Lara Wahlster

PROTEIN DEGRADATION PATHWAYS IN PARKINSON'S DISEASE - CURSE OR BLESSING

Protein misfolding, aggregation and deposition are common disease mechanisms in many neurodegenerative diseases including Parkinson’s disease (PD). Accumulation of damaged or abnormally modified proteins may lead to perturbed cellular function and eventually to cell death. Thus, neurons rely on elaborated pathways of protein quality control and removal to maintain intracellular protein homeostasis. Molecular chaperones, the ubiquitin–proteasome system (UPS) and the autophagy–lysosomal pathway (ALP) are critical pathways that mediate the refolding or removal of abnormal proteins. The successive failure of these protein degradation pathways, as a cause or consequence of early pathological alterations in vulnerable neurons at risk, may present a key step in the pathological cascade that leads to spreading neurodegeneration. A growing number of studies in disease models and patients have implicated dysfunction of the UPS and ALP in the pathogenesis of Parkinson’s disease and related disorders. Deciphering the exact mechanism by which the different proteolytic systems contribute to the elimination of pathogenic proteins, like α-synuclein, is therefore of paramount importance. We herein review the role of protein degradation pathways in Parkinson’s disease and elaborate on the different contributions of the UPS and the ALP to the clearance of altered proteins. We examine the interplay between different degradation pathways and provide a model for the role of the UPS and ALP in the evolution and progression of α-synuclein pathology. With regards to exciting recent studies we also discuss the putative potential of using protein degradation pathways as novel therapeutic targets in Parkinson’s disease.

Molecular chaperones and protein folding as therapeutic targets in Parkinson’s disease and other synucleinopathies

Changes in protein metabolism are key to disease onset and progression in many neurodegenerative diseases. As a prime example, in Parkinson’s disease, folding, post-translational modification and recycling of the synaptic protein α-synuclein are clearly altered, leading to a progressive accumulation of pathogenic protein species and the formation of intracellular inclusion bodies. Altered protein folding is one of the first steps of an increasingly understood cascade in which α-synuclein forms complex oligomers and finally distinct protein aggregates, termed Lewy bodies and Lewy neurites. In neurons, an elaborated network of chaperone and co-chaperone proteins is instrumental in mediating protein folding and re-folding. In addition to their direct influence on client proteins, chaperones interact with protein degradation pathways such as the ubiquitin-proteasome-system or autophagy in order to ensure the effective removal of irreversibly misfolded and potentially pathogenic proteins. Because of the vital role of proper protein folding for protein homeostasis, a growing number of studies have evaluated the contribution of chaperone proteins to neurodegeneration. We herein review our current understanding of the involvement of chaperones, co-chaperones and chaperone-mediated autophagy in synucleinopathies with a focus on the Hsp90 and Hsp70 chaperone system. We discuss genetic and pathological studies in Parkinson’s disease as well as experimental studies in models of synucleinopathies that explore molecular chaperones and protein degradation pathways as a novel therapeutic target. To this end, we examine the capacity of chaperones to prevent or modulate neurodegeneration and summarize the current progress in models of Parkinson’s disease and related neurodegenerative disorders.

Presenilin-1 adopts pathogenic conformation in normal aging and in sporadic Alzheimer’s disease

Accumulation of amyloid-β (Aβ) and neurofibrillary tangles in the brain, inflammation and synaptic and neuronal loss are some of the major neuropathological hallmarks of Alzheimer’s disease (AD). While genetic mutations in amyloid precursor protein and presenilin-1 and -2 (PS1 and PS2) genes cause early-onset familial AD, the etiology of sporadic AD is not fully understood. Our current study shows that changes in conformation of endogenous wild-type PS1, similar to those found with mutant PS1, occur in sporadic AD brain and during normal aging. Using a mouse model of Alzheimer’s disease (Tg2576) that overexpresses the Swedish mutation of amyloid precursor protein but has normal levels of endogenous wild-type presenilin, we report that the percentage of PS1 in a pathogenic conformation increases with age. Importantly, we found that this PS1 conformational shift is associated with amyloid pathology and precedes amyloid-β deposition in the brain. Furthermore, we found that oxidative stress, a common stress characteristic of aging and AD, causes pathogenic PS1 conformational change in neurons in vitro, which is accompanied by increased Aβ42/40 ratio. The results of this study provide important information about the timeline of pathogenic changes in PS1 conformation during aging and suggest that structural changes in PS1/γ-secretase may represent a molecular mechanism by which oxidative stress triggers amyloid-β accumulation in aging and in sporadic AD brain.

Molecular chaperones in Parkinson's disease--present and future.

Parkinsons disease, like many other neurodegenerative disorders, is characterized by the progressive accumulation of pathogenic protein species and the formation of intracellular inclusion bodies. The cascade by which the small synaptic protein α-synuclein misfolds to form distinctive protein aggregates, termed Lewy bodies and Lewy neurites, has been the subject of intensive research for more than a decade. Genetic and pathological studies in Parkinsons disease patients as well as experimental studies in disease models have clearly established altered protein metabolism as a key element in the pathogenesis of Parkinsons disease. Alterations in protein metabolism include misfolding and aggregation, post-translational modification and dysfunctional degradation of cytotoxic protein species. Protein folding and re-folding are both mediated by a highly conserved network of molecules, called molecular chaperones and co-chaperones. In addition to the regulatory role in protein folding, molecular chaperone function is intimately associated with pathways of protein degradation, such as the ubiquitin-proteasome system and the autophagy-lysosomal pathway, to effectively remove irreversibly misfolded proteins. Because of the central role of molecular chaperones in maintaining protein homeostasis, we herein review our current knowledge on the involvement of molecular chaperones and co-chaperones in Parkinsons disease. We further discuss the capacity of molecular chaperones to prevent or modulate neurodegeneration, an important concept for future neuroprotective strategies and summarize the current progress in preclinical studies in models of Parkinsons disease and other neurodegenerative disorders. Finally we include a discussion on the future potential of using molecular chaperones as a disease modifying therapy.

Drug discovery for Diamond-Blackfan anemia using reprogrammed hematopoietic progenitors

A stem cell reprogramming approach enables disease modeling and drug discovery for a genetic blood disorder and uncovers a candidate therapeutic. Inducing autophagy to improve anemia Diamond-Blackfan anemia (DBA) is a rare blood disorder characterized by insufficient red blood cell production that is treated with corticosteroids and transfusion therapy. To identify additional therapeutics for DBA, Doulatov et al. performed a chemical screen with hematopoietic progenitor cells derived from iPSCs from two DBA patients with RPS19 and RPL5 genetic mutations. The autophagy inducing small-molecule SMER28 rescued erythroid differentiation in an autophagy factor ATG5-dependent manner in iPSC-derived patient cells, in zebrafish models of DBA, and in several mouse models. These results demonstrate the utility of iPSC-based screens for drug discovery for rare blood disorders and identify SMER28 and the autophagy pathway as promising targets for DBA therapy. Diamond-Blackfan anemia (DBA) is a congenital disorder characterized by the failure of erythroid progenitor differentiation, severely curtailing red blood cell production. Because many DBA patients fail to respond to corticosteroid therapy, there is considerable need for therapeutics for this disorder. Identifying therapeutics for DBA requires circumventing the paucity of primary patient blood stem and progenitor cells. To this end, we adopted a reprogramming strategy to generate expandable hematopoietic progenitor cells from induced pluripotent stem cells (iPSCs) from DBA patients. Reprogrammed DBA progenitors recapitulate defects in erythroid differentiation, which were rescued by gene complementation. Unbiased chemical screens identified SMER28, a small-molecule inducer of autophagy, which enhanced erythropoiesis in a range of in vitro and in vivo models of DBA. SMER28 acted through autophagy factor ATG5 to stimulate erythropoiesis and up-regulate expression of globin genes. These findings present an unbiased drug screen for hematological disease using iPSCs and identify autophagy as a therapeutic pathway in DBA.

Emerging role of autophagy in pediatric neurodegenerative and neurometabolic diseases

Pediatric neurodegenerative diseases are a heterogeneous group of diseases that result from specific genetic and biochemical defects. In recent years, studies have revealed a wide spectrum of abnormal cellular functions that include impaired proteolysis, abnormal lipid trafficking, accumulation of lysosomal content, and mitochondrial dysfunction. Within neurons, elaborated degradation pathways such as the ubiquitin–proteasome system and the autophagy–lysosomal pathway are critical for maintaining homeostasis and normal cell function. Recent evidence suggests a pivotal role for autophagy in major adult and pediatric neurodegenerative diseases. We herein review genetic, pathological, and molecular evidence for the emerging link between autophagy dysfunction and lysosomal storage disorders such as Niemann–Pick type C, progressive myoclonic epilepsies such as Lafora disease, and leukodystrophies such as Alexander disease. We also discuss the recent discovery of genetically deranged autophagy in Vici syndrome, a multisystem disorder, and the implications for the role of autophagy in development and disease. Deciphering the exact mechanism by which autophagy contributes to disease pathology may open novel therapeutic avenues to treat neurodegeneration. To this end, an outlook on novel therapeutic approaches targeting autophagy concludes this review.

Progress towards generation of human haematopoietic stem cells

De novo generation of haematopoietic stem cells from different human pluripotent stem cell sources remains a high priority for haematology and regenerative medicine. At present, efficient derivation of functional haematopoietic stem cells with the capability for definitive in vivo engraftment and multi-lineage potential remains challenging. Here, we discuss recent progress and strategies to overcome obstacles that have thwarted past efforts. In addition, we review promising advances in the generation of mature blood lineages and the potential of induced pluripotent stem cells.

Familial Mediterranean fever in Germany: clinical presentation and amyloidosis risk.

Objective: To characterize patients with familial Mediterranean fever (FMF) with and without AA amyloidosis living in Germany. Method: Clinical and genetic data from 64 FMF patients were analysed for amyloidosis risk factors. Results: Fifty-five patients (85%) were of Turkish or Armenian origin. Thirty-one patients (48%) developed FMF symptoms before the age of 16 years. Sixteen patients (26%) became symptomatic after age 20. Symptoms reported were peritonitis (95%), fever (78%), pleuritis (59%), arthralgia (60%), arthritis (32%), erysipelas-like erythema (23%), and vasculitis (8%). FMF diagnosis was delayed for a median of 8.0 years. Genetic analysis confirmed M694V as the most prevalent Mediterranean fever (MEFV) gene mutation in 46 out of 59 patients (78%). M694V homozygosity was associated with an earlier FMF onset (median age 5.5 years, p = 0.0001) and a higher prevalence of peritonitis (p = 0.007) and pleuritis (p = 0.0007) compared to patients without an M694V mutation. AA amyloidosis was detected in 16 patients (25%) at a median age of 36.5 years and tended to be associated with a higher age at disease onset (p = 0.062) and a higher FMF activity score (p = 0.093). AA amyloidosis was significantly associated with a higher age at FMF diagnosis (p = 0.0022). Conclusions: Clinical symptoms of FMF-affected migrants living in Germany resemble those observed in their home country. In particular, patients with an onset of FMF symptoms after age 20 and a later FMF diagnosis have a high risk of AA amyloidosis. Symptomatic patients who originate from countries with a higher FMF prevalence should be screened for FMF and proteinuria.

Reduction of TMEM97 increases NPC1 protein levels and restores cholesterol trafficking in Niemann-pick type C1 disease cells

Niemann-Pick type C disease (NP-C) is a progressive lysosomal lipid storage disease caused by mutations in the NPC1 and NPC2 genes. NPC1 is essential for transporting cholesterol and other lipids out of lysosomes, but little is known about the mechanisms that control its cellular abundance and localization. Here we show that a reduction of TMEM97, a cholesterol-responsive NPC1-binding protein, increases NPC1 levels in cells through a post-transcriptional mechanism. Reducing TMEM97 through RNA-interference reduces lysosomal lipid storage and restores cholesterol trafficking to the endoplasmic reticulum in cell models of NP-C. In TMEM97 knockdown cells, NPC1 levels can be reinstated with wild type TMEM97, but not TMEM97 missing an ER-retention signal suggesting that TMEM97 contributes to controlling the availability of NPC1 to the cell. Importantly, knockdown of TMEM97 also increases levels of residual NPC1 in NPC1-mutant patient fibroblasts and reduces cholesterol storage in an NPC1-dependent manner. Our findings propose TMEM97 inhibition as a novel strategy to increase residual NPC1 levels in cells and a potential therapeutic target for NP-C.

Clinical manifestations and longterm followup of a patient with CINCA/NOMID syndrome.

To the Editor: Chronic infantile neurological cutaneous and articular (CINCA) syndrome1 is a rare, genetic autoinflammatory disease that belongs to the spectrum of cryopyrin-associated periodic syndromes (CAPS), along with the familial cold autoinflammatory syndrome and the Muckle-Wells syndrome. CAPS are associated with autosomal-dominant mutations in the NLRP3 gene (formerly CIAS1), which encodes the protein cryopyrin2,3. Within the spectrum of CAPS, the CINCA syndrome, also known as neonatal-onset multisystem inflammatory disease (NOMID), is considered to be the most severe phenotype. A triad of urticarial rashes, neurological manifestations, and arthropathy, accompanied by recurrent fever episodes and systemic inflammation, originally defined CINCA syndrome1,4. Systemic AA-amyloidosis is a serious longterm complication that can lead to renal failure and increased mortality4. We describe a 23-year-old Caucasian woman who had developed urticarial skin lesions, lymphadenopathy, and recurrent febrile episodes within the first week after birth. The persistent nonpruritic and migratory urticaria were most pronounced at the patient’s face, trunk, and lower limbs and would intensify during recurrent attacks of fever (Figure 1D). Acute-phase reactants were constantly elevated [C-reactive protein (CRP) up to 170 mg/l, serum amyloid … Address correspondence to Dr. N. Blank, University of Heidelberg, Internal Medicine 5, Division of Rheumatology, Im Neuenheimer Feld 410, D-69120 Heidelberg, Germany. E-mail: norbert.blank{at}med.uni-heidelberg.de