Upregulation of APP, ADAM10 and ADAM17 in the Denervated Mouse Dentate Gyrus

Abstract

The disintegrin and metalloproteinases ADAM10 and ADAM17 are regarded as the most important α-secretases involved in the physiological processing of amyloid precursor protein (APP) in brain. Since it has been suggested that processing of APP by α-secretases could be involved in the reorganization of the brain following injury, we studied mRNA expression of the two α-secretases Adam10 and Adam17, the ß-secretase Bace1, and the App-gene family (App, Aplp1, Aplp2) in the dentate gyrus of the mouse following entorhinal denervation. Using laser microdissection, tissue was harvested from the outer molecular layer and the granule cell layer of the denervated dentate gyrus. Expression levels of candidate genes were assessed using Affymetrix GeneChip Mouse Gene 1.0 ST arrays and reverse transcription-quantitative PCR, revealing an upregulation of Adam10 mRNA and Adam17 mRNA in the denervated outer molecular layer and an upregulation of Adam10 mRNA and App mRNA in the dentate granule cell layer. Immunolabeling for ADAM10 or ADAM17 in combination with markers for astro- and microglia revealed an increased labeling of ADAM10 and ADAM17 in the denervated outer molecular layer that was associated with reactive astrocytes but not with microglia. Collectively, these data show that denervation affects the expression level of APP and its two most important α-secretases. This suggests that APP-processing could be shifted towards the non-amyloidogenic pathway in denervated areas of the brain and, thus, towards the formation of neuroprotective APP cleavage products, such as APPsα.

Region-Specific Differences in Amyloid Precursor Protein Expression in the Mouse Hippocampus

“…They concluded that in vivo APP levels in astrocytes may be too low for detection even under reactive conditions (Guo et al, 2012). In our own investigations, in which we used entorhinal cortex lesions (Lynch et al, 1978; Steward, 1994; Deller and Frotscher, 1997) to denervate the DG, we also failed to see an increase in App mRNA in the denervated outer molecular layer (Del Turco et al, 2014). In this layer, reactive glia are particularly abundant (Deller et al, 2000, 2007; Del Turco et al, 2014).…”

“…In our own investigations, in which we used entorhinal cortex lesions (Lynch et al, 1978; Steward, 1994; Deller and Frotscher, 1997) to denervate the DG, we also failed to see an increase in App mRNA in the denervated outer molecular layer (Del Turco et al, 2014). In this layer, reactive glia are particularly abundant (Deller et al, 2000, 2007; Del Turco et al, 2014). Although these two reports cannot rule out the possibility that under some other conditions APP is expressed in vivo by glial cells, they certainly suggest that glial APP is not the primary source of APP in the intact or injured brain.…”

“…In our own investigations using the entorhinal cortex lesion model we initially failed to observe an increase in App mRNA using screening methods. Only after using the sensitive LMD/qPCR approach (Burbach et al, 2003), which made it possible to measure App mRNA within microdissected cell and fiber layers did we detect a ~1.3-fold increase of App mRNA in denervated granule cells at 7 days post lesion (Del Turco et al, 2014). We conclude that neuronal App expression is tightly regulated and even under extreme conditions, e.g., brain injury, App gene expression changes range between 1- to 2-fold.…”

“…To provide first evidence for this hypothesis and to reliably quantify differences in APP expression between granule cells of the DG and pyramidal cells of area CA1, we studied layer-specific expression levels of APP in the principal cell layers using laser microdissection (LMD) in combination with quantitative polymerase chain reaction (qPCR) and western blot analysis (e.g., Burbach et al, 2003; Del Turco et al, 2014). Since APP is alternatively spliced into three major isoforms (Kang et al, 1987; Tanzi et al, 1988; Sisodia et al, 1993; Rohan de Silva et al, 1997), i.e., APP-770, APP-695 and APP-751, assays detecting all major isoforms were employed.…”

Fractalkine shedding is mediated by p38 and the ADAM10 protease under pro-inflammatory conditions in human astrocytes

“…For example, immunolabelling has revealed increased expression of ADAM10 and ADAM17 associated with reactive astrocytes in murine dentate gyrus [32]. ADAM10 has also been found to be increased in immunohistochemical studies of HIV encephalitis clinical samples in both astrocytes and neurons [33].…”