Cellular senescence is an altered cell state associated with permanent cell cycle arrest and an immunogenic, pro-inflammatory secretome that can contribute to the development and progression of age-related diseases. Because cellular senescence can occur in different cell types (i.e. pancreatic beta cells, vascular smooth muscle cells, astrocytes) that undertake different biological functions, then their appearance can manifest differently and we refer to these manifestations as different diseases. These include, diabetes, cardiovascular disease, COPD and cancer. The mechanisms by which senescent cells can cause disease include:
(1) Loss of cellular regenerative capacity.
(2) Loss of normal cell function.
(3) Persistent pro-inflammatory tissue damage.
(4) Altering the behaviour of neighbouring cells.
(5) Protease-mediated degradation of extracellular structural proteins.
Although scientists researching cell senescence have long suspected that senescent cells play an important role in ageing and age-related disease, convincing evidence had not been provided until 2011 when Scientists from the Mayo Clinic in the US published their findings on the elimination of senescent cells in mice. The elimination of senescent cells using transgenic (genetically engineered) mice delayed the onset of disease, thereby increasing healthspan. However, likely owing to the use of an accelerated ageing mouse model, no life extension was observed in this instance. However, a follow-up study by the same group using naturally aged mice lead to delayed tumorigenesis and reduced age-related decline leading to significant increase (up to 35%) in lifespan. Studies like these thus provide a convincing rationale for developing therapeutic approaches for targeting senescent cells, so-called “senotherapeutics”. These may include:
- Specifically inducing cell death in senescent cells (i.e. small-molecule compounds).
- Inhibiting the senescent secretome (i.e. inhibitors of inflammation).
- Preventing senescence induction (i.e. telomerase activators, geroprotectors).
- Boost immune response towards senescent cells (i.e. immunotherapy).
A few recent studies have published findings regarding the elimination of senescent cells by small-molecule compounds. Wang et al (2016) identified the compound ABT-263 as a potent inducer of cell death in senescent cells leading to rejuvenation of aged tissue stem cells. In another study, Yosef et al (2016) identified ABT-737 which through the elimination of senescent cells from the epidermis of the skin of mice lead to increased hair-follicle stem cell proliferation. Both ABT-263 and ABT-737 inhibit proteins (BCL-2 family) known to play a role in cell survival.
Studies focused on the elimination of senescent cells are only beginning to emerge and will no doubt gain momentum as they show tremendous potential for improving health and wellbeing. One intriguing notion that may arise from this research is concerned with the question of whether it may one day be possible to treat many diseases with a single drug. If senescent cells play a role in the development of many different diseases, then a drug that can eliminate senescent cells in all cell types could act as both a preventative and a treatment for many diseases.
One of the obstacles preventing research into senotherapeutics from advancing and ultimately becoming translational to help increase healthspan of individuals within the general public, is funding. However, this has not discouraged some researchers who were determined enough to acquire funding through the help of crowdfunding. The Major Mouse Testing Programme (MMTP) raised over $50,000 towards research focused on eliminating senescent cells and is still ongoing (Click Here).
A new start-up company, CellAge (click here) is also interested in targeting senescent cells and has recently announced a crowdfunding campaign (click here) to raise funds for their ongoing research. CellAge aims are to “Increase human healthspan and reduce the incidence of age-related diseases by helping the human body eliminate senescent cells. Our breakthrough technology concept harvests the promise of synthetic biology and recent findings in ageing research to deliver novel products and therapies to enable people to live healthier longer lives”
So if you are interested in stimulating research in this field for the benefit of all, then please make a donation (link here).