Old age begins with familiar things getting stiffer: skin, joints, blood vessel walls. The intestine is no exception. Its muscular coat accumulates collagen with age, and the tissue stops being elastic. This used to be seen as simply a consequence of wear and tear, but a new study shows that stiffness itself is a command that makes smooth muscle cells forget their job.
In the membrane of these cells sits the protein Piezo1, a mechanosensitive ion channel. When a stiff environment stretches the membrane, the channel opens and lets calcium in. Calcium triggers a signaling cascade that reaches the nucleus and switches the genetic program: the cell stops producing contractile proteins and starts secreting components of the extracellular matrix, that is, building material that makes the tissue even stiffer. It becomes a vicious circle.
The researchers tested this in mice. In old animals, intestinal transit slowed almost twofold by 24 months, and the contraction force of muscle strips dropped by up to fivefold. At the same time, the proportion of contractile smooth muscle cells decreased from 91.3% to 76.1%. Then the scientists deleted Piezo1 only in smooth muscle cells and repeated the measurements. In such mice, the intestine kept working like that of young animals even at 24 months, which is equivalent to about 70 human years.
In cell culture on a stiff substrate (50 kPa), contractile markers were suppressed, while on a soft one (1 kPa) they were not. Inhibitors of calcineurin and NFAT abolished this effect, confirming the pathway: stiffness → Piezo1 → calcium → calcineurin → NFAT → synthetic phenotype. In humans, PIEZO1 expression in the colon positively correlated with age, and carriers of the hyperfunctional variant E756del under 50 showed a tendency toward slower transit.
Previously, age-related dysmotility was explained by nerve degeneration or loss of interstitial cells of Cajal. Now it appears that the main culprit may be in the muscle cells themselves, which hear the stiffness of their environment and stop contracting. This changes the therapeutic approach: instead of trying to reverse remodeling that has already occurred, one can block the mechanosensitive pathway itself, preserving motility into deep old age.
In mice with Piezo1 deleted in intestinal smooth muscle, the gut kept working like that of young animals even at 24 months, which is equivalent to about 70 human years. Meanwhile, activating the channel in young mice slowed transit to the level of old animals in just two weeks.
In Liu Cixin's novel The Three-Body Problem, an alien civilization uses sophons to block fundamental physics. Here the mechanosensitive channel Piezo1 acts as a molecular sophon: it intercepts the physical signal of stiffness and rewrites the cell's program, making it forget its contractile function.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.