Understanding the impact of ageing on ‘active Extracellular Vesicles’ from Mesenchymal Stromal Cells (MSC) and consequences on repair responses: towards novel therapies in wound healing

Poor wound healing is a challenge that is becoming more important with the advancing age of our population and incidence of important co-morbidities such as diabetes.

Estimates suggest that each year 3.8 million patients are managed by the NHS for wounds, with over 130 million patient visits from healthcare staff, at an annual NHS cost of £8.3 billion, of which £5.6 billion is associated with managing non-healing wounds.

Consequently, there is an urgent and unmet need to understand the immune control that becomes impaired with ageing and to develop novel approaches to promote wound healing.

Chronic (non-healing) wounds are a great health burden, both financially and personally, and are a significant and increasing challenge within an ageing society.

A number of approaches (e.g. debridement, topical growth factors and dressings and antibiotics) are taken to manage these hard-to-treat conditions and reduce healing times.

However, some wounds fail to heal and become ‘stalled’ and this typically happens within the inflammatory phase of wound healing.

This is the phase in which the innate immune system acts to both clear any challenge (e.g. microbial or damaged cells) before promoting a ‘repair’ response.

This repair stage is heavily reliant on macrophages which switch from a pro-defence phenotype (‘classically-activated’, often called M1) to a pro-repair phenotype (‘alternatively-activated’, often called M2) to help drive wound healing.

Mesenchymal Stromal Cells (MSC) have great potential for promoting repair responses and it has become increasingly clear over recent years that a major mechanism by which MSC may promote repair is through modulation of immune responses, particularly inflammatory responses and macrophage phenotype.

Extracellular Vesicles (EV) released by MSC (MSC-derived EV: MSCdEV) also promote these beneficial macrophage phenotype changes towards a pro-repair phenotype.

However, MSC from older individuals are much less competent to modulate macrophage phenotype and this may explain the profound defect in repair responses as we age.

This seed-funding will support our programme of work to begin to define a molecular mechanism by which MSC and their EV control macrophage phenotype – a novel mechanism that we hypothesise becomes defective in ageing.

We have recently shown that EV from dying, apoptotic cells (Apoptotic Cell-derived EV: ACdEV) carry a family of inflammation modulating enzymes (Lipoxygenase: LOX).

Different LOX isoforms can promote and inhibit inflammation and the balance of these different isoforms is crucial to deciding the outcome of inflammatory control and wound healing.

We have called these enzyme-carrying EV ‘active EV’ and have shown that these are responsible for promoting repair responses in macrophages through promoting macrophage phenotype change.

Our recent preliminary data now reveals that MSCdEV also carry these same enzymes and, importantly, the activity is altered in MSC from older donors.

This proposed programme of work will now characterise the presence, balance and activity of LOX isoforms within MSC and MSCdEV from older and younger donors.

This will define the altered carriage of LOX isoforms in MSCdEV from older individuals, and crucially whether they are less able to drive macrophages from older and younger individuals towards a ‘pro-repair’ phenotype.

Cellular senescence is also known to have profound effects on the inflammatory environment as we age, promoting a pro-inflammatory (non-repair) environment.

Here, we will also consider the senescent MSCdEV to understand their LOX composition and activity to understand how this may also contribute to the senescence-associated secretome and its profound inflammatory consequences.

This work will provide new insight in to the control of macrophage phenotype and repair responses and those defects that may occur with ageing. It will define the ageing-associated changes in active EV and defects in modulating macrophage repair responses.

This has important implications for MSC-based therapies used clinically for both chronic inflammatory conditions and solid organ transplantation.

Future work will then seek to mitigate these defects through the development of novel approaches to overcome the defect (e.g. through synthetic vesicles carrying the necessary enzymes or their encoding messenger RNA).

Using this approach, we will enable the development of novel therapeutic agents to be targeted for important, debilitating, and hard-to-treat wounds associated with ageing.