Aging is at the origin of a significant number of diseases and cancers, for which the epistemological link is increasingly detailed. At the cellular level, the accumulation of senescent cells (SC) in tissues emerges as a key factor in aging. It is now well established that SC can be either eliminated by our immune system (pre-oncogenic SC for instance) but also can accumulate progressively during life and be tolerated in our tissues. We still do not know the molecular events regulating senescence immune clearance. Those SC, appearing even during the youth (i.e., the melanocytic naevi), are not eliminated despite a potent immune system and can be maintained for decades. This suggests that immune checkpoints expressed by SC must regulate their immunogenicity.

We show that SC, elicited by various stressors other than oncogenic activation, triggers immune escape toward natural killer (NK) cells. We reveal that SC reshuffle their glycocalyx composition, toward a marked increase in the ganglioside content, including the appearance of disialylated ganglioside GD3. The high level of GD3 leads to a strong immunosuppressive signal affecting NK cell-mediated immunosurveillance. In lung fibrosis mouse model, senescent cell-dependent NK cell immunosuppression is blunted by in vivoadministration of anti-GD3 monoclonal antibodies leading to a clear anti-fibrotic effect. These results demonstrate that GD3 upregulation in SC drives a switch from immune clearance toward immune tolerance. Therefore, we propose that GD3 level acts as a Senescence Immune Checkpoint (SIC) that determine senescent cell fate (Iltis et al., 2021, preprint BioRxiv DOI 10.1101/2021.04.23.440408; Patent ADN11450685PR).

Older adults (≥65 years) have increased morbidity and mortality from skin infections and cancers, and reduced vaccine efficacy. There is a need to improve health-span in older adults, reducing the burden on health services and improving quality of life.

We have observed that older adults have reduced cutaneous antigen recall responses as compared to young – due reduced number of T-cells and Dendritic cells recruited to the site of antigen challenge. Surprisingly, we also found that older adults have an inflammatory response to saline challenge – which negatively correlated with antigen-specific cutaneous immunity. The aim of this project was to identify which cells were responsible for the inflammatory response to saline and in turn identify if it could be therapeutically targeted to boost immunity in older adults.

We observed that inflammatory monocytes were recruited to the site of saline challenge. Inflammatory monocytes were recruited irrespective of what was injected into skin (air, antigen or saline) and was an inappropriate damage response to needle challenge. Inflammatory monocytes were recruited by CCL2 produced by senescent fibroblasts. The inflammatory monocytes expressed COX2 and produced prostaglandin E2 (PGE2) which in turn inhibited resident memory T cells found in the skin – blocking antigen-specific immunity. Blockade of the inflammatory monocytes cascade utilising either a p38-MAPK inhibitor or Vitamin-D3 resulted in significantly less monocytes infiltrating the skin and in turn reduced production of PGE2 which overall led to a restoration of antigen-specific immunity.

The findings here, propose two therapeutic options to boost immunity in older adults.

The rapidly developing field of cellular senescence has grown beyond a process of merely removing unwanted cells to playing key roles in both physiology and pathology.  Within the context of tissue repair, for example, transient senescence is required for wound healing, while chronic senescence drives tissue over-scarring/fibrosis. As the diverse functions of senescent cells in the tissue are continuing to be revealed, the upstream regulation of this phenomena remains ill-defined.  For instance, it has been debated whether wound-induced senescence arises through intrinsic cellular program or environmental factors (or both).  We have found that specific inflammatory conditions in the skin can induce senescence in dermal cells.  Interestingly, these senescent cells can secrete cytokines that can promulgate the inflammatory response that is a hallmark of senescence.  As such we have uncovered a feedback loop in which inflammation is both a cause and consequence of senescence and thus a target for therapeutic intervention.

Skin tissue engineering aimed at faithfully recapitulating all the functions of the in vivo skin has made remarkable progress over the years but still represents a major challenge to repair skin damage, develop drugs and test cosmetics. One of the main limitations is the lack of vascularization and perfusion in reconstructed tissues for i) oxygen and nutrients transport and ii) waste disposal. Vascularization of reconstructed tissues is thus one of the remaining hurdles to be considered to improve both the functionality and viability of skin grafts and the relevance of in vitro applications such as basic research (e.g. study vascular remodeling during wound healing, aging, cancer, etc) but also for the evaluation of drug efficacy and toxicity in cosmetic and pharmaceutical research (e.g. screening pro- and anti-angiogenic drugs, evaluation of systemic toxicity, percutaneous absorption of chemicals and drugs). I will thus focus on state-of-the art manufacturing strategies and provide perspectives on future directions in prevascularized skin tissue engineering.

During cold exposure, sympathetic vasoconstriction occurs in the skin, followed by restorative vasodilation, that acts to restore blood flow to the skin. These phases are crucial to preventing heat loss and cold-induced injuries.  We have developed a murine model of cold exposure and have investigated the mechanisms involved. We identified the role of the cold-sensitive transient receptor potential (TRP) A1, M8 receptors as vascular cold sensors in mouse skin that initiate the sympathetic vasoconstriction and that the vasodilator neuropeptide CGRP is in part responsible for the vasodilator phase.

Ageing is linked with increased vulnerability to the cold. We have used our murine model, to investigate how cutaneous vascular responses to local environmental cooling are affected. We find changes with moderate ageing that include reduced TRPM8 gene/protein expression. The chemical blockade of the residual TRPA1/TRPM8 component substantially diminished the response in aged, compared with young mice. This implies the reliance of the already reduced cold-induced vascular response in ageing mice on remaining TRP receptor activity. The sympathetic-induced vasoconstriction was also related to the downregulation of the α_2c adrenoceptor expression in ageing. To summarise, the cold-induced vascular response is important for sensing cold and retaining body heat and health.

These findings reveal that cold sensors, essential for this neurovascular pathway, decline as ageing onsets. We are now investigating how the vascular cold response may be altered in diabetic conditions with changes that are distinct from those involved in ageing.

Propranolol, a nonselective β-adrenergic receptor blocker, is the first-line treatment for severe infantile hemangiomas (IH). The antitumor effect of propranolol is still largely misunderstood, due to the lack of a validated in vitro model of IH. Aquaporin-1 (AQP1), an aqueous channel modulated in angiogenesis and in tumor cell migration, was decreased in propranolol treated mice and correlated with tumor growth inhibition, whereas overexpression was associated with increased tumor growth. We therefore looked at AQP1 in IH, which also made it possible to identify interstitial cell named telocytes (TC). Theses recently described interstitial cells are characterized by long cytoplasmic processes, the telopods, which form a three-dimensional communication network between cells, in multiple organs including the skin, especially around dermal vessels.

The localization and markers of TC have been studied in a panel of HI, healthy skin and other vascular tumors. Then from fresh IH tissue, three cell types were isolated and cultured for functional study: endothelial cells, pericytes and telocytes. To study the functional role of TC in the pathophysiology of IH and its response to propranolol, we performed capillary like tube formation assays, seeding IH endothelial cells, pericytes and telocytes together as an IH model. We then studied the response to propranolol with AQP1 downregulated by shRNA. Moreover, we quantified adrenergic agonist catecholamines in IH tissues and studied in our model their role in the pathophysiology of IH and in propranolol response.

Our immunostaining analysis revealed that expression profile AQP1 is different in IH compared to other vascular tumors. Furthermore, AQP1 expression is exclusively restricted to perivascular TC in IH. Our in vitro IH model was then instrumental into identifying the roles of AQP1 and noradrenaline in propranolol response.

We conclude that the IH’s sensitivity to propranolol depends on crosstalk between the endothelial cells, pericytes and telocytes in the context of a high local amount of local NA.