Kallikrein-related peptidase's significance in Alzheimer's disease pathogenesis: A comprehensive survey

Alzheimer's disease (AD) and related dementias constitute an important global health challenge. Detailed understanding of the multiple molecular mechanisms underlying their pathogenesis constitutes a clue for the management of the disease. Kallikrein-related peptidases (KLKs), a lead family of serine proteases, have emerged as potential biomarkers and therapeutic targets in the context of AD and associated cognitive decline. Hence, KLKs were proposed to display multifaceted impacts influencing various aspects of neurodegeneration, including amyloid-beta aggregation, tau pathology, neuroinflammation, and synaptic dysfunction. We propose here a comprehensive survey to summarize recent findings, providing an overview of the main kallikreins implicated in AD pathophysiology namely KLK8, KLK6 and KLK7. We explore the interplay between KLKs and key AD molecular pathways, shedding light on their significance as potential biomarkers for early disease detection. We also discuss their pertinence as therapeutic targets for disease-modifying interventions to develop innovative therapeutic strategies aimed at halting or ameliorating the progression of AD and associated dementias.

KLK7, KLK10, and KLK11 in Papillary Thyroid Cancer: Bioinformatic Analysis and Experimental Validation

Despite many studies on papillary thyroid carcinoma (PTC) in the past few decades, some critical and significant genes remain undiscovered. To explore genes that may play crucial roles in PTC, a detailed analysis of the expression levels, mutations, and clinical significance of Kallikrein-related peptidases (KLKs) family genes in PTC was undertaken to provide new targets for the precise treatment of the disease. A comprehensive analysis of KLK family genes was performed using various online tools, such as GEPIA, Kaplan-Meier Plotter, LinkedOmics, GSCA, TIMER, and Cluego. KLK7, KLK10, and KLK11 were critical factors of KLK family genes. Then, functional assays were carried out on KLK7/10/11 to determine their proliferation, migration, and invasion capabilities in PTC. The mRNA expression levels of KLK7, KLK10, KLK11, and KLK13 were significantly elevated in thyroid carcinoma, while KLK1, KLK2, KLK3 and KLK4 mRNA levels were decreased compared to normal tissues. Correlations between KLK2/7-12/15 expression levels and tumor stage were also observed in thyroid carcinoma. Survival analysis demonstrated that KLK4/5/7/9-12/14 was associated with overall survival in patients with thyroid cancer. Not only were KLK genes strongly associated with cancer-related pathways, but also KLK7/10/11 was associated with immune-cell infiltration. Finally, silencing KLK7/10/11 impaired human papillary thyroid carcinoma cells' growth, migration ability, and invasiveness. The increased expression of KLK7, KLK10, and KLK11 may serve as molecular markers to identify PTC patients. KLK7, KLK10, and KLK11 could be potential prognostic indicators and targets for precision therapy against PTC.

Tissue kallikrein-related peptidase8 accentuates cardiac fibrosis after myocardial ischemia-reperfusion injury via regulation of cardiac fibroblasts

AIMS

Tissue kallikrein-related peptidase8 (KLK8) has been found to mitigate acute myocardial ischemia-reperfusion (IR) injury. However, the effect of KLK8 on cardiac remodeling in response to IR injury has not been determined.

MATERIALS AND METHODS

KLK8 overexpressing transgenic rat (KLK8-TG) was used as the animal model. IR injury was induced by ligating the left anterior descending coronary artery for 1 h and subsequent reperfusion. The functional and morphological changes of the heart were examined 14 days after the injury. Neonatal rat cardiac fibroblasts (CFs) were used to investigate the molecular mechanisms in vitro.

KEY FINDINGS

KLK8 overexpression enhanced cardiac diastolic dysfunction, fibrosis, and hypertrophy after IR injury, indicating that KLK8 accentuated cardiac remodeling in response to IR injury. Moreover, KLK8 overexpression increased epidermal growth factor (EGF) release and promoted the phosphorylation of EGF receptor (EGFR) and ERK1/2 in the heart after IR injury. It was interesting to find that both EGFR antagonist (AG 1478) and MEK inhibitor (PD98059) attenuated the KLK8-induced proliferation and activation of CFs in vitro, indicating that EGFR signaling might mediate the pro-fibrotic action of KLK8.

SIGNIFICANCE

KLK8 plays a crucial role in cardiac remodeling after myocardial infarction. KLK8 accentuates cardiac fibrosis after IR injury, possibly mediated by EGFR signaling in CFs.

Minireview: functional roles of tissue kallikrein, kinins, and kallikrein-related peptidases in lung cancer

Despite campaigns and improvements in detection and treatment, lung cancer continues to increase worldwide and represents a major public health problem. One approach to treating patients suffering from lung cancer is to target surface receptors overexpressed on tumor cells, such as GPCR-family kinin receptors, and proteases that control tumor progression, such as kallikrein-related peptidases (KLKs). These proteases have been visualized in recent years due to their contribution to the progression of cancers, such as prostate and ovarian cancer, facilitating the invasive and metastatic capacity of tumor cells in these tissues. In fact, KLK3 is the specific prostate antigen, the only tissue-specific biomarker used to diagnose this malignancy. In lung cancer to date, evidence indicates that KLK5, KLK6, KLK8, KLK11, and KLK14 are the major peptidases regulated and involved in its progression. The expression levels of KLKs in this neoplasm are modulated by the secretome of the different cell types present in the tumor microenvironment, the cancer subtype and the tumor stage, among others. Considering the multiple functions of kinin receptors and KLKs, this review highlights their roles, even considering the SARS-CoV-2 effects. Since lung cancer is often diagnosed in advanced stages, our efforts should focus on early diagnosis, validating for example specific KLKs, especially in high-risk populations such as smokers and people exposed to carcinogenic fumes, oil fields, and contaminated workplaces, unexplored fields to investigate. Furthermore, their modulation could be considered as a promising approach in lung cancer therapeutics.

Aberrant serine protease activities in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease; the three major factors responsible for AD, i.e., epidermal barrier dysfunction, allergic inflammation, and itching, interact with each other to form a pathological condition. Excessive protease activities are characteristic abnormalities that affect the epidermal barrier in patients with AD. In normal skin, epidermal serine protease activities are controlled by kallikrein-related peptidases (KLKs) and their inhibitors, including lympho-epithelial Kazal-type-related inhibitor (LEKTI). In AD lesions, KLKs are excessively expressed, which results in the enhancement of epidermal serine protease activities and facilitates the invasion by allergens and microorganisms. In addition, some KLKs can activate protease-activated receptor 2 (PAR2) in epidermal keratinocytes and peripheral nerves, resulting in the induction of inflammation and itching. Furthermore, in AD patients with single nucleotide polymorphism (SNP) such as E420K and D386N of SPINK5 which encodes LEKTI, LEKTI function is attenuated, resulting in the activation of KLKs and easy invasion by allergens and microorganisms. Further analysis is needed to elucidate the detailed mechanism underlying the control of serine protease activities, which may lead to the development of new therapeutic and prophylactic agents for AD.

Tissue kallikrein-related peptidase8 protects rat heart against acute ischemia reperfusion injury

Tissue kallikrein-related peptidases (KLKs) play important roles in acute cardiac injury and cardiac remodeling. However, the exact cardiac actions of KLK8 have not been determined. Transgenic rat overexpressing KLK8 was established to examine the role of KLK8 in the heart. Cardiac injury was induced by ischemia/reperfusion (I/R) and examined by infarct size measurement and TUNEL staining. The molecular mechanisms were investigated in cultured neonatal rat cardiomyocytes (CMs). Western blot analysis was used to determine the protein levels. KLK8 protein level was significantly increased in the cardiac ischemic risk area. KLK8 overexpression mitigated I/R-induced cardiac injury, as evidenced by decreased infarct size and apoptosis in cardiac ischemic risk area in vivo. Via in vitro studies, it was found that KLK8 overexpression attenuated the Hypoxia/Reoxygenation (H/R) injury in CMs; both B2R and PAR2 antagonist significantly attenuated KLK8-induced protective actions under H/R injury. Moreover, KLK8 overexpressed CMs showed significant higher phosphorylation levels of Akt, ERK1/2 and PKA under H/R stimulation; B2R antagonist attenuated the phosphorylation levels of Akt and ERK1/2, while PAR2 antagonist attenuated the phosphorylation levels of PKA and ERK1/2. KLK8 protects the heart against I/R-induced cardiac injury, which may represent a new therapeutic target in cardiac medicine.

Expression and clinical significance of KLK5-8 in endometrial cancer

Kallikrein-related peptidase (KLK) family is one of the major serine proteases in tumor microenvironment, which plays a crucial role in cancer invasion and metastasis. A number of KLK family members have been found to be upregulated or downregulated in some cancers, and some KLKs may be potential biomarkers for cancers. However, little is known about the role of KLKs in endometrial carcinoma (EC). In this study, we analyzed the mRNA sequencing data of EC from The Cancer Genome Atlas (TCGA) public database and found that the higher expression of KLK family members 5-8 (KLK5-8) was associated with an aggressive clinicopathologic phenotype and worse prognosis in EC patients. High expression of KLK5-8 was also confirmed in our patients with advanced stage and high-grade EC, as well as in a highly invasive cell line. Our study also demonstrated the differences between the subcellular localization of KLK5-8 and the co-expression of different splicing variants of KLK5-8 in EC cells, suggesting that various isoforms of KLK5-8 may work synergistically to regulate invasion and migration. We found that the elevation of more KLKs in a patient's sample indicated a higher risk of worse survival. Combination of KLK5-8 was shown to be an independent prognostic factor for overall survival by multivariate Cox regression (hazard ratio: 2.215, 95% confidence interval: 1.045-4.694, P=0.038), and may be a promising biomarker.

Identifying Candidate Biomarkers for Pleomorphic Adenoma: A Case-Control Study

Pleomorphic adenoma (PA) is the most common benign salivary gland tumor. Kallikrein-related peptidases have been identified as biomarkers in many human tumors and may influence tumor behavior. We investigated KLK1-15 messenger ribonucleic acid and proteins in PA specimens to determine a KLK expression profile for this tumor. Fresh frozen PA tissue specimens (n = 26) and matched controls were subjected to quantitative real-time reverse transcription polymerase chain reaction to detect KLK1-15 mRNA. Expression of KLK1, KLK12, KLK13, and KLK8 proteins were then evaluated via immunostaining techniques. Statistical analyses were performed with the level of significance set at P < .05. We observed downregulation of KLK1, KLK12, and KLK13 mRNA expression, and immunostaining studies revealed downregulation of the corresponding proteins. Histologic evidence of capsular perforation was associated with increased KLK1 protein expression. Tumor size was not associated with capsular invasion and/or perforation. This study is the first to detail a KLK expression profile for PA at both the transcriptional level and the protein level. Future work is required to develop clinical applications of these findings.

Downregulated KLK13 expression in bladder cancer highlights tumor aggressiveness and unfavorable patients' prognosis

PURPOSE

Despite recent research advantages on the molecular and subcellular background, bladder cancer (BlCa) remains a clinically neglected malignancy. This is strongly reflected by the generic approach of disease diagnosis and management. Additionally, patients' prognosis became a rather demanding task due to the great disease heterogeneity. Here, we aimed to evaluate, for the first time, the clinical value of KLK13 in BlCa.

METHODS

A total of 279 bladder specimens (137 tumors, 107 adjacent normal tissues and 35 healthy samples) were included. Total RNA was extracted, reverse transcribed, and KLK13 expression was assessed by quantitative real-time PCR.

RESULTS

KLK13 expression is significantly increased in bladder tumors compared to normal adjacent epithelium. However, reduced KLK13 expression is correlated with disease aggressiveness, including higher tumor stage and grade, and high-risk TaT1 tumors according to the EORTC stratification. Moreover, Kaplan-Meier and Cox regression analysis highlighted the prognostic value of the reduced KLK13 expression for the prediction of TaT1 patients' recurrence and shorter disease-free survival following TURBT. Finally, the combination of KLK13 expression with EORTC-risk stratification results to an improved prediction of TaT1 patients' outcome.

CONCLUSION

This first clinical study of KLK13 in BlCa reveals its deregulated expression in bladder tumors and highlights KLK13 as a promising marker for improving TaT1 patients' prognosis following treatment.

Improving the Specificity of Screening for Lethal Prostate Cancer Using Prostate-specific Antigen and a Panel of Kallikrein Markers: A Nested Case-Control Study

BACKGROUND

A disadvantage of prostate-specific antigen (PSA) for the early detection of prostate cancer (PCa) is that many men must be screened, biopsied, and diagnosed to prevent one death.

OBJECTIVE

To increase the specificity of screening for lethal PCa at an early stage.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a case-control study nested within a population-based cohort. PSA and three additional kallikreins were measured in cryopreserved blood from a population-based cohort in Västerbotten, Sweden. Of 40379 men providing blood at ages 40, 50, and 60 yr from 1986 to 2009, 12542 men were followed for >15 yr. From this cohort, the Swedish Cancer Registry identified 1423 incident PCa cases, 235 with distant metastasis.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Risk of distant metastasis for different PSA levels and a prespecified statistical model based on the four kallikrein markers.

RESULTS AND LIMITATIONS

Most metastatic cases occurred in men with PSA in the top quartile at age 50 yr (69%) or 60 yr (74%), whereas 20-yr risk of metastasis for men with PSA below median was low (≤0.6%). Among men with PSA >2 ng/ml, a prespecified model based on four kallikrein markers significantly enhanced the prediction of metastasis compared with PSA alone. About half of all men with PSA >2 ng/ml were defined as low risk by this model and had a ≤1% 15-yr risk of metastasis.

CONCLUSIONS

Screening at ages 50-60 yr should focus on men with PSA in the top quartile. A marker panel can aid biopsy decision making.

PATIENT SUMMARY

For men in their fifties, screening should focus on those in the top 10% to 25% of PSA values because the majority of subsequent cases of distant metastasis are found among these men. Testing of four kallikrein markers in men with an elevated PSA could aid biopsy decision making.

Comparison Between the Four-kallikrein Panel and Prostate Health Index for Predicting Prostate Cancer

BACKGROUND

The four-kallikrein panel and the Prostate Health Index (PHI) have been shown to improve prediction of prostate cancer (PCa) compared with prostate-specific antigen (PSA). No comparison of the four-kallikrein panel and PHI has been presented.

OBJECTIVE

To compare the four-kallikrein panel and PHI for predicting PCa in an independent cohort.

DESIGN, SETTING, AND PARTICIPANTS

Participants were from a population-based cohort of PSA-tested men in Stockholm County. We included 531 men with PSA levels between 3 and 15 ng/ml undergoing first-time prostate biopsy during 2010-2012.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Models were fitted to case status. We computed calibration curves, the area under the receiver-operating characteristics curve (AUC), decision curves, and percentage of saved biopsies.

RESULTS AND LIMITATIONS

The four-kallikrein panel showed AUCs of 69.0 when predicting any-grade PCa and 71.8 when predicting high-grade cancer (Gleason score ≥7). Similar values were found for PHI: 70.4 and 71.1, respectively. Both models had higher AUCs than a base model with PSA value and age (p<0.0001 for both); differences between models were not significant. Sensitivity analyses including men with any PSA level or a previous biopsy did not materially affect our findings. Using 10% predicted risk of high-grade PCa by the four-kallikrein panel or PHI of 39 as cut-off for biopsy saved 29% of performed biopsies at a cost of delayed diagnosis for 10% of the men with high-grade cancers. Both models showed limited net benefit in decision analysis. The main study limitation was lack of digital rectal examination data and biopsy decision being based on PSA information.

CONCLUSIONS

The four-kallikrein panel and PHI similarly improved discrimination when predicting PCa and high-grade PCa. Both are simple blood tests that can reduce the number of unnecessary biopsies compared with screening with total PSA, representing an important new option to reduce harm.

PATIENT SUMMARY

Prostate-specific antigen screening is controversial due to limitations of the test. We found that two blood tests, the Prostate Health Index and the four-kallikrein panel, performed similarly and could both aid in decision making among Swedish men undergoing a prostate biopsy.

KLKB1 mRNA overexpression: A novel molecular biomarker for the diagnosis of chronic lymphocytic leukemia

OBJECTIVES

Plasma kallikrein, also known as Fletcher factor or kallikrein B1 (KLKB1), is a serine endopeptidase, like its homologs tissue kallikrein and kallikrein-related peptidases (KLKs). Its physiological role is to catalyze the release of kinins and other vasoactive peptides. Several KLKs have been proposed as putative tumor biomarkers with significant diagnostic and/or prognostic value in human malignancies arising from solid tumors; the most prominent example is the worldwide use of KLK3 (prostate-specific antigen, PSA) in prostate cancer diagnostics. The aim of this study was to analyze KLKB1 mRNA expression in B-cell chronic lymphocytic leukemia (CLL) patients and to examine its diagnostic value as a novel molecular biomarker in CLL.

DESIGN AND METHODS

Total RNA was isolated from peripheral blood mononuclear cells of sixty-nine patients previously diagnosed with CLL and thirty-one healthy blood donors. After cDNA preparation, a sensitive and cost-effective quantitative real-time PCR (qRT-PCR) methodology was developed and applied for KLKB1 mRNA quantification. Last, we carried out a biostatistical analysis to assess the clinical significance of KLKB1 mRNA expression.

RESULTS

According to our findings, KLKB1 mRNA expression is significantly higher in CLL patients than in healthy blood donors. Furthermore, KLKB1 mRNA levels are negatively correlated with CD38 expression, an established prognostic biomarker in CLL. Most importantly, KLKB1 mRNA expression possesses important diagnostic value, distinguishing very efficiently CLL patients from non-leukemic population.

CONCLUSIONS

KLKB1 mRNA expression is a putative molecular biomarker in CLL, meriting investigation in large cohorts of CLL patients and non-leukemic controls.

Predictive value of four kallikrein markers for pathologically insignificant compared with aggressive prostate cancer in radical prostatectomy specimens: results from the European Randomized Study of Screening for Prostate Cancer section Rotterdam

BACKGROUND

Treatment decisions can be difficult in men with low-risk prostate cancer (PCa).

OBJECTIVE

To evaluate the ability of a panel of four kallikrein markers in blood-total prostate-specific antigen (PSA), free PSA, intact PSA, and kallikrein-related peptidase 2-to distinguish between pathologically insignificant and aggressive disease on pathologic examination of radical prostatectomy (RP) specimens as well as to calculate the number of avoidable surgeries.

DESIGN, SETTING, AND PARTICIPANTS

The cohort comprised 392 screened men participating in rounds 1 and 2 of the Rotterdam arm of the European Randomized Study of Screening for Prostate Cancer. Patients were diagnosed with PCa because of an elevated PSA ≥3.0 ng/ml and were treated with RP between 1994 and 2004.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

We calculated the accuracy (area under the curve [AUC]) of statistical models to predict pathologically aggressive PCa (pT3-T4, extracapsular extension, tumor volume >0.5cm(3), or any Gleason grade ≥4) based on clinical predictors (age, stage, PSA, biopsy findings) with and without levels of four kallikrein markers in blood.

RESULTS AND LIMITATIONS

A total of 261 patients (67%) had significant disease on pathologic evaluation of the RP specimen. While the clinical model had good accuracy in predicting aggressive disease, reflected in a corrected AUC of 0.81, the four kallikrein markers enhanced the base model, with an AUC of 0.84 (p < 0.0005). The model retained its ability in patients with low-risk and very-low-risk disease and in comparison with the Steyerberg nomogram, a published prediction model. Clinical application of the model incorporating the kallikrein markers would reduce rates of surgery by 135 of 1000 patients overall and 110 of 334 patients with pathologically insignificant disease. A limitation of the present study is that clinicians may be hesitant to make recommendations against active treatment on the basis of a statistical model.

CONCLUSIONS

Our study provided proof of principle that predictions based on levels of four kallikrein markers in blood distinguish between pathologically insignificant and aggressive disease after RP with good accuracy. In the future, clinical use of the model could potentially reduce rates of immediate unnecessary active treatment.