KLK6 proteolysis is implicated in the turnover and uptake of extracellular alpha-synuclein species

Abstract

KLK6 is a serine protease highly expressed in the nervous system. In synucleinopathies, including Parkinson disease, the levels of KLK6 inversely correlate with α-synuclein in CSF. Recently, we suggested that recombinant KLK6 mediates the degradation of extracellular α-synuclein directly and via a proteolytic cascade that involves unidentified metalloproteinase(s). Here, we show that recombinant and naturally secreted KLK6 can readily cleave α-synuclein fibrils that have the potential for cell-to-cell propagation in “a prion-like mechanism”. Importantly, KLK6-deficient primary cortical neurons have increased ability for α-synuclein fibril uptake. We also demonstrate that KLK6 activates proMMP2, which in turn can cleave α-synuclein. The repertoire of proteases activated by KLK6 in a neuronal environment was analyzed by degradomic profiling, which also identified ADAMTS19 and showed that KLK6 has a limited number of substrates indicating specific biological functions such as the regulation of α-synuclein turnover. We generated adenoviral vectors for KLK6 delivery and demonstrated that the levels of extracellular α-synuclein can be reduced by neuronally secreted KLK6. Our findings open the possibility to exploit KLK6 as a novel therapeutic target for Parkinson disease and other synucleinopathies.

How is alpha‐synuclein cleared from the cell?

“…Significantly, in a study by the Masliah group, KLK6 expression was inversely correlated with a-Syn accumulation in brains with DLB (Dementia with Lewy bodies), and the lentiviral-driven expression of mouse KLK6 reduced intracellular and neuropil aggregates of a-Syn and reversed the pathology in WT but not in A53T a-Syn transgenic mice (Spencer et al 2013). In addition, KLK6 can efficiently degrade recombinant as well as naturally secreted oligomeric forms of a-Syn (Pampalakis et al 2017). These studies suggest the potential therapeutic benefit of targeting KLK6 in synucleinopathies.…”

“…In addition, KLK6 can efficiently degrade recombinant as well as naturally secreted oligomeric forms of α‐Syn (Pampalakis et al . ). These studies suggest the potential therapeutic benefit of targeting KLK6 in synucleinopathies.…”

A proinflammatory role of KLK6 protease in Netherton syndrome

“…Klk6 À/À have been developed in collaboration with Prof Andras Nagy (University of Toronto, Toronto, Ontario, Canada). The design of Klk6 À/À inactivation cassette has been published previously [20]. All experiments with animals were conducted in accordance with EU and national legislation.…”

Kallikrein-related peptidase 6 orchestrates astrocyte form and function through proteinase activated receptor-dependent mechanisms

“…First, Klk6 is the most abundant serine proteinase in the adult CNS and its levels are dynamically altered in the context of CNS injury and disease (Scarisbrick 2012). In the human CNS, KLK6 levels are increased in active MS lesions (Scarisbrick et al 2002), after traumatic spinal cord injury SCI (Scarisbrick et al 2006; Radulovic et al 2013; Radulovic et al 2015) and in high grade astrocytoma (Drucker et al 2013; Drucker et al 2015), but decreased in Alzheimers (Little et al 1997; Diamandis et al 2000; Ogawa et al 2000; Zarghooni et al 2002; Ashby et al 2010) and Parkinsons disease (Iwata et al 2003; Spencer et al 2013; Spencer et al 2015; Pampalakis et al 2017). Indeed, astrocytes express very low levels of Klk6 in the intact CNS (Scarisbrick et al 1997; Scarisbrick et al 2000), however astrocyte Klk6 is up regulated in response to a variety of insults.…”

“…For example, studies show heat-denatured collagen, laminin, fibronectin and aggrecan are all hydrolyzed by Klk6 (Bernett et al 2002; Blaber et al 2002; Scarisbrick et al 2006). Also, KLK6 cleaves several disease relevant proteins, such as myelin basic protein and myelin oligodendrocyte glycoprotein (Bernett et al 2002; Blaber et al 2002; Scarisbrick et al 2002; Blaber et al 2004; Angelo et al 2006), amyloid precursor protein (Little et al 1997; Magklara et al 2003), and α-syneuclein (Iwata et al 2003; Kasai et al 2008; Tatebe et al 2010; Spencer et al 2015; Pampalakis et al 2017). In addition, it is now clear that certain kallikrein-related peptidases, including Klk6, can site-specifically cleave the extracellular N terminal domain of a subset of proteinase activated receptors (PARs) to alter intracellular signaling and cell behavior directly in a hormone or cytokine-like fashion (Angelo et al 2006; Oikonomopoulou et al 2006a; Oikonomopoulou et al 2006b; Vandell et al 2008; Scarisbrick et al 2011; Scarisbrick et al 2012b; Radulovic et al 2015; Radulovic et al 2016).…”