Johannes Prox

The Disintegrin/Metalloproteinase ADAM10 Is Essential for the Establishment of the Brain Cortex

The metalloproteinase and major amyloid precursor protein (APP) α-secretase candidate ADAM10 is responsible for the shedding of proteins important for brain development, such as cadherins, ephrins, and Notch receptors. Adam10 −/− mice die at embryonic day 9.5, due to major defects in development of somites and vasculogenesis. To investigate the function of ADAM10 in brain, we generated Adam10 conditional knock-out (cKO) mice using a Nestin-Cre promotor, limiting ADAM10 inactivation to neural progenitor cells (NPCs) and NPC-derived neurons and glial cells. The cKO mice die perinatally with a disrupted neocortex and a severely reduced ganglionic eminence, due to precocious neuronal differentiation resulting in an early depletion of progenitor cells. Premature neuronal differentiation is associated with aberrant neuronal migration and a disorganized laminar architecture in the neocortex. Neurospheres derived from Adam10 cKO mice have a disrupted sphere organization and segregated more neurons at the expense of astrocytes. We found that Notch-1 processing was affected, leading to downregulation of several Notch-regulated genes in Adam10 cKO brains, in accordance with the central role of ADAM10 in this signaling pathway and explaining the neurogenic phenotype. Finally, we found that α-secretase-mediated processing of APP was largely reduced in these neurons, demonstrating that ADAM10 represents the most important APP α-secretase in brain. Our study reveals that ADAM10 plays a central role in the developing brain by controlling mainly Notch-dependent pathways but likely also by reducing surface shedding of other neuronal membrane proteins including APP.

The disintegrin/metalloproteinase Adam10 is essential for epidermal integrity and Notch-mediated signaling

The disintegrin and metalloproteinase Adam10 has been implicated in the regulation of key signaling pathways that determine skin morphogenesis and homeostasis. To address the in vivo relevance of Adam10 in the epidermis, we have selectively disrupted Adam10 during skin morphogenesis and in adult skin. K14-Cre driven epidermal Adam10 deletion leads to perinatal lethality, barrier impairment and absence of sebaceous glands. A reduction of spinous layers, not associated with differences in either proliferation or apoptosis, indicates that loss of Adam10 triggers a premature differentiation of spinous keratinocytes. The few surviving K14-Adam10-deleted mice and mice in which Adam10 was deleted postnatally showed loss of hair, malformed vibrissae, epidermal hyperproliferation, cyst formation, thymic atrophy and upregulation of the cytokine thymic stromal lymphopoetin (TSLP), thus indicating non cell-autonomous multi-organ disease resulting from a compromised barrier. Together, these phenotypes closely resemble skin specific Notch pathway loss-of-function phenotypes. Notch processing is indeed strongly reduced resulting in decreased levels of Notch intracellular domain fragment and functional Notch signaling. The data identify Adam10 as the major Site-2 processing enzyme for Notch in the epidermis in vivo, and thus as a central regulator of skin development and maintenance.

Lack of a-disintegrin-and-metalloproteinase ADAM10 leads to intracellular accumulation and loss of shedding of the cellular prion protein in vivo

BackgroundThe cellular prion protein (PrPC) fulfils several yet not completely understood physiological functions. Apart from these functions, it has the ability to misfold into a pathogenic scrapie form (PrPSc) leading to fatal transmissible spongiform encephalopathies. Proteolytic processing of PrPC generates N- and C-terminal fragments which play crucial roles both in the pathophysiology of prion diseases and in transducing physiological functions of PrPC. A-disintegrin-and-metalloproteinase 10 (ADAM10) has been proposed by cell culture experiments to be responsible for both shedding of PrPC and its α-cleavage. Here, we analyzed the role of ADAM10 in the proteolytic processing of PrPCin vivo.ResultsUsing neuron-specific Adam10 knockout mice, we show that ADAM10 is the sheddase of PrPC and that its absence in vivo leads to increased amounts and accumulation of PrPC in the early secretory pathway by affecting its posttranslational processing. Elevated PrPC levels do not induce apoptotic signalling via p53. Furthermore, we show that ADAM10 is not responsible for the α-cleavage of PrPC.ConclusionOur study elucidates the proteolytic processing of PrPC and proves a role of ADAM10 in shedding of PrPCin vivo. We suggest that ADAM10 is a mediator of PrPC homeostasis at the plasma membrane and, thus, might be a regulator of the multiple functions discussed for PrPC. Furthermore, identification of ADAM10 as the sheddase of PrPC opens the avenue to devising novel approaches for therapeutic interventions against prion diseases.

Tetraspanin15 regulates cellular trafficking and activity of the ectodomain sheddase ADAM10

A disintegrin and metalloproteinase10 (ADAM10) has been implicated as a major sheddase responsible for the ectodomain shedding of a number of important surface molecules including the amyloid precursor protein and cadherins. Despite a well-documented role of ADAM10 in health and disease, little is known about the regulation of this protease. To address this issue we conducted a split-ubiquitin yeast two-hybrid screen to identify membrane proteins that interact with ADAM10. The yeast experiments and co-immunoprecipitation studies in mammalian cell lines revealed tetraspanin15 (TSPAN15) to specifically associate with ADAM10. Overexpression of TSPAN15 or RNAi-mediated knockdown of TSPAN15 led to significant changes in the maturation process and surface expression of ADAM10. Expression of an endoplasmic reticulum (ER) retention mutant of TSPAN15 demonstrated an interaction with ADAM10 already in the ER. Pulse-chase experiments confirmed that TSPAN15 accelerates the ER-exit of the ADAM10–TSPAN15 complex and stabilizes the active form of ADAM10 at the cell surface. Importantly, TSPAN15 also showed the ability to mediate the regulation of ADAM10 protease activity exemplified by an increased shedding of N-cadherin and the amyloid precursor protein. In conclusion, our data show that TSPAN15 is a central modulator of ADAM10-mediated ectodomain shedding. Therapeutic manipulation of its expression levels may be an additional approach to specifically regulate the activity of the amyloid precursor protein alpha-secretase ADAM10.

Postnatal Disruption of the Disintegrin/Metalloproteinase ADAM10 in Brain Causes Epileptic Seizures, Learning Deficits, Altered Spine Morphology, and Defective Synaptic Functions

The metalloproteinase ADAM10 is of importance for Notch-dependent cortical brain development. The protease is tightly linked with α-secretase activity toward the amyloid precursor protein (APP) substrate. Increasing ADAM10 activity is suggested as a therapy to prevent the production of the neurotoxic amyloid β (Aβ) peptide in Alzheimer′s disease. To investigate the function of ADAM10 in postnatal brain, we generated Adam10 conditional knock-out (A10cKO) mice using a CaMKIIα-Cre deleter strain. The lack of ADAM10 protein expression was evident in the brain cortex leading to a reduced generation of sAPPα and increased levels of sAPPβ and endogenous Aβ peptides. The A10cKO mice are characterized by weight loss and increased mortality after weaning associated with seizures. Behavioral comparison of adult mice revealed that the loss of ADAM10 in the A10cKO mice resulted in decreased neuromotor abilities and reduced learning performance, which were associated with altered in vivo network activities in the hippocampal CA1 region and impaired synaptic function. Histological and ultrastructural analysis of ADAM10-depleted brain revealed astrogliosis, microglia activation, and impaired number and altered morphology of postsynaptic spine structures. A defect in spine morphology was further supported by a reduction of the expression of NMDA receptors subunit 2A and 2B. The reduced shedding of essential postsynaptic cell adhesion proteins such as N-Cadherin, Nectin-1, and APP may explain the postsynaptic defects and the impaired learning, altered network activity, and synaptic plasticity of the A10cKO mice. Our study reveals that ADAM10 is instrumental for synaptic and neuronal network function in the adult murine brain.

Physiological functions of the amyloid precursor protein secretases ADAM10, BACE1, and Presenilin

Alzheimers disease causing mutations in the amyloid precursor protein (APP) or in the Presenilin 1 (PS1) or Presenilin 2 (PS2) genes increase the production of amyloid peptides (Aβ) that precipitate in amyloid plaques. Since amyloid plaques are also a prominent feature of sporadic Alzheimers disease (AD), abnormal proteolysis of APP and the generation of amyloid beta (Aβ) are key events in the pathogenesis of AD. The proteases (secretases) that cleave APP are therefore important therapeutic targets, both for the rare familial forms but likely also for the sporadic forms of AD. The identification and understanding of the (neuro)biological functions of the α-, β-, and presenilin/γ-secretase (complexes) is important for the development of drugs and the delineation of their associated side effects. The potential impact of this type of research exceeds the AD field since the function of these secretases are also linked to cellular pathways like ectodomain shedding of growth factors and regulated intramembrane proteolysis of receptors in developmental biology, tissue homeostasis, and tumorigenesis. The generation of mice deficient in presenilin 1, presenilin 2, the α-secretase ADAM10, and the β-secretases BACE1 and BACE2 were instrumental for the elucidation of the physiological functions of these proteases. Using these mouse models understanding how these secretases regulate amyloid peptide formation and how they exert their diverse biological functions could be significantly increased. This review attempts to summarize selected aspects of the current view of the multiple roles such proteases play in health and disease.

Activity-dependent α-Cleavage of Nectin-1 Is Mediated by A Disintegrin and Metalloprotease 10 (ADAM10)

Nectin-1 is known to undergo ectodomain shedding by α-secretase and subsequent proteolytic processing by γ-secretase. How secretase-mediated cleavage of nectin-1 is regulated in neuronal cells and how nectin-1 cleavage affects synaptic adhesion is poorly understood. We have investigated α-and γ-secretase-mediated processing of nectin-1 in primary cortical neurons and identified which protease acts as a α-secretase. We report here that NMDA receptor activation, but not stimulation of AMPA or metabotropic glutamate receptors, resulted in robust α- and γ-secretase cleavage of nectin-1 in mature cortical neurons. Cleavage of nectin-1 required influx of Ca2+ through the NMDA receptor, and activation of calmodulin, but was not dependent on calcium/calmodulin-dependent protein kinase II (CaMKII) activation. We found that ADAM10 is the major secretase responsible for nectin-1 ectodomain cleavage in neurons and the brain. These observations suggest that α- and γ-secretase processing of nectin-1 is a Ca2+/calmodulin-regulated event that occurs under conditions of activity-dependent synaptic plasticity and ADAM10 and γ-secretase are responsible for these cleavage events.

Roles of endoproteolytic α‐cleavage and shedding of the prion protein in neurodegeneration

The cellular prion protein (PrPC) plays important roles in neurodegenerative diseases. First, it is the well‐established substrate for the conformational conversion into its pathogenic isoform (PrPSc) giving rise to progressive and fatal prion diseases. Moreover, several recent reports highlight important roles of PrPC in other neurodegenerative conditions such as Alzheimers disease. Since PrPC is subject to proteolytic processing, here we discuss the two main cleavage events under physiological conditions, α‐cleavage and shedding. We focus on how these cleavages and the resulting fragments may impact prion diseases as well as other neurodegenerative proteinopathies. Finally, we discuss the recently identified sheddase of PrPC, namely the metalloprotease ADAM10, with regard to therapeutic potential against neurodegenerative diseases.

The sheddase ADAM10 is a potent modulator of prion disease

The prion protein (PrPC) is highly expressed in the nervous system and critically involved in prion diseases where it misfolds into pathogenic PrPSc. Moreover, it has been suggested as a receptor mediating neurotoxicity in common neurodegenerative proteinopathies such as Alzheimers disease. PrPC is shed at the plasma membrane by the metalloprotease ADAM10, yet the impact of this on prion disease remains enigmatic. Employing conditional knockout mice, we show that depletion of ADAM10 in forebrain neurons leads to posttranslational increase of PrPC levels. Upon prion infection of these mice, clinical, biochemical, and morphological data reveal that lack of ADAM10 significantly reduces incubation times and increases PrPSc formation. In contrast, spatiotemporal analysis indicates that absence of shedding impairs spread of prion pathology. Our data support a dual role for ADAM10-mediated shedding and highlight the role of proteolytic processing in prion disease. DOI: http://dx.doi.org/10.7554/eLife.04260.001

Meprin α and meprin β: Procollagen proteinases in health and disease.

Metalloproteases meprin α and meprin β were recently discovered as procollagen proteinases, capable of cleaving off the globular C- and N-terminal prodomains of fibrillar collagen type I and type III. This proteolytic process is indeed sufficient to induce collagen fibril assembly as visualized by transmission electron microscopy. The biological relevance was demonstrated with the help of meprin α and meprin β knock-out mice, which exhibit decreased collagen deposition in skin resulting in impaired tensile strength. On the other hand, overexpression of meprin metalloproteases was found under fibrotic conditions in the skin (keloids) and the lung (pulmonary hypertension). Thus, regulation of meprin activity by specific inhibition to reduce collagen maturation might be a suitable approach for the treatment of certain pathological conditions.