouse brain of relevance to aging and sex/age-dependent neurodegenerative pathogenesis and response to potential therapies.

Natural product 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose is a reversible inhibitor of glyceraldehyde 3-phosphate dehydrogenase

Aerobic glycolysis, also known as the Warburg effect, is a hallmark of cancer cell glucose metabolism and plays a crucial role in the activation of various types of immune cells. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyzes the conversion of D-glyceraldehyde 3-phosphate to D-glycerate 1,3-bisphosphate in the 6th critical step in glycolysis. GAPDH exerts metabolic flux control during aerobic glycolysis and therefore is an attractive therapeutic target for cancer and autoimmune diseases. Recently, GAPDH inhibitors were reported to function through common suicide inactivation by covalent binding to the cysteine catalytic residue of GAPDH. Herein, by developing a high-throughput enzymatic screening assay, we discovered that the natural product 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) is an inhibitor of GAPDH with K_i = 0.5 μM. PGG blocks GAPDH activity by a reversible and NAD⁺ and Pi competitive mechanism, suggesting that it represents a novel class of GAPDH inhibitors. In-depth hydrogen deuterium exchange mass spectrometry (HDX-MS) analysis revealed that PGG binds to a region that disrupts NAD⁺ and inorganic phosphate binding, resulting in a distal conformational change at the GAPDH tetramer interface. In addition, structural modeling analysis indicated that PGG probably reversibly binds to the center pocket of GAPDH. Moreover, PGG inhibits LPS-stimulated macrophage activation by specific downregulation of GAPDH-dependent glucose consumption and lactate production. In summary, PGG represents a novel class of GAPDH inhibitors that probably reversibly binds to the center pocket of GAPDH. Our study sheds new light on factors for designing a more potent and specific inhibitor of GAPDH for future therapeutic applications.

Role of O-Linked N-Acetylglucosamine Protein Modification in Cellular (Patho)Physiology

In the mid-1980s, the identification of serine and threonine residues on nuclear and cytoplasmic proteins modified by a N-acetylglucosamine moiety (O-GlcNAc) via an O-linkage overturned the widely held assumption that glycosylation only occurred in the endoplasmic reticulum, Golgi apparatus, and secretory pathways. In contrast to traditional glycosylation, the O-GlcNAc modification does not lead to complex, branched glycan structures and is rapidly cycled on and off proteins by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery, O-GlcNAcylation has been shown to contribute to numerous cellular functions, including signaling, protein localization and stability, transcription, chromatin remodeling, mitochondrial function, and cell survival. Dysregulation in O-GlcNAc cycling has been implicated in the progression of a wide range of diseases, such as diabetes, diabetic complications, cancer, cardiovascular, and neurodegenerative diseases. This review will outline our current understanding of the processes involved in regulating O-GlcNAc turnover, the role of O-GlcNAcylation in regulating cellular physiology, and how dysregulation in O-GlcNAc cycling contributes to pathophysiological processes.

Moonlighting glyceraldehyde-3-phosphate dehydrogenase: posttranslational modification, protein and nucleic acid interactions in normal cells and in human pathology

Moonlighting glyceraldehyde-3-phosphate dehydrogenase (GAPDH) exhibits multiple functions separate and distinct from its historic role in energy production. Further, it exhibits dynamic changes in its subcellular localization which is an a priori requirement for its multiple activities. Separately, moonlighting GAPDH may function in the pathology of human disease, involved in tumorigenesis, diabetes, and age-related neurodegenerative disorders. It is suggested that moonlighting GAPDH function may be related to specific modifications of its protein structure as well as the formation of GAPDH protein: protein or GAPDH protein: nucleic acid complexes.

Inactivation of glyceraldehyde-3-phosphate dehydrogenase by the dopamine metabolite, 3,4-dihydroxyphenylacetaldehyde

BACKGROUND

The aldehyde metabolite of dopamine, 3,4-dihydroxyphenylacetaldehyde (DOPAL) is an endogenous neurotoxin implicated in Parkinson's Disease. Elucidating protein targets of DOPAL is essential in understanding it's pathology. The enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a target of DOPAL.

METHODS

GAPDH activity was measured via reduction of NAD⁺ cofactor (340 nm). Protein aggregation was assessed with SDS-PAGE methods and specific modification via chemical probes.

RESULTS

Low micromolar levels of DOPAL caused extensive GAPDH aggregation and irreversibly inhibited enzyme activity. The inactivation of GAPDH was dependent on both the catechol and aldehyde moieties of DOPAL. It is suggested that Cys are modified and oxidized by DOPAL.

CONCLUSIONS

The mechanism by which DOPAL modifies GAPDH can serve as a mechanistic explanation to the pathological events in Parkinson's Disease.

Drosophila Ringmaker regulates microtubule stabilization and axonal extension during embryonic development

Axonal growth and targeting are fundamental to the organization of the nervous system, and require active engagement of the cytoskeleton. Polymerization and stabilization of axonal microtubules is central to axonal growth and maturation of neuronal connectivity. Studies have suggested that members of the tubulin polymerization promoting protein (TPPP, also known as P25α) family are involved in cellular process extension. However, no in vivo knockout data exists regarding its role in axonal growth during development. Here, we report the characterization of Ringmaker (Ringer; CG45057), the only Drosophila homolog of long p25α proteins. Immunohistochemical analyses indicate that Ringer expression is dynamically regulated in the embryonic central nervous system (CNS). ringer-null mutants show cell misplacement, and errors in axonal extension and targeting. Ultrastructural examination of ringer mutants revealed defective microtubule morphology and organization. Primary neuronal cultures of ringer mutants exhibit defective axonal extension, and Ringer expression in cells induced microtubule stabilization and bundling into rings. In vitro assays showed that Ringer directly affects tubulin, and promotes microtubule bundling and polymerization. Together, our studies uncover an essential function of Ringer in axonal extension and targeting through proper microtubule organization.

Protein Recognition in Drug-Induced DNA Alkylation: When the Moonlight Protein GAPDH Meets S23906-1/DNA Minor Groove Adducts

DNA alkylating drugs have been used in clinics for more than seventy years. The diversity of their mechanism of action (major/minor groove; mono-/bis-alkylation; intra-/inter-strand crosslinks; DNA stabilization/destabilization, etc.) has undoubtedly major consequences on the cellular response to treatment. The aim of this review is to highlight the variety of established protein recognition of DNA adducts to then particularly focus on glyceraldehyde-3-phosphate dehydrogenase (GAPDH) function in DNA adduct interaction with illustration using original experiments performed with S23906-1/DNA adduct. The introduction of this review is a state of the art of protein/DNA adducts recognition, depending on the major or minor groove orientation of the DNA bonding as well as on the molecular consequences in terms of double-stranded DNA maintenance. It reviews the implication of proteins from both DNA repair, transcription, replication and chromatin maintenance in selective DNA adduct recognition. The main section of the manuscript is focusing on the implication of the moonlighting protein GAPDH in DNA adduct recognition with the model of the peculiar DNA minor groove alkylating and destabilizing drug S23906-1. The mechanism of action of S23906-1 alkylating drug and the large variety of GAPDH cellular functions are presented prior to focus on GAPDH direct binding to S23906-1 adducts.

Targeting the interface of the pathological complex of α-synuclein and TPPP/p25

The pathological interaction of intrinsically disordered proteins, such as α-synuclein (SYN) and Tubulin Polymerization Promoting Protein (TPPP/p25), is often associated with neurodegenerative disorders. These hallmark proteins are co-enriched and co-localized in brain inclusions of Parkinson's disease and other synucleinopathies; yet, their successful targeting does not provide adequate effect due to their multiple functions. Here we characterized the interactions of the human recombinant wild type SYN, its truncated forms (SYN(1-120), SYN(95-140)), a synthetized peptide (SYN(126-140)) and a proteolytic fragment (SYN(103-140)) with TPPP/p25 to identify the SYN segment involved in the interaction. The binding of SYN(103-140) to TPPP/p25 detected by ELISA suggested the involvement of a segment within the C-terminal of SYN. The studies performed with ELISA, Microscale Thermophoresis and affinity chromatography proved that SYN(95-140) and SYN(126-140) - in contrast to SYN(1-120) - displayed significant binding to TPPP/p25. Fluorescence assay with ANS, a molten globule indicator, showed that SYN, but not SYN(1-120) abolished the zinc-induced local folding of both the full length as well as the N- and C-terminal-free (core) TPPP/p25; SYN(95-140) and SYN(126-140) were effective as well. The aggregation-prone properties of the SYN species with full length or core TPPP/p25 visualized by immunofluorescent microscopy demonstrated that SYN(95-140) and SYN(126-140), but not SYN(1-120), induced co-enrichment and massive intracellular aggregation after their premixing and uptake from the medium. These data with their innovative impact could contribute to the development of anti-Parkinson drugs with unique specificity by targeting the interface of the pathological TPPP/p25-SYN complex.

Genetic variants in GAPDH confer susceptibility to sporadic Parkinson's disease in a Chinese Han population

BACKGROUND

Accumulating evidence has demonstrated that the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a part of Lewy body inclusions and involves the pathogenesis of Parkinson's disease (PD). However, it remains unknown whether or not genetic variation at the GAPDH locus contributes to the risk for PD.

METHODS

A total of 302 sporadic PD patients and 377 control subjects were recruited in our study for assessing two single nucleotide polymorphisms (rs3741918 and rs1060619) in the GAPDH gene. Both allelic association and additive models were used to analyze association between GAPDH variants and risk for PD.

RESULTS

Both polymorphisms were significantly associated with risk for PD after correction by Bonferroni multiple testing. The minor allele of rs3741918 was associated with decreased risk of sporadic PD (allelic contrast, OR = 0.74, 95% CI: 0.59-0.93, corrected P = 0.028; additive model, OR = 0.73, 95% CI: 0.58-0.92, corrected P = 0.018). While for the rs1060619 locus, the minor allele conferred increased risk for PD (allelic contrast, OR = 1.41, 95% CI: 1.14-1.75, corrected P = 0.007; additive model, OR = 1.43, 95% CI: 1.15-1.79, corrected P = 0.002).

CONCLUSION

Our study indicates that GAPDH variants confer susceptibility to sporadic PD in a Chinese Han population, which is consistent with the role of GAPDH protein in neuronal apoptosis. To our knowledge, this is the first study of genetic association between GAPDH locus and risk for PD in the Chinese population.

Relocation of p25α/tubulin polymerization promoting protein from the nucleus to the perinuclear cytoplasm in the oligodendroglia of sporadic and COQ2 mutant multiple system atrophy

p25α/tubulin polymerization promoting protein (TPPP) is an oligodendroglial protein that plays crucial roles including myelination, and the stabilization of microtubules. In multiple system atrophy (MSA), TPPP is suggested to relocate from the myelin sheath to the oligodendroglial cell body, before the formation of glial cytoplasmic inclusions (GCIs), the pathologic hallmark of MSA. However, much is left unknown about the re-distribution of TPPP in MSA. We generated new antibodies against the N- and C-terminus of TPPP, and analyzed control and MSA brains, including the brain of a familial MSA patient carrying homozygous mutations in the coenzyme Q2 gene (COQ2). In control brain tissues, TPPP was localized not only in the cytoplasmic component of the oligodendroglia including perinuclear cytoplasm and peripheral processes in the white matter, but also in the nucleus of a fraction (62.4%) of oligodendroglial cells. Immunoelectron microscopic analysis showed TPPP in the nucleus and mitochondrial membrane of normal oligodendroglia, while western blot also supported its nuclear and mitochondrial existence. In MSA, the prevalence of nuclear TPPP was 48.6% in the oligodendroglia lacking GCIs, whereas it was further decreased to 19.6% in the oligodendroglia with phosphorylated α-synuclein (pα-syn)-positive GCIs, both showing a significant decrease compared to controls (62.4%). In contrast, TPPP accumulated in the perinuclear cytoplasm where mitochondrial membrane (TOM20 and cytochrome C) and fission (DRP1) proteins were often immunoreactive. We conclude that in MSA-oligodendroglia, TPPP is reduced, not only in the peripheral cytoplasm, but also in the nucleus and relocated to the perinuclear cytoplasm.

The Lewy body in Parkinson's disease and related neurodegenerative disorders

The histopathological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates referred to as Lewy bodies (LBs), in which α-synuclein is a major constituent. Pale bodies, the precursors of LBs, may serve the material for that LBs continue to expand. LBs consist of a heterogeneous mixture of more than 90 molecules, including PD-linked gene products (α-synuclein, DJ-1, LRRK2, parkin, and PINK-1), mitochondria-related proteins, and molecules implicated in the ubiquitin-proteasome system, autophagy, and aggresome formation. LB formation has been considered to be a marker for neuronal degeneration because neuronal loss is found in the predilection sites for LBs. However, recent studies have indicated that nonfibrillar α-synuclein is cytotoxic and that fibrillar aggregates of α-synuclein (LBs and pale bodies) may represent a cytoprotective mechanism in PD.

Molecular interaction of TPPP with PrP antagonized the CytoPrP-induced disruption of microtubule structures and cytotoxicity

Background

Tubulin polymerization promoting protein/p25 (TPPP/p25), known as a microtubule-associated protein (MAP), is a brain-specific unstructured protein with a physiological function of stabilizing cellular microtubular ultrastructures. Whether TPPP involves in the normal functions of PrP or the pathogenesis of prion disease remains unknown. Here, we proposed the data that TPPP formed molecular complex with PrP. We also investigated its influence on the aggregation of PrP and fibrillization of PrP106–126 in vitro, its antagonization against the disruption of microtubule structures and cytotoxicity of cytosolic PrP in cells, and its alternation in the brains of scrapie-infected experimental hamsters.

Methodology/Principal Findings

Using pull-down and immunoprecipitation assays, distinct molecular interaction between TPPP and PrP were identified and the segment of TPPP spanning residues 100–219 and the segment of PrP spanning residues 106–126 were mapped as the regions responsible for protein interaction. Sedimentation experiments found that TPPP increased the aggregation of full-length recombinant PrP (PrP23–231) in vitro. Transmission electron microscopy and Thioflavin T (ThT) assays showed that TPPP enhanced fibril formation of synthetic peptide PrP106–126 in vitro. Expression of TPPP in the cultured cells did not obviously change the microtubule networks observed by a tubulin-specific immunofluorescent assay and cell growth features measured by CCK8 tests, but significantly antagonized the disruption of microtubule structures and rescued the cytotoxicity caused by the accumulation of cytosolic PrP (CytoPrP). Furthermore, Western blots identified that the levels of the endogenous TPPP in the brains of scrapie-infected experimental hamsters were significantly reduced.

Conclusion/Significance

Those data highlight TPPP may work as a protective factor for cells against the damage effects of the accumulation of abnormal forms of PrPs, besides its function as an agent for dynamic stabilization of microtubular ultrastructures.

On the functional diversity of glyceraldehyde-3-phosphate dehydrogenase: biochemical mechanisms and regulatory control

BACKGROUND

New studies provide evidence that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is not simply a classical glycolytic protein of little interest. Instead, it is a multifunctional protein with significant activity in a number of fundamental cell pathways. GAPDH is a highly conserved gene and protein, with a single mRNA transcribed from a unique gene. Control mechanisms must exist which regulate its functional diversity.

SCOPE OF REVIEW

This review focuses on new, timely studies defining not only its diverse activities but also those which define the regulatory mechanisms through which those functions may be controlled. The reader is referred to the author's prior review for the consideration of past reports which first indicated GAPDH multiple activities (Sirover, Biochim. Biophys. Acta 1432 (1999) 159-184.)

CONCLUSIONS

These investigations demonstrate fundamental roles of GAPDH in vivo, dynamic changes in its subcellular localization, and the importance of posttranslational modifications as well as protein:protein interactions as regulatory control mechanisms.

GENERAL SIGNIFICANCE

GAPDH is the prototype "moonlighting" protein which exhibits activities distinct from their classically identified functions. Their participation in diverse cell pathways is essential. Regulatory mechanisms exist which control those diverse activities as well as changes in their subcellular localization as a consequence of those new functions.

Tubulin polymerization promoting protein (TPPP/p25) as a marker for oligodendroglial changes in multiple sclerosis

Multiple sclerosis (MS) is an idiopathic chronic inflammatory demyelinating disease of the central nervous system with variable extent of remyelination. Remyelination originates from oligodendrocyte (OG) precursor cells, which migrate and differentiate into mature OG. Tubulin polymerization promoting protein (TPPP/p25) is located in mature OG and aggregates in oligodendroglial cytoplasmic inclusions in multiple system atrophy. We developed a novel monoclonal anti-TPPP/p25 antibody to quantify OG in different subtypes and disease stages of MS, and possible degenerative changes in OG. We evaluated autopsy material from 25 MS cases, including acute, primary progressive, secondary progressive, relapsing remitting MS, and five controls. Demyelinated lesions revealed loss of TPPP/p25-positive OG within the plaques. In remyelination, TPPP/p25 was first expressed in OG cytoplasms and later became positive in myelin sheaths. We observed increased numbers of TPPP/p25 immunoreactive OG in the normal appearing white matter (NAWM) in MS patients. In MS cases, the cytoplasmic area of TPPP/p25 immunoreactivity in the OG was higher in the periplaque area when compared with NAWM and the plaque, and TPPP/p25 immunoreactive OG cytoplasmic area inversely correlated with the disease duration. There was a lack of phospho-TDP-43, phospho-tau, α-synuclein, and ubiquitin immunoreactivity in OG with enlarged cytoplasm. Our data suggest impaired differentiation, migration, and activation capacity of OG in later disease stages of MS. Upregulation of TPPP/p25 in the periplaque white matter OG without evidence for inclusion body formation might reflect an activation state. Distinct and increased expression of TPPP/p25 in MS renders it a potential prognostic and diagnostic marker of MS.

Increased oxidation of certain glycolysis and energy metabolism enzymes in the frontal cortex in Lewy body diseases

Lipoxidative damage of aldolase A, enolase 1, and glyceraldehyde dehydrogenase (GAPDH) was found in the frontal cortex in a percentage of aged controls by bidimensional gel electrophoresis, Western blot test, in-gel digestion, and mass spectrometry. Aldolase A and enolase 1 were altered in 12 of 19 cases, whereas oxidation of GAPDH was found in 6 of 19 controls. The three enzymes were oxidized in the frontal cortex in the majority of cases of incidental Parkinson's disease (iPD), PD, and dementia with Lewy bodies (DLB). Differences were statistically significant (chi(2) test) for GAPDH in PD and DLB. Densitometric studies have shown that the ratio of oxidized protein per spot is higher in iPD, PD, and DLB compared with controls. These findings show oxidation of three enzymes linked with glycolysis and energy metabolism in the adult human brain as well as increased oxidation of aldolase A, enolase 1, and GAPDH in the frontal cortex in Lewy body diseases. Modifications of these enzymes may result in decreased activity and may partly account for impaired metabolism and function of the frontal lobe in PD.

Lysosomal enzyme cathepsin D protects against alpha-synuclein aggregation and toxicity

α-synuclein (α-syn) is a main component of Lewy bodies (LB) that occur in many neurodegenerative diseases, including Parkinson's disease (PD), dementia with LB (DLB) and multi-system atrophy. α-syn mutations or amplifications are responsible for a subset of autosomal dominant familial PD cases, and overexpression causes neurodegeneration and motor disturbances in animals. To investigate mechanisms for α-syn accumulation and toxicity, we studied a mouse model of lysosomal enzyme cathepsin D (CD) deficiency, and found extensive accumulation of endogenous α-syn in neurons without overabundance of α-syn mRNA. In addition to impaired macroautophagy, CD deficiency reduced proteasome activity, suggesting an essential role for lysosomal CD function in regulating multiple proteolytic pathways that are important for α-syn metabolism. Conversely, CD overexpression reduces α-syn aggregation and is neuroprotective against α-syn overexpression-induced cell death in vitro. In a C. elegans model, CD deficiency exacerbates α-syn accumulation while its overexpression is protective against α-syn-induced dopaminergic neurodegeneration. Mutated CD with diminished enzymatic activity or overexpression of cathepsins B (CB) or L (CL) is not protective in the worm model, indicating a unique requirement for enzymatically active CD. Our data identify a conserved CD function in α-syn degradation and identify CD as a novel target for LB disease therapeutics.

FKBP36 is an inherent multifunctional glyceraldehyde-3-phosphate dehydrogenase inhibitor

FKBP36 has been previously shown to be a crucial factor in spermatogenesis because of its interplay with the synaptonemal complex protein SCPI. Here we show that beyond this function, FKBP36 forms complexes with glyceraldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12) and Hsp90. Both proteins bind independently to different sites of the FKBP36 tetratricopeptide repeat domain. The interaction between FKBP36 and GAPDH directly inhibits the catalytic activity of GAPDH. In addition, FKBP36 expression causes a significant reduction of the GAPDH level and activity in COS-7 cells. Particularly in the cytosolic fraction, GAPDH was depleted by FKBP36 expression. Thus, FKBP36 diminishes GAPDH activity by direct interaction and down-regulation of GAPDH, which represents a previously unknown mechanism of GAPDH regulation and a novel function of FKBP36 in testis-specific signaling.

Proteomics of human neurodegenerative diseases

The technology, experimental approaches, and bioinformatics that support proteomic research are evolving rapidly. The application of these new capabilities to the study of neurodegenerative diseases is providing insight into the biochemical pathogenesis of neurodegeneration as well as fueling major efforts in biomarker discovery. Here, we review the fundamentals of commonly used proteomic approaches and the outcomes of these investigations with autopsy and cerebrospinal fluid samples from patients with neurodegenerative diseases.

Proteomic identification of proteins in the human brain: Towards a more comprehensive understanding of neurodegenerative disease

Proteomics has revealed itself as a powerful tool in the identification and determination of proteins and their biological significance. More recently, several groups have taken advantage of the high-throughput nature of proteomics in order to gain a more in-depth understanding of the human brain. In turn, this information has provided researchers with invaluable insight into the potential pathways and mechanisms involved in the pathogenesis of several neurodegenerative disorders, e.g., Alzheimer and Parkinson disease. Furthermore, these findings likely will improve methods to diagnose disease and monitor disease progression as well as generate novel targets for therapeutic intervention. Despite these advances, comprehensive understanding of the human brain proteome remains challenging, and requires development of improved sample enrichment, better instrumentation, and innovative analytic techniques. In this review, we will focus on the most recent progress related to identification of proteins in the human brain under normal as well as pathological conditions, mainly Alzheimer and Parkinson disease, their potential application in biomarker discovery, and discuss current advances in protein identification aimed at providing a more comprehensive understanding of the brain.

The Lewy body in Parkinson's disease: molecules implicated in the formation and degradation of alpha-synuclein aggregates

The histological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates called Lewy bodies (LBs). LB formation has been considered to be a marker for neuronal degeneration, because neuronal loss is found in the predilection sites for LBs. To date, more than 70 molecules have been identified in LBs, in which alpha-synuclein is a major constituent of LB fibrils. Alpha-synuclein immunohistochemistry reveals that diffuse cytoplasmic staining develops into pale bodies via compaction, and that LBs arise from the peripheral portion of pale bodies. This alpha-synuclein abnormality is found in 10% of pigmented neurons in the substantia nigra and more than 50% of those in the locus ceruleus in PD. Recent studies have suggested that oligomers and protofibrils of alpha-synuclein are cytotoxic, and that LBs may represent a cytoprotective mechanism in PD.

p25alpha relocalizes in oligodendroglia from myelin to cytoplasmic inclusions in multiple system atrophy

p25alpha is an oligodendroglial protein that can induce aggregation of alpha-synuclein and accumulates in oligodendroglial cell bodies containing fibrillized alpha-synuclein in the neurodegenerative disease multiple system atrophy (MSA). We demonstrate biochemically that p25alpha is a constituent of myelin and a high-affinity ligand for myelin basic protein (MBP), and in situ immunohistochemistry revealed that MBP and p25alpha colocalize in myelin in normal human brains. Analysis of MSA cases reveals dramatic changes in p25alpha and MBP throughout the course of the disease. In situ immunohistochemistry revealed a cellular redistribution of p25alpha immunoreactivity from the myelin to the oligodendroglial cell soma, with no overall change in p25alpha protein concentration using immunoblotting. Concomitantly, an approximately 80% reduction in the concentration of full-length MBP protein was revealed by immunoblotting along with the presence of immunoreactivity for MBP degradation products in oligodendroglia. The oligodendroglial cell bodies in MSA displayed an enlargement along with the relocalization of p25alpha, and this was enhanced after the deposition of alpha-synuclein in the glial cytoplasmic inclusions. Overall, the data indicate that changes in the cellular interactions between MBP and p25alpha occur early in MSA and contribute to abnormalities in myelin and subsequent alpha-synuclein aggregation and the ensuing neuronal degeneration that characterizes this disease.

Phosphorylation blocks the activity of tubulin polymerization-promoting protein (TPPP): identification of sites targeted by different kinases

Tubulin polymerization-promoting protein (TPPP), an unfolded brain-specific protein interacts with the tubulin/microtubule system in vitro and in vivo, and is enriched in human pathological brain inclusions. Here we show that TPPP induces tubulin self-assembly into intact frequently bundled microtubules, and that the phosphorylation of specific sites distinctly affects the function of TPPP. In vitro phosphorylation of wild type and the truncated form (Delta3-43TPPP) of human recombinant TPPP was performed by kinases involved in brain-specific processes. A stoichiometry of 2.9 +/- 0.3, 2.2 +/- 0.3, and 0.9 +/- 0.1 mol P/mol protein with ERK2, cyclin-dependent kinase 5 (Cdk5), and cAMP-dependent protein kinase (PKA), respectively, was revealed for the full-length protein, and 0.4-0.5 mol P/mol protein was detected with all three kinases when the N-terminal tail was deleted. The phosphorylation sites Thr(14), Ser(18), Ser(160) for Cdk5; Ser(18), Ser(160) for ERK2, and Ser(32) for PKA were identified by mass spectrometry. These sites were consistent with the bioinformatic predictions. The three N-terminal sites were also found to be phosphorylated in vivo in TPPP isolated from bovine brain. Affinity binding experiments provided evidence for the direct interaction between TPPP and ERK2. The phosphorylation of TPPP by ERK2 or Cdk5, but not by PKA, perturbed the structural alterations induced by the interaction between TPPP and tubulin without affecting the binding affinity (K(d) = 2.5-2.7 microM) or the stoichiometry (1 mol TPPP/mol tubulin) of the complex. The phosphorylation by ERK2 or Cdk5 resulted in the loss of microtubule-assembling activity of TPPP. The combination of our in vitro and in vivo data suggests that ERK2 can regulate TPPP activity via the phosphorylation of Thr(14) and/or Ser(18) in its unfolded N-terminal tail.

The brain-specific protein TPPP/p25 in pathological protein deposits of neurodegenerative diseases

Immunohistochemical detection of protein components of pathological inclusions is widely used for neuropathological diagnosis of neurodegenerative disorders. However, different antibodies and antigen unmasking methods may account for variability between research studies and thus may affect diagnostic accuracy. Using two different antibodies raised against either a segment (184-200 aa) or the full length of human recombinant brain-specific tubulin polymerization promoting protein TPPP/p25, we immunohistochemically screened neurodegenerative disorders, both with and without pathological alpha-synuclein structures. We tested three different epitope unmasking methods, we applied laser confocal microscopy to evaluate double immunolabelling, and we compared the amount of structures exhibiting TPPP/p25 and alpha-synuclein immunoreactivity. We demonstrate that there are a variety of staining patterns depending on the epitope retrieval method and antibody used. The antibody raised against aa 184-200 segment of TPPP/p25 is better in immunolabelling the majority of alpha-synuclein immunopositive neuronal and glial pathological profiles detectable in Parkinson's disease, diffuse Lewy-body disease, and multiple system atrophy, in addition to immunostaining some extracellular huntingtin immunoreactive structures, lipofuscin, and neuromelanin particles. In contrast, the one raised against the full-length human recombinant TPPP/p25 is more suitable to immunodetect normal oligodendrocytes. Exposition of the segment aa 184-200 of TPPP/p25 in the aggregates of pathological inclusions renders this antibody a reliable marker of all types of alpha-synucleinopathies and suggests a role for TPPP/p25 in the aggregation process of some neurodegenerative conditions.