Recombinant Danio rerio Solute carrier family 25 member 47-A (slc25a47a)

Basic Research Questions

• What is slc25a47a and what is its function in zebrafish?

  Solute carrier family 25 member 47-A (slc25a47a) is a mitochondrial inner-membrane transport protein expressed in Danio rerio (zebrafish). It belongs to the SLC25A solute carrier protein family, which comprises 53 members in mammals that constitute the largest family of mitochondrial inter-membrane metabolite carriers . Unlike most SLC25A members that are ubiquitously expressed across tissues, slc25a47a demonstrates selective expression in the liver, making it unique among mitochondrial carriers .

  Functionally, slc25a47a plays a crucial role in:

  • Regulating hepatic metabolism, particularly gluconeogenesis

  • Controlling mitochondrial pyruvate flux

  • Influencing energy homeostasis

  Research indicates that slc25a47a may control either pyruvate import to the mitochondrial matrix or pyruvate flux within the mitochondria, as evidenced by mitochondrial metabolomics analyses showing altered metabolite profiles in slc25a47-deficient mice .

• How is slc25a47a expressed in zebrafish tissues?

  The expression pattern of slc25a47a in zebrafish is highly tissue-specific. Studies show that:

  • slc25a47a is selectively expressed in the liver of zebrafish

  • Within the liver, hepatocytes are the primary cell type expressing slc25a47a

  • According to single-cell RNA-seq data, hepatocytes account for approximately 90% of total slc25a47a transcripts in the liver, while Kupffer cells contribute about 10%

  • The selective liver expression is regulated by an open chromatin architecture specific to the liver, while the same region forms a heterochromatin structure in other tissues like heart and lung

  • Hepatocyte nuclear factor 4 alpha (HNF4α) is a critical transcription factor that binds to the slc25a47a gene locus and is required for its hepatic expression

  This liver-specific expression pattern makes slc25a47a a potentially valuable target for studying liver-specific metabolic pathways and developing targeted interventions for hepatic metabolic disorders.

• What experimental models are available for studying slc25a47a?

  Several experimental models and approaches have been developed for studying slc25a47a:

  a. Zebrafish models:

  • Zebrafish (Danio rerio) serve as an excellent model organism for studying slc25a47a due to their well-annotated genome, transparent embryos, small size, and short generation time

  • Laboratory-bred zebrafish maintained in controlled conditions (26-28°C, pH 7.0-7.5, 14/10-h light/dark cycle) in ZebTec Active Blue recirculating systems

  • Zebrafish feeding protocols incorporating various diets for nutritional studies

  b. Genetic models:

  • Knockout/knockdown models: slc25a47a-mutant mice generated using the knockout-first strategy from EUCOMM/KOMP repository

  • Tissue-specific knockout using Cre-lox system (e.g., Albumin-Cre for liver-specific deletion)

  • Overexpression models using viral vectors (adenoviral-mediated overexpression)

  c. Cell culture systems:

  • Hepa 1-6 cells (which do not endogenously express slc25a47a) for transient transfection studies

  • Primary hepatocytes isolated from mice or zebrafish

  d. Recombinant protein:

  • Commercially available recombinant slc25a47a protein expressed in mammalian cells, provided with His-tag for purification and detection

  • Available in liquid or lyophilized powder form with >80% purity

  These models provide versatile platforms for investigating slc25a47a function from molecular to organismal levels, enabling comprehensive characterization of its physiological roles.

Advanced Research Questions

• What role does slc25a47a play in mitochondrial function and metabolism?

  slc25a47a has been implicated in several aspects of mitochondrial function and metabolism, particularly in the liver:

  Mitochondrial metabolite transport:

  • Functions as a mitochondrial inner membrane transporter, potentially regulating metabolite flux

  • Influences the transport of TCA cycle intermediates and metabolites involved in gluconeogenesis

  Impact on TCA cycle and related metabolites:
  Mitochondrial metabolomics analyses in slc25a47-deficient mice revealed significant alterations in metabolite profiles compared to wild-type controls:

  Metabolite	Change in slc25a47-/- vs. Control	Pathway Involvement
  Isocitrate	Increased	TCA cycle
  Fumarate	Increased	TCA cycle
  Malate	Increased	TCA cycle/Gluconeogenesis
  Phosphoenolpyruvate (PEP)	Decreased	Gluconeogenesis
  NAD+	Increased	Redox reactions
  GTP	Increased	Energy carrier
  Pyruvate	No significant change	-
  Citrate	No significant change	-
  α-Ketoglutarate	No significant change	-
  Succinyl-CoA	No significant change	-
  Succinate	No significant change	-
  Oxaloacetate	No significant change	-

  Proposed functions:

  • Initially proposed to function as a liver-specific mitochondrial uncoupling protein

  • More recent evidence suggests it primarily regulates metabolite transport rather than uncoupling

  • Experimental studies in Hepa 1-6 cells and permeabilized livers showed no significant differences in respiratory parameters between slc25a47a-expressing and control samples, arguing against an uncoupling role

  The specific metabolite(s) transported by slc25a47a remains to be definitively identified, though pyruvate and related gluconeogenic intermediates are prime candidates based on the observed metabolic alterations in deficient models.

• How does slc25a47a affect gluconeogenesis and energy homeostasis?

  slc25a47a has emerged as a critical regulator of hepatic gluconeogenesis and whole-body energy homeostasis:

  Gluconeogenesis regulation:

  • Liver-specific depletion of slc25a47a impairs hepatic gluconeogenesis specifically from lactate, while having minimal effects on glucose production from other substrates

  • Mechanism involves reduced mitochondrial pyruvate flux and altered malate metabolism, which restricts hepatic gluconeogenic capacity

  • Acute depletion of slc25a47a by approximately 50% in adult mice improves insulin tolerance and restricts excess hepatic gluconeogenesis without causing liver fibrosis or mitochondrial dysfunction

  Energy expenditure and FGF21 expression:

  • slc25a47a deficiency significantly enhances whole-body energy expenditure

  • Associated with increased hepatic expression of fibroblast growth factor 21 (FGF21), a key metabolic regulator

  • The enhanced energy expenditure and FGF21 production occur independently of liver damage or mitochondrial dysfunction when slc25a47a is acutely depleted in adult mice

  Human genetic associations:
  Human genetic studies from the Type 2 Diabetes Knowledge Portal show significant associations between SLC25A47 variants and metabolic parameters:

  Parameter	Association with SLC25A47 variants
  Fasting glucose (BMI-adjusted)	Lower levels
  Random glucose	Lower levels
  HbA1c (BMI-adjusted)	Lower levels
  HDL cholesterol	Higher levels
  AST-ALT ratio	Significant association

  These findings suggest that SLC25A47 plays a conserved role in glucose and lipid homeostasis in humans, making it a potential therapeutic target for metabolic disorders such as type 2 diabetes .

• What are the effects of slc25a47a deficiency on metabolic parameters?

  Research on slc25a47a deficiency has revealed complex effects on various metabolic parameters:

  Metabolomic alterations:
  In slc25a47-/- mice, metabolomic analyses revealed significant changes across multiple matrices:

  Matrix	Significantly altered metabolites (P<0.01, FC>1.5)
  Plasma	Homocitrulline, α-ketoglutaric acid, malic acid, ureidosuccinic acid, maleic acid, fumaric acid, N-acetylaspartic acid (all elevated)
  Liver	Modest alterations in TCA cycle intermediates and amino acid metabolism
  Mitochondria	Altered levels of isocitrate, fumarate, malate, and phosphoenolpyruvate

  These metabolites are primarily involved in the TCA cycle and amino acid metabolism, supporting the role of slc25a47a in these pathways .

  Physiological effects:

  • Glucose metabolism: Improved glucose tolerance in high-fat fed slc25a47a-/- mice

  • Lipid metabolism: Modest, reproducible reductions in plasma triglycerides and glycerol in fasted slc25a47a-/- mice

  • Energy expenditure: No significant influence on energy expenditure in models using adenoviral-mediated overexpression or complete knockout , though other studies reported enhanced energy expenditure in liver-specific knockouts

  Conditional vs. chronic deficiency:

  • Chronic slc25a47a deletion has been associated with mitochondrial dysfunction, mitochondrial stress, and liver fibrosis in some studies

  • In contrast, acute or partial depletion (approximately 50%) improved insulin tolerance and restricted excess hepatic gluconeogenesis without causing liver damage or mitochondrial dysfunction

  This discrepancy suggests that the effects of slc25a47a deficiency are highly dependent on:

  1. The extent of deficiency (partial vs. complete)

  2. The timing of deficiency (developmental vs. adult-onset)

  3. The specific metabolic context (fasting vs. fed state, regular diet vs. high-fat diet)

• What are the protein interactions and functional partners of slc25a47a?

  Understanding the protein interaction network of slc25a47a provides insights into its functional role in metabolic pathways. Analysis using the STRING database reveals several predicted functional partners:

  Protein Partner	Description	Interaction Score	Functional Relevance
  slc22a13a	Solute carrier family 22 member 13a	0.834	Transport of small molecules
  slc5a12	Sodium-coupled monocarboxylate transporter 2	0.831	Transport of monocarboxylates including lactate and pyruvate
  faub/faua	40S ribosomal protein S30	0.777	Protein synthesis
  slc13a3	Solute carrier family 13 member 3	0.766	Transport of dicarboxylates
  ppp2r5cb	Serine/threonine protein phosphatase 2A regulatory subunit	0.742	Cellular signaling
  slc15a2	Solute carrier family 15 member 2	0.734	Oligopeptide transport
  rps29	Ribosomal protein S29	0.698	Protein synthesis
  slc33a1	Solute carrier family 33 member 1	0.692	Acetyl-CoA transporter
  rpl14	Ribosomal protein L14	0.678	Protein synthesis

  The strong interaction with transporters for monocarboxylates (slc5a12) and dicarboxylates (slc13a3) suggests functional cooperation in metabolite transport pathways, particularly those involving pyruvate, lactate, and TCA cycle intermediates .

  The interaction with slc33a1 (acetyl-CoA transporter) further supports slc25a47a's involvement in energy metabolism pathways, potentially coordinating the transport of metabolites between cellular compartments to regulate gluconeogenesis and energy homeostasis .

  These protein interactions provide a molecular framework for understanding how slc25a47a integrates into broader metabolic networks in the liver and may guide future research into its precise molecular function.

• What is the relationship between slc25a47a and liver-specific metabolic regulation?

  slc25a47a demonstrates a unique liver-specific expression pattern that is tightly connected to hepatic metabolic regulation:

  Liver-specific expression mechanism:

  • Analysis of ATAC-seq data revealed an open chromatin architecture in the slc25a47a gene locus specific to the liver, whereas the same region forms a heterochromatin structure in other tissues

  • The euchromatin region contains binding sites for hepatocyte nuclear factor 4 alpha (HNF4α), a master regulator of hepatic and pancreatic transcriptional networks

  • Genetic loss of HNF4α significantly attenuates the expression of slc25a47a in the mouse liver, confirming that HNF4α is required for the hepatic expression of slc25a47a

  Connection to hepatic metabolic pathways:

  • slc25a47a is regulated by peroxisome proliferator-activated receptor-alpha (PPARα), a central regulator of lipid metabolism in the liver

  • Expression of slc25a47a is significantly induced by PPARα activation in human hepatocytes, human liver slices, and human hepatoma HepG2 cells

  • Similarly, slc25a47a expression is induced by PPARα activation in mouse hepatocytes, rat FAO hepatoma cells, and mouse liver

  • ChIP-seq data revealed several PPARα binding sites immediately upstream of the transcriptional start site of slc25a47a, suggesting it is a direct PPARα target gene

  Induction during fasting:

  • slc25a47a is a fasting-induced gene in human and mouse hepatocytes

  • This fasting induction is consistent with its role in regulating gluconeogenesis, which is essential during fasting to maintain blood glucose levels

  Metabolic function:

  • Controls pyruvate import or flux within hepatic mitochondria

  • Regulates gluconeogenesis specifically from lactate

  • Interacts with other liver-specific metabolic pathways, including lipid metabolism

  This liver-specific expression and regulation pattern, coupled with its role in gluconeogenesis, positions slc25a47a as a specialized component of hepatic metabolic regulation that has evolved to meet the unique metabolic demands of the liver, particularly during fasting states.

Methodological Questions

• What protocols are recommended for zebrafish maintenance when studying slc25a47a?

  Proper zebrafish maintenance is crucial for obtaining reliable and reproducible results when studying slc25a47a. Based on established protocols, the following parameters are recommended:

  Housing conditions:

  • Maintain zebrafish in ZebTec Active Blue recirculating systems or equivalent

  • Water temperature: 26-28°C

  • Water pH: 7.0-7.5

  • Photoperiod: 14/10-h light/dark cycle

  • Tank density: 20 fish per 3L system for adults; 45 fish in 9L tanks for juveniles

  Breeding protocol:

  1. Select 4-month-old male and female zebrafish for breeding

  2. Place breeding pairs in dedicated breeding tanks during morning hours

  3. Collect eggs in petri dishes

  4. Incubate eggs at 28°C until hatching

  5. Begin feeding larvae with appropriate-sized food 5 days post-fertilization

  Feeding regimen by developmental stage:

  Age	Feed Type	Feed Size	Frequency	Notes
  5-14 dpf	Zebrafeed	<100 μm	2x daily	Early larval stage
  14-30 dpf	Zebrafeed	100-200 μm	2x daily	Late larval stage
  30-60 dpf	Zebrafeed	200-400 μm	2x daily	Juvenile stage
  >60 dpf	Zebrafeed + Artemia	400-600 μm	2x daily	0.2-0.4 mL concentrated artemia per fish

  Experimental design considerations:

  • For treatment studies, maintain 3.5L tanks with 10-20 fish per treatment group

  • Feed experimental groups at 3% body weight

  • Distribute feeding 3 times daily (08:00-09:00, 14:00-15:00, 20:00-21:00)

  • Record average body weights before and after treatment periods

  • Sample collection at specific timepoints (e.g., day 14 and day 28) for consistent comparisons

  Ethical considerations:

  • All procedures must comply with institutional animal ethics guidelines

  • Use appropriate euthanasia methods (e.g., cold ice treatment) followed by tissue collection

  • Minimize isolation stress during individual monitoring by maintaining visual contact with conspecifics

  Following these standardized protocols ensures optimal health of the zebrafish and minimizes variables that could affect expression and function of slc25a47a.

• What are the best methods for protein isolation and analysis of slc25a47a?

  Studying slc25a47a at the protein level requires specialized techniques for isolation, quantification, and functional analysis:

  Protein isolation from zebrafish tissue:

  1. Homogenization protocol:

     • Homogenize frozen intestine or liver samples with 200 μL buffer containing:

       • SDS lysis buffer

       • 0.5 M TEAB buffer (pH 8.5)

       • 1× Protease Inhibitor cocktail

     • Incubate homogenized samples at 90°C for 30 min

     • Cool samples on ice for 5 min

     • Centrifuge at 14,000 × g for 20 min at 4°C

  2. Protein precipitation:

     • Transfer supernatant to a new tube

     • Add four volumes of ice-cold acetone

     • Incubate at -20°C for 24 h

     • Centrifuge at 14,000 × g for 10 min at 4°C

     • Wash pellets twice with ice-cold acetone

     • Dry pellets at 22°C

  3. Resolubilization and quantification:

     • Resolubilize pellets in 200 μL of 5× SDS lysis buffer

     • Quantify using Qubit Protein Assay Kit or equivalent

  Protein digestion for mass spectrometry:

  S-Trap digestion protocol for 100 μg protein:

  1. Add 3.5 μL of 100 mM TCEP for reduction (55°C, 10 min)

  2. Add 7 μL of 200 mM MMTS for alkylation (22°C, 10 min)

  3. Add 7 μL of 12% phosphoric acid

  4. Add 420 μL of S-Trap binding buffer (90% MeOH, 100 mM TEAB, pH 7.1)

  5. Load onto S-Trap column, centrifuge at 4,000 × g

  6. Wash 4 times with 150 μL S-Trap binding buffer

  7. Add trypsin (1:25 w/w ratio to protein)

  8. Incubate at 47°C for 1-2 h

  9. Elute sequentially with TEAB, formic acid, and ACN solutions

  Advanced proteomic analysis:

  For comprehensive characterization of slc25a47a and associated proteins:

  1. iTRAQ labeling:

     • Enables quantitative comparison across multiple samples

     • Protocol using 8-plex iTRAQ reagents for labeling peptides

     • 2D LC-MS/MS analysis using RP-HPLC separation at high pH (first dimension) followed by nanoLC separation (second dimension)

  2. Functional assays:

     • Subcellular localization: Immunofluorescence with Mitotracker Red FM to confirm mitochondrial localization

     • Mitochondrial function: High-resolution respirometry on Oroboros Oxygraph-2k or similar system

     • Substrate transport: Isotope-labeled substrate uptake in isolated mitochondria or reconstituted proteoliposomes

  3. Mitochondrial isolation and respirometry:

     • Isolate liver mitochondria using differential centrifugation

     • Assess respiratory states using Coupling Control Protocol

     • Measure parameters including:

       • LEAK respiration (L)

       • OXPHOS capacity (P)

       • ETS capacity (E)

       • ROX (residual oxygen consumption)

  For optimal results in studying low-abundance membrane proteins like slc25a47a, combining enrichment strategies with sensitive detection methods is recommended.

• How can one design knockdown or knockout experiments for slc25a47a in zebrafish?

  Designing effective genetic manipulation experiments for slc25a47a requires careful consideration of targeting strategies, validation methods, and phenotypic analyses:

  CRISPR-Cas9 knockout strategy:

  1. Guide RNA design:

     • Target early exons (preferably exons 5-6 based on previous successful targeting)

     • Design multiple gRNAs to increase targeting efficiency

     • Verify low off-target potential using tools like CHOPCHOP or CRISPOR

  2. Delivery method:

     • Microinject Cas9 protein (or mRNA) with gRNAs into one-cell stage embryos

     • Typical injection mix:

       • 300 ng/μL Cas9 protein (or 300 ng/μL Cas9 mRNA)

       • 25-50 ng/μL of each gRNA

       • 0.05% phenol red (for visualization)

     • Inject 1-2 nL per embryo

  3. Mutation screening and validation:

     • Extract genomic DNA from 24-48 hpf embryos

     • PCR amplify the targeted region

     • Screen F0 embryos using T7 Endonuclease I assay or Sanger sequencing

     • Raise potential founders to adulthood

     • Outcross F0 adults with wild-type fish

     • Genotype F1 offspring to identify germline mutations

     • Establish homozygous lines through incrossing

  Morpholino knockdown (for rapid assessment):

  1. Morpholino design:

     • Translation-blocking: Target the 5' UTR or start codon region

     • Splice-blocking: Target exon-intron boundaries

     • Include standard control morpholino and p53 morpholino

  2. Delivery and dosage:

     • Inject 1-2 nL of morpholino (0.2-0.4 mM) into one-cell stage embryos

     • Perform dose-response studies to determine optimal concentration

     • Include rescue experiments by co-injecting morpholino-resistant slc25a47a mRNA

  3. Validation of knockdown:

     • For translation-blocking MO: Western blot with anti-slc25a47a antibody

     • For splice-blocking MO: RT-PCR to detect aberrant splicing

     • qPCR to assess compensatory expression of related genes

  Conditional knockout strategies:

  For temporal control of slc25a47a expression, consider using:

  1. LexPR system:

     • Generate driver lines expressing LexPR under liver-specific promoters

     • Create effector lines with slc25a47a under LexOP control

     • Induce expression using mifepristone

  2. Liver-specific Cre-lox system:

     • Cross floxed slc25a47a fish with liver-specific fabp10a:Cre or similar line

     • Induce recombination with tamoxifen if using CreERT2

  Phenotypic analysis:

  1. Liver-specific assays:

     • Histology: H&E, Oil Red O for lipid accumulation

     • Biochemical: Triglyceride content, glycogen levels

     • Gene expression: qPCR for gluconeogenic and lipid metabolism genes

  2. Metabolic assessment:

     • Glucose and pyruvate tolerance tests

     • Metabolomics of liver tissue and isolated mitochondria

     • Respirometry of isolated liver mitochondria

  3. Mitochondrial analyses:

     • Mitochondrial morphology using electron microscopy

     • Mitochondrial membrane potential using fluorescent probes

     • Oxygen consumption and ATP production rates

  Combining these approaches allows for comprehensive characterization of slc25a47a function in zebrafish liver metabolism.

• What analytical techniques are best for studying the metabolic impact of slc25a47a?

  Investigating the metabolic impact of slc25a47a requires a multi-faceted approach combining biochemical, molecular, and physiological techniques:

  Metabolomic profiling:

  1. Targeted metabolomics:

     • Focus on TCA cycle intermediates, gluconeogenic metabolites, and amino acids

     • Prepare samples from:

       • Plasma

       • Whole liver tissue

       • Isolated liver mitochondria

     • Analyze using LC-MS/MS with optimized methods for organic acids and related metabolites

     • Key metabolites to measure:

       • TCA cycle: citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, oxaloacetate

       • Gluconeogenesis: pyruvate, lactate, phosphoenolpyruvate, glyceraldehyde-3-phosphate

       • Redox carriers: NAD+, NADH, NADP+, NADPH, FAD

  2. Untargeted metabolomics:

     • Provides comprehensive metabolic fingerprint

     • Sample preparation options:

       • Methanol/chloroform/water extraction for polar and non-polar metabolites

       • Perchloric acid extraction for energy-related compounds

     • Analysis by high-resolution mass spectrometry (Q-TOF or Orbitrap)

     • Data analysis using:

       • Principal Component Analysis (PCA)

       • Partial Least Squares Discriminant Analysis (PLS-DA)

       • Pathway analysis using KEGG

  Functional metabolic assays:

  1. Gluconeogenesis assessment:

     • Primary hepatocyte isolation from zebrafish liver

     • Measure glucose production from various precursors:

       • Pyruvate (1-5 mM)

       • Lactate (10 mM)

       • Alanine (5 mM)

       • Glycerol (5 mM)

     • Analyze using glucose oxidase-based assays or LC-MS

     • Include appropriate controls:

       • Insulin (100 nM, inhibits gluconeogenesis)

       • Glucagon (100 nM, stimulates gluconeogenesis)

  2. Substrate flux analysis:

     • Use isotope-labeled substrates (13C-pyruvate, 13C-lactate)

     • Trace labeled carbon through metabolic pathways

     • Measure isotopomer distribution using GC-MS or LC-MS

     • Calculate flux rates through specific pathways

  3. Mitochondrial function:

     • High-resolution respirometry using Oroboros Oxygraph-2k

     • Protocol for isolated mitochondria or permeabilized tissue:

       • LEAK state: Measure with substrate but no ADP

       • OXPHOS capacity: Add ADP to stimulate respiration

       • Electron transfer system capacity: Add uncoupler

       • Substrate-specific rates: Use specific substrates and inhibitors

  Molecular and biochemical approaches:

  1. Gene expression analysis:

     • qRT-PCR for key genes in:

       • Gluconeogenesis: pck1, g6pc, fbp1

       • TCA cycle: cs, idh, sdh

       • Mitochondrial function: ucp2, ppargc1a

     • RNA-Seq for global transcriptional changes

     • Analysis using gene set enrichment (GSEA) and pathway analysis

  2. Protein analysis:

     • Western blotting for key metabolic enzymes

     • Immunoprecipitation to identify protein interactions

     • Proteomics using iTRAQ or TMT labeling for quantitative comparisons

     • Phosphoproteomics to assess regulatory modifications

  Physiological techniques:

  1. Whole-organism metabolic assessment:

     • Glucose and pyruvate tolerance tests

     • Insulin tolerance test

     • Metabolic cage studies for:

       • Energy expenditure

       • Respiratory exchange ratio

       • Activity monitoring

  2. Liver-specific assays:

     • Glycogen content (PAS staining, biochemical quantification)

     • Lipid accumulation (Oil Red O staining, triglyceride assays)

     • ATP content measurements

  Integration of these complementary approaches provides comprehensive insights into the metabolic impact of slc25a47a alterations at molecular, cellular, and organismal levels.