Recombinant Bovine Trans-2,3-enoyl-CoA reductase-like (TECRL)

What is the molecular structure and primary function of TECRL in cardiac tissue?

TECRL (Trans-2,3-enoyl-CoA reductase-like) is an endoplasmic reticulum protein involved in fatty acid metabolism and mitochondrial function. The protein plays a crucial role in maintaining proper cardiac electrical activity through regulation of calcium handling. Structurally, TECRL contains conserved domains typical of short-chain dehydrogenase/reductase family proteins, with functional regions responsible for cofactor binding and catalytic activity.

Research indicates that TECRL deficiency impairs mitochondrial respiration, characterized by reduced adenosine triphosphate production, increased fatty acid synthase (FAS) activity, and elevated reactive oxygen species (ROS) production . The protein has been shown to regulate mitochondrial function primarily through PI3K/AKT signaling and interaction with the mitochondrial fusion protein MFN2 . Expression studies demonstrate that TECRL is predominantly expressed in cardiac tissue, suggesting tissue-specific functions potentially related to the high metabolic demands of cardiomyocytes.

How can researchers effectively isolate and purify recombinant bovine TECRL for functional studies?

Isolation and purification of recombinant bovine TECRL requires careful consideration of protein solubility and stability. The recommended methodological approach includes:

• Expression system selection: Mammalian expression systems (HEK293 or CHO cells) are preferable over bacterial systems due to the need for post-translational modifications. When using bacterial systems, consider fusion tags (GST or MBP) to enhance solubility.

• Solubilization strategy: For membrane-associated TECRL, use mild detergents (0.5-1% DDM or CHAPS) for efficient extraction while maintaining protein integrity.

• Purification protocol: Implement a two-step chromatography approach combining affinity purification with size exclusion chromatography. For affinity purification, Ni-NTA columns work effectively with His-tagged constructs, while ion exchange chromatography can be used as an intermediate step if needed.

• Stability assessment: Verify protein stability using circular dichroism and thermal shift assays before proceeding to functional studies.

The isolation of functionally active TECRL requires preservation of its native conformation, particularly important when studying the protein's interaction with MFN2 and its effects on PI3K/AKT signaling pathways .

What experimental models are most appropriate for studying TECRL function in cardiovascular research?

Several experimental models have proven valuable for TECRL research, each with specific advantages for different research questions:

Table 1: Experimental Models for TECRL Research

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been particularly informative, as demonstrated in the Sudanese family study where hiPSC-CMs from a homozygous TECRL mutation carrier (TECRLHom-hiPSCs) showed smaller calcium transient amplitudes and elevated diastolic calcium levels compared to control hiPSC-CMs . Action potential recordings in these cells revealed marked prolongation of action potential duration at 20% repolarization (APD20) with trends toward increases in APD50 and APD90 . These cellular phenotypes correspond well with the clinical arrhythmia presentation.

What techniques are optimal for measuring TECRL-dependent alterations in mitochondrial function?

Comprehensive assessment of TECRL's impact on mitochondrial function requires multiple complementary approaches:

• Oxygen consumption rate (OCR) measurement: Using instruments like Seahorse XF Analyzer to quantify basal respiration, maximal respiration, and spare respiratory capacity. TECRL deficiency significantly reduces these parameters, indicating compromised mitochondrial function .

• Membrane potential assessment: JC-1 or TMRM dyes can be used to monitor mitochondrial membrane potential, which is typically depolarized in TECRL-deficient cells.

• ROS detection: MitoSOX Red or DCF-DA fluorescent probes are effective for quantifying increased ROS production associated with TECRL deficiency. Measurement protocols should include both basal and stress-induced conditions.

• ATP production assays: Luminescence-based ATP assays reveal decreased ATP synthesis in TECRL-deficient cells, particularly under metabolic stress conditions.

• Mitochondrial dynamics analysis: Live-cell imaging with mitochondria-targeted fluorescent proteins enables visualization of mitochondrial fusion/fission events, which are altered in TECRL-deficient cells due to decreased MFN2 expression .

• Electron microscopy: Ultrastructural analysis provides insights into cristae morphology changes that may not be detectable with fluorescence microscopy.

Research has shown that TECRL deficiency leads to impaired mitochondrial respiration, reduced ATP production, and increased ROS generation . These changes are mechanistically linked to decreased expression of mitochondrial fusion protein MFN2 and reduced activation (phosphorylation) of AKT at Ser473 .

How should researchers design experiments to investigate TECRL's role in calcium handling and arrhythmogenesis?

Investigating TECRL's impact on calcium handling requires careful experimental design that captures both steady-state and dynamic aspects of calcium regulation:

• Calcium transient recording: Use ratiometric calcium indicators (Fura-2 or Indo-1) rather than single-wavelength dyes for quantitative measurements. Pacing protocols should include both regular stimulation and premature beats to assess arrhythmia susceptibility.

• SR calcium content measurement: Implement caffeine-induced calcium release to evaluate sarcoplasmic reticulum calcium stores, which may be altered in TECRL-deficient cardiomyocytes.

• Calcium spark analysis: Confocal line-scan imaging allows detection of spontaneous calcium release events that may underlie triggered arrhythmias. Analysis should include spark frequency, amplitude, duration, and spatial spread.

• β-adrenergic challenge: Include isoproterenol (100 nM) protocols to mimic stress conditions that trigger arrhythmias in patients with TECRL mutations .

• Multiparameter correlation: Simultaneously record action potentials and calcium transients to establish causal relationships between calcium dysregulation and electrical abnormalities.

Analysis of intracellular calcium dynamics in hiPSC-CMs from a homozygous TECRL mutation carrier revealed smaller calcium transient amplitudes and elevated diastolic calcium levels compared to control cells . These alterations in calcium handling likely contribute to the clinical phenotype characterized by stress-induced atrial and ventricular tachycardia and QT prolongation with adrenergic stimulation .

What approaches are most effective for analyzing TECRL interactions with metabolic and signaling pathways?

Effective analysis of TECRL's pathway interactions requires a multi-level investigative approach:

• Proteomic interaction mapping: Employ proximity labeling methods (BioID or APEX) to identify TECRL interaction partners in living cells. This approach has advantages over traditional co-immunoprecipitation for capturing transient or context-specific interactions.

• Pathway phosphorylation profiling: Use phospho-specific antibody arrays to monitor multiple signaling nodes simultaneously. This has revealed TECRL's regulatory effect on the PI3K/AKT pathway, with decreased p-AKT (Ser473) in TECRL-deficient cells .

• Metabolomic analysis: Combine targeted and untargeted metabolomics to characterize alterations in fatty acid metabolism and related pathways. LC-MS/MS methods are particularly effective for analyzing acylcarnitine species that may be affected by TECRL dysfunction.

• Live-cell pathway reporters: Implement FRET-based biosensors to monitor pathway activity in real time. For example, AKT activity sensors can reveal the dynamics of TECRL-dependent regulation.

• Transcriptomic response: RNA-seq analysis comparing wild-type and TECRL-deficient cells provides insights into downstream transcriptional consequences and potential compensatory mechanisms.

Research has established that TECRL regulates mitochondrial function primarily through the PI3K/AKT signaling pathway and the mitochondrial fusion protein MFN2 . TECRL deficiency leads to decreased expression of NRF2, a key regulator of antioxidant responses, potentially explaining the increased ROS production observed in TECRL-deficient cells .

How do specific TECRL mutations affect protein function and contribute to arrhythmia phenotypes?

Different TECRL mutations produce distinct molecular consequences that ultimately converge on disrupted cardiac electrophysiology:

Table 2: Characterized TECRL Mutations and Their Functional Effects

The homozygous p.Arg196Gln mutation identified in two unrelated French Canadian patients results in an arginine to glutamine substitution at position 196 . This substitution is predicted to be "probably damaging" by PolyPhen-2 and deleterious by SIFT, occurring at a highly conserved residue with a high Genomic Evolutionary Rate Profiling score (5.11) .

The c.331+1G>A splice site mutation found in a Sudanese family causes complete skipping of exon 3, as demonstrated by PCR analysis showing a single 126-bp product in homozygous patient-derived cells compared to the expected 171-bp product containing exon 3 in control cells . This 45-bp deletion likely disrupts the protein's structure and function.

Both mutations lead to similar cellular phenotypes characterized by calcium handling abnormalities, but with some variation in the severity and specific aspects of calcium dysregulation. These differences may explain the clinical phenotypic spectrum ranging from predominant LQTS features to more CPVT-like presentations.

What molecular mechanisms link TECRL dysfunction to alterations in mitochondrial function and calcium homeostasis?

The connection between TECRL dysfunction and cardiac arrhythmias involves several interconnected molecular mechanisms:

• Altered lipid metabolism: TECRL deficiency disrupts fatty acid processing, potentially altering membrane composition and the function of embedded ion channels and transporters.

• Mitochondrial respiration impairment: TECRL deficiency reduces mitochondrial respiratory capacity and ATP production, compromising energy-dependent calcium handling processes .

• Increased oxidative stress: Elevated ROS production in TECRL-deficient cells can directly affect ryanodine receptor function through oxidative modifications, leading to calcium leak from the sarcoplasmic reticulum.

• Disrupted calcium storage proteins: Research using shRNA-mediated TECRL knockdown in hESC-CMs revealed a 56% decrease in RYR2 protein and 18% decrease in CASQ2, two critical calcium handling proteins . These reductions likely contribute directly to the observed calcium handling abnormalities.

• PI3K/AKT signaling disruption: Decreased p-AKT (Ser473) in TECRL-deficient cells leads to downstream alterations in survival pathways and mitochondrial function .

• Mitochondrial fusion defects: Reduced MFN2 expression in TECRL-deficient cells impairs mitochondrial fusion, leading to fragmented mitochondria with compromised function .

These mechanisms create a positive feedback cycle where mitochondrial dysfunction leads to energy deficiency and oxidative stress, which further impairs calcium handling and exacerbates mitochondrial damage, ultimately resulting in electrical instability and arrhythmogenesis.

How do the electrophysiological consequences of TECRL deficiency differ from other arrhythmia-associated genes?

TECRL deficiency produces a distinctive electrophysiological signature that differs from classical LQTS and CPVT genes:

• Action potential abnormalities: TECRL-deficient cardiomyocytes display marked prolongation of early repolarization (APD20) with a trend toward prolongation of later phases (APD50 and APD90) . This pattern differs from KCNQ1-associated LQTS (predominant late phase prolongation) and RYR2-associated CPVT (minimal baseline AP changes).

• Calcium handling profile: TECRL deficiency causes both reduced calcium transient amplitude and elevated diastolic calcium levels , representing a hybrid abnormality pattern between CASQ2-associated CPVT (primarily diastolic leak) and NCX1 dysregulation (impaired calcium extrusion).

• Adrenergic response: Patients with TECRL mutations show QT prolongation and both atrial and ventricular arrhythmias with adrenergic stimulation , representing an overlap between LQTS and CPVT that is relatively unique.

• Inheritance pattern: TECRL-associated arrhythmias follow an autosomal recessive inheritance pattern , unlike the dominant inheritance typical of most LQTS and CPVT genes.

• Cellular triggers: While CASQ2/RYR2-mediated CPVT primarily involves calcium-dependent triggered activity, TECRL dysfunction appears to create substrate for both triggered activity and reentry by affecting both calcium handling and repolarization.

Understanding these distinctive features is essential for accurately identifying patients with TECRL mutations, who may be misdiagnosed with either LQTS or CPVT if genetic testing is limited to canonical genes for these conditions.

What are the optimal strategies for developing TECRL-targeted therapeutics for arrhythmia prevention?

Development of TECRL-targeted therapeutics requires addressing multiple aspects of the underlying pathophysiology:

• Mechanistic targeting priorities:

  • Enhance mitochondrial function and reduce oxidative stress

  • Stabilize calcium handling

  • Modulate PI3K/AKT signaling pathway

  • Restore normal expression of affected proteins (RYR2, CASQ2)

• Small molecule approaches:

  • Mitochondrial antioxidants (MitoQ, SS-31) to reduce ROS-induced damage

  • PI3K/AKT pathway activators to compensate for reduced pathway activity

  • RyR2 stabilizers to prevent abnormal calcium release

• Gene therapy considerations:

  • AAV9-based delivery systems for cardiac-specific TECRL gene replacement

  • CRISPR-based approaches for correction of specific mutations

  • Challenges include the recessive nature of the condition and potential off-target effects

• Drug screening methodology:

  • Patient-derived iPSC-CMs provide the most relevant platform for high-throughput screening

  • Multiparametric assessment combining calcium handling, mitochondrial function, and electrophysiology endpoints

  • Stress protocols that recapitulate adrenergic triggering of arrhythmias in patients

Given TECRL's regulation of mitochondrial function through PI3K/AKT signaling and MFN2 , compounds targeting these pathways represent promising therapeutic directions. The fact that TECRL deficiency leads to release of apoptosis inducing factor (AIF) and cytochrome C from mitochondria suggests that mitochondrial membrane stabilizers might also provide therapeutic benefit.

How should genetic testing and clinical management guidelines be developed for TECRL-associated cardiac disorders?

Comprehensive guidelines for TECRL-associated disorders should address several key aspects:

• Genetic testing recommendations:

  • Include TECRL in comprehensive arrhythmia gene panels for both LQTS and CPVT

  • Consider TECRL testing particularly in cases with features of both LQTS and CPVT

  • Prioritize TECRL analysis in consanguineous families with recessive arrhythmia patterns

  • Test for specific founder mutations in relevant populations (e.g., p.Arg196Gln in French Canadians)

• Clinical surveillance protocol:

  • Regular 12-lead ECG with emphasis on QT measurement during both rest and exercise

  • Exercise stress testing with careful monitoring for arrhythmias and QT dynamics

  • Consider implantable loop recorders for high-risk patients or those with syncope

  • Echocardiography to assess for subclinical structural abnormalities

• Treatment approach:

  • Beta-blockers as first-line therapy for all patients with confirmed TECRL mutations

  • Consider flecainide or other sodium channel blockers for refractory cases

  • Low threshold for implantable cardioverter-defibrillator placement given high SCD risk

  • Lifestyle modifications including exercise restriction and avoidance of QT-prolonging medications

As noted in the literature, TECRL should be considered as a possible cause in patients presenting with stress-induced complex ventricular arrhythmias or cardiac arrest at a young age, whether diagnosed with gene-elusive LQTS or CPVT . The identification of additional families with the same syndrome and genetic defect will help better characterize and categorize the phenotype .

What are the most promising research directions for understanding tissue-specific effects of TECRL dysfunction?

Several innovative research directions hold particular promise for advancing our understanding of TECRL biology:

• Cardiac-specific metabolic regulation:

  • Investigate why TECRL mutations primarily affect cardiac tissue despite TECRL expression in other tissues

  • Explore potential cardiac-specific interaction partners that may explain tissue-restricted phenotypes

  • Examine cardiac-specific metabolic pathways that might be particularly dependent on TECRL function

• Multi-omics integration approaches:

  • Combine transcriptomics, proteomics, and metabolomics data from TECRL-deficient models

  • Apply machine learning algorithms to identify key nodes in affected networks

  • Develop computational models of TECRL's role in cardiac metabolism and electrophysiology

• Developmental considerations:

  • Study TECRL's role during cardiac development and maturation

  • Investigate potential compensatory mechanisms in different developmental stages

  • Examine age-dependent changes in TECRL-associated phenotypes

• Environmental interactions:

  • Explore how environmental factors (diet, exercise, stress) modulate TECRL-associated phenotypes

  • Investigate potential protective or exacerbating factors that could inform lifestyle recommendations

  • Develop personalized risk prediction models incorporating genetic and environmental factors

• Comparative species analysis:

  • Examine species-specific differences in TECRL function and regulation

  • Identify conserved and divergent aspects of TECRL biology across mammals

  • Leverage evolutionary insights to understand fundamental aspects of TECRL function

These research directions should be pursued using complementary approaches including in vitro studies with patient-derived cells, in vivo models with tissue-specific TECRL manipulation, and clinical studies correlating genotype with detailed phenotypic characterization.