Inhibition of excessive kallikrein-8 improves neuroplasticity in Alzheimer's disease mouse model

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.

Neuropsin promotes hippocampal synaptogenesis by regulating the expression and cleavage of L1CAM

During early postnatal brain development, the formation of proper synaptic connections between neurons is crucial for the development of functional neural networks. Recent studies have established the involvement of protease-mediated modulations of extracellular components in both synapse formation and elimination. The secretory serine protease neuropsin (also known as kallikrein-8) cleaves a few transmembrane or extracellular matrix proteins in a neural activity-dependent manner and regulates neural plasticity. However, neuropsin-dependent proteolysis of extracellular components and the involvement of these components in mouse brain development are poorly understood. We have observed that during hippocampus development, expression of neuropsin and levels of full-length or cleaved fragments of the neuropsin substrate protein L1 cell adhesion molecule (L1CAM) positively correlate with synaptogenesis. Our subcellular fractionation studies show that the expression of neuropsin and its proteolytic activity on L1CAM are enriched at developing hippocampal synapses. Activation of neuropsin expression upregulates the transcription and cleavage of L1CAM. Furthermore, blocking of neuropsin activity, as well as knockdown of L1CAM expression, significantly downregulates in vitro hippocampal synaptogenesis. Taken together, these findings provide evidence for the involvement of neuropsin activity-dependent regulation of L1CAM expression and cleavage in hippocampal synaptogenesis.

Inflammatory regulation by restraining M2 microglial polarization: Neurodestructive effects of Kallikrein-related peptidase 8 activation in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a cerebrovascular disease. Kallikrein-related peptidase 8 (KLK8) is a serine peptidase, while its role in ICH remains unclarified. Western blot (WB) showed that KLK8 was upregulated in rat perihematomal tissues 24 h following autologous blood injection. KLK8 overexpression aggravated behavioral deficits and increased water content and Fluoro-Jade B (FJB)-positive neuron numbers in brain tissue of rats. Immunofluorescence (IF) assay showed that overexpressed-KLK8 promoted Iba-1 and iNOS expression in perihematomal tissue of rats. Overexpressed-KLK8 increased COX-2, iNOS, and Arg-1 expression and the content of IL-6, IL-1β, and TNF-α in perihematomal tissue of rats, confirmed by WB and ELISA. IF staining confirmed the expression of CCR5 was co-expressed with Iba-1, and the WB results shown increased CCR5 expression and decreased p-PKA and p-CREB expression in perihematomal tissue. Maraviroc (MVC, CCR5 inhibitor) administration rescued KLK8-induced behavioral deficits and brain injury (decreased water content and FJB-positive neuron numbers) in rats. Additionally, MVC suppressed p-PKA and p-CREB expression and the content of IL-6, IL-1β, and TNF-α in perihematomal tissue, induced by overexpressed-KLK8. Co-IP confirmed the binding of CCR5 and CCL14 in HMC3 cells. Transwell assay shown that KLK8 plus CCL4 promoted the chemotactic activity of cells, which was rescued by MVC. The biological function of KLK8/CCL14/CCR5 axis in ICH injury was also proved by MVC administration in HMC3 cells. Overall, our work revealed that KLK8 overexpression aggravated ICH process and involved in microglial activation. KLK8 might activate CCL14 thereby turning on downstream CCR5/PKA/CREB pathway, providing a theoretical basis for future therapy.

Upregulation of KLK8 contributes to CUMS-induced hippocampal neuronal apoptosis by cleaving NCAM1

Neuronal apoptosis has been well-recognized as a critical mediator in the pathogenesis of depressive disorders. Tissue kallikrein-related peptidase 8 (KLK8), a trypsin-like serine protease, has been implicated in the pathogenesis of several psychiatric disorders. The present study aimed to explore the potential function of KLK8 in hippocampal neuronal cell apoptosis associated with depressive disorders in rodent models of chronic unpredictable mild stress (CUMS)-induced depression. It was found that depression-like behavior in CUMS-induced mice was associated with hippocampal KLK8 upregulation. Transgenic overexpression of KLK8 exacerbated, whereas KLK8 deficiency attenuated CUMS-induced depression-like behaviors and hippocampal neuronal apoptosis. In HT22 murine hippocampal neuronal cells and primary hippocampal neurons, adenovirus-mediated overexpression of KLK8 (Ad-KLK8) was sufficient to induce neuron apoptosis. Mechanistically, it was identified that the neural cell adhesion molecule 1 (NCAM1) may associate with KLK8 in hippocampal neurons as KLK8 proteolytically cleaved the NCAM1 extracellular domain. Immunofluorescent staining exhibited decreased NCAM1 in hippocampal sections obtained from mice or rats exposed to CUMS. Transgenic overexpression of KLK8 exacerbated, whereas KLK8 deficiency largely prevented CUMS-induced loss of NCAM1 in the hippocampus. Both adenovirus-mediated overexpression of NCAM1 and NCAM1 mimetic peptide rescued KLK8-overexpressed neuron cells from apoptosis. Collectively, this study identified a new pro-apoptotic mechanism in the hippocampus during the pathogenesis of CUMS-induced depression via the upregulation of KLK8, and raised the possibility of KLK8 as a potential therapeutic target for depression.

Blood Kallikrein-8 and Non-Amnestic Mild Cognitive Impairment: An Exploratory Study

Background: Blood kallikrein-8 is supposed to be a biomarker for mild cognitive impairment (MCI) due to Alzheimer’s disease (AD), a precursor of AD dementia. Little is known about the association of kallikrein-8 and non-AD type dementias. Objective: To investigate whether blood kallikrein-8 is elevated in individuals with non-amnestic MCI (naMCI), which has a higher probability to progress to a non-AD type dementia, compared with cognitively unimpaired (CU) controls. Methods: We measured blood kallikrein-8 at ten-year follow-up (T2) in 75 cases and 75 controls matched for age and sex who were participants of the population-based Heinz Nixdorf Recall study (baseline: 2000–2003). Cognitive performance was assessed in a standardized manner at five (T1) and ten-year follow-up. Cases were CU or had subjective cognitive decline (SCD) at T1 and had naMCI at T2. Controls were CU at both follow-ups. The association between kallikrein-8 (per 500 pg/ml increase) and naMCI was estimated using conditional logistic regression: odds ratios (OR) and 95% confidence intervals (95% CI) were determined, adjusted for inter-assay variability and freezing duration. Results: Valid kallikrein-8 values were measured in 121 participants (45% cases, 54.5% women, 70.5±7.1 years). In cases, the mean kallikrein-8 was higher than in controls (922±797 pg/ml versus 884±782 pg/ml). Kallikrein-8 was not associated with having naMCI compared to being CU (adjusted; OR: 1.03 [95% CI: 0.80–1.32]). Conclusion: This is the first population-based study that shows that blood kallikrein-8 tends not to be elevated in individuals with naMCI compared with CU. This adds to the evidence of the possible AD specificity of kallikrein-8.

Proteomics and functional study reveal kallikrein-6 enhances communicating hydrocephalus

Background

Communicating hydrocephalus (CH) is a common neurological disorder caused by a blockage of cerebrospinal fluid. In this study, we aimed to explore the potential molecular mechanism underlying CH development.

Methods

Quantitative proteomic analysis was performed to screen the differentially expressed proteins (DEPs) between patients with and without CH. A CH rat model was verified by Hoechst staining, and the co-localization of the target protein and neuron was detected using immunofluorescence staining. Loss-of-function experiments were performed to examine the effect of KLK6 on the synapse structure.

Results

A total of 11 DEPs were identified, and kallikrein 6 (KLK6) expression was found to be significantly upregulated in patients with CH compared with that in patients without CH. The CH rat model was successfully constructed, and KLK6 was found to be co-localized with neuronal nuclei in brain tissue. The expression level of IL-1β, TNF-α, and KLK6 in the CH group was higher than that in the control group. After knockdown of KLK6 expression using small-interfering RNA (siRNA), the expression levels of synapsin-1 and PSD95 in neuronal cells were increased, and the length, number, and structure of synapses were significantly improved. Following siRNA interference KLK6 expression, 5681 differentially expressed genes (DEGs) were identified in transcriptome profile. The upregulated DEGs of Appl2, Nav2, and Nrn1 may be involved in the recovery of synaptic structures after the interference of KLK6 expression.

Conclusions

Collectively, KLK6 participates in the development of CH and might provide a new target for CH treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12014-021-09335-9.

Is kallikrein-8 a blood biomarker for detecting amnestic mild cognitive impairment? Results of the population-based Heinz Nixdorf Recall study

Background

Kallikrein-8 (KLK8) might be an early blood-biomarker of Alzheimer’s disease (AD). We examined whether blood KLK8 is elevated in persons with amnestic mild cognitive impairment (aMCI) which is a precursor of AD, compared to cognitively unimpaired (CU) controls.

Methods

Forty cases and 80 controls, matched by sex and age (± 3years), were participants of the longitudinal population-based Heinz Nixdorf Recall study (baseline: 2000–2003). Standardized cognitive performance was assessed 5 (T1) and 10 years after baseline (T2). Cases were CU at T1 and had incidental aMCI at T2. Controls were CU at T1 and T2. Blood KLK8 was measured at T2. Using multiple logistic regression the association between KLK8 in cases vs. controls was investigated by estimating odds ratios (OR) and 95% confidence intervals (95%CI), adjusted for inter-assay variability and freezing duration. Using receiver operating characteristic (ROC) analysis, the diagnostic accuracy of KLK8 was determined by estimating the area under the curve (AUC) and 95%CI (adjusted for inter-assay variability, freezing duration, age, sex).

Results

Thirty-seven participants with aMCI vs. 72 CU (36.7%women, 71.0±8.0 (mean±SD) years) had valid KLK8 measurements. Mean KLK8 was higher in cases than in controls (911.6±619.8 pg/ml vs.783.1±633.0 pg/ml). Fully adjusted, a KLK8 increase of 500pg/ml was associated with a 2.68 (1.05–6.84) higher chance of having aMCI compared to being CU. With an AUC of 0.92 (0.86–0.97), blood KLK8 was a strong discriminator for aMCI and CU.

Conclusion

This is the first population-based study to demonstrate the potential clinical utility of blood KLK8 as a biomarker for incipient AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00945-x.

Roles and Mechanisms of Axon-Guidance Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive memory decline and cognitive dysfunctions. Although the causes of AD have not yet been established, many mechanisms have been proposed. Axon-guidance molecules play the roles in the occurrence and development of AD by participating in different mechanisms. Therefore, what roles do axon-guidance molecules play in AD? This study aimed at elucidating how axon-guidance molecules Netrins, Slits, Semaphorins, and Ephrins regulate the levels of Aβ, hyperphosphorylation of tau protein, Reelin, and other ways through different signaling pathways, in order to show the roles of axon-guidance molecules in the occurrence and development of AD. And it is hoped that this study can provide a theoretical basis and new perspectives in the search for new therapeutic targets for AD.

A novel role of kallikrein-related peptidase 8 in the pathogenesis of diabetic cardiac fibrosis

Rationale: Among all the diabetic complications, diabetic cardiomyopathy, which is characterized by myocyte loss and myocardial fibrosis, is the leading cause of mortality and morbidity in diabetic patients. Tissue kallikrein-related peptidases (KLKs) are secreted serine proteases, that have distinct and overlapping roles in the pathogenesis of cardiovascular diseases. However, whether KLKs are involved in the development of diabetic cardiomyopathy remains unknown.The present study aimed to determine the role of a specific KLK in the initiation of endothelial-to-mesenchymal transition (EndMT) during the pathogenesis of diabetic cardiomyopathy.

Methods and Results-By screening gene expression profiles of KLKs, it was found that KLK8 was highly induced in the myocardium of mice with streptozotocin-induced diabetes. KLK8 deficiency attenuated diabetic cardiac fibrosis, and rescued the impaired cardiac function in diabetic mice. Small interfering RNA (siRNA)-mediated KLK8 knockdown significantly attenuated high glucose-induced endothelial damage and EndMT in human coronary artery endothelial cells (HCAECs). Diabetes-induced endothelial injury and cardiac EndMT were significantly alleviated in KLK8-deficient mice. In addition, transgenic overexpression of KLK8 led to interstitial and perivascular cardiac fibrosis, endothelial injury and EndMT in the heart. Adenovirus-mediated overexpression of KLK8 (Ad-KLK8) resulted in increases in endothelial cell damage, permeability and transforming growth factor (TGF)-β1 release in HCAECs. KLK8 overexpression also induced EndMT in HCAECs, which was alleviated by a TGF-β1-neutralizing antibody. A specificity protein-1 (Sp-1) consensus site was identified in the human KLK8 promoter and was found to mediate the high glucose-induced KLK8 expression. Mechanistically, it was identified that the vascular endothelial (VE)-cadherin/plakoglobin complex may associate with KLK8 in HCAECs. KLK8 cleaved the VE-cadherin extracellular domain, thus promoting plakoglobin nuclear translocation. Plakoglobin was required for KLK8-induced EndMT by cooperating with p53. KLK8 overexpression led to plakoglobin-dependent association of p53 with hypoxia inducible factor (HIF)-1α, which further enhanced the transactivation effect of HIF-1α on the TGF-β1 promoter. KLK8 also induced the binding of p53 with Smad3, subsequently promoting pro-EndMT reprogramming via the TGF-β1/Smad signaling pathway in HCAECs. The in vitro and in vivo findings further demonstrated that high glucose may promote plakoglobin-dependent cooperation of p53 with HIF-1α and Smad3, subsequently increasing the expression of TGF-β1 and the pro-EndMT target genes of the TGF-β1/Smad signaling pathway in a KLK8-dependent manner.

Conclusions: The present findings uncovered a novel pro-EndMT mechanism during the pathogenesis of diabetic cardiac fibrosis via the upregulation of KLK8, and may contribute to the development of future KLK8-based therapeutic strategies for diabetic cardiomyopathy.

Genetic knockdown of Klk8 has sex-specific multi-targeted therapeutic effects on Alzheimer's pathology in mice

AIMS

Previous work in our lab has identified the protease kallikrein-8 (KLK8) as a potential upstream mover in the pathogenesis of Alzheimer's disease (AD). We showed pathologically elevated levels of KLK8 in the cerebrospinal fluid and blood of patients with mild cognitive impairment or dementia due to AD, and in brains of patients and transgenic CRND8 (TgCRND8) mice in incipient stages of the disease. Furthermore, short-term antibody-mediated KLK8 inhibition in moderate stage disease alleviated AD pathology in female mice. However, it remains to be shown whether long-term reversal of KLK8 overexpression can also counteract AD. Therefore, the effects of genetic Klk8-knockdown were determined in TgCRND8 mice.

METHODS

The effects of heterozygous ablation of murine Klk8 (mKlk8) gene on AD pathology of both sexes were examined by crossbreeding TgCRND8 [hAPP+/-] with mKlk8-knockdown [mKlk8+/-] mice resulting in animals with or without AD pathology which revealed pathologically elevated or normal KLK8 levels.

RESULTS

mKlk8-knockdown had negligible effects on wildtype animals but led to significant decline of amyloid beta (Aβ) and tau pathology as well as an improvement of structural neuroplasticity in a sex-specific manner in transgenics. These changes were mediated by a shift to non-amyloidogenic cleavage of the human amyloid precursor protein (APP), recovery of the neurovascular unit and maintaining microglial metabolic fitness. Mechanistically, Klk8-knockdown improved Aβ phagocytosis in primary glia and Aβ resistance in primary neurons. Most importantly, transgenic mice revealed less anxiety and a better memory performance.

CONCLUSIONS

These results reinforce the potential of KLK8 as a therapeutic target in AD.