Recombinant Rat Protein FAM210A (Fam210a)

What is FAM210A and where is it primarily expressed?

FAM210A (Family With Sequence Similarity 210 Member A) is a mitochondrial protein with high conservation across 213 organisms including humans, mice, rats and other vertebrates. It is primarily expressed in skeletal muscle, heart, and brain tissues . Within cells, the majority of FAM210A localizes to mitoplasts (mitochondrial inner membrane and matrix), with a smaller fraction at the mitochondrial outer membrane . Importantly, while FAM210A strongly influences bone structure and strength, histochemical analysis using X-Gal staining in Fam210a heterozygous global knockout mice shows no expression in bone tissue itself .

What are the primary cellular functions of FAM210A?

FAM210A plays a critical role in regulating mitochondrial encoded protein (MEG) expression. It functions in the mitochondrial translation machinery by interacting with multiple proteins, particularly ATAD3A and mitochondrial elongation factor EF-Tu (TUFM) . Through these interactions, FAM210A modulates the translation efficiency of mitochondrial-encoded genes at the elongation step. Pulse-chase AHA labeling assays demonstrate that overexpression of FAM210A increases translation of multiple MEG proteins, including several mitochondrial-encoded electron transport chain (ETC) complex components from Complexes I, III, IV, and V . FAM210A appears to coordinate the expression balance between mitochondrial-encoded genes (MEG) and nuclear-encoded mitochondrial genes (NEMG) proteins in cardiomyocytes and other cells .

How does FAM210A affect muscle tissue?

FAM210A expression is positively associated with muscle mass in mice. Deletion of Fam210a using Myl1-driven Cre recombinase in muscle cells leads to progressive myopathy and severe muscle weakness in mice, resulting in systemic metabolic defects and premature death . At the cellular level, loss of Fam210a disrupts mitochondrial cristae structure and reduces mitochondrial abundance in myofibers, accompanied by deficiencies in mitochondrial energy metabolism . Parameters of muscle function and structure, including grip strength and lean mass of all limbs, are decreased in Fam210a knockout mice .

How is FAM210A expression regulated?

FAM210A is regulated by microRNA-574, with both miR-574-5p and miR-574-3p targeting the Fam210a transcript. Upon cardiac stress, such as thoracic aortic constriction (TAC), miR-574-5p is induced, likely as a protective mechanism to restrict FAM210A expression . In wild-type mice, FAM210A protein levels remain relatively stable at early stages of TAC (days 3 and 7) but become significantly induced at later stages (days 14 and 21) . In miR-574-null mice, FAM210A protein is significantly induced at an earlier stage following TAC, indicating that miR-574 normally acts as a molecular brake on FAM210A expression . Additional experiments confirmed that miR-574-3p target sites in the Fam210a 3'UTR are functional through luciferase reporter assays .

What molecular pathways does FAM210A influence in mitochondria?

FAM210A affects mitochondrial function through multiple mechanisms:

• Mitochondrial translation: FAM210A interacts with EF-Tu and ATAD3A to increase translation efficiency in mitochondria at the elongation step. Polysome profiling shows that mRNAs of ND3, CYTB, CO1, and ATP6 are more enriched in large mitoribosome subunits and heavy polysome fractions when FAM210A is overexpressed .

• TCA cycle regulation: Loss of Fam210a reverses the oxidative TCA cycle towards the reductive direction, resulting in acetyl-CoA accumulation .

• Protein acetylation: The acetyl-CoA accumulation leads to hyperacetylation of cytosolic proteins, particularly ribosomal proteins, causing ribosome disassembly and translational defects .

• Inter-organelle crosstalk: FAM210A mediates critical communication between mitochondria and ribosomes, as demonstrated by the finding that transplantation of Fam210a-knockout mitochondria into wildtype myoblasts is sufficient to elevate protein acetylation in recipient cells .

What experimental models are available for studying FAM210A function?

Several genetically modified mouse models have been developed to study FAM210A:

• Global knockout model: Fam210a heterozygous and homozygous knockout mice (Fam210a+/- and Fam210a-/-) have been generated to study systemic effects of Fam210a deletion .

• Muscle-specific knockout model: Myl1-driven Cre Fam210a knockout mice (Fam210a MKO) have been created to study muscle-specific effects. These mice exhibit progressive muscle atrophy and premature death .

• Reporter systems: Fam210a heterozygous global knockout mice expressing a lacZ reporter under the control of the Fam210a promoter have been used to study tissue expression patterns through X-Gal staining .

These models have revealed that FAM210A strongly influences the structure and strength of both muscle and bone, despite being expressed in muscle but not in bone, suggesting an indirect mechanism of action on bone tissue .

What techniques can be used to assess FAM210A's role in mitochondrial translation?

To assess FAM210A's role in mitochondrial translation, researchers can employ:

• Polysome profiling: This technique separates ribosomes based on their sedimentation properties, allowing analysis of the association between specific mRNAs and ribosomes. For FAM210A studies, polysome profiling of mitochondrial fractions from cells overexpressing FAM210A (with mock transfection as control) can reveal enrichment of mitochondrial-encoded mRNAs in large mitoribosome subunits and heavy polysome fractions .

• AHA labeling assay: This pulse-chase method uses azidohomoalanine (AHA), a methionine analog, to label newly synthesized proteins. For FAM210A research, short time pulse-chase AHA labeling can demonstrate that overexpression of FAM210A increases translation of multiple mitochondrial-encoded proteins .

• Immunoprecipitation-mass spectrometry: Using a FAM210A-specific antibody to pull down endogenous FAM210A from purified mitochondria, followed by mass spectrometry analysis, reveals its interactome including translation machinery proteins like EF-Tu and ATAD3A .

How does FAM210A contribute to cardiac pathology?

In the context of cardiac stress and tissue injury, FAM210A appears to exacerbate pathological remodeling responses by over-activating mitochondrial protein expression and altering the balance between cytoplasmic and mitochondrial electron transport chain component proteins . This imbalance may promote heart failure progression. Experiments in mouse models show that:

• FAM210A protein expression is induced in hearts of wild-type mice upon isoproterenol (ISO) treatment, with significantly higher levels in miR-574-/- mice .

• Thoracic aortic constriction (TAC) surgery leads to increased reactive oxygen species (ROS) production in the hearts of miR-574-/- mice compared to wild-type mice, correlating with higher FAM210A levels .

• Nanoparticle delivery of miR-574-5p and miR-574-3p mimics reduces FAM210A protein expression in therapeutic mouse models, accompanied by decreased ROS production and restored ATP production compared to control miRNA mimics injection in mice under TAC surgery .

These findings suggest that FAM210A plays a potentially pathogenic role in cardiac remodeling, with miR-574 serving as a protective regulator.

What is the relationship between FAM210A and human musculoskeletal conditions?

Genetic variation near FAM210A has been strongly associated with both appendicular and whole body lean mass, as well as bone mineral density in humans . This makes FAM210A a potential therapeutic target for age-related musculoskeletal conditions like osteoporosis and sarcopenia. In genetically modified mouse models, Fam210a strongly influences the structure and strength of both muscle and bone .

The dual effect on both tissues is particularly interesting because Fam210a is expressed in muscle but not in bone, suggesting an indirect mechanism whereby muscle-expressed Fam210a affects bone structure and strength. This presents a novel pathway that may lead to the development of new treatments for both osteoporosis and sarcopenia .

What controls should be included when designing FAM210A knockout experiments?

When designing FAM210A knockout experiments, the following controls should be included:

• Wild-type controls: Use littermate wild-type mice (Fam210a+/+) as primary controls to minimize genetic background differences.

• Cre-only controls: For tissue-specific knockouts using Cre-loxP systems (e.g., Myl1-Cre for muscle-specific deletion), include Cre-positive but flox-negative mice to control for potential Cre toxicity or off-target effects.

• Heterozygous models: Include Fam210a+/- mice to examine potential gene dosage effects, as seen in studies showing intermediate phenotypes in heterozygous knockout mice .

• Age-matched controls: As Fam210a knockout leads to progressive myopathy, age-matching is essential to accurately assess phenotypic changes over time.

• Tissue specificity verification: Confirm the tissue-specific deletion through methods like X-Gal staining in reporter models or quantitative RT-PCR of target tissues, as demonstrated in studies verifying Fam210a expression in muscle but not bone .

How can researchers resolve contradictory data in FAM210A studies?

Researchers may encounter contradictory data when studying FAM210A due to its complex roles in multiple tissues and cellular compartments. To resolve such contradictions:

• Consider tissue specificity: FAM210A functions may differ between tissues. While expressed in muscle, heart, and brain, its absence in bone tissue despite effects on bone structure suggests tissue-specific mechanisms .

• Examine temporal dynamics: FAM210A's effects may be time-dependent. For example, in wild-type mice under TAC, FAM210A protein levels remain stable early (days 3-7) but increase significantly later (days 14-21) .

• Analyze subcellular localization: FAM210A localizes primarily to mitoplasts with a smaller fraction at the mitochondrial outer membrane. Subcellular fractionation experiments should be performed to determine if contradictory results stem from different subcellular pools .

• Consider interacting partners: FAM210A interacts with multiple proteins including ATAD3A and EF-Tu. Different experimental conditions may affect these interactions, leading to variable results .

• Examine microRNA regulation: Both strands of miR-574 regulate FAM210A. Variations in miR-574 expression across experimental models could explain discrepancies in FAM210A levels and function .

What are the best methods for detecting and quantifying FAM210A protein?

For optimal detection and quantification of FAM210A protein:

• Western blotting: Use FAM210A-specific antibodies validated against knockout controls. Subcellular fractionation should be performed to separate mitochondrial fractions where FAM210A is primarily localized .

• Immunofluorescence: This technique can visualize the subcellular localization of FAM210A, which has been shown to be present in mitochondria and cytoplasm of muscle cells and myotubes .

• Mass spectrometry: This approach can be used for absolute quantification of FAM210A protein levels and to identify post-translational modifications that may affect function.

• Reporter systems: X-Gal staining in mice expressing lacZ under the Fam210a promoter provides tissue-specific expression patterns, as demonstrated in studies showing expression in skeletal muscle, heart, and brain but not in bone .

When analyzing FAM210A levels, it's important to note that it is not detectable in serum, indicating it may not be a secreted protein under normal conditions (though it might be released from severely damaged muscle) .

How should researchers analyze the impact of FAM210A on mitochondrial function?

To comprehensively analyze FAM210A's impact on mitochondrial function:

• Respiratory analysis: Measure oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) using platforms like Seahorse XF Analyzer to assess mitochondrial respiration in cells with modified FAM210A expression.

• Mitochondrial morphology: Examine mitochondrial cristae structure using electron microscopy, as loss of Fam210a has been shown to disrupt cristae structure .

• Mitochondrial abundance: Quantify mitochondrial content using mitochondrial DNA copy number, MitoTracker staining, or immunofluorescence for mitochondrial markers.

• TCA cycle analysis: Perform metabolomic analysis focusing on TCA cycle intermediates, as Fam210a knockout reverses the oxidative TCA cycle towards the reductive direction .

• Protein acetylation assessment: Measure acetylation levels of cytosolic proteins, especially ribosomal proteins, which become hyperacetylated due to acetyl-CoA accumulation in Fam210a knockout models .

• Mitochondrial translation: Use techniques like polysome profiling of mitochondrial fractions and AHA labeling assays to assess translation of mitochondrial-encoded proteins .