Pterostilbene accelerates wound healing response in diabetic mice through Nrf2 regulation.

Pterostilbene (PTS), known for its diverse beneficial effects via Nuclear factor erythroid-2 related factor (Nrf2) activation, holds potential for Diabetic Foot Ulcer (DFU) treatment. However, PTS-mediated Nrf2 regulation in diabetic wounds has yet to be elucidated. We used IC21 macrophage-conditioned media to simulate complex events that can influence the fibroblast phenotype using L929 cells during the wound healing process under a hyperglycemic microenvironment. We found that PTS attenuated fibroblast migration and alpha-smooth muscle actin (α-SMA) levels and hypoxia-inducible factor- 1 alpha (HIF1α). Furthermore, we demonstrated that wounds in diabetic mice characterized by impaired wound closure in a heightened inflammatory milieu, such as the NOD-like receptor P3 (NLRP3) and intercellular adhesion molecule 1 (ICAM1), and deficient Nrf2 response accompanying lowered Akt signaling and heme oxygenase1 (HO1) expression along with the impaired macrophage M2 marker CD206 expression, was rescued by administration of PTS. Such an elicited response was also compared favorably with the standard treatment using Regranex, a commercially available topical formulation for treating DFUs. Our findings suggest that PTS regulates Nrf2 in diabetic wounds, triggering a pro-wound healing response mediated by macrophages. This insight holds the potential for developing targeted therapies to heal chronic wounds, including DFUs.

Pterostilbene attenuates hemin-induced dysregulation of macrophage M2 polarization via Nrf2 activation in experimental hyperglycemia.

Macrophages exhibit a high degree of plasticity that is physiologically relevant in wound healing, and disruption in normal macrophage response leads to delayed wound closure resulting in chronic wounds. Here, we attempt to discern macrophage responses to hemin via regulation of the nuclear factor-erythroid factor 2-related factor 2 (Nrf2) that could help us better understand the pathophysiology of diabetic foot ulcers (DFU). We demonstrate the alleviation of hemin-mediated Nrf2 suppression and M2 macrophage polarization by pterostilbene (PTS), a proven Nrf2 activator. IC-21 macrophages were treated with hemin under the normoglycemic or hyperglycemic environment with or without PTS and the expression levels of various markers, such as Nrf2 and its downstream target Heme Oxygenase-1 (HO-1), CD206, Ferroportin-1 among others were analyzed using qPCR and Western blot. Our results revealed that hemin under hyperglycemia reduced Nrf2 activation and its downstream targets, M2 polarization, and the induction of a proinflammatory cellular environment, and interestingly all of these were remedied by PTS treatment. Gelatin zymography of matrix metalloproteinase2 (MMP2) expression revealed that hemin under hyperglycemic condition significantly elevated MMP2 expression, which was reversed by PTS treatment. Further proteomic analysis using liquid chromatography with tandem mass spectrometry (LC-MS/MS) revealed a heightened cellular stress profile accompanying inflammation that was suppressed by PTS. This study has furthered our understanding on the role of Nrf2 in attenuating hemin-induced perturbations in macrophage responses and suggests a potential therapeutic target in the management of DFU.

Nrf2 driven macrophage responses in diverse pathophysiological contexts: Disparate pieces from a shared molecular puzzle.

The wide anatomical distribution of macrophages and their vast array of functions match various polarization states and their involvement in homeostasis and disease. The confluence of different cellular signaling networks, including direct involvement in inflammation, at the doorstep of the transcription factor Nuclear Factor- erythroid (NF-E2) p45-related factor 2 (Nrf2) activation raises the importance of deciphering the molecular circuitry at the background of multiple-discrete and antagonistic yet flexible and contextual pathways. While we primarily focus on wound healing and repair mechanisms that are affected in diabetic foot ulcers (DFUs), we strive to explore the striking similarities and differences in molecular events including inflammation, angiogenesis, and fibrosis during tissue injury and wound persistence that accumulates pro-inflammatory senescent macrophages, as a means to identify possible targets or cellular mediators to lessen DFU disease burden. In addition, the role of iron in the modulation of Nrf2 response in macrophages is crucial and reviewed here. Targeted approaches, unlike conventional treatments, in DFU management will require the review and re-assessment of mediators with relevance to other pathological conditions.

Metabolic reprogramming and immune regulation in viral diseases.

The recent outbreak and transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) worldwide and the ensuing coronavirus disease 2019 (COVID-19) pandemic has left us scrambling for ways to contain the disease and develop vaccines that are safe and effective. Equally important, understanding the impact of the virus on the host system in convalescent patients, healthy otherwise or with co-morbidities, is expected to aid in developing effective strategies in the management of patients afflicted with the disease. Viruses possess the uncanny ability to redirect host metabolism to serve their needs and also limit host immune response to ensure their survival. An ever-increasingly powerful approach uses metabolomics to uncover diverse molecular signatures that influence a wide array of host signalling networks in different viral infections. This would also help integrate experimental findings from individual studies to yield robust evidence. In addition, unravelling the molecular mechanisms harnessed by both viruses and tumours in their host metabolism will help broaden the repertoire of therapeutic tools available to combat viral disease.

Dysregulation of Nrf2 redox pathway in macrophages under diabetic microenvironment.

In the present study, we characterized the aberration in Nrf2 signaling in macrophages under a hyperglycemic microenvironment that reflects diabetic wounds in vitro and studied the effect of an Nrf2 activator pterostilbene (PTS) in these experimental conditions. Macrophages were exposed to pro-inflammatory cytokines TNFα and IFNγ with (HG+) or without high glucose (NG+) followed by the treatment with or without PTS. Western blotting was undertaken to assess the Nrf2 translocation from cytosol to nucleus followed by its downstream and upstream mediators, heme oxygenase-1 and Akt, respectively, the latter via phosphorylation. Quantitative PCR was also carried out to check the expression of macrophage mannose receptor CD206. We found a 2-fold reduction in the activation of Nrf2 in the HG+ group at 24 h compared to NG+, which was significantly improved by the treatment with PTS. Reduction in the levels of heme oxygenase-1 and phosphorylation of Akt in the HG+ group was also ameliorated by PTS. Furthermore, the gene expression of CD206 that was significantly reduced in the HG+ group was also restored by PTS treatment. The disruption of Nrf2 signaling in macrophages in a hyperglycemic microenvironment in vitro may indeed reflect diabetic wounds, as opposed to other non-diabetic wounds.

Macrophage mediation in normal and diabetic wound healing responses.

PURPOSE: The failure in timely healing of wounds is a central feature in chronic wounds that leads to physiological, psychological and economic burdens. Macrophages have been demonstrated to have various functions in wounds including host defense, the promotion and resolution of inflammation, the removal of apoptotic cells and tissue restoration following injury. Accumulated evidence suggests that macrophage dysfunction is a component of the pathogenesis of non-healing wounds. While the overall signaling cascades have been well understood, their complex interplay and a detailed characterization of events that are disrupted in chronic wounds have still not emerged satisfactorily. METHODS: The existing literature was reviewed to summarize the regulation of macrophage polarization in wound closure and dysregulation in non-healing wounds. Further, the review also underscored the role of Nrf2 in promoting macrophage-mediated regulation in wound responses and in particular, macrophage involvement in iron homeostasis that is impaired in chronic wounds such as in diabetes. RESULTS: The mechanisms involved in the reprogramming of macrophage subtypes in chronic wounds are still emerging. Furthermore, treating non-healing wounds has increasingly been shifting focus from generic treatments to the development of targeted therapies. Increasing evidence suggests the need for modeling wound tissue in vitro which may very well serve a critical aspect to characterize the relevant factors that sustain chronic wounds in vivo such as the constant iron overload at the wound site from recurrent infection and bleeding. CONCLUSION: The development of targeted therapies and also developing a reliable means to monitor assisted healing of chronic wounds are two major goals to be pursued. In addition, identifying molecular targets that can regulate macrophages to aid tissue restoration in chronic wounds would serve the crucial step in realizing both aforementioned goals.

Mast cell chymase degrades the alarmins heat shock protein 70, biglycan, HMGB1, and interleukin-33 (IL-33) and limits danger-induced inflammation.

During infection and tissue damage, virulence factors and alarmins are pro-inflammatory and induce activation of various immune cells including macrophages and mast cells (MCs). Activated MCs instantly release preformed inflammatory mediators, including several proteases. The chymase mouse mast cell protease (MCPT)-4 is thought to be pro-inflammatory, whereas human chymase also degrades pro-inflammatory cytokines, suggesting that chymase instead limits inflammation. Here we explored the contribution of MCPT4 and human chymase to the control of danger-induced inflammation. We found that protein extracts from wild type (WT), carboxypeptidase A3-, and MCPT6-deficient mice and MCs and recombinant human chymase efficiently degrade the Trichinella spiralis virulence factor heat shock protein 70 (Hsp70) as well as endogenous Hsp70. MC-(W(sash))-, serglycin-, NDST2-, and MCPT4-deficient extracts lacked this capacity, indicating that chymase is responsible for the degradation. Chymase, but not MC tryptase, also degraded other alarmins, i.e. biglycan, HMGB1, and IL-33, a degradation that was efficiently blocked by the chymase inhibitor chymostatin. IL-7, IL-22, GM-CSF, and CCL2 were resistant to chymase degradation. MCPT4-deficient conditions ex vivo and in vivo showed no reduction in added Hsp70 and only minor reduction of IL-33. Peritoneal challenge with Hsp70 resulted in increased neutrophil recruitment and TNF-α levels in the MCPT4-deficient mice, whereas IL-6 and CCL2 levels were similar to the levels found in WT mice. The rapid and MC chymase-specific degradation of virulence factors and alarmins may depend on the presence of accessible extended recognition cleavage sites in target substrates and suggests a protective and regulatory role of MC chymase during danger-induced inflammation.