Recombinant Human Transmembrane protein 150C (TMEM150C)

What is TMEM150C and what is its primary function?

TMEM150C/Tentonin3 functions as a regulator of mechano-gated ion channels rather than as a mechanosensitive ion channel itself. While initially proposed to mediate mechano-activated current in proprioceptive neurons, research now demonstrates that TMEM150C modulates the activity of established mechano-gated ion channels including Piezo1, Piezo2, and TREK-1 .

When expressed alone in specialized cell lines (HEK293T ΔP1 cells lacking endogenous Piezo1), TMEM150C does not confer mechanosensitivity, strongly suggesting its role as a regulatory protein rather than an independent ion channel .

Where is TMEM150C expressed in the nervous system?

TMEM150C was initially identified in proprioceptive neurons, but its expression profile has been expanded to include trigeminal neurons. Research has demonstrated co-expression with Piezo2 in trigeminal neurons, suggesting its regulatory role extends beyond proprioception to other mechanosensory systems .

Is TMEM150C evolutionarily conserved across species?

TMEM150C shows significant evolutionary conservation among vertebrates. Studies have cloned TMEM150C from the trigeminal neurons of the tactile-foraging domestic duck, demonstrating 87% protein identity with mouse TMEM150C . Both orthologs exhibit similar functional properties when co-expressed with mechano-gated channels, indicating that TMEM150C's regulatory function is preserved across distantly related vertebrate species .

How does TMEM150C modify the properties of mechano-gated ion channels?

TMEM150C exerts distinct modulatory effects on different mechano-gated channels, as summarized in the following table:

These effects were consistent across different methods of mechanical stimulation, indicating that TMEM150C is a general regulator of mechanosensitivity regardless of the mechanical stimulus applied .

What molecular evidence supports TMEM150C's role as a channel regulator?

Several lines of molecular evidence support TMEM150C as a regulator rather than an ion channel:

• TMEM150C co-immunoprecipitates with both TREK-1 and Piezo2, suggesting it forms a complex with these channels or exists within the same lipid domain .

• When co-expressed with TREK-1 (a potassium-selective channel), the resultant mechanically-activated current maintains potassium selectivity, consistent with TMEM150C modulating TREK-1 rather than forming an independent non-selective cation channel .

• Co-expression with TMEM150C does not change the reversal potential of Piezo2-mediated currents, indicating that TMEM150C does not alter ion selectivity of the channel .

• The voltage dependence of inactivation remains characteristic of the host channel (e.g., Piezo2) even when modified by TMEM150C, suggesting preservation of fundamental channel properties while selectively enhancing particular aspects of channel function .

How do I address contradictory findings regarding TMEM150C's role in mechanosensitivity?

Recent research has questioned TMEM150C's role, with at least one study unable to evoke mechanosensitive currents in neuroblastoma cells expressing TMEM150C, despite using three different mechanical stimulation methods (indentation, membrane stretch, and substrate deflection) .

When addressing such contradictions, consider:

• Experimental context differences: Cell type, expression levels, and recording conditions may affect results.

• Technical challenges in knockout models: One study found that ablation of the Tmem150c gene using a LacZ cassette insertion was incomplete in sensory neurons of dorsal root ganglia (DRG) .

• Potential requirement for co-factors: TMEM150C may require specific cellular components or co-factors that vary between experimental systems.

• Methodological differences in mechanical stimulation: The parameters of mechanical stimulation (force, duration, rate of application) may influence results.

• Construct design: Different tagged versions or expression constructs of TMEM150C may have altered functionality.

What expression systems are recommended for studying TMEM150C function?

For rigorous investigation of TMEM150C function:

• Use HEK293T ΔP1 cells (PIEZO1 knockout cells) to eliminate background mechanosensitive currents that could confound interpretation .

• For co-expression studies, maintain consistent expression levels by using standardized transfection protocols and expression vectors.

• Include appropriate controls: cells expressing TMEM150C alone, cells expressing only the channel of interest, and cells co-expressing both proteins .

• Consider using inducible expression systems to control timing and level of protein expression.

• For neuronal studies, primary cultures of trigeminal or dorsal root ganglion neurons provide relevant physiological context .

What are effective methods for measuring TMEM150C's effects on mechanosensitivity?

Two independent methods have been validated for assessing TMEM150C's effects:

• Mechanical indentation: Using calibrated probes to indent the cell membrane while recording whole-cell currents. This approach revealed TMEM150C's effects on Piezo2 activation threshold and inactivation kinetics .

• High-speed pressure clamp (HSPC): Applying negative pressure to the patch pipette to induce membrane stretch. This method confirmed TMEM150C's effects on TREK-1 inactivation kinetics .

Key parameters to measure include:

• Activation threshold (minimum stimulus required to evoke detectable current)

• Peak current amplitude

• Inactivation kinetics (τ inact) at different voltages

• Persistent current after stimulus removal

• Current-voltage relationships to assess ion selectivity

How should I design TMEM150C knockout or knockdown experiments?

Based on previous challenges with TMEM150C genetic models:

• Verify knockout efficiency: A mouse model using LacZ cassette insertion with a splice acceptor failed to achieve complete ablation of TMEM150C in DRG neurons .

• Consider multiple targeting strategies: Both transcript disruption (e.g., LacZ insertion) and gene deletion (CRISPR/Cas9) approaches have been attempted .

• Validate knockouts at multiple levels:

  • Genomic PCR to confirm targeting

  • RT-PCR to assess transcript levels

  • Western blotting or immunostaining to verify protein absence

  • Functional assays to confirm phenotypic changes

• Assess effects in multiple neuron populations (proprioceptive, trigeminal, DRG) due to potential differences in regulation or expression .

What are potential mechanisms by which TMEM150C regulates mechano-gated channels?

Several mechanisms warrant investigation:

• Direct protein-protein interaction: Co-immunoprecipitation studies suggest TMEM150C forms complexes with mechano-gated channels .

• Membrane environment modification: TMEM150C may alter local lipid composition or membrane properties, affecting channel gating.

• Cytoskeletal interaction: TMEM150C could influence interactions between mechano-gated channels and cytoskeletal components, which are known to affect mechanosensitivity .

• Modulation of post-translational modifications: TMEM150C might influence phosphorylation or other modifications of mechano-gated channels.

• Stabilization of open channel states: The prolonged inactivation kinetics and persistent current suggest TMEM150C may stabilize open channel conformations .

How can recombinant TMEM150C be optimized for structural and functional studies?

For optimal production and utilization of recombinant TMEM150C:

• Expression tags: rho-1D4 tagged versions have been successfully used in functional studies .

• Expression systems: Mammalian cell expression systems are recommended for proper folding and post-translational modifications of this multi-pass transmembrane protein .

• Purification considerations: Due to its transmembrane nature, careful selection of detergents for solubilization is critical.

• Functional validation: Since TMEM150C functions as a regulator rather than an independent channel, its activity should be validated through co-expression with known mechano-gated channels in electrophysiological assays .

• Structural studies: Consider lipid nanodiscs or other membrane mimetics to maintain native conformation for structural analysis.

What is the significance of TMEM150C's effect on mechano-gated channel inactivation kinetics?

The prolongation of inactivation kinetics by TMEM150C has profound physiological implications:

• Neuronal excitability: Longer-lasting mechanically activated currents could enhance neuronal excitability in response to mechanical stimuli .

• Sensory adaptation: Modified inactivation kinetics may alter how quickly sensory neurons adapt to sustained mechanical stimuli .

• Signal integration: Prolonged currents provide a larger temporal window for integration of mechanical signals with other sensory inputs.

• Tissue-specific tuning: Different expression levels of TMEM150C across tissues may help tune mechanosensitivity to specific physiological requirements .

• Pathophysiological relevance: Dysregulation of TMEM150C could potentially contribute to altered mechanosensitivity in conditions like mechanical hyperalgesia or proprioceptive disorders.

How do I interpret changes in mechanosensitive currents when studying TMEM150C?

When analyzing mechanosensitive currents in the context of TMEM150C research:

• Distinguish threshold effects from kinetic effects: TMEM150C appears to have channel-specific effects on activation threshold (primarily affecting Piezo2) versus inactivation kinetics (affecting all tested channels) .

• Consider voltage dependence: The effects of TMEM150C on inactivation kinetics are maintained across voltages, preserving the voltage-dependent properties characteristic of the parent channel .

• Assess persistent currents: The presence of current persisting after stimulus removal appears to be specific to TMEM150C-Piezo1 interactions and may serve as a signature of TMEM150C activity .

• Evaluate dose-dependency: Consider whether TMEM150C effects scale with expression level or exhibit threshold-dependent effects.

What common pitfalls should I avoid when researching TMEM150C?

Based on the literature, researchers should be aware of:

• Background mechanosensitivity: Wild-type HEK293T cells express endogenous Piezo1, which can confound results. Using PIEZO1-knockout cell lines (HEK293T ΔP1) is recommended .

• Incomplete genetic ablation: Gene disruption strategies may not achieve complete knockout, as observed in a mouse model using LacZ cassette insertion .

• Mistaking modulation for direct channel activity: The initial characterization of TMEM150C suggested it was a mechanosensitive ion channel, but subsequent evidence supports a regulatory role .

• Overlooking species differences: While functionally conserved, there are sequence differences between species (e.g., 87% identity between duck and mouse orthologs) that could affect specific interactions or antibody recognition .

• Neglecting controls for expression levels: Changes in channel properties might be influenced by expression levels, requiring careful control of transfection conditions and quantification of protein expression.