After reconstitution, will the activity of the recombinant protein significantly decrease if stored at 4°C for one week?

Repeated freeze-thaw cycles of the entire vial are not recommended. A more practical approach is to aliquot by single-use amount on the day of reconstitution. For example, if you add 10 ng/mL at a time, calculate the amount needed per use based on the culture volume, aliquot into 20 to 50 µL per tube, and store at -80°C. If used frequently within a week, take 3 to 5 tubes and place them at 4°C as a weekly working solution, thaw only what you need, and discard after 72 hours. The working solution must be supplemented with the carrier protein 0.1% BSA and used with low-protein-binding tubes. Do not use buffers containing sodium azide, as it will inhibit cell experiments. This avoids repeated freeze-thaw cycles and shortens the 4°C storage time to about 3 days.

I've worked with EGF and FGF types. The most common cause of activity loss isn't time, but adsorption and contamination. For reconstitution, don't use pure water and leave it for extended periods. After reconstitution, I recommend diluting to near working concentration with PBS or Tris buffer containing 0.1% BSA, keeping pH between 7.2 and 7.4. Tubes stored at 4°C should ideally be low-adsorption PP or siliconized tubes; regular EP tubes show significant adsorption of low-concentration growth factors. During handling, aliquot quickly in a biosafety cabinet, avoiding repeated opening of caps and hand warmth. One more detail: confirm that the BSA is endotoxin-free and cell culture grade, otherwise it will introduce new variables. Given your usage density, I recommend preparing working solution on a weekly schedule, not exceeding 5 days at 4°C; activity loss can be more controllable than repeated freeze-thaw cycles.

Adding 0.1% BSA and storing at 4°C, EGF activity generally will not be completely lost within one week, but it will decline; the extent depends on buffer pH and aseptic technique. EGF is a small peptide and readily adsorbs to tube walls and is susceptible to microbial degradation. The mesenchymal stem cell proliferation assay itself has moderate sensitivity; if activity declines by 20% to 30% at 10 ng/mL, obvious differences may not be seen, but the dose-response curve will shift right. It is recommended to perform a parallel comparison: take samples from the -80°C aliquot and the sample stored at 4°C for 7 days on the same day, and run CCK-8 or EdU proliferation to determine the EC50. If the EC50 deviation is less than 20%, it can be considered acceptable within one week; if strict conclusions are needed, do not judge based only on morphological changes.