With the arrival of an aging population, the incidence of bone and soft tissue infections is increasing, with spinal infections being common (1–3). Kehrer found that the incidence of spinal infections has increased dramatically to 2.2-5.8/100000 since 2000 (4). If spinal infections are not taken seriously or if treatment is ineffective, it can easily lead to the spread of infection and the formation of abscesses in the spine, causing serious complications such as nerve root or spinal cord compression and neurological dysfunction. Current surgical approaches often advocate for one-stage posterior lesion clearance combined with bone graft fusion and internal fixation, but they have drawbacks such as high trauma, low cure rates, and high mortality rates (5). Studies have shown that if the infection is not completely cleared from the body, it can lead to the continuous production of pro-inflammatory cytokines such as IL-1β, IL-6, IL-8, and TNF-α, which can limit the formation of granulation tissue and microvessels (6).

In recent years, multiple randomized controlled trials have highlighted the significant advantages of NPWT in treating infected wounds. NPWT is a sealed dressing system that applies mechanical stress to the wound, promoting healing through various biological mechanisms (7, 8). Piezo1, a mechanosensitive, non-selective cation channel, plays a pivotal role in transmitting mechanical-chemical signals that regulate cellular responses to external mechanical stress (9). Previous clinical evidence has demonstrated the benefits of NPWT in treating spinal infections, including promoting neutrophil chemotaxis to control infection spread and improving systemic inflammatory markers (10, 11). The primary mechanisms by which NPWT aids in treating infected wounds involve enhancing microvascular formation, stimulating granulation tissue generation, reducing bacterial load, and alleviating inflammation and edema (12–14). However, research on the impact of NPWT on the local immune microenvironment in spinal infections remains limited. Therefore, this study aims to further investigate the mechanisms underlying NPWT’s regulation of the local immune response in spinal infections, focusing on Piezo1-mediated mechanical stress and its effects on local inflammatory factors, with the goal of providing a more comprehensive theoretical foundation for the clinical application of this therapy.

Among 7 patients diagnosed with spinal infections, 5 were male and 2 were female, with an average age of 52.7 ± 13.0 years (ranging from 38 to 72 years). The affected spinal levels were L2/3 in 1 case, L3/4 in 3 cases, and L4/5 in 3 cases. Following NPWT treatment, there was an improvement in systemic inflammatory markers such as CRP and ESR. Moreover, there was a significant short-term improvement in VAS (7.00 ± 0.82 Vs. 2.29 ± 0.76, P<0.05). The average time for complete healing was 45.71 ± 9.49 days, and there were no instances of recurrence or mortality during the 2-year postoperative follow-up. Surgical data revealed an average operation duration of 96.57 ± 13.31 mins, intraoperative blood loss of 65.71 ± 29.36ml, and postoperative drainage of 163.57 ± 11.07ml ( Table 1 ).

The immunohistochemical analysis of Piezo1 and inflammatory factors in the infection lesions before and after treatment is shown in Table 2 , Figure 2 . The results of immunohistochemical examination suggest a significant decrease in inflammatory factors in the infected tissues after NPWT treatment, with a statistically significant difference.

Spinal infection, as a special type of bone infection, has a higher recurrence rate and mortality rate compared to other bone infections, with reported recurrence rates of 10% and mortality rates reaching 20% (5). The main drawback of traditional treatment approaches is the inadequate blood supply to tissues, which significantly reduces the effectiveness of antibiotics. Additionally, the specific location of the wound also makes complete debridement challenging. NPWT has proven effective in promoting the healing of various complex wounds, such as extensive burns, postoperative incision infections, necrotizing fasciitis, and skin graft sites (16–19). Several randomized controlled trials have demonstrated that NPWT offers significant benefits in treating infected wounds by reducing local inflammation and edema, stimulating granulation tissue and microvascular formation, and lowering bacterial load (7, 8, 12–14). Our team has achieved favorable clinical outcomes using NPWT to treat spinal infections (10, 11). Pappalardo et al. (20) clearly highlighted the safety and effectiveness of NPWT in managing post-spinal surgery infections through a systematic review. In this study, all seven patients who received NPWT treatment experienced positive clinical outcomes, with an average healing time of 45.71 ± 9.49 days and no recurrence or mortality during the two-year follow-up period. Furthermore, all patients showed significant improvements in postoperative VAS scores, CRP, and ESR within a short period. Our clinical findings indicate that NPWT treatment is significantly more effective than traditional methods, consistent with reports in the literature. This suggests that NPWT not only facilitates drainage but also offers therapeutic benefits.

In addition to draining, NPWT also exerts mechanical force through negative pressure suction. Nonetheless, mechanical physical signals, in contrast to soluble chemical signals like cytokines, are less investigated as regulators of immune cell function. Atcha et al. (21) found that physical mechanical stress and soluble signals synergistically regulate macrophage morphology and function, proposing that the crosstalk between CD11b and Piezo1 plays a crucial role in mechanical transduction in macrophages. Orsini et al. (22) discussed the role of mechanical sensitive channels such as Piezo1 in immune cells under various physiological and pathological conditions. They believe that mechanical signals can activate various signaling pathways within cells through the activation of mechanosensitive ion channels and receptors, including MAPKs, YAP/TAZ, EDN1, NF-kB, and HIF-1a, thereby altering the physiological state of the cell. Mulhall et al. (23) used nanoscale fluorescence imaging technology to directly observe the conformational changes of Piezo1 within the cell membrane, demonstrating its direct response to mechanical stress. Following mechanical stimulation, Piezo1 enhances integrin β1 (ITGB1) activity, forming the Piezo1/ITGB1 signaling axis, which triggers cell cytoskeletal reorganization through the RhoA/ROCK pathway, thereby enhancing Piezo1’s mechanosensitivity and establishing a positive feedback loop (24, 25). Chen et al. (9) found that high blood flow shear stress activates Piezo1, leading to the activation of various inflammatory signaling pathways such as NF-κB in a rat model of pulmonary arterial hypertension induced by left pulmonary artery ligation. This results in upregulation of Piezo1 expression in pulmonary vascular endothelial cells. Similarly, by comparing infected tissue samples before and after NPWT treatment, we found a significant increase in Piezo1 expression levels after NPWT treatment, suggesting that the mechanical stress provided by NPWT and high blood flow shear stress may both upregulate Piezo1 expression in cells.

IL-1β, IL-6, IL-8, and TNF-α are inflammatory factors that play important roles in the immune microenvironment during the entire immune response process. IL-1β is an inductive cytokine mainly produced by activating M1 macrophages (26). Tao et al. (27) found that NPWT treatment for diabetic foot infection significantly reduced IL-1β expression after 7 days of use. IL-6 has a wide range of effects in immune regulation, acute phase response, regeneration, and bone homeostasis (28). Wang et al. (29) found that NPWT can significantly reduce the expression levels of IL-6 in infected wounds of diabetic foot patients, inhibit chronic inflammation, and promote wound healing. IL-8 is a leukocyte-specific chemotactic cytokine that plays an important role in recruiting polymorphonuclear neutrophils in the early inflammatory stage of wound healing (30). TNF-α is a classical pro-inflammatory cytokine mainly produced by activated macrophages, playing a crucial role in immune responses in the immune microenvironment, including regulating inflammation, cell apoptosis, and immune cell proliferation. Norbury et al. found that the levels of TNF-α in wound drainage fluid decreased after NPWT treatment in experimental animals (31). This study focuses on the changes in the expression levels of inflammatory factors IL-1β, IL-6, IL-8, and TNF-α in infected local tissues. Continuous application of NPWT mechanical stress was found to decrease the expression of IL-1β, IL-6, IL-8, and TNF-α.

Research has shown a close association between Piezo1 and most inflammatory factors (32, 33). Piezo1, as a mechanosensitive ion channel protein, mediates calcium influx into immune cells such as macrophages, dendritic cells, and neutrophils under NPWT mechanical stress intervention, activating various downstream signaling pathways to elicit a series of immune response reactions. For example, Yang et al. found that Piezo1 activation enhances NF-κB pathway activity, promoting the production of inflammatory factors such as IL-1β, IL-6, IL-8, and TNF-α (34). However, in our clinical practice, we found that the expression levels of inflammatory factors in local tissues decreased after 7 days of NPWT mechanical stress intervention. This may be due to two reasons: (1) Piezo1 promotes wound healing by regulating the proliferation, migration, and collagen synthesis of fibroblasts, reducing continuous tissue damage and indirectly slowing down the duration and severity of the inflammatory response (35); (2) Piezo1 has a certain pro-angiogenic effect, which helps improve local blood circulation, reduce wound edema, and promote early wound healing (36).

During the early stages of normal healing, a temporary increase in inflammatory factors helps promote immune cells (such as neutrophils, macrophages, etc.) to accelerate the clearance of bacteria and tissue necrosis. Activation of Piezo1 can enhance local immune responses. However, in the late stages of healing, prolonged excessive presence of inflammatory cells and factors can lead to continued inflammation, hindering tissue repair and healing. Therefore, it is necessary to regulate inflammation appropriately to avoid excessive inflammation affecting the healing process. This study found that after 7 days of NPWT on spinal infection lesions, the expression of inflammatory factors such as IL-1β, IL-6, IL-8, and TNF-α in the local immune microenvironment significantly decreased, indicating that the spinal infection had gradually been controlled and entered the tissue repair stage. Therefore, it is speculated that NPWT can regulate local tissue immune changes, allowing various inflammatory factors to be produced, elevated, and decreased in an orderly manner, thereby promoting the clearance of local bacteria and tissue repair.

Although there is limited research on the mechanism of NPWT in treating spinal infections, we speculate that NPWT promotes healing by regulating the local immune microenvironment based on clinical and immunohistochemical analysis. Research has shown that inflammatory factors such as IL-1β, IL-6, IL-8, and TNF-α can induce and recruit various types of white blood cells to participate in immune responses, which may lead to tissue damage and affect the healing of infections if present long-term (26, 37, 38). Therefore, changes in the expression of inflammatory factors in the local immune microenvironment are closely related to the progression of infections. Piezo1, as a key protein that allows immune cells to receive mechanical signals and convert them into chemical signals, can sense the mechanical stress of NPWT and regulate immune response reactions in the local immune microenvironment of infections.

NPWT has the potential to enhance the local immune response in spinal infections through Piezo1 mediation. Clinical studies have shown that NPWT can improve outcomes, reduce healing times, and manage infection rates in patients with spinal infections. Immunohistochemical analysis has demonstrated an increase in Piezo1 protein expression levels and a significant decrease in inflammatory factors (IL-1β, IL-6, IL-8, TNF-α) in the immune microenvironment following NPWT treatment. This indicates that NPWT activates Piezo1 protein to regulate the immune response at the site of spinal infection, leading to inflammation control and tissue repair. However, further research involving cellular and animal experiments is necessary to fully understand the physiological functions of the Piezo1 signaling pathway. It is important to consider individual differences among patients that may impact treatment outcomes, and future studies should aim to include a larger sample size for more reliable conclusions.