Benign prostatic diseases (BPDs), mainly including benign prostatic hyperplasia (BPH) and prostatitis, are prevalent urological ailments affecting males globally (1, 2). Compression of the urethra caused by BPH results in clinical symptoms that impact the quality of life for individuals with BPH, including lower urinary tract symptoms (LUTS), episodes of acute urinary retention, and recurring urinary infections (3). Numerous investigations have been carried out regarding the development of BPH; nevertheless, the factors responsible for its occurrence and advancement are still poorly understood (4). Prostatitis is classified into types I–IV by the National Institutes of Health (NIH) in the United States. Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) of Type III is categorized into inflammatory CPPS (IIIa) and noninflammatory CPPS (IIIb), making up approximately 90%–95% of cases related to prostatitis (5). Individuals diagnosed with CP/CPPS typically encounter discomfort in the pelvic region, such as pain in the pubic region or perineum, discomfort during sexual activity or ejaculation, painful urination, frequent urination at night and/or a sense of urgency, sexual difficulties, impotence, mental health disorders, and reduced sperm quality (6, 7). Exploring the etiology, diagnosis, and treatment of BPDs in public health has significant practical implications by identifying the causal association of risk factors that can be modified.

The group of lysosomal proteolytic enzymes known as cathepsins plays a crucial role in preserving cellular homeostasis, which are classified into multiple families, including serine proteases (cathepsins A and G), cysteine proteases (cathepsins B, C, F, H, K, L, O, S, V, W, and X), and aspartyl proteases (cathepsins D and E) (8, 9). They are associated with many cellular activities including protein and lipid metabolism, autophagy, antigen presentation, growth factor receptor recycling, cellular stress signaling, extracellular matrix degradation, and lysosome-mediated cell death (10). Various cathepsins have significant roles in various diseases due to their participation in these essential processes (11). The association between cathepsins and prostate cancer (PCa) has been reported, such as cathepsin B. Nalle et al. found that the inhibition of invasion and migration and the activation of apoptosis in PC3 and DU145 prostate cancer cell lines can be achieved by targeting cathepsin B (12). Moreover, the rise in serum levels of cathepsin B and the density of cathepsin B may serve as innovative indicators for the progression of the disease. However, they do not impact the survival of individuals diagnosed with PCa (13). Furthermore, the generation of sphingosine 1-phosphate through acid ceramidase facilitates the invasion of PCa by increasing the expression of cathepsin B (14). Despite several studies suggesting potential applications of cathepsins in PCa disease, there is a lack of studies exploring cathepsins in relation to BPDs. Based on this, we will use Mendelian randomization (MR) to do such a thing.

MR designs utilize genetic diversity as instrumental variables (IVs) to explore the causal association between potential factors and the specific disease, offering several advantages absent in conventional epidemiology (15). In addition, using MR designs can decrease the likelihood of reverse causality and minimize the impact of confounding variables (16). The objective of this study was to examine the causal connection between cathepsins and BPDs, potentially identifying novel avenues for diagnosing and treating BPDs.

Table 2 displays the results of bidirectional two-sample MR between cathepsins and BPDs, and we found three statistically significant positive results. By utilizing the 12 SNPs associated with cathepsin O, we discovered that elevated levels of cathepsin O can decrease the risk of BPH (OR=0.94, 95%CI=0.89–0.98, p-value=0.00553) through the implementation of IVW techniques ( Table 2 ; Supplementary Table 1 ; Supplementary Figure 1 ). Moreover, the absence of significant heterogeneity (P-value > 0.05) was confirmed by the MR-Egger and IVW heterogeneity tests. The absence of any impact was shown when using P-values obtained from MR-Pleiotropy Residual Sum and Outlier methods (MR-PRESSO) to evaluate horizontal pleiotropy ( Table 3 ; Supplementary Table 2 ). In the Leave-one-out sensitivity analysis ( Supplementary Figure 2A ), there was no individual SNP that significantly undermined the overall impact of cathepsin O on BPH. The symmetrical funnel plot also suggests the absence of pleiotropy ( Supplementary Figure 2B ). Furthermore, by employing 12SNPs, we discovered a correlation between elevated cathepsin X levels and heightened susceptibility to prostatitis (OR=1.08, 95% CI=1.00–1.16, p-value=0.0477) through the implementation of IVW techniques ( Table 2 ; Supplementary Table 3 ; Supplementary Figure 3 ). Comparable to the findings mentioned above, there was an absence of heterogeneity or horizontal pleiotropy in the outcomes (P-value > 0.05) ( Table 3 ; Supplementary Table 4 ; Supplementary Figure 4 ).

In reverse MR, we found an association between genetically predicted prostatitis and cathepsin V levels by utilizing 15 prostatitis-related SNPs ( Supplementary Table 5 ). Using IVW methods ( Supplementary Figure 5 ), there is a decrease in the expression of cathepsin V in prostatitis cases (OR=0.89, 95% CI=0.80–0.99, p-value=0.0349). Similar to the analysis mentioned earlier, no signs of pleiotropy and heterogeneity were detected in the findings (P-value > 0.05) ( Table 3 ; Supplementary Table 6 ; Supplementary Figure 6 ).

This study used MR to examine the reciprocal causal connections between cathepsins and BPDs. The results indicate that cathepsin O protected BPH, cathepsin X posed a risk for prostatitis, and prostatitis had a negative impact on cathepsin V. The findings provide valuable insights into the role of cathepsins in developing BPDs, potentially influencing the development of diagnostic and therapeutic strategies for cathepsins in patients with BPDs.

Previous research has indicated an association between cathepsins and PCa, which shows the possibility of clinical application value. Incorporating 474 males who had a prostate-specific antigen (PSA) concentration ranging from 2.0 to 10 ng/mL, a negative digital rectal examination, and an enlarged prostate (volume of at least 35 mL), a retrospective study revealed that combining thrombospondin 1, cathepsin D with %fPSA in a model could enhance the diagnosis of PCa and potentially decrease the need for unnecessary prostate biopsies. This model demonstrated improved specificity for PCa compared to using %fPSA alone (27). In PCa patients, a different protein expression test showed elevated levels of cathepsin S secreted by macrophages, indicating the progression of PCa. Another research by Jennica found that cathepsin H could regulate the migration of PCa cells (PC3) (28). Moreover, cathepsin E amplifies the effectiveness of doxorubicin against PCa cells in humans, which exhibit resistance to apoptosis induced by TRAIL. The up-regulation of cathepsin B promotes the invasion of PCa by producing sphingosine 1-phosphate by acid ceramidase (29). PCa is linked to the heightened presence of cathepsin B in plasma membrane/endosomal fractions, whereas BPH or normal prostate are not (30). Despite several studies suggesting potential applications of cathepsins in PCa disease, more studies need to explore cathepsins for BPDs. Importantly, this study is the initial MR to explore the correlation between cathepsins and BPDs, which warrants additional experimental and clinical investigation for validation.

There are multiple advantages to the current research. Initially, it was the primary study to investigate the impact of cathepsins on BPDs by utilizing extensive GWAS data from Finngen Biobank and the IEU OpenGWAS. Furthermore, since the chosen IVs were situated on a distinct chromosome, it is plausible that any potential gene-gene interaction would have minimal impact on the projected outcome. Furthermore, we employed various reliable techniques to acquire the MR effects, including MR-PRESSO and the Steiger test. Additionally, we assessed the existence of horizontal pleiotropy. By employing the two-step MR analysis, we successfully pinpointed the association between cathepsins and BPDs.

There are certain constraints in the current investigation. Initially, while three cathepsins were found to be associated with BPDs in our study, the effect was marginal and, probably, of limited clinical relevance. At present, there is a paucity of studies investigating the mechanism between cathepsins and BPDs. Previous studies have demonstrated that cathepsins are involved in all aspects of cellular activity and are strongly linked to the development of various diseases. Further research may yet reveal cathepsins to be a new diagnostic and therapeutic target for BPDs. Nevertheless, this hypothesis requires further experimental verification. Furthermore, the GWAS data may give rise to potential nonlinear relationships or stratification effects. Additionally, the findings might have restricted applicability to individuals of non-European origin because only participants with European heritage were included exclusively. This implies that the causal relationship postulated in this paper is applicable solely to European populations. The emergence of future GWAS data from other ethnic groups will be useful to further explore this causal inference. A comprehensive assessment of mixed populations will be more useful to explore the causal relationship between Cathepsins and BPDs at the genetic level. Lastly, given the complexity of genetic and environmental factors influencing BPDs and levels of cathepsins, we did not include possible confounding factors in our analysis. It is very difficult to identify confounding factors that affect both, and future studies should further identify confounding factors that can affect both to further improve the accuracy of results.

To summarize, our findings indicate that cathepsin O played a beneficial role in BPH, cathepsin X posed a potential risk for prostatitis, and prostatitis had an adverse impact on the expression of cathepsin V. These cathepsins may become new targets for future BPDs diagnosis and treatment, but further validation is needed.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding authors.

HC: Writing – original draft, Supervision, Software, Formal analysis, Conceptualization. BL: Writing – review & editing, Software, Formal analysis, Data curation. KG: Writing – original draft, Software, Formal analysis, Data curation. HW: Writing – review & editing, Software, Formal analysis, Data curation. YW: Writing – review & editing, Software, Data curation. HZ: Writing – original draft, Software, Data curation. CS: Writing – original draft, Supervision. PW: Writing – review & editing, Supervision. HD: Writing – review & editing, Supervision. HZ: Writing – original draft, Investigation, Conceptualization. SW: Writing – review & editing, Investigation, Conceptualization.