In the current study, we highlight that the key enzyme of glycolysis, hexokinase 2 is overexpressed in both OVA/Alum and OVA/LPS-induced asthmatic airway inflammation. Human airway cell line Beas-2b also shows aberrant HK2 in a time and dose-dependent way after IL-1β exposure. HK2 deficiency specifically in the airway cell protected mice against airway inflammation and airway hyperresponsiveness following repeated OVA challenges. In particular, we discovered that HK2 may be involved in asthma by regulating chemokine activity, immunological response, and cell death signaling through PPIF. Reducing HK2 activity by using 2-DG may considerably improve airway hyperresponsiveness and lung inflammation in asthmatic mice. Finally, it may be said that HK2 might be a possible asthma treatment target.
Metabolic reprogramming including Glycolysis reprogramming occurs in pathological conditions including cancer and inflammatory diseases. Glycolysis effectively provides cells with large amounts of energy which allows cells to survive. Aberrant glycolysis can occur even in conditions with sufficient oxygen, this phenomenon is known as the Warburg effect in cancers[11, 12, 14–16]. A plethora of clinical evidence indicates that aberrant glycolysis is present in chronic asthmatic patients and HDM-induced allergic airway diseases[20–24]. Consistent with previous studies we discovered that increasing expression of HK2 in the lung of OVA/Alum or OVA/LPS-induced asthmatic mice, including the airway epithelium. Important immunological responses in airway remodeling, mucus production, airway inflammation, and airway hyperresponsiveness (AHR) were mediated by T cells.[25]. Depending on their cluster, T cells have different metabolic requirements, Th2 cells seem to have a higher glycolytic ability, whereas Th17 cells mostly use mitochondrial oxidative phosphorylation. T cells have different metabolic requirements for their energy source. [26]. Inhibiting glycolysis deterred immune cells from skewing towards the Th2 phenotype and ameliorated experimental asthma[27], however, it was discovered that elevated HK2 served other redundant roles in the function of T cells[28]. We need to determine whether HK2 is beneficial in the first line of defense in the airway epithelium during asthma. Herein we generate HK2-specific loss in the airway epithelium by crossing scgb1a1-iCre+/+ and HK2 flox/flox mice. Although the body weight of HK2-CKO mice during normal growth was slower than that of control mice, there was no significant difference. There was also no observed difference in terms of pathological staining and lung function. HK2-CKO mice exhibit substantial protection against inflammation following OVA/LPS or OVA/Alum induction. In particular, when we applied inhibitors of HK2, 2-DG, lung inflammation, and airway hyperresponsiveness in asthmatic mice were significantly improved. These results imply that HK2 participates in the onset of asthma and could be a promising target for asthma treatment.
As a component of structural cells, airway epithelial cells in asthma serve as both a barrier to infections as well as sentinels of the innate immune system, they provide protection against allergens, and pollutants which can worsen and prolong asthma attacks [29, 30]. Bronchial epithelial cells react to allergens by producing the inflammatory cytokines thymic stromal lymphopoietin (TSLP), IL-25, and IL-33, which support innate inflammatory responses[31]. However, they also cause apoptosis in bronchial epithelial cells, which compromises the integrity of the epithelial barrier [32]. HK2 is implicated in the apoptosis process of several cancers[33, 34], which was consistent with the results of our RNA-Seq analysis. Results from both in vivo and in vitro experiments show that elevated HK2 in airway epithelial contributes to the process of apoptosis. Although overexpression of HK2 in vitro only partially exacerbated the apoptosis process, knockdown of HK2 significantly alleviated apoptosis in vivo and in vitro. Additionally, HK2 plays a significant role in inflammatory illnesses like colitis and rheumatoid arthritis [35]. We also found that HK2 impacted inflammation in asthma. Knockdown of HK2 by airway epithelial cells does not only reduce classical type 2 and type 1 inflammatory factors but can also improve the production of chemokines, thereby reducing the inflammatory cell infiltration in the lungs. Thus, we postulated that via controlling the expression of inflammatory interleukins and airway epithelial apoptosis, HK2 participates in the onset of asthma.
Hexokinase (HK) has five known isoforms; of these, HK2 is the most effective at stimulating aerobic glycolysis[15, 17]. Many mechanisms mediated by HK2 have been investigated[36–38]. There are two distinct locations for HK2 in a cell: it can be found free in the cytosol or attached to the mitochondria [15, 39]. HK2 bound to mitochondria and plays a role in the maintenance of the integrity of mitochondrial membrane. The voltage-dependent anion channel 1(VDAC1) interacting with HK2 prevents cytochrome c release from mitochondria and the resulting apoptosis after Bax activation. An interaction between PPIF and HK2 supports a key function regulating cell death[36–38]. According to other studies, PPIF is downregulated when HK2 is silenced in airway epithelial cells, but VDAC1 does not appear to be significantly different. This suggests that HK2 in vivo may primarily work with PPIF to control cell death.
Our study has several limitations. Firstly, our verification of increased HK2 expression was limited to cellular levels and mouse models. To make our experiment optimal, we need to recruit asthma patients of different endotypes. Secondly, asthma is a long-term inflammatory illness involving both innate and adaptive immunity, among other immunological responses. We exclusively focused on the airway epithelial cells in this investigation. It is unknown if increased HK2 expression in other immune cells contributes to the development of asthma. Lastly, the mechanism of HK2 involvement in asthma has only been partially established; more research is still needed to determine the precise mechanism and whether any novel molecules are involved.