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Related Experiment Video

Updated: Apr 18, 2026

In Vitro and In Vivo Assessment of T, B and Myeloid Cells Suppressive Activity and Humoral Responses from Transplant Recipients

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Gerosuppression in confluent cells.

Olga V Leontieva¹, Mikhail V Blagosklonny¹

¹Department of Cell Stress Biology, Roswell Park Cancer Institute, Elms and Carlson Streets, Buffalo, NY 14263, USA.

|January 15, 2015

Summary

Contact inhibition prevents cell senescence by inactivating mTOR (mechanistic target of rapamycin). Reactivating mTOR can trigger senescence, even in dense cultures, mimicking organismal gerosuppression.

Area of Science:

Cellular senescence
Cell cycle regulation
Gerontology

Background:

Contact inhibition is a physiological cell cycle arrest in dense cultures, yet it is poorly understood.
Contact-inhibited cells do not senesce, suggesting a mechanism suppressing senescence (geroconversion).
Mammalian target of rapamycin (mTOR) is inactive in contact-inhibited cells, suppressing geroconversion.

Purpose of the Study:

To extend the gerosuppression model by investigating senescence induction in contact-inhibited cells.
To explore the role of mTOR reactivation in etoposide-induced senescence in confluent cells.
To compare senescence suppression in vitro with gerosuppression observed in vivo.

Main Methods:

Induction of senescence using etoposide in cells at normal and high densities.

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Manipulation of mTOR activity in confluent, contact-inhibited cells.

Analysis of senescence markers (p16, p21) and signaling pathways (mTOR, p-S6, p-Akt) in cell culture and murine tissues.

Main Results:

Etoposide induced senescence in normal cell density but failed in contact-inhibited cells.
Transient mTOR reactivation in etoposide-treated confluent cells promoted geroconversion.
p16, similar to p21, did not induce senescence in high cell density cultures.
Low p-S6 and high p-Akt levels in murine tissues mirrored suppressed geroconversion, contrasting with cell culture findings.

Conclusions:

Suppression of geroconversion in contact-inhibited cells mimics organismal gerosuppression.
mTOR activity is a key regulator of geroconversion, with its inactivation preventing senescence in dense cultures.
In vivo signaling (low p-S6, high p-Akt) supports the concept of inherent gerosuppression in tissues.