Inhibition of heme synthesis alters Amyloid Precursor Protein processing

The Cleavage-Specific Tau 12A12mAb Exerts an Anti-Amyloidogenic Action by Modulating the Endocytic and Bioenergetic Pathways in Alzheimer's Disease Mouse Model

Beyond deficits in hippocampal-dependent episodic memory, Alzheimer's Disease (AD) features sensory impairment in visual cognition consistent with extensive neuropathology in the retina. 12A12 is a monoclonal cleavage specific antibody (mAb) that in vivo selectively neutralizes the AD-relevant, harmful N-terminal 20-22 kDa tau fragment(s) (i.e., NH₂htau) without affecting the full-length normal protein. When systemically injected into the Tg2576 mouse model overexpressing a mutant form of Amyloid Precursor Protein (APP), APPK670/671L linked to early onset familial AD, this conformation-specific tau mAb successfully reduces the NH₂htau accumulating both in their brain and retina and, thus, markedly alleviates the phenotype-associated signs. By means of a combined biochemical and metabolic experimental approach, we report that 12A12mAb downregulates the steady state expression levels of APP and Beta-Secretase 1 (BACE-1) and, thus, limits the Amyloid beta (Aβ) production both in the hippocampus and retina from this AD animal model. The local, antibody-mediated anti-amyloidogenic action is paralleled in vivo by coordinated modulation of the endocytic (BIN1, RIN3) and bioenergetic (glycolysis and L-Lactate) pathways. These findings indicate for the first time that similar molecular and metabolic retino-cerebral pathways are modulated in a coordinated fashion in response to 12A12mAb treatment to tackle the neurosensorial Aβ accumulation in AD neurodegeneration.

Untargeted Metabolomics Reveals Lipid Impairment in the Liver of Adult Zebrafish (Danio rerio) Exposed to Carbendazim

Carbendazim is a systemic fungicide used in several countries, particularly in Brazil. However, studies suggest that it is related to the promotion of tumors, endocrine disruption, and toxicity to organisms, among other effects. As a result, carbendazim is not allowed in the United States, Australia, and some European Union countries. Therefore, further studies are necessary to evaluate its effects, and zebrafish is a model routinely used to provide relevant information regarding the acute and long-term effects of xenobiotics. In this way, zebrafish water tank samples (water samples from aquari containing zebrafish) and liver samples from animals exposed to carbendazim at a concentration of 120 μg/L were analyzed by liquid chromatography coupled to high-resolution mass spectrometry, followed by multivariate and univariate statistical analyses, using the metabolomics approach. Our results suggest impairment of lipid metabolism with a consequent increase in intrahepatic lipids and endocrine disruption. Furthermore, the results suggest two endogenous metabolites as potential biomarkers to determine carbendazim exposure. Finally, the present study showed that it is possible to use zebrafish water tank samples to assess the dysregulation of endogenous metabolites to understand biological effects. Environ Toxicol Chem 2023;42:437-448. © 2022 SETAC.

Abnormal Vasculature Development in Zebrafish Embryos with Reduced Expression of Pantothenate Kinase 2 Gene

Mutations in pank2 gene encoding pantothenate kinase 2 determine a pantothenate kinase-associated neurodegeneration, a rare disorder characterized by iron deposition in the globus pallidus. To extend our previous work, we performed microinjections of a new pank2-specific morpholino to zebrafish embryos and thoroughly analyzed vasculature development. Vessels development was severely perturbed in the head, trunk, and tail, where blood accumulation was remarkable and associated with dilation of the posterior cardinal vein. This phenotype was specific as confirmed by p53 expression analysis and injection of the same morpholino in pank2-mutant embryos. We can conclude that pank2 gene is involved in vasculature development in zebrafish embryos. The comprehension of the underlining mechanisms could be of relevance for understanding of pantothenate kinase-associated neurodegeneration.

Proteomics for Studying the Effects of Ketogenic Diet Against Lithium Chloride/Pilocarpine Induced Epilepsy in Rats

The ketogenic diet (KD) demonstrates antiepileptogenic and neuroprotective efficacy, but the precise mechanisms are unclear. Here we explored the mechanism through systematic proteomics analysis of the lithium chloride-pilocarpine rat model. Sprague-Dawley rats (postnatal day 21, P21) were randomly divided into control (Ctr), seizure (SE), and KD treatment after seizure (SE + KD) groups. Tandem mass tag (TMT) labeling and liquid chromatography-tandem mass spectroscopy (LC-MS/MS) were utilized to assess changes in protein abundance in the hippocampus. A total of 5,564 proteins were identified, of which 110 showed a significant change in abundance between the SE and Ctr groups (18 upregulated and 92 downregulated), 278 between SE + KD and SE groups (218 upregulated and 60 downregulated), and 180 between Ctr and SE + KD groups (121 upregulated and 59 downregulated) (all p < 0.05). Seventy-nine proteins showing a significant change in abundance between SE and Ctr groups were reciprocally regulated in the SD + KD group compared to the SE group (i.e., the seizure-induced change was reversed by KD). Of these, five (dystrobrevin, centromere protein V, oxysterol-binding protein, tetraspanin-2, and progesterone receptor membrane component 2) were verified by parallel reaction monitoring. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis indicated that proteins of the synaptic vesicle cycle pathway were enriched both among proteins differing in abundance between SE and Ctr groups as well as between SE + KD and SE groups. This comprehensive proteomics analyze of KD-treated epilepsy by quantitative proteomics revealed novel molecular mechanisms of KD antiepileptogenic efficacy and potential treatment targets.

Possible Clues for Brain Energy Translation via Endolysosomal Trafficking of APP-CTFs in Alzheimer's Disease

Vascular dysfunctions, hypometabolism, and insulin resistance are high and early risk factors for Alzheimer's disease (AD), a leading neurological disease associated with memory decline and cognitive dysfunctions. Early defects in glucose transporters and glycolysis occur during the course of AD progression. Hypometabolism begins well before the onset of early AD symptoms; this timing implicates the vulnerability of hypometabolic brain regions to beta-secretase 1 (BACE-1) upregulation, oxidative stress, inflammation, synaptic failure, and cell death. Despite the fact that ketone bodies, astrocyte-neuron lactate shuttle, pentose phosphate pathway (PPP), and glycogenolysis compensate to provide energy to the starving AD brain, a considerable energy crisis still persists and increases during disease progression. Studies that track brain energy metabolism in humans, animal models of AD, and in vitro studies reveal striking upregulation of beta-amyloid precursor protein (β-APP) and carboxy-terminal fragments (CTFs). Currently, the precise role of CTFs is unclear, but evidence supports increased endosomal-lysosomal trafficking of β-APP and CTFs through autophagy through a vague mechanism. While intracellular accumulation of Aβ is attributed as both the cause and consequence of a defective endolysosomal-autophagic system, much remains to be explored about the other β-APP cleavage products. Many recent works report altered amino acid catabolism and expression of several urea cycle enzymes in AD brains, but the precise cause for this dysregulation is not fully explained. In this paper, we try to connect the role of CTFs in the energy translation process in AD brain based on recent findings.

Silencing of pantothenate kinase 2 reduces endothelial cell angiogenesis

Coenzyme A (CoA) is an essential cofactor of cellular metabolism that is involved in ~4% of cellular reactions. Its de novo production relies on five subsequent enzymatic steps, starting with the phosphorylation of vitamin B5. Pantothenate kinase 2 (PANK2) and coenzyme A synthase (COASY) catalyze the first and last steps of this pathway. Mutations in these genes lead to severe and progressive movement disorders, with neurodegeneration and iron accumulation in the basal ganglia, known as PANK2‑ and COASY protein‑associated neurodegeneration, respectively. Given the ubiquitous role of CoA in cellular metabolism, it is still not clear why patients carrying PANK2 and COASY mutations develop almost exclusively neurological symptoms. Important clues are the energetic profile of neural cells as well as the high levels of PANK2 expression in the brain; however, other features may contribute to this selective tissue vulnerability. Notably, when pank2 or coasy expression was suppressed in zebrafish evident perturbation of neuronal development was observed, as well as severe defects in vasculature formation. Supplementation of CoA to fish water prevented the appearance of the phenotype, thereby confirming the specific connection with the availability of the metabolic cofactor. The present study investigated the associations between PANK2 defects and angiogenesis in a mammalian setting, and revealed that PANK2 expression was required for normal angiogenetic properties of human umbilical vein endothelial cells.

Overexpression of Human Mutant PANK2 Proteins Affects Development and Motor Behavior of Zebrafish Embryos

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is a genetic and early-onset neurodegenerative disorder characterized by iron accumulation in the basal ganglia. It is due to mutations in Pantothenate Kinase 2 (PANK2), an enzyme that catalyzes the phosphorylation of vitamin B5, first and essential step in coenzyme A (CoA) biosynthesis. Most likely, an unbalance of the neuronal levels of this important cofactor represents the initial trigger of the neurodegenerative process, yet a complete understanding of the connection between PANK2 malfunctioning and neuronal death is lacking. Most PKAN patients carry mutations in both alleles and a loss of function mechanism is proposed to explain the pathology. When PANK2 mutants were analyzed for stability, dimerization capacity, and enzymatic activity in vitro, many of them showed properties like the wild-type form. To further explore this aspect, we overexpressed the wild-type protein, two mutant forms with reduced kinase activity and two retaining the catalytic activity in zebrafish embryos and analyzed the morpho-functional consequences. While the wild-type protein had no effects, all mutant proteins generated phenotypes that partially resembled those observed in pank2 and coasy morphants and were rescued by CoA and vitamin B5 supplementation. The overexpression of PANK2 mutant forms appears to be associated with perturbation in CoA availability, irrespective of their catalytic activity.

Down-regulation of coasy, the gene associated with NBIA-VI, reduces Bmp signaling, perturbs dorso-ventral patterning and alters neuronal development in zebrafish

Mutations in Pantothenate kinase 2 and Coenzyme A (CoA) synthase (COASY), genes involved in CoA biosynthesis, are associated with rare neurodegenerative disorders with brain iron accumulation. We showed that zebrafish pank2 gene plays an essential role in brain and vasculature development. Now we extended our study to coasy. The gene has high level of sequence identity with the human ortholog and is ubiquitously expressed from the earliest stages of development. The abrogation of its expression led to strong reduction of CoA content, high lethality and a phenotype resembling to that of dorsalized mutants. Lower doses of morpholino resulted in a milder phenotype, with evident perturbation in neurogenesis and formation of vascular arborization; the dorso-ventral patterning was severely affected, the expression of bone morphogenetic protein (Bmp) receptors and activity were decreased, while cell death increased. These features specifically correlated with the block in CoA biosynthesis and were rescued by the addition of CoA to fish water and the overexpression of the human wild-type, but not mutant gene. These results confirm the absolute requirement for adequate levels of CoA for proper neural and vascular development in zebrafish and point to the Bmp pathway as a possible molecular connection underlining the observed phenotype.

Heme Stabilization of α-Synuclein Oligomers during Amyloid Fibril Formation

α-Synuclein (αSyn), which forms amyloid fibrils, is linked to the neuronal pathology of Parkinson's disease, as it is the major fibrillar component of Lewy bodies, the inclusions that are characteristic of the disease. Oligomeric structures, common to many neurodegenerative disease-related proteins, may in fact be the primary toxic species, while the amyloid fibrils exist either as a less toxic dead-end species or even as a beneficial mechanism for clearing damaged proteins. To alter the progression of the aggregation and gain insights into the prefibrillar structures, we determined the effect of heme on αSyn oligomerization by several different techniques, including native (nondenaturing) polyacrylamide gel electrophoresis, thioflavin T fluorescence, transmission electron microscopy, atomic force microscopy, circular dichroism, and membrane permeation using a calcein release assay. During aggregation, heme is able to bind the αSyn in a specific fashion, stabilizing distinct oligomeric conformations and promoting the formation of αSyn into annular structures, thereby delaying and/or inhibiting the fibrillation process. These results indicate that heme may play a regulatory role in the progression of Parkinson's disease; in addition, they provide insights into how the aggregation process may be altered, which may be applicable to the understanding of many neurodegenerative diseases.

5-aminolevulinic acid, a precursor of heme, reduces both fasting and postprandial glucose levels in mildly hyperglycemic subjects

OBJECTIVE

The aim of this study was to evaluate the combined effects of 5-aminolevulinic acid phosphate (ALA-P) and iron on the glycemic index in mildly hyperglycemic adults.

METHODS

This double-blind, randomized placebo-controlled trial comprised 212 subjects (ages 35-70 y, fasting plasma glucose 105-125 mg/dL or hemoglobin (Hb)A1c 6.1%-7.1%). These participants were randomly assigned to four groups receiving either one of three doses of ALA-P and iron as sodium ferrous citrate (5 mg and 0.6 mg, 5 mg and 1.8 mg, or 15 mg and 1.8 mg, respectively) or a placebo, administered orally once a day over a 12-wk period.

RESULTS

Fifteen mg ALA-P plus 1.8 mg iron decreased the fasting plasma glucose level (2.32 mg/dL, 95% confidence interval [CI], 0.24-4.42, P = 0.029), serum glycoalbumin (0.22%, 95% CI, 0.02-0.42; P = 0.031), and 2h-oral glucose tolerance test levels (14.2 mg/dL, 95% CI, 1.8-26.6; P = 0.025) more than the placebo. However, the levels of HbA1c, fasting insulin, serum 1,5-anhydro-d-glucitol, and Homeostasis Model of Assessment-Insulin Resistance showed no appreciable changes. The participant numbers with impaired glucose tolerance and impaired fasting glucose decreased in the highest dosage group of ALA-P plus iron compared with the placebo group.

CONCLUSION

An oral intake of ALA would be a novel approach to prevent type 2 diabetes mellitus.

Salicylic acid induces mitochondrial injury by inhibiting ferrochelatase heme biosynthesis activity

Salicylic acid is a classic nonsteroidal anti-inflammatory drug. Although salicylic acid also induces mitochondrial injury, the mechanism of its antimitochondrial activity is not well understood. In this study, by using a one-step affinity purification scheme with salicylic acid-immobilized beads, ferrochelatase (FECH), a homodimeric enzyme involved in heme biosynthesis in mitochondria, was identified as a new molecular target of salicylic acid. Moreover, the cocrystal structure of the FECH-salicylic acid complex was determined. Structural and biochemical studies showed that salicylic acid binds to the dimer interface of FECH in two possible orientations and inhibits its enzymatic activity. Mutational analysis confirmed that Trp301 and Leu311, hydrophobic amino acid residues located at the dimer interface, are directly involved in salicylic acid binding. On a gel filtration column, salicylic acid caused a shift in the elution profile of FECH, indicating that its conformational change is induced by salicylic acid binding. In cultured human cells, salicylic acid treatment or FECH knockdown inhibited heme synthesis, whereas salicylic acid did not exert its inhibitory effect in FECH knockdown cells. Concordantly, salicylic acid treatment or FECH knockdown inhibited heme synthesis in zebrafish embryos. Strikingly, the salicylic acid-induced effect in zebrafish was partially rescued by FECH overexpression. Taken together, these findings illustrate that FECH is responsible for salicylic acid-induced inhibition of heme synthesis, which may contribute to its antimitochondrial and anti-inflammatory function. This study establishes a novel aspect of the complex pharmacological effects of salicylic acid.

Neuronal brain-derived neurotrophic factor is synthesized in excess, with levels regulated by sortilin-mediated trafficking and lysosomal degradation

Brain-derived neurotrophic factor (BDNF) regulates neuronal differentiation, synaptic plasticity, and morphology, and modest changes in BDNF levels results in complex behavioral phenotypes. BDNF levels and intracellular localization in neurons are regulated by multiple mechanisms, including use of distinct promoters, mRNA and protein transport, and regulated cleavage of proBDNF to mature BDNF. Sortilin is an intracellular chaperone that binds to the prodomain of BDNF to traffic it to the regulated secretory pathway. However, sortilin binds to numerous ligands and plays a major role in mannose 6-phosphate receptor-independent transport of lysosomal hydrolases utilizing motifs in the intracellular domain that mediate trafficking from the Golgi and late endosomes. Sortilin is modified by ectodomain shedding, although the biological implications of this are not known. Here we demonstrate that ADAM10 is the preferred protease to cleave sortilin in the extracellular stalk region, to release the ligand binding sortilin ectodomain from the transmembrane and cytoplasmic domains. We identify sortilin shedding at the cell surface and in an intracellular compartment. Both sortilin and BDNF are trafficked to and degraded by the lysosome in neurons, and this is dependent upon the sortilin cytoplasmic tail. Indeed, expression of the sortilin ectodomain, which corresponds to the domain released after shedding, impairs lysosomal targeting and degradation of BDNF. These findings characterize the regulation of sortilin shedding and identify a novel mechanism by which sortilin ectodomain shedding acts as a regulatory switch for delivery of BDNF to the secretory pathway or to the lysosome, thus modulating the bioavailability of endogenous BDNF.

Therapeutic approaches to delay the onset of Alzheimer's disease

The key cytopathologies in the brains of Alzheimer's disease (AD) patients include mitochondrial dysfunction and energy hypometabolism, which are likely caused by the accumulation of small aggregates of amyloid-β (Aβ) peptides. Thus, targeting these two abnormalities of the AD brain may hold promising therapeutic value for delaying the onset of AD. In his paper, we discuss two potential approaches to delay the onset of AD. The first is the use of low dose of diaminophenothiazins (redox active agents) to prevent mitochondrial dysfunction and to attenuate energy hypometabolism. Diaminophenothiazines enhance mitochondrial metabolic activity and heme synthesis, both key factors in intermediary metabolism of the AD brain.The second is to use the naturally occurring osmolytes to prevent the formation of toxic forms of Aβ and prevent oxidative stress. Scientific evidence suggests that both approaches may change course of the basic mechanism of neurodegeneration in AD. Osmolytes are brain metabolites which accumulate in tissues at relatively high concentrations following stress conditions. Osmolytes enhance thermodynamic stability of proteins by stabilizing natively-folded protein conformation, thus preventing aggregation without perturbing other cellular processes. Osmolytes may inhibit the formation of Aβ oligomers in vivo, thus preventing the formation of soluble oligomers. The potential significance of combining diaminophenothiazins and osmolytes to treat AD is discussed.

Analysis of the genes coding for subunit 10 and 15 of cytochrome c oxidase in Alzheimer's disease

Decay of mitochondria and oxidative stress are associated with normal aging, but many neurodegenerative diseases, and particularly Alzheimer's disease (AD), are characterized by a significant increase in the intensity of these traits. Recent data suggest the possible contribution of heme deficiency to the progressive derangement of mitochondria in AD brain; shortage of heme, and particularly of heme-a, actually leads to loss of mitochondrial cytochrome c oxidase (COX), abnormal production of reactive oxygen species and altered amyloid precursor protein metabolism. We reasoned that differences in the amount and/or functioning of COX assembly subunit 10 (COX10) and 15 (COX15), the key enzymes involved in heme-a biosynthesis, could be linked to variations of the individual risk to develop AD. We analyzed their mRNA expression in the hippocampus from AD patients and controls, investigated the existence of nucleotide variations in their DNA sequences and analyzed their distribution in large groups of AD and control individuals. COX 15 mRNA was significantly more abundant in the cerebral tissue of AD patients (3.18 +/- 1.70 vs. 1.22 +/- 0.66 microg, normalized dose, P = 0.01). The IVS-178G>A SNP in COX10 and the c+1120C>T SNP in COX15 were significantly less represented in the patient group (P < 0.001 and P = 0.017, respectively) with respective odd ratios of 0.22 and 0.59, suggesting a possible protective role toward the risk for AD.

Down-regulation of aminolevulinate synthase, the rate-limiting enzyme for heme biosynthesis in Alzheimer's disease

Heme is an essential cell metabolite, intracellular regulatory molecule, and protein prosthetic group. Given the known alterations in heme metabolism and redox metal distribution and the up-regulation of heme oxygenase enzyme in Alzheimer's disease (AD), we hypothesized that heme dyshomeostasis plays a key role in the pathogenesis. To begin testing this hypothesis, we used qRT-PCR to quantify the expression of aminolevulinate synthase (ALAS1) and porphobilinogen deaminase (PBGD), rate-limiting enzymes in the heme biosynthesis pathway. The relative expression of ALAS1 mRNA, the first and rate-limiting enzyme for heme biosynthesis under normal physiological conditions, was significantly (p<0.05) reduced by nearly 90% in AD compared to control. Coordinately, the relative expression of PBGD mRNA, which encodes porphobilinogen deaminase, the third enzyme in the heme synthesis pathway and a secondary rate-limiting enzyme in heme biosynthesis, was also significantly (p<0.02) reduced by nearly 60% in AD brain compared to control and significantly related to apolipoprotein E genotype (p<0.005). In contrast, the relative expression of ALAD mRNA, which encodes aminolevulinate dehydratase, the second and a non-rate-limiting enzyme for heme biosynthesis, was unchanged between the two groups. Taken together, our results suggest regulation of cerebral heme biosynthesis is profoundly altered in AD and may contribute toward disease pathogenesis by affecting cell metabolism as well as iron homeostasis.

Human and rodent amyloid-beta peptides differentially bind heme: relevance to the human susceptibility to Alzheimer's disease

Amyloid-beta (Abeta) peptides are implicated in the neurodegeneration of Alzheimer's disease (AD). We previously investigated the mechanism of neurotoxicity of Abeta and found that human Abeta (huAbeta) binds and depletes heme, forming an Abeta-heme complex with peroxidase activity. Rodent Abeta (roAbeta) is identical to huAbeta, except for three amino acids within the proposed heme-binding motif (Site-H). We studied and compared heme-binding between roAbeta and huAbeta. Unlike roAbeta, huAbeta binds heme tightly (K(d)=140+/-60 nM) and forms a peroxidase. The plot of bound (huAbeta-heme) vs. unbound heme fits best to a two site binding hyperbola, suggesting huAbeta possesses two heme-binding sites. Consistently, a second high affinity heme-binding site was identified in the lipophilic region (site-L) of huAbeta (K(d)=210+/-80 nM). The plot of (roAbeta-heme) vs. unbound heme, on the other hand, was different as it fits best to a sigmoidal binding curve, indicating different binding and lower affinity of roAbeta for heme (K(d)=1 microM). The effect of heme-binding to site-H on heme-binding to site-L in roAbeta and huAbeta is discussed. While both roAbeta and huAbeta form aggregates equally, rodents lack AD-like neuropathology. High huAbeta/heme ratio increases the peroxidase activity. These findings suggest that depletion of regulatory heme and formation of Abeta-heme peroxidase contribute to huAbeta's neurotoxicity in the early stages of AD. Phylogenic variations in the amino acid sequence of Abeta explain tight heme-binding to huAbeta and likely contribute to the increased human susceptibility to AD.