Dietary rescue of fumble--a Drosophila model for pantothenate-kinase-associated neurodegeneration

Mitochondrial iron deficiency triggers cytosolic iron overload in PKAN hiPS-derived astrocytes

Disease models of neurodegeneration with brain iron accumulation (NBIA) offer the possibility to explore the relationship between iron dyshomeostasis and neurodegeneration. We analyzed hiPS-derived astrocytes from PANK2-associated neurodegeneration (PKAN), an NBIA disease characterized by progressive neurodegeneration and high iron accumulation in the globus pallidus. Previous data indicated that PKAN astrocytes exhibit alterations in iron metabolism, general impairment of constitutive endosomal trafficking, mitochondrial dysfunction and acquired neurotoxic features. Here, we performed a more in-depth analysis of the interactions between endocytic vesicles and mitochondria via superresolution microscopy experiments. A significantly lower number of transferrin-enriched vesicles were in contact with mitochondria in PKAN cells than in control cells, confirming the impaired intracellular fate of cargo endosomes. The investigation of cytosolic and mitochondrial iron parameters indicated that mitochondrial iron availability was substantially lower in PKAN cells compared to that in the controls. In addition, PKAN astrocytes exhibited defects in tubulin acetylation/phosphorylation, which might be responsible for unregulated vesicular dynamics and inappropriate iron delivery to mitochondria. Thus, the impairment of iron incorporation into these organelles seems to be the cause of cell iron delocalization, resulting in cytosolic iron overload and mitochondrial iron deficiency, triggering mitochondrial dysfunction. Overall, the data elucidate the mechanism of iron accumulation in CoA deficiency, highlighting the importance of mitochondrial iron deficiency in the pathogenesis of disease.

PPAR Gamma Agonist Leriglitazone Recovers Alterations Due to Pank2-Deficiency in hiPS-Derived Astrocytes

The novel brain-penetrant peroxisome proliferator-activated receptor gamma agonist leriglitazone, previously validated for other rare neurodegenerative diseases, is a small molecule that acts as a regulator of mitochondrial function and exerts neuroprotective, anti-oxidative and anti-inflammatory effects. Herein, we tested whether leriglitazone can be effective in ameliorating the mitochondrial defects that characterize an hiPS-derived model of Pantothenate kinase-2 associated Neurodegeneration (PKAN). PKAN is caused by a genetic alteration in the mitochondrial enzyme pantothenate kinase-2, whose function is to catalyze the first reaction of the CoA biosynthetic pathway, and for which no effective cure is available. The PKAN hiPS-derived astrocytes are characterized by mitochondrial dysfunction, cytosolic iron deposition, oxidative stress and neurotoxicity. We monitored the effect of leriglitazone in comparison with CoA on hiPS-derived astrocytes from three healthy subjects and three PKAN patients. The treatment with leriglitazone did not affect the differentiation of the neuronal precursor cells into astrocytes, and it improved the viability of PKAN cells and their respiratory activity, while diminishing the iron accumulation similarly or even better than CoA. The data suggest that leriglitazone is well tolerated in this cellular model and could be considered a beneficial therapeutic approach in the treatment of PKAN.

Pantothenate kinase 2 interacts with PINK1 to regulate mitochondrial quality control via acetyl-CoA metabolism

Human neurodegenerative disorders often exhibit similar pathologies, suggesting a shared aetiology. Key pathological features of Parkinson's disease (PD) are also observed in other neurodegenerative diseases. Pantothenate Kinase-Associated Neurodegeneration (PKAN) is caused by mutations in the human PANK2 gene, which catalyzes the initial step of de novo CoA synthesis. Here, we show that fumble (fbl), the human PANK2 homolog in Drosophila, interacts with PINK1 genetically. fbl and PINK1 mutants display similar mitochondrial abnormalities, and overexpression of mitochondrial Fbl rescues PINK1 loss-of-function (LOF) defects. Dietary vitamin B5 derivatives effectively rescue CoA/acetyl-CoA levels and mitochondrial function, reversing the PINK1 deficiency phenotype. Mechanistically, Fbl regulates Ref(2)P (p62/SQSTM1 homolog) by acetylation to promote mitophagy, whereas PINK1 regulates fbl translation by anchoring mRNA molecules to the outer mitochondrial membrane. In conclusion, Fbl (or PANK2) acts downstream of PINK1, regulating CoA/acetyl-CoA metabolism to promote mitophagy, uncovering a potential therapeutic intervention strategy in PD treatment.

Inter-Species Rescue of Mutant Phenotype-The Standard for Genetic Analysis of Human Genetic Disorders in Drosophila melanogaster Model

Drosophila melanogaster (the fruit fly) is arguably a superstar of genetics, an astonishing versatile experimental model which fueled no less than six Nobel prizes in medicine. Nowadays, an evolving research endeavor is to simulate and investigate human genetic diseases in the powerful D. melanogaster platform. Such a translational experimental strategy is expected to allow scientists not only to understand the molecular mechanisms of the respective disorders but also to alleviate or even cure them. In this regard, functional gene orthology should be initially confirmed in vivo by transferring human or vertebrate orthologous transgenes in specific mutant backgrounds of D. melanogaster. If such a transgene rescues, at least partially, the mutant phenotype, then it qualifies as a strong candidate for modeling the respective genetic disorder in the fruit fly. Herein, we review various examples of inter-species rescue of relevant mutant phenotypes of the fruit fly and discuss how these results recommend several human genes as candidates to study and validate genetic variants associated with human diseases. We also consider that a wider implementation of this evolutionist exploratory approach as a standard for the medicine of genetic disorders would allow this particular field of human health to advance at a faster pace.

Massive iron accumulation in PKAN-derived neurons and astrocytes: light on the human pathological phenotype

Neurodegeneration associated with defective pantothenate kinase-2 (PKAN) is an early-onset monogenic autosomal-recessive disorder. The hallmark of the disease is the massive accumulation of iron in the globus pallidus brain region of patients. PKAN is caused by mutations in the PANK2 gene encoding the mitochondrial enzyme pantothenate kinase-2, whose function is to catalyze the first reaction of the CoA biosynthetic pathway. To date, the way in which this alteration leads to brain iron accumulation has not been elucidated. Starting from previously obtained hiPS clones, we set up a differentiation protocol able to generate inhibitory neurons. We obtained striatal-like medium spiny neurons composed of approximately 70-80% GABAergic neurons and 10-20% glial cells. Within this mixed population, we detected iron deposition in both PKAN cell types, however, the viability of PKAN GABAergic neurons was strongly affected. CoA treatment was able to reduce cell death and, notably, iron overload. Further differentiation of hiPS clones in a pure population of astrocytes showed particularly evident iron accumulation, with approximately 50% of cells positive for Perls staining. The analysis of these PKAN astrocytes indicated alterations in iron metabolism, mitochondrial morphology, respiratory activity, and oxidative status. Moreover, PKAN astrocytes showed signs of ferroptosis and were prone to developing a stellate phenotype, thus gaining neurotoxic features. This characteristic was confirmed in iPS-derived astrocyte and glutamatergic neuron cocultures, in which PKAN glutamatergic neurons were less viable in the presence of PKAN astrocytes. This newly generated astrocyte model is the first in vitro disease model recapitulating the human phenotype and can be exploited to deeply clarify the pathogenetic mechanisms underlying the disease.

Activation of Anopheles stephensi Pantothenate Kinase and Coenzyme A Biosynthesis Reduces Infection with Diverse Plasmodium Species in the Mosquito Host

Malaria parasites require pantothenate from both human and mosquito hosts to synthesize coenzyme A (CoA). Specifically, mosquito-stage parasites cannot synthesize pantothenate de novo or take up preformed CoA from the mosquito host, making it essential for the parasite to obtain pantothenate from mosquito stores. This makes pantothenate utilization an attractive target for controlling sexual stage malaria parasites in the mosquito. CoA is synthesized from pantothenate in a multi-step pathway initiated by the enzyme pantothenate kinase (PanK). In this work, we manipulated A. stephensi PanK activity and assessed the impact of mosquito PanK activity on the development of two malaria parasite species with distinct genetics and life cycles: the human parasite Plasmodium falciparum and the mouse parasite Plasmodium yoelii yoelii 17XNL. We identified two putative A. stephensi PanK isoforms encoded by a single gene and expressed in the mosquito midgut. Using both RNAi and small molecules with reported activity against human PanK, we confirmed that A. stephensi PanK manipulation was associated with corresponding changes in midgut CoA levels. Based on these findings, we used two small molecule modulators of human PanK activity (PZ-2891, compound 7) at reported and ten-fold EC50 doses to examine the effects of manipulating A. stephensi PanK on malaria parasite infection success. Our data showed that oral provisioning of 1.3 nM and 13 nM PZ-2891 increased midgut CoA levels and significantly decreased infection success for both Plasmodium species. In contrast, oral provisioning of 62 nM and 620 nM compound 7 decreased CoA levels and significantly increased infection success for both Plasmodium species. This work establishes the A. stephensi CoA biosynthesis pathway as a potential target for broadly blocking malaria parasite development in anopheline hosts. We envision this strategy, with small molecule PanK modulators delivered to mosquitoes via attractive bait stations, working in concert with deployment of parasite-directed novel pantothenamide drugs to block parasite infection in the human host. In mosquitoes, depletion of pantothenate through manipulation to increase CoA biosynthesis is expected to negatively impact Plasmodium survival by starving the parasite of this essential nutrient. This has the potential to kill both wild type parasites and pantothenamide-resistant parasites that could develop under pantothenamide drug pressure if these compounds are used as future therapeutics for human malaria.

Mitochondrial Dysfunction, Oxidative Stress and Neuroinflammation in Neurodegeneration with Brain Iron Accumulation (NBIA)

The syndromes of neurodegeneration with brain iron accumulation (NBIA) encompass a group of invalidating and progressive rare diseases that share the abnormal accumulation of iron in the basal ganglia. The onset of NBIA disorders ranges from infancy to adulthood. Main clinical signs are related to extrapyramidal features (dystonia, parkinsonism and choreoathetosis), and neuropsychiatric abnormalities. Ten NBIA forms are widely accepted to be caused by mutations in the genes PANK2, PLA2G6, WDR45, C19ORF12, FA2H, ATP13A2, COASY, FTL1, CP, and DCAF17. Nonetheless, many patients remain without a conclusive genetic diagnosis, which shows that there must be additional as yet undiscovered NBIA genes. In line with this, isolated cases of known monogenic disorders, and also, new genetic diseases, which present with abnormal brain iron phenotypes compatible with NBIA, have been described. Several pathways are involved in NBIA syndromes: iron and lipid metabolism, mitochondrial dynamics, and autophagy. However, many neurodegenerative conditions share features such as mitochondrial dysfunction and oxidative stress, given the bioenergetics requirements of neurons. This review aims to describe the existing link between the classical ten NBIA forms by examining their connection with mitochondrial impairment as well as oxidative stress and neuroinflammation.

Health Benefits of Anti-aging Drugs

Aging, as a physiological process mediated by numerous regulatory pathways and transcription factors, is manifested by continuous progressive functional decline and increasing risk of chronic diseases. There is an increasing interest to identify pharmacological agents for treatment and prevention of age-related disease in humans. Animal models play an important role in identification and testing of anti-aging compounds; this step is crucial before the drug will enter human clinical trial or will be introduced to human medicine. One of the main goals of animal studies is better understanding of mechanistic targets, therapeutic implications and side-effects of the drug, which may be later translated into humans. In this chapter, we summarized the effects of different drugs reported to extend the lifespan in model organisms from round worms to rodents. Resveratrol, rapamycin, metformin and aspirin, showing effectiveness in model organism life- and healthspan extension mainly target the master regulators of aging such as mTOR, FOXO and PGC1α, affecting autophagy, inflammation and oxidative stress. In humans, these drugs were demonstrated to reduce inflammation, prevent CVD, and slow down the functional decline in certain organs. Additionally, potential anti-aging pharmacologic agents inhibit cancerogenesis, interfering with certain aspects of cell metabolism, proliferation, angioneogenesis and apoptosis.

Neurodegeneration with Brain Iron Accumulation Disorders: Valuable Models Aimed at Understanding the Pathogenesis of Iron Deposition

Neurodegeneration with brain iron accumulation (NBIA) is a set of neurodegenerative disorders, which includes very rare monogenetic diseases. They are heterogeneous in regard to the onset and the clinical symptoms, while the have in common a specific brain iron deposition in the region of the basal ganglia that can be visualized by radiological and histopathological examinations. Nowadays, 15 genes have been identified as causative for NBIA, of which only two code for iron-proteins, while all the other causative genes codify for proteins not involved in iron management. Thus, how iron participates to the pathogenetic mechanism of most NBIA remains unclear, essentially for the lack of experimental models that fully recapitulate the human phenotype. In this review we reported the recent data on new models of these disorders aimed at highlight the still scarce knowledge of the pathogenesis of iron deposition.

Modeling human Coenzyme A synthase mutation in yeast reveals altered mitochondrial function, lipid content and iron metabolism

Mutations in nuclear genes associated with defective coenzyme A biosynthesis have been identified as responsible for some forms of neurodegeneration with brain iron accumulation (NBIA), namely PKAN and CoPAN. PKAN are defined by mutations in PANK2, encoding the pantothenate kinase 2 enzyme, that account for about 50% of cases of NBIA, whereas mutations in CoA synthase COASY have been recently reported as the second inborn error of CoA synthesis leading to CoPAN. As reported previously, yeast cells expressing the pathogenic mutation exhibited a temperature-sensitive growth defect in the absence of pantothenate and a reduced CoA content. Additional characterization revealed decreased oxygen consumption, reduced activities of mitochondrial respiratory complexes, higher iron content, increased sensitivity to oxidative stress and reduced amount of lipid droplets, thus partially recapitulating the phenotypes found in patients and establishing yeast as a potential model to clarify the pathogenesis underlying PKAN and CoPAN diseases.

Conserved metallomics in two insect families evolving separately for a hundred million years

Μetal cofactors are required for enzymatic catalysis and structural stability of many proteins. Physiological metal requirements underpin the evolution of cellular and systemic regulatory mechanisms for metal uptake, storage and excretion. Considering the role of metal biology in animal evolution, this paper asks whether metal content is conserved between different fruit flies. A similar metal homeostasis was previously observed in Drosophilidae flies cultivated on the same larval medium. Each species accumulated in the order of 200 µg iron and zinc and approximately ten-fold less manganese and copper per gram dry weight of the adult insect. In this paper, data on the metal content in fourteen species of Tephritidae, which are major agricultural pests worldwide, are presented. These fruit flies can be polyphagous (e.g., Ceratitis capitata) or strictly monophagous (e.g., Bactrocera oleae) or oligophagous (e.g., Anastrepha grandis) and were maintained in the laboratory on five distinct diets based on olive oil, carrot, wheat bran, zucchini and molasses, respectively. The data indicate that overall metal content and distribution between the Tephritidae and Drosophilidae species was similar. Reduced metal concentration was observed in B. oleae. Feeding the polyphagous C. capitata with the diet of B. oleae resulted in a significant quantitative reduction of all metals. Thus, dietary components affect metal content in some Tephritidae. Nevertheless, although the evidence suggests some fruit fly species evolved preferences in the use or storage of particular metals, no metal concentration varied in order of magnitude between these two families of Diptera that evolved independently for over 100 million years.

A new in vivo model of pantothenate kinase-associated neurodegeneration reveals a surprising role for transcriptional regulation in pathogenesis

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is a neurodegenerative disorder with a poorly understood molecular mechanism. It is caused by mutations in Pantothenate Kinase, the first enzyme in the Coenzyme A (CoA) biosynthetic pathway. Here, we developed a Drosophila model of PKAN (tim-fbl flies) that allows us to continuously monitor the modeled disease in the brain. In tim-fbl flies, downregulation of fumble, the Drosophila PanK homologue in the cells containing a circadian clock results in characteristic features of PKAN such as developmental lethality, hypersensitivity to oxidative stress, and diminished life span. Despite quasi-normal circadian transcriptional rhythms, tim-fbl flies display brain-specific aberrant circadian locomotor rhythms, and a unique transcriptional signature. Comparison with expression data from flies exposed to paraquat demonstrates that, as previously suggested, pathways others than oxidative stress are affected by PANK downregulation. Surprisingly we found a significant decrease in the expression of key components of the photoreceptor recycling pathways, which could lead to retinal degeneration, a hallmark of PKAN. Importantly, these defects are not accompanied by changes in structural components in eye genes suggesting that changes in gene expression in the eye precede and may cause the retinal degeneration. Indeed tim-fbl flies have diminished response to light transitions, and their altered day/night patterns of activity demonstrates defects in light perception. This suggest that retinal lesions are not solely due to oxidative stress and demonstrates a role for the transcriptional response to CoA deficiency underlying the defects observed in dPanK deficient flies. Moreover, in the present study we developed a new fly model that can be applied to other diseases and that allows the assessment of neurodegeneration in the brains of living flies.

Late onset atypical pantothenate-kinase-associated neurodegeneration

Introduction. Pantothenate-kinase-associated neurodegeneration (PKAN) is a rare genetic disease and a form of neurodegeneration with brain iron accumulation (NBIA). It most commonly begins in the first two decades of life but should be considered in the differential diagnosis of patients at any age with an atypical progressive extrapyramidal disorder and cognitive impairment. Few late-adult cases have been reported. Case Report. A 50-year-old woman presented with a history of progressive dysarthria and dysphagia secondary to orolingual dystonia. Initial work-up was normal. There was no family history. Her initial symptoms were followed by the onset of blepharospasm, cervical dystonia, Parkinsonism, and cognitive impairment. Follow-up MRI four years after presentation revealed the diagnostic “eye-of-the-tiger” sign. Genetic testing confirmed a homozygous missense mutation consistent with the diagnosis of PKAN. Conclusion. Although PKAN is a rare genetic disorder most commonly seen in childhood, it should be considered in adult patients with a history of progressive focal dystonia or atypical Parkinsonism. As the radiographic findings are quite characteristic, genetic testing should be performed if the MRI shows evidence of iron accumulation. Optimal treatment strategies are not known, and at the current time therapies should be directed at the specific manifestations of the disease.

Lipid metabolism in Drosophila: development and disease

Proteins, nucleic acids, and lipids are three major components of the cell. Despite a few basic metabolic pathways, we know very little about lipids, compared with the explosion of knowledge about proteins and nucleic acids. How many different forms of lipids are there? What are the in vivo functions of individual lipid? How does lipid metabolism contribute to normal development and human health? Many of these questions remain unanswered. For over a century, the fruit fly Drosophila melanogaster has been used as a model organism to study basic biological questions. In recent years, increasing evidences proved that Drosophila models are highly valuable for lipid metabolism and energy homeostasis researches. Some recent progresses of lipid metabolic regulation during Drosophila development and in Drosophila models of human diseases will be discussed in this review.

Metabolic consequences of mitochondrial coenzyme A deficiency in patients with PANK2 mutations

Pantothenate kinase-associated neurodegeneration (PKAN) is a rare, inborn error of metabolism characterized by iron accumulation in the basal ganglia and by the presence of dystonia, dysarthria, and retinal degeneration. Mutations in pantothenate kinase 2 (PANK2), the rate-limiting enzyme in mitochondrial coenzyme A biosynthesis, represent the most common genetic cause of this disorder. How mutations in this core metabolic enzyme give rise to such a broad clinical spectrum of pathology remains a mystery. To systematically explore its pathogenesis, we performed global metabolic profiling on plasma from a cohort of 14 genetically defined patients and 18 controls. Notably, lactate is elevated in PKAN patients, suggesting dysfunctional mitochondrial metabolism. As predicted, but never previously reported, pantothenate levels are higher in patients with premature stop mutations in PANK2. Global metabolic profiling and follow-up studies in patient-derived fibroblasts also reveal defects in bile acid conjugation and lipid metabolism, pathways that require coenzyme A. These findings raise a novel therapeutic hypothesis, namely, that dietary fats and bile acid supplements may hold potential as disease-modifying interventions. Our study illustrates the value of metabolic profiling as a tool for systematically exploring the biochemical basis of inherited metabolic diseases.

Childhood disorders of neurodegeneration with brain iron accumulation (NBIA)

Neurodegeneration with brain iron accumulation (NBIA) comprises a heterogeneous group of progressive complex motor disorders characterized by the presence of high brain iron, particularly within the basal ganglia. A number of autosomal recessive NBIA syndromes can present in childhood, most commonly pantothenate kinase-associated neurodegeneration (PKAN; due to mutations in the PANK2 gene) and phospholipase A2 group 6-associated neurodegeneration (PLAN; associated with genetic defects in PLA2G6). Mutations in the genes that cause these two neuroaxonal dystrophies are thought to disrupt the normal cellular functions of phospholipid remodelling and fatty acid metabolism. A significant proportion of children with an NBIA phenotype have no genetic diagnosis and there are, no doubt, additional as yet undiscovered genes that account for a number of these cases. NBIA disorders can be diagnostically challenging as there is often phenotypic overlap between the different disease entities. This review aims to define the clinical, radiological, and genetic features of such disorders, providing the clinician with a stepwise approach to appropriate neurological and genetic investigation, as well as a clinical management strategy for these neurodegenerative syndromes.

Zinc accumulation in heterozygous mutants of fumble, the pantothenate kinase homologue of Drosophila

Coenzyme A (CoA) functions in the intracellular trafficking of acetyl groups. In humans, mutations in the pantothenate kinase-2 gene, which encodes a key enzyme in CoA biosynthesis, are associated with neurodegeneration and premature death. Diagnosis is based on iron accumulation in the globus pallidus observed by magnetic resonance imaging. We investigated the elemental composition of the fumble mutant, a model of the human disease. Surprisingly, flies carrying a fumble loss-of-function allele had a three-fold increase in total zinc levels per dry weight when compared to control strains, but no change in total iron, copper or manganese levels. Accordingly, zinc supplementation had an adverse impact on the development of fumble mutant larvae, but zinc chelation failed to protect.

Pantothenate kinase-associated neurodegeneration: insights from a Drosophila model

Pantothenate-Kinase-Associated-Neurodegeneration (PKAN) is a devastating disease, resulting from mutations in pantothenate kinase 2 (PANK2), one of the four human pantothenate kinase genes (PANK1-4). Interestingly, PanK2 appears to be the only mitochondria-targeted human PanK. It is unknown whether the mitochondria-targeted PanK is associated with any unique function, nor whether PKAN is due solely to the loss of pantothenate kinase activity. Drosophila PANK [fumble (fbl)] encodes several isoforms of pantothenate kinase products, one of which localizes to mitochondria and the others cytosol. fbl flies exhibit many characteristic features reminiscent of PKAN patients. Various forms of Drosophila fbl and human PANK2 were introduced into fbl flies to study their in vivo functions. Only mitochondria-targeted Fbl or human PanK2 was able to rescue fbl mutation, with the rescuing ability sensitive to the expression level of the transgene. Transgenic lines with low expression of normal Fbl or PanK2 displayed similar phenotypes as PANK2 mutant transgenic flies. These PanK2 mutants all showed reduced and phenotype severity-correlated in vitro pantothenate kinase activities. Amazingly, cytosolic PanK3 and PanK4 could mostly, but not fully, rescue fbl defects except the male sterility. Therefore, fbl appears to be the orthologue of human PANK2, and PanK2 is functionally more potent than PanK3 and PanK4 in vivo. We suggest that mitochondria-located pantothenate kinase is required to achieve the maximal enzymatic activity to fulfill the most challenging task such as maintaining male fertility and optimal neuronal functions, and PKAN features are mainly due to the reduction of the total cellular pantothenate kinase activity in the most susceptible regions.

The effects of vitamin supplementation on Drosophila life span under normoxia and under oxidative stress

Vitamin A (retinol), vitamin C (ascorbic acid), and vitamin E (alpha-tocopherol) are each thought to play an important role in the aging process. Here, we investigated the effects of these vitamins on Drosophila melanogaster life span under different oxidative stress conditions. Among the vitamins tested, alpha-tocopherol exhibited the strongest antioxidant activity, extending average and maximum life span for wild-type flies under hyperoxia and for Cu/Zn superoxide dismutase-deficient (SOD1-deficient) flies under normoxia. Retinol supplementation extended life span of SOD1-deficient flies under normoxia, and ascorbic acid supplementation extended life span of wild-type flies under normoxia. However, both retinol and ascorbic acid exhibited a strong prooxidant activity under hyperoxia and shortened life span. Furthermore, ascorbic acid supplementation enhanced the toxic effects of iron, with the iron pool significantly increased in adult whole-body extracts. Taken together, our results document antioxidant and prooxidant contributions of vitamins to D. melanogaster life-span determination under normoxia and under oxidative stress.