Heal Thyself: SGLT2 Inhibition Limits Regenerative Cell Exhaustion and Heals Damaged Vessels

Chronic metabolic dysfunction as a result of type 2 diabetes (T2D) increases susceptibility to the development of ischemic cardiovascular disease (CVD) (1). The search for therapies to improve cardiovascular health in individuals afflicted with T2D has led to the discovery and utilization of a novel class of glucose-lowering drugs called sodium–glucose cotransporter 2 inhibitors (SGLT2i). Located in the proximal tubule of the kidney, the SGLT2 receptor directs the reuptake of glucose and sodium into the circulation (2,3). Inhibition of this pathway results in glucosuria/natriuresis and represents a novel metabolic mechanism to reduce hyperglycemia during T2D.

Several randomized clinical trials in people with and without diabetes have now established a critical role for SGLT2i in the reduction of cardiovascular and cardiorenal events (4,5). While direct myocardial and indirect metabolic effects have been proposed to explain these benefits, recent data suggest that SGLT2 inhibition stimulates vascular repair via increased trafficking of bone marrow–derived provascular progenitor cells essential for vessel regeneration (6–9).

In this issue of Diabetes, Albiero et al. (10) definitively demonstrate that despite low levels of expression of SGLT2 on hematopoietic cells, SGLT2 inhibition with dapagliflozin improved endothelial repair through enhanced recruitment of hematopoietic stem/progenitor cell (HSPC) progeny from the bone marrow (BM) to the site of vessel injury. In concept, circulating HSPC represent critical intermediates in blood vessel homeostasis via the coordination of angiogenic, arteriogenic, and vasculogenic processes (11). Seminal contributions by the Fadini group and others have previously established a significant depletion in circulating provascular HSPC during T2D, which contributes to vascular dysfunction and increased risk of CVD (12–14). To assess the role of HSPC following SGLT2i treatment, streptozotocin (STZ)-treated mice were administered dapagliflozin or vehicle for 2 weeks at a dose that decreased hyperglycemia by 20% and did not alter LKS (Lin⁻/c-kit⁺/Sca-1⁺) progenitor cell frequency in the BM (10).

Albiero et al. first revealed that dapagliflozin administration reduced the frequency of SIGLEC-1–expressing (CD169⁺) macrophages in the BM of STZ-treated mice by 70% (10). Although the role of CD169⁺ macrophages in the M1 versus M2 polarization spectrum is unclear, elevated CD169⁺ macrophage content in the BM of patients with diabetes acts to retain HSPC in the BM niche and prevents HSPC mobilization (15). Indeed, dapagliflozin treatment in STZ-treated mice normalized BM CD169⁺ macrophage content and partially rescued the HSPC mobilization defect in response to granulocyte colony-stimulating factor (10).

Next, the authors examined the effect of improved HSPC mobilization on the induction of carotid artery wound healing. Remarkably, re-endothelialization after denudation injury was decreased 10-fold in hyperglycemic mice, and endothelial healing was significantly improved after dapagliflozin treatment (10). Elegant experiments, involving carotid artery denudation in chimeric mice reconstituted with green fluorescent protein–positive (GFP⁺) BM cells, effectively traced GFP⁺ HSPC progeny localized to the site of carotid injury. Reduced recruitment of GFP⁺ cells to the site of carotid injury in STZ-treated diabetic chimeric mice was reversed by dapagliflozin treatment (10). What was the phenotype of these regenerative GFP⁺ cells? Multiparametric flow cytometry analyses demonstrated GFP⁺/LKS cells were rarely detected (<0.1) at the site of injury, whereas mature monocyte and neutrophil recruitment was abundant, with F4/80⁺ macrophage and CD49d⁺ granulocyte recruitment significantly increased after dapagliflozin treatment (Fig. 1). Previously documented as a provascular population by this group (16), CD49d⁺ granulocyte mobilization, recruitment, and adhesion at the site of injury promoted re-endothelialization after dapagliflozin administration, identifying CD49d⁺ granulocytes as novel therapeutic targets to promote endothelial repair during T2D (10).

Is it simply glucose lowering that should be targeted, or are there unique benefits of SGLT2i beyond glucose lowering on BM cell regenerative flux? To address this question, the authors evaluated the influence of glucose lowering on endothelial wound healing through exogenous insulin administration or use of a ketogenic diet. Notably, insulin reduced systemic blood glucose (25%) and improved carotid endothelial healing—results similar to those seen with dapagliflozin therapy (10). In contrast, administration of a ketone drink did not reduce hyperglycemia but equally preserved endothelial healing (10). Therefore, endogenous vascular repair was stimulated, in part, through distinct alterations in systemic metabolism, including the improvement of glucose control and the induction of ketogenesis.

This report provides key mechanistic insights into cardiovascular protection following SGLT2i administration. Metabolic stabilization in the BM niche altered CD169⁺ macrophage content to augment the differentiation and mobilization of circulating HSPC progeny that recruit to sites of endothelial damage to mediate healing. It is well known that chronic metabolic diseases like T2D increase glucotoxicity and oxidative stress in the BM (17,18) and contribute to a chronic phenotype, termed provascular regenerative cell exhaustion, which alters the balance of HSPC differentiation to favor production of inflammatory versus regenerative cells (18). While several groups have established the potential of SGLT2i to restore provascular progenitor cell content in peripheral blood, Albiero et al. revealed the ability of SGLT2i to modify the BM niche through the production and release of mature provascular macrophage and CD49d⁺ granulocyte subsets sensitive to chronic metabolic abnormalities. Thus, low-dose SGLT2 inhibition may reverse regenerative cell exhaustion and delay the onset or inhibit the progression of vascular dysfunction in patients with early T2D (HbA_1c 6.0–6.5%) (19).

Arguably, the most transformative finding in this study is the introduction of CD49d⁺ granulocytes with vascular-reparative function. Indeed, dapagliflozin treatment enhanced provascular CD49d⁺ granulocyte recruitment to the site of injury and directly improved vascular repair within 3 days of damage (10). Further work on the characterization of these provascular cells in the peripheral circulation and the examination of CD49d⁺ cell function in human patients with T2D administered SGLT2i or placebo is now warranted. This novel vascular regenerative mechanism may also have implications in nondiabetic models of atherosclerosis, such as in ApoE^−/− mice with or without high-fat diet, and using other vascular injury models, such as femoral artery ligation-induced limb ischemia, as a model for lower extremity arterial disease (20).

Collectively, the study of Albiero et al. establishes novel mechanisms that clarify the critical role of BM-derived cellular subsets to directly enhance endothelial healing during diabetes. These findings will usher in a new vascular regenerative paradigm for the translation of metabolism-altering approaches to reverse provascular regenerative cell depletion and dysfunction during chronic metabolic diseases associated with ischemic CVD.