Cell-type-specific quantification of protein synthesis in vivo

Protein synthesis is a fundamental process in cellular function and regulation. While broadly conserved, its regulation varies across cell types, influencing cell fate and physiological outcomes. Traditional methods for measuring protein synthesis rely on radiolabeled amino acids or analogs, which require specialized conditions. These methods are often limited to simpler organisms like yeast and bacteria. Application in mammalian systems in vivo has been limited due to technical challenges. Recent advances include the development of O-propargyl-puromycin (OP-Puro), an amino acid analog that allows for in vivo detection of protein synthesis. This compound incorporates into nascent polypeptides and can be visualized using click chemistry with fluorescent azides. These innovations have enabled more precise quantification of protein synthesis at the single-cell level in mammalian systems. However, the adaptation of these techniques to diverse tissues and cell types remains an active area of investigation.

This study aims to provide a detailed protocol for measuring cell-type-specific protein synthesis in vivo using OP-Puro. The goal is to quantify protein synthesis rates in individual cells, particularly in bone marrow-derived cells such as hematopoietic stem cells (HSCs). The method is designed to be broadly applicable across mammalian tissues. The protocol involves administering OP-Puro to mice and isolating cells for analysis via flow cytometry. By detecting OP-Puro incorporation, the study enables the measurement of protein synthesis per hour in specific cell populations. The approach is intended to overcome limitations of traditional methods by allowing in vivo analysis without requiring specialized growth conditions. The study also seeks to demonstrate the utility of this technique by showing differences in protein synthesis rates between HSCs and other hematopoietic cells.

The protocol involves administering OP-Puro to mice and isolating bone marrow cells one hour post-treatment. OP-Puro is a puromycin analog with a terminal alkyne group that incorporates into nascent proteins. The compound is detected using click chemistry, which links it to a fluorescently tagged azide. Flow cytometry is then used to quantify the amount of OP-Puro incorporated per cell. The process includes harvesting cells, preparing them for flow cytometry, and analyzing fluorescence to estimate protein synthesis rates. The method is optimized for rapid execution, allowing for measurements to be completed within 8–10 hours for a cohort of six mice. The technique is adaptable to other cell types and tissues, making it suitable for broader applications in mammalian systems. The use of click chemistry ensures specificity and sensitivity in detecting OP-Puro incorporation.

The study demonstrates that hematopoietic stem cells (HSCs) exhibit significantly lower rates of protein synthesis compared to other hematopoietic cells. The protocol enables the quantification of protein synthesis per hour in individual cells using flow cytometry. OP-Puro incorporation is detected via click chemistry with fluorescent azides, allowing for precise measurement of synthesis rates. The method is validated by showing consistent results across six mice within an 8–10 hour timeframe. The technique is shown to be highly sensitive and specific, with minimal background fluorescence. The incorporation of OP-Puro into nascent proteins is confirmed through fluorescence detection. The study also highlights the adaptability of the method to other cell types and tissues in vivo. The results suggest that cell-type-specific differences in protein synthesis can be reliably measured using this approach.

The study concludes that the described protocol allows for accurate and rapid quantification of protein synthesis in individual cells in vivo. The use of OP-Puro and click chemistry enables detection of synthesis rates in hematopoietic stem cells (HSCs) and other cell types. The findings suggest that HSCs have lower protein synthesis rates compared to other hematopoietic cells. The protocol is efficient, requiring only 8–10 hours to process a cohort of six mice. The method is adaptable to various mammalian tissues and cell types. The authors propose that this approach can be used to investigate cell-type-specific regulation of protein synthesis in diverse physiological contexts. The study supports the use of OP-Puro as a reliable tool for in vivo protein synthesis measurement. The technique provides a valuable alternative to traditional radiolabeled methods in mammalian systems.