Recombinant Human Protein FAM210A (FAM210A)

What is FAM210A and where is it primarily expressed?

FAM210A is a novel mitochondrial protein that has been identified as a key regulator of both bone and muscle structure and function. In humans, genetic variation near the FAM210A gene is strongly associated with bone mineral density (BMD), fracture risk, and measures of lean mass . Expression studies in mice show that Fam210a is predominantly expressed in muscle mitochondria and cytoplasm, as well as in heart and brain, but notably not in bone tissue despite its significant effects on bone structure . Among these tissues, the heart shows particularly high expression levels, where Fam210a has been identified as a hub gene in cardiac remodeling through multi-omics studies .

What is the subcellular localization of FAM210A?

FAM210A is primarily a mitochondrial inner membrane protein . It contains a mitochondrial targeting signal sequence that directs its localization to mitochondria . This localization is consistent with its observed functions in mitochondrial translation and homeostasis. Microscopy studies have confirmed its presence in muscle mitochondria and cytoplasm, where it plays crucial roles in maintaining mitochondrial function .

What are the main physiological functions of FAM210A?

FAM210A serves several critical physiological functions:

• Regulation of mitochondrial translation: FAM210A modulates the translation of mitochondrial-encoded mRNAs by interacting with mitochondrial elongation factor EF-Tu .

• Maintenance of muscle structure and function: FAM210A influences grip strength and limb lean mass in mouse models .

• Influence on bone mineralization and structure: Despite not being expressed in bone, FAM210A significantly affects bone mineral density and microarchitecture .

• Cardiac function: FAM210A maintains mitochondrial homeostasis in cardiomyocytes, which is essential for normal cardiac contractile function .

• Mitochondrial calcium handling: It interacts with LETM1 (leucine zipper and EF-hand containing transmembrane protein 1) and regulates mitochondrial Ca²⁺ efflux .

How does FAM210A knockout affect phenotypes in animal models?

The effects of FAM210A knockout vary depending on the model system used:

Table 1: Phenotypes in Different FAM210A Knockout Models

What methodology has been developed for purifying recombinant FAM210A?

A specific methodology has been developed for the purification of human FAM210A as a recombinant protein:

• Expression system: The protocol uses MBP-His₁₀ fusion tag for expression in Escherichia coli, with deletion of the mitochondrial targeting signal sequence .

• Membrane insertion and isolation: The recombinant FAM210A protein spontaneously inserts into the E. coli cell membrane, requiring isolation of bacterial cell membranes as a first step .

• Two-step purification process:

  • Ni-NTA resin-based immobilized-metal affinity chromatography (IMAC)

  • Ion exchange purification

• Validation of functionality: The purified FAM210A remains functionally active, as demonstrated by pulldown assays showing interaction with human mitochondrial elongation factor EF-Tu in HEK293T cell lysates .

This purification method provides opportunities for further biochemical and structural studies of FAM210A, including crystallization trials, interaction studies, and functional assays.

How does FAM210A regulate mitochondrial translation?

FAM210A functions as a mitochondrial translation regulator through several mechanisms:

• Protein complex formation: FAM210A interacts with mitochondrial translation elongation factor EF-Tu in a protein complex that regulates mitochondrial-encoded mRNA translation .

• Translation efficiency: Mitochondrial polysome profiling analysis demonstrates that FAM210A loss of function compromises mitochondrial mRNA translation, leading to reduced levels of mitochondrial-encoded proteins .

• Proteostasis maintenance: By ensuring proper mitochondrial translation, FAM210A helps maintain mitochondrial proteostasis, which is essential for normal mitochondrial function .

• Impact on respiratory chain: The translation regulation by FAM210A particularly affects the expression of mitochondrial DNA-encoded components of the electron transport chain complexes, impacting respiratory capacity .

The molecular details of how FAM210A influences the translation machinery beyond its interaction with EF-Tu require further investigation, but its role appears to be critical for the proper synthesis of mitochondrially-encoded proteins.

What is the role of FAM210A in cardiac function and heart disease?

FAM210A plays a crucial role in maintaining cardiac function and preventing heart disease:

• Mitochondrial homeostasis: FAM210A maintains mitochondrial homeostasis in cardiomyocytes by regulating the translation of mitochondria-encoded mRNAs .

• Cardiac pathophysiology: Cardiomyocyte-specific knockout of Fam210a in mice leads to progressive dilated cardiomyopathy, heart failure, and ultimately mortality at approximately 70 days post-knockout .

• Early mitochondrial defects: Before contractile dysfunction and heart failure appear, FAM210A deficiency causes increased mitochondrial ROS production, disturbed mitochondrial membrane potential, and reduced respiratory activity in cardiomyocytes .

• Clinical relevance: Decreased FAM210A protein expression has been observed in human ischemic heart failure and mouse myocardial infarction tissue samples .

• Therapeutic potential: AAV9-mediated overexpression of FAM210A promotes mitochondrial-encoded protein expression, improves cardiac mitochondrial function, and partially rescues murine hearts from cardiac remodeling and damage in ischemia-induced heart failure .

These findings suggest that FAM210A is a potential therapeutic target for treating ischemic heart disease and heart failure.

How does FAM210A deficiency activate the integrated stress response?

FAM210A deficiency leads to persistent activation of the integrated stress response (ISR) in cardiac tissue:

• Multi-omics reprogramming: FAM210A deficiency results in transcriptomic, translatomic, proteomic, and metabolomic reprogramming through ISR activation .

• Temporal progression: The activation of ISR occurs early in the pathogenic cascade and persists throughout the progression to heart failure .

• Mitochondrial dysfunction connection: The primary trigger for ISR activation appears to be mitochondrial dysfunction resulting from impaired mitochondrial translation .

• Stress signaling: Although the exact molecular pathway is not fully detailed in the search results, the chronic activation of ISR represents a major component of the disease etiology in FAM210A-deficient hearts .

Understanding the link between FAM210A and ISR activation could provide insights into novel therapeutic approaches that target this stress pathway in mitochondrial and cardiac diseases.

What is the molecular mechanism by which FAM210A influences both bone and muscle simultaneously?

The dual effect of FAM210A on both bone and muscle represents an intriguing paradox:

• Expression pattern: FAM210A is expressed in muscle mitochondria and cytoplasm but not in bone tissue .

• Genetic associations: In humans, genetic variation near FAM210A is associated with both bone mineral density and measures of appendicular and whole body lean mass .

• Knockout effects: Despite its absence in bone, FAM210A knockout models show decreased BMD, bone biomechanical strength, and bone formation, along with elevated osteoclast activity and microarchitectural deterioration .

• Muscle-bone axis: These findings suggest a muscle-to-bone signaling pathway where FAM210A in muscle somehow influences bone metabolism remotely, representing a novel mechanism of muscle-bone cross-talk .

• Therapeutic implications: Further study of this novel pathway may lead to the development of new treatments that simultaneously target both osteoporosis and sarcopenia, common comorbid diseases of aging .

The exact signaling factors or metabolites that mediate this cross-tissue effect remain to be identified.

How can researchers effectively evaluate FAM210A function in vitro and in vivo?

Based on the current research approaches, several strategies can be employed to evaluate FAM210A function:

• Genetic models:

  • Global knockout models to assess systemic effects

  • Tissue-specific conditional knockout models using Cre-loxP systems to evaluate tissue-specific functions

  • Tamoxifen-inducible knockout systems for temporal control of gene deletion

• Functional assays:

  • Mitochondrial function: Respiratory activity, membrane potential, ROS production

  • Muscle function: Grip strength, limb lean mass measurements

  • Bone parameters: BMD, microarchitecture via μCT, biomechanical testing

  • Cardiac function: Echocardiography for chamber dimensions and contractile function

• Molecular analyses:

  • Mitochondrial polysome profiling to assess translation efficiency

  • Multi-omics analyses (transcriptomics, proteomics, metabolomics)

  • Protein interaction studies via pulldown assays

• Therapeutic interventions:

  • AAV9-mediated gene delivery for overexpression studies

  • Testing in disease models such as myocardial infarction

These methodologies provide a comprehensive framework for investigating the multifaceted functions of FAM210A across different tissues and physiological contexts.

What are the challenges in studying FAM210A interactions with the mitochondrial translation machinery?

Studying FAM210A's interactions with the mitochondrial translation machinery presents several challenges:

• Membrane protein constraints: As a mitochondrial inner membrane protein, FAM210A is challenging to express, purify, and study structurally .

• Complex formation: FAM210A likely functions in a multi-protein complex, requiring techniques that preserve these interactions during isolation .

• Mitochondrial environment: Replicating the unique biochemical environment of the mitochondrial matrix for in vitro studies is technically challenging.

• Translation system reconstitution: Complete reconstitution of the mitochondrial translation system for mechanistic studies is complex due to its unique components that differ from cytoplasmic translation.

• Tissue specificity: The function and interactions of FAM210A may vary across different tissues, requiring tissue-specific approaches .

A breakthrough in this field has been the development of a method to purify recombinant FAM210A with deleted mitochondrial targeting signal sequence using the MBP-His₁₀ fusion in E. coli, which maintains functional interaction with EF-Tu .

How can FAM210A be targeted therapeutically in disease models?

The search results suggest several approaches for targeting FAM210A therapeutically:

• Gene therapy approach: AAV9-mediated overexpression of FAM210A has been demonstrated to promote mitochondrial-encoded protein expression, improve cardiac mitochondrial function, and partially rescue murine hearts from cardiac remodeling and damage in ischemia-induced heart failure .

• Target tissues:

  • Cardiac tissue for heart failure and ischemic heart disease

  • Muscle tissue for sarcopenia

  • Potentially bone for osteoporosis, through muscle-bone cross-talk mechanisms

• Therapeutic goals:

  • Enhance mitochondrial translation efficiency

  • Improve mitochondrial respiratory function

  • Reduce integrated stress response activation

  • Restore normal calcium handling in mitochondria

• Potential modalities:

  • Viral vector-based gene delivery (demonstrated with AAV9)

  • Small molecules that enhance FAM210A function or stability

  • Peptide mimetics that replicate FAM210A's interaction with EF-Tu

These therapeutic approaches could be applicable to diseases involving mitochondrial dysfunction, including cardiomyopathies, sarcopenia, and potentially osteoporosis.

What are the critical factors for successful expression and purification of recombinant FAM210A?

Based on the methodology developed in source , several critical factors must be considered for successful expression and purification of recombinant FAM210A:

• Expression construct design:

  • Deletion of the mitochondrial targeting signal sequence

  • Use of MBP-His₁₀ fusion tags for improved solubility and purification

  • Selection of appropriate bacterial expression systems (E. coli)

• Membrane protein handling:

  • Efficient isolation of bacterial cell membranes containing the inserted recombinant protein

  • Careful solubilization using appropriate detergents that maintain protein structure and function

• Purification strategy:

  • Two-step purification process:
    a. Ni-NTA resin-based immobilized-metal affinity chromatography (IMAC)
    b. Ion exchange purification

  • Buffer optimization to maintain protein stability

• Functional validation:

  • Verification of proper folding and function through interaction studies

  • Pulldown assays with known interaction partners such as EF-Tu

This methodology provides a framework for obtaining purified FAM210A for further biochemical and structural studies, including understanding its role in mitochondrial translation.

How can researchers validate the specificity of FAM210A interactions with mitochondrial proteins?

To validate the specificity of FAM210A interactions with mitochondrial proteins, researchers can employ several complementary approaches:

• Co-immunoprecipitation (Co-IP): Using antibodies against FAM210A or its interaction partners to pull down protein complexes from mitochondrial extracts, followed by mass spectrometry or western blotting to identify interacting proteins.

• Pulldown assays: Similar to the approach used in source , where purified recombinant FAM210A was shown to interact with human mitochondrial elongation factor EF-Tu in HEK293T cell lysates.

• Proximity labeling: Techniques such as BioID or APEX2 can be used to identify proteins in close proximity to FAM210A within the mitochondrial inner membrane.

• Yeast two-hybrid or mammalian two-hybrid assays: For initial screening of potential interacting proteins, with validation in mitochondrial contexts.

• Mitochondrial polysome profiling: As used in source , to assess the impact of FAM210A on mitochondrial translation complexes.

• Mutational analysis: Creating point mutations in key domains of FAM210A to disrupt specific interactions and assess functional consequences.

• Crosslinking mass spectrometry: To map the interaction interfaces between FAM210A and its binding partners such as EF-Tu and LETM1.

These approaches can help establish the specificity and functional relevance of FAM210A interactions with components of the mitochondrial translation machinery and calcium handling systems.

How should researchers reconcile FAM210A's absence in bone tissue with its effects on bone structure?

The paradoxical finding that FAM210A influences bone structure despite not being expressed in bone tissue presents an interesting data interpretation challenge:

• Cross-tissue communication: The data suggests a muscle-to-bone signaling pathway where FAM210A in muscle somehow influences bone metabolism remotely .

• Potential mechanisms to investigate:

  • Secreted factors from muscle that affect bone metabolism

  • Metabolic changes in muscle that indirectly influence bone

  • Neuronal or hormonal pathways connecting muscle and bone

  • Altered mechanical loading due to muscle changes

• Experimental approaches to reconcile these findings:

  • Parabiosis experiments to identify circulating factors

  • Conditional knockout in different tissues to pinpoint the source of bone effects

  • Transcriptomic and proteomic analyses of muscle secretome in FAM210A-deficient models

  • Bone marrow transplantation to determine if effects are mediated by bone marrow-derived cells

• Comparative analysis: Examine other genes/proteins that show similar discrepancies between expression patterns and phenotypic effects across tissues.

This apparent contradiction represents an opportunity to discover novel mechanisms of muscle-bone cross-talk that could lead to integrated therapies for osteoporosis and sarcopenia .

How do researchers interpret the complex phenotypes resulting from FAM210A deficiency?

The complex phenotypes observed in FAM210A-deficient models require careful interpretation:

• Primary vs. secondary effects: Distinguishing direct consequences of FAM210A loss from compensatory or downstream effects:

  • Mitochondrial translation defects are likely primary effects

  • Integrated stress response activation may be a secondary response

  • Cardiac remodeling and failure represent tertiary consequences

• Tissue-specific vs. systemic effects: Understanding how localized FAM210A deficiency leads to systemic consequences:

  • Muscle-specific effects on bone structure

  • Cardiomyocyte-specific knockout leading to heart failure

• Temporal progression: Analyzing the sequence of events from early molecular changes to later physiological dysfunction:

  • Early mitochondrial dysfunction preceding contractile abnormalities in cardiac models

  • Progressive development of cardiomyopathy leading to heart failure

• Multi-omics integration: Combining transcriptomic, proteomic, and metabolomic data to build comprehensive models of FAM210A function .

• Comparative analysis: Comparing phenotypes across different knockout models (global, muscle-specific, cardiac-specific) to identify common pathways and tissue-specific effects .

This multi-layered interpretation approach can help researchers untangle the complex web of molecular and physiological changes resulting from FAM210A deficiency.