Novel protease activated receptor-mediated mechanisms of oligodendrocyte pathophysiology

There is mounting evidence that dysregulation of select kallikrein-related peptidases (KLKs) may contribute to the pathophysiology of demyelinating and neurodegenerative CNS disorders. Kallikrein 6 (KLK6) is a secreted serine protease preferentially expressed by oligodendroglia in CNS white matter. Elevated levels of KLK6 occur in actively demyelinating multiple sclerosis lesions and in cases of spinal cord injury, cerebral ischemia and excitotoxic injury. Taken with recent evidence establishing KLK6 as a CNS-endogenous activator of protease-activated receptors (PARs) in neurons and astrocytes, we hypothesized that KLK6 activates a subset of PARs to regulate oligodendrocyte physiology and potentially pathophysiology. Here, oligodendrocyte cultures derived from wild type or PAR1-/- mice were used to demonstrate that KLK6 mediates loss of oligodendrocyte processes and impedes morphological differentiation of oligodendrocyte progenitors in a PAR1-dependent fashion. Comparable gliopathy was also elicited by PAR1 agonists, thrombin and PAR1-activating peptides. Klk6 also exacerbated ATP- mediated oligodendrogliopathy in vitro, pointing to a potential role in augmenting excitotoxicity. In addition, Klk6 suppressed the expression of proteolipid protein RNA in cultured oligodendrocytes by a mechanism involving PAR1-mediated Erk1/2 signaling. Microinjection of PAR1 agonists, including Klk6 or PAR1-APs, into the dorsal column white matter of PAR1+/+ but not PAR1-/- mice promoted vacuolating myelopathy and a loss of immunoreactivity for myelin basic protein and CC-1+ oligodendrocytes. These results demonstrate a functional role for Klk6- PAR1 signaling in oligodendroglial pathophysiology and suggest that antagonists of PAR1 or its protease-agonists may represent new modalities to moderate demyelination and to promote myelin regeneration in cases of CNS white matter injury or disease.