Heart failure (HF) is a manifestation of cardiac dysfunction secondary to abnormalities in cardiac structure, which progress to a state of decompensation and then fail to keep up with the metabolic needs of the body [1]. With the growing numbers of elderly populations and increased incidence of risk factors [e.g., coronary artery disease (CAD), hypertension, diabetes mellitus (DM), obesity, and smoking], the prevalence of HF is rapidly rising, leading to increasing medical and socioeconomic burdens world-wide [2, 3]. A prior report showed a 12-month mortality rate of 16.5% for HF and the absolute mortality rate within 5 years after a diagnosis of HF may reach approximately 50% [4]. HF has been classified into different phenotypes to help guide the clinical management for this disease. The survival and hospitalization rate of HF with reduced ejection fraction (HFrEF) has benefited from the development of medical therapies and cardiac assist equipment [5]. Once HF with preserved ejection fraction (HFpEF) occurs, the typical dyspnea symptoms manifested in HFrEF will not appear because this phenotype of HF is characterized by restricted filling and disturbed relaxation of the myocardium whereas the systolic function is close to normal. The risk of this specific subset of HF is not fully understood [6]. Hence, the overall prognosis for HF still remains unsatisfactory. There have been numerous biomarkers for the diagnosis of HF [7], but the pathophysiology regarding the progression and evolution of this disease still needs to be further elucidated. Therefore, it is important to investigate new potential diagnostic and therapeutic biomarkers for these patients, especially for those with HFpEF.

The heart is the most metabolically active organ in the human body, and it accounts for approximately 8% of daily ATP consumption [8]. Mitochondria act as the powerhouse of the cells and are responsible for normal cell metabolism, protecting cells against damage from reactive oxygen species (ROS) [9]. Dynamin-related protein 1 (Drp1) belongs to the dynamin family of GTP-binding proteins. They often translocate from the cytoplasm to the mitochondria and then bind to their targets located in the outer mitochondrial membrane (OMM) to induce mitochondrial fission, thereby mediating mitophagy to affect programmed cell death and cell metabolism [10, 11, 12]. Drp1 can be expressed as multiple splice variants, which are highly expressed in the human heart, skeletal muscle, brain, and kidney [13, 14]. Several studies have demonstrated the association between mitochondrial bioenergetic capacity and progression of HF, in which impaired mitochondrial energetics greatly contributed to the onset and progression of maladaptive cardiac hypertrophy [15, 16]. Therefore, there may be a potential association between Drp1 and HF. This study was undertaken to explore the role of serum Drp1 in HF patients, especially in those with HFpEF.

This observational study represents the first evaluation for the clinical values of serum Drp1. We found that serum Drp1 concentrations were much higher in HFpEF than in HFrEF (p = 0.001), and the ROC curve analysis indicated it could be a potential diagnostic biomarker for distinguishing the phenotype of HF (AUC = 0.659). When we combined the results of K-M survival analyses with the generated ROC curve of Drp1 for freedom from the composite endpoint, low serum concentrations of Drp1 (cut-off value = 2.5 ng/mL, AUC = 0.738) were found to be associated with a poor prognosis from HF. A low serum concentration of Drp1 was identified as an independent risk predictor for rehospitalization for HF (OR: 6.671, 95% CI: 2.166–20.540, p = 0.001), and led to a significantly increased risk of the composite endpoint. These findings suggested that low serum concentrations of Drp1 might serve as a biomarker for distinguishing HF phenotypes and the overall prognosis of HF, as well as providing a new potential therapeutic target for HF patients.

In adult cardiomyocytes, mitochondria account for about 30% of the total cell volume and produce vast amounts of ATP through oxidative phosphorylation to maintain contractile function [12]. HF commonly occurs with cardiac remodeling, in which there are significant molecular changes due to oxidative stress and myocyte loss through autophagy, including mitophagy, apoptosis, and fibrosis [17]. Thus, both the decrease in the number of contractile units and the damaged mitochondrial bioenergetic capacity in residual cardiomyocytes after myocardial injuries are directly linked with the progression of HF [18, 19]. The coordinated cycle of mitochondrial fission and fusion is known as mitochondrial dynamics, whose homeostasis has been demonstrated to have a critical role in maintaining cardiac structure and function [20, 21]. Drp1 is known as a crucial regulator of mitochondrial fission and is involved in mitophagy for degradation of depolarized mitochondria in the heart [22]. Parkin-dependent mitophagy is considered to be more critical for the maintenance of mitochondrial respiratory function in the absence of Drp1-dependent mitophagy [22]. In contrast, several other studies indicated that Parkin-dependent mitophagy would be hyper-activated in Drp1-deficient mouse hearts, which was thought to be detrimental to the heart because the downregulation of Drp1 induced constitutive recruitment of Parkin to the elongated mitochondria and increased degradation of healthy mitochondria [23, 24]. Based on the findings from these studies, Drp1 has been recognized as having an important role in affecting programmed cell death and cardiac metabolism through the mediation of mitophagy. Values of serum Drp1 may be an alternative way to determine myocardial damage compared to the more costly and invasive myocardial biopsy.

Our ROC curve analysis suggested that serum Drp1 can be a potential diagnostic biomarker for distinguishing HFpEF from HFrEF (AUC = 0.659), with a sensitivity of 45.9% and specificity of 83.7%. Currently, the diagnosis of HFpEF mainly depends on echocardiography findings. In clinical practice, the most commonly used biomarkers for the diagnosis of HF are plasma BNP or NT-proBNP levels, showing a much higher sensitivity (BNP at a threshold of $\le$100 ng/L is 0.95, while NT-proBNP at a threshold of $\le$300 ng/L is 0.99) but a relatively low specificity (BNP $\le$100 ng/L is 0.63, and NT-proBNP $\le$300 ng/L is 0.43), which may limit accurate risk stratification for HF [25, 26]. Although the sensitivity of serum Drp1 for the diagnosis of HFpEF is slightly lower compared to these classical markers, the specificity is much higher. A new concept of HF with improved EF has been raised by the latest ESC guidelines to provide more precise risk stratification of HF to optimize the clinical management of these patients [7]. Moreover, the NT-proBNP levels were much higher in these HF patients but showed no significant difference between the low and high Drp1 groups (2340.0 pg/mL vs. 1810.0 pg/mL, p = 0.126). Therefore, serum Drp1 combined with plasma BNP or NT-proBNP may provide more accurate definitions of HF phenotypes.

ROC curves were also generated for Drp1 to assess its role in determining freedom from the risk of the composite endpoint. The AUC was 0.738 (95% CI: 0.656–0.820, p 0.001), and the optimal cut-off point was identified as 2.5 ng/mL. Combined with the results of the K-M survival analyses and binary logistic regression, low concentrations of Drp1 (Drp1 2.5 ng/mL) were associated with poorer outcomes from HF and were identified as an independent risk predictor of rehospitalization for HF (OR: 6.671, 95% CI: 2.166–20.540, p = 0.001). The source of serum Drp1 remains unclear. Our prior study established an MI model in SD rats for 6 weeks and indicated that the decreased expression of Drp1 in the infarcted myocardium leads to structural and functional damage to cardiac mitochondria, which results in worse cardiac function [27]. The biological function of Drp1 mainly depends on its translocation from the cytoplasm to OMM to bind with the localized target genes [10, 11, 12]. Under these conditions, few Drp1 proteins would be released though large amounts of cardiomyocytes are ruptured. A prior study also demonstrated that Drp1-dependent mitochondrial autophagy would be transiently activated when stimulated by pressure overload, and the pathway was downregulated [28]. This may be a potential explanation for the clinical measurements of serum Drp1 found in this study. To date, no cell types have been identified for the secretion of Drp1 and further explorations for the source of serum Drp1 are still necessary.

In our study, we found no significant difference in mortality between the low and high Drp1 groups. HF patients usually die from a sudden cause (commonly recognized as a malignant arrhythmia) or from multiple organ dysfunction caused by end-stage respiratory and circulatory failure [29, 30]. In our study, IHD was confirmed as the main cause of HF, and more than half of the patients suffered from a prior MI. However, the serum Drp1 concentrations showed no significance between these groups divided by different etiologies of HF, suggesting Drp1 can be used to predict the prognosis of HF.

Several limitations should be acknowledged in the current study. First, this is a single-center, observational study with a small sample size. Larger trials are warranted. Second, the potential regulation of oral agents on Drp1 could not be completely eliminated, especially with the use of Dapagliflozin (DAPA), which could regulate the expression level of Drp1 in the infarcted myocardium [27]. However, the baseline usage of DAPA showed no significant difference in this study. Third, longer follow-up is necessary for strengthening the association between serum Drp1 and the prognosis of HF. In addition, dynamic detection of Drp1 might help us better understand the variation of Drp1 along with changes in patient status. Finally, missing data of several inflammatory markers, including hypersensitive C-reactive protein and procalcitonin, also limited our ability to further explore their relevant effects on patient outcomes.

Our results indicated that serum Drp1 concentrations are significantly higher in patients with HFpEF versus those with HFrEF. It might serve as a good diagnostic marker for the distinction of HF phenotypes. A low serum concentration of Drp1 was identified as an independent risk predictor for poor clinical outcomes among these HF patients. In summary, serum Drp1 may serve as a meaningful biomarker to discriminate the diagnosis of HF phenotypes and the overall prognosis of HF, as well as become a potential therapeutic target for treating this disease.

All data generated or analyzed during this study are included in this published article.

GSM conceived the project and designed the study; ZGF, MYJ and WXW assessed for eligibility; ZGF, YX and WXW performed the ELISA; JL evaluated and recorded all the clinical events; ZGF, MYJ and YX constructed the maps. ZGF wrote the manuscript and GSM critically revised it. All authors contributed to data analysis, drafting and critically revising the paper. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

The ethics committee of Zhongda Hospital approved the study protocol and informed consent (No. 2020ZDSYLL306-P01). All participants in the study provided written informed consent.

We are grateful to the staff in Biobank of Zhongda Hospital Affiliated to Southeast University for technical assistance.

The present study was supported by National Natural Science Foundation of China (granted number 82070295) and Jiangsu Provincial Key Medical Discipline (Laboratory ZDXKA2016023).

The authors declare no conflict of interest.