Drosophila metalloproteases in development and differentiation: The role of ADAM proteins and their relatives

Neprilysin 4: an essential peptidase with multifaceted physiological relevance

Neprilysins are highly conserved ectoenzymes that hydrolyze and thus inactivate signaling peptides in the extracellular space. Herein, we focus on Neprilysin 4 from Drosophila melanogaster and evaluate the existing knowledge on the physiological relevance of the peptidase. Particular attention is paid to the role of the neprilysin in regulating feeding behavior and the expression of insulin-like peptides in the central nervous system. In addition, we assess the function of the peptidase in controlling the activity of the sarcoplasmic and endoplasmic reticulum Ca²⁺ ATPase in myocytes, as well as the underlying molecular mechanism in detail.

Identification of the extracellular metallo-endopeptidases ADAM and ADAMTS in the yellow fever mosquito Aedes aegypti

The mosquito Aedes aegypti is a major vector for dengue, Zika, yellow fever, and chikungunya (CHIKV) viruses, which cause significant morbidity and mortality among human populations in the tropical regions of the world. Following ingestion of a viremic bloodmeal from a vertebrate host, an arbovirus needs to productively infect the midgut epithelium of the mosquito. De novo synthesized virions then exit the midgut by traversing the surrounding basal lamina (BL) in order to disseminate to secondary tissues and infect those. Once the salivary glands are infected, the virus is transmitted to a vertebrate host along with saliva released during probing of the mosquito. Midgut tissue distention due to bloodmeal ingestion leads to remodeling of the midgut structure and facilitates virus dissemination from the organ. Previously, we described the matrix-metalloproteinases (MMP) of Ae. aegypti as zinc ion dependent endopeptidases (Metzincins) and showed MMP activity during midgut BL rearrangement as a consequence of bloodmeal ingestion and subsequent digestion thereby affecting arbovirus dissemination from the midgut. Here we investigate the ADAM/ADAMTS of Ae. aegypti, which form another major group of multi-domain proteinases within the Metzincin superfamily and are active during extra-cellular matrix (ECM) remodeling. Seven different ADAM and five ADAMTS were identified in Ae. aegypti. The functional protein domain structures of the identified mosquito ADAM resembled those of human ADAM10, ADAM12, and ADAM17, while two of the five mosquito ADAMTS had human orthologs. Expression profiling of Ae. aegypti ADAM/ADAMTS in immature forms, whole body-females, midguts, and ovarian tissues showed transcriptional activity of the proteinases during metamorphosis, bloodmeal ingestion/digestion, and female reproduction. Custom-made antibodies to ADAM10a and ADAM12c showed that both were strongly expressed in midgut and ovarian tissues. Furthermore, transient silencing of ADAM12c significantly reduced the carcass infection rate with CHIKV at 24 h post-infection, while silencing of ADAM12a significantly increased viral titers in secondary tissues at the same time point. Our results indicate a functional specificity for several ADAM/ADAMTS in those selected mosquito tissues.

Neprilysins regulate muscle contraction and heart function via cleavage of SERCA-inhibitory micropeptides

Muscle contraction depends on strictly controlled Ca²⁺ transients within myocytes. A major player maintaining these transients is the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase, SERCA. Activity of SERCA is regulated by binding of micropeptides and impaired expression or function of these peptides results in cardiomyopathy. To date, it is not known how homeostasis or turnover of the micropeptides is regulated. Herein, we find that the Drosophila endopeptidase Neprilysin 4 hydrolyzes SERCA-inhibitory Sarcolamban peptides in membranes of the sarcoplasmic reticulum, thereby ensuring proper regulation of SERCA. Cleavage is necessary and sufficient to maintain homeostasis and function of the micropeptides. Analyses on human Neprilysin, sarcolipin, and ventricular cardiomyocytes indicates that the regulatory mechanism is evolutionarily conserved. By identifying a neprilysin as essential regulator of SERCA activity and Ca²⁺ homeostasis in cardiomyocytes, these data contribute to a more comprehensive understanding of the complex mechanisms that control muscle contraction and heart function in health and disease.

Proteomics of purified lamellocytes from Drosophila melanogaster HopTum-l identifies new membrane proteins and networks involved in their functions

In healthy Drosophila melanogaster larvae, plasmatocytes and crystal cells account for 95% and 5% of the hemocytes, respectively. A third type of hemocytes, lamellocytes, are rare, but their number increases after oviposition by parasitoid wasps. The lamellocytes form successive layers around the parasitoid egg, leading to its encapsulation and melanization, and finally the death of this intruder. However, the total number of lamellocytes per larva remains quite low even after parasitoid infestation, making direct biochemical studies difficult. Here, we used the Hop^Tum-l mutant strain that constitutively produces large numbers of lamellocytes to set up a purification method and analyzed their major proteins by 2D gel electrophoresis and their plasma membrane surface proteins by 1D SDS-PAGE after affinity purification. Mass spectrometry identified 430 proteins from 2D spots and 344 affinity-purified proteins from 1D bands, for a total of 639 unique proteins. Known lamellocyte markers such as PPO3 and the myospheroid integrin were among the components identified with specific chaperone proteins. Affinity purification detected other integrins, as well as a wide range of integrin-associated proteins involved in the formation and function of cell-cell junctions. Overall, the newly identified proteins indicate that these cells are highly adapted to the encapsulation process (recognition, motility, adhesion, signaling), but may also have several other physiological functions (such as secretion and internalization of vesicles) under different signaling pathways. These results provide the basis for further in vivo and in vitro studies of lamellocytes, including the development of new markers to identify coexisting populations and their respective origins and functions in Drosophila immunity.

Identification and bioinformatic analysis of neprilysin and neprilysin-like metalloendopeptidases in Drosophila melanogaster

The neprilysin (M13) family of metalloendopeptidases comprises highly conserved ectoenzymes that cleave and thereby inactivate many physiologically relevant peptides in the extracellular space. Impaired neprilysin activity is associated with numerous human diseases. Here, we present a comprehensive list and classification of M13 family members in Drosophila melanogaster. Seven Neprilysin (Nep) genes encode active peptidases, while 21 Neprilysin-like (Nepl) genes encode proteins predicted to be catalytically inactive. RNAseq data demonstrate that all 28 genes are expressed during development, often in a tissue-specific pattern. Most Nep proteins possess a transmembrane domain, whereas almost all Nepl proteins are predicted to be secreted.

Drosophila Middle-Term Memory: Amnesiac is Required for PKA Activation in the Mushroom Bodies, a Function Modulated by Neprilysin 1

In Drosophila, the mushroom bodies (MB) constitute the central brain structure for olfactory associative memory. As in mammals, the cAMP/PKA pathway plays a key role in memory formation. In the MB, Rutabaga (Rut) adenylate cyclase acts as a coincidence detector during associative conditioning to integrate calcium influx resulting from acetylcholine stimulation and G-protein activation resulting from dopaminergic stimulation. Amnesiac encodes a secreted neuropeptide required in the MB for two phases of aversive olfactory memory. Previous sequence analysis has revealed strong homology with the mammalian pituitary adenylate cyclase-activating peptide (PACAP). Here, we examined whether amnesiac is involved in cAMP/PKA dynamics in response to dopamine and acetylcholine co-stimulation in living flies. Experiments were conducted with both sexes, or with either sex. Our data show that amnesiac is necessary for the PKA activation process that results from coincidence detection in the MB. Since PACAP peptide is cleaved by the human membrane neprilysin hNEP, we searched for an interaction between Amnesiac and Neprilysin 1 (Nep1), a fly neprilysin involved in memory. We show that when Nep1 expression is acutely knocked down in adult MB, memory deficits displayed by amn hypomorphic mutants are rescued. Consistently, Nep1 inhibition also restores normal PKA activation in amn mutant flies. Taken together, the results suggest that Nep1 targets Amnesiac degradation to terminate its signaling function. Our work thus highlights a key role for Amnesiac in establishing within the MB the PKA dynamics that sustain middle-term memory (MTM) formation, a function modulated by Nep1.SIGNIFICANCE STATEMENT The Drosophila amnesiac gene encodes a secreted neuropeptide whose expression is required for specific memory phases in the mushroom bodies (MB), the olfactory memory center. Here, we show that Amnesiac is required for PKA activation resulting from coincidence detection, a mechanism by which the MB integrate two spatially distinct stimuli to encode associative memory. Furthermore, our results uncover a functional relationship between Amnesiac and Neprilysin 1 (Nep1), a membrane peptidase involved in memory and expressed in the MB. These results suggest that Nep1 modulates Amnesiac levels. We propose that on conditioning, Amnesiac release from the MB allows, via an autocrine process, the sustaining of PKA activation-mediating memory, which subsequently is inactivated by Nep1 degradation.

20-Hydroxyecdysone-upregulated proteases involved in Bombyx larval fat body destruction

During insect larval-pupal metamorphosis, the obsolete larval organs and tissues undergo histolysis and programmed cell death to recycle cellular materials. It has been demonstrated that some cathepsins are essential for histolysis in larval tissues, but the process of tissue destruction is not well documented. Fat body, the homologous organ to mammalian liver and adipose tissue, goes through a distinct destruction process during larval-pupal transition. Herein, we found that most of the Bombyx proteases - including Bombyx cathepsin B (BmCatB) (BmCatLL-2), Bombyx cathepsin D (BmCatD), Bombyx cathepsin L like-1 (BmCatLL-1) and -2(BmCatLL-2), Bombyx fibroinase (BmBcp), Bombyx matrix metalloprotease (BmMmp), Bombyx A disintegrin and metalloproteinase with thrombospondin motifs 1 (BmAdamTS-1), Bombyx A disintegrin and metalloproteinase with thrombospondin motifs like (BmAdamTS L) and Bombyx cysteine protease inhibitor (Bmbcpi)- were expressed highly in fat body during feeding and metamorphosis, with a peak occurring during the nonfeeding moulting or prepupal stage, as well as being responsive to 20-hydroxyecdysone (20E). The aforementioned protease genes expression was upregulated by injection of 20E into the feeding larvae, while blocking 20E signalling transduction led to downregulation. Western blotting and immunofluorescent staining of BmCatB and BmBcp confirmed the coincident variation of their messenger RNA (mRNA) and protein level during the development and after the treatments. Moreover, BmCatB, BmBcp, BmMmp and BmAdamTS-1 RNA interference all led to blockage of larval fat body destruction. Taken together, we conclude that 20E regulates larval fat body destruction by upregulating related protease gene expression and protein levels during larval-pupal transition.

Drosophila Neprilysin 1 Rescues Memory Deficits Caused by Amyloid-β Peptide

Neprilysins are Type II metalloproteinases known to degrade and inactivate a number of small peptides, in particular the mammalian amyloid-β peptide (Aβ). In Drosophila, several neprilysins expressed in the brain are required for middle-term (MTM) and long-term memory (LTM) in the dorsal paired medial (DPM) neurons, a pair of large neurons that broadly innervate the mushroom bodies (MB), the center of olfactory memory. These data indicate that one or several peptides need to be degraded for MTM and LTM. We have previously shown that the fly amyloid precursor protein (APPL) is required for memory in the MB. We show here that APPL is also required in adult DPM neurons for MTM and LTM formation. This finding prompted us to search for an interaction between neprilysins and Drosophila Aβ (dAβ), a cleavage product of APPL. To find out whether dAβ was a neprilysin's target, we used inducible drivers to modulate neprilysin 1 (Nep1) and dAβ expression in adult DPM neurons. Experiments were conducted either in both sexes or in females. We show that Nep1 inhibition makes dAβ expression detrimental to both MTM and LTM. Conversely, memory deficits displayed by dAβ-expressing flies are rescued by Nep1 overexpression. Consistent with behavioral data, biochemical analyses confirmed that Nep1 degrades dAβ. Together, our findings establish that Nep1 and dAβ expressed in DPM neurons are functionally linked for memory processes, suggesting that dAβ is a physiological target for Nep1.SIGNIFICANCE STATEMENT Neprilysins are endopeptidases known to degrade a number of small peptides and in particular the amyloid peptide. We previously showed that all four neprilysins expressed in the Drosophila brain are involved in specific phases of olfactory memory. Here we show that an increase in the level of the neprilysin 1 peptidase overcomes memory deficits induced by amyloid peptide in young flies. Together, the data reveal a functional interaction between neprilysin 1 and amyloid peptide, suggesting that neprilysin 1 degrades amyloid peptide. These findings raise the possibility that, under nonpathological conditions, mammalian neprilysins degrade amyloid peptide to ensure memory formation.

Drosophila Neprilysins Are Involved in Middle-Term and Long-Term Memory

Neprilysins are type II metalloproteinases known to degrade and inactivate a number of small peptides. Neprilysins in particular are the major amyloid-β peptide-degrading enzymes. In mouse models of Alzheimer's disease, neprilysin overexpression improves learning and memory deficits, whereas neprilysin deficiency aggravates the behavioral phenotypes. However, whether these enzymes are involved in memory in nonpathological conditions is an open question. Drosophila melanogaster is a well suited model system with which to address this issue. Several memory phases have been characterized in this organism and the neuronal circuits involved are well described. The fly genome contains five neprilysin-encoding genes, four of which are expressed in the adult. Using conditional RNA interference, we show here that all four neprilysins are involved in middle-term and long-term memory. Strikingly, all four are required in a single pair of neurons, the dorsal paired medial (DPM) neurons that broadly innervate the mushroom bodies (MBs), the center of olfactory memory. Neprilysins are also required in the MB, reflecting the functional relationship between the DPM neurons and the MB, a circuit believed to stabilize memories. Together, our data establish a role for neprilysins in two specific memory phases and further show that DPM neurons play a critical role in the proper targeting of neuropeptides involved in these processes.

SIGNIFICANCE STATEMENT

Neprilysins are endopeptidases known to degrade a number of small peptides. Neprilysin research has essentially focused on their role in Alzheimer's disease and heart failure. Here, we use Drosophila melanogaster to study whether neprilysins are involved in memory. Drosophila can form several types of olfactory memory and the neuronal structures involved are well described. Four neprilysin genes are expressed in adult Drosophila Using conditional RNA interference, we show that all four are specifically involved in middle-term memory (MTM) and long-term memory (LTM) and that their expression is required in the mushroom bodies and also in a single pair of closely connected neurons. The data show that these two neurons play a critical role in targeting neuropeptides essential for MTM and LTM.

Natural and laboratory mutations in kuzbanian are associated with zinc stress phenotypes in Drosophila melanogaster

Organisms must cope with altered environmental conditions such as high concentrations of heavy metals. Stress response to heavy metals is mediated by the metal-responsive transcription factor 1 (MTF-1), which is conserved from Drosophila to humans. MTF-1 binds to metal response elements (MREs) and changes the expression of target genes. kuzbanian (kuz), a metalloendopeptidase that activates the evolutionary conserved Notch signaling pathway, has been identified as an MTF-1 target gene. We have previously identified a putatively adaptive transposable element in the Drosophila melanogaster genome, named FBti0019170, inserted in a kuz intron. In this work, we investigated whether a laboratory mutant stock overexpressing kuz is associated with zinc stress phenotypes. We found that both embryos and adult flies overexpressing kuz are more tolerant to zinc compared with wild-type flies. On the other hand, we found that the effect of FBti0019170 on zinc stress tolerance depends on developmental stage and genetic background. Moreover, in the majority of the genetic backgrounds analyzed, FBti0019170 has a deleterious effect in unpolluted environments in pre-adult stages. These results highlight the complexity of natural mutations and suggest that besides laboratory mutations, natural mutations should be studied in order to accurately characterize gene function and evolution.

Role of Drosophila Amyloid Precursor Protein in Memory Formation

The amyloid precursor protein (APP) is a membrane protein engaged in complex proteolytic pathways. APP and its derivatives have been shown to play a central role in Alzheimer’s disease (AD), a progressive neurodegenerative disease characterized by memory decline. Despite a huge effort from the research community, the primary cause of AD remains unclear, making it crucial to better understand the physiological role of the APP pathway in brain plasticity and memory. Drosophila melanogaster is a model system well-suited to address this issue. Although relatively simple, the fly brain is highly organized, sustains several forms of learning and memory, and drives numerous complex behaviors. Importantly, molecules and mechanisms underlying memory processes are conserved from flies to mammals. The fly encodes a single non-essential APP homolog named APP-Like (APPL). Using in vivo inducible RNA interference strategies, it was shown that APPL knockdown in the mushroom bodies (MB)—the central integrative brain structure for olfactory memory—results in loss of memory. Several APPL derivatives, such as secreted and full-length membrane APPL, may play different roles in distinct types of memory phases. Furthermore, overexpression of Drosophila amyloid peptide exacerbates the memory deficit caused by APPL knockdown, thus potentiating memory decline. Data obtained in the fly support the hypothesis that APP acts as a transmembrane receptor, and that disruption of its normal function may contribute to cognitive impairment during early AD.

Drosophila neprilysins control insulin signaling and food intake via cleavage of regulatory peptides

Insulin and IGF signaling are critical to numerous developmental and physiological processes, with perturbations being pathognomonic of various diseases, including diabetes. Although the functional roles of the respective signaling pathways have been extensively studied, the control of insulin production and release is only partially understood. Herein, we show that in Drosophila expression of insulin-like peptides is regulated by neprilysin activity. Concomitant phenotypes of altered neprilysin expression included impaired food intake, reduced body size, and characteristic changes in the metabolite composition. Ectopic expression of a catalytically inactive mutant did not elicit any of the phenotypes, which confirms abnormal peptide hydrolysis as a causative factor. A screen for corresponding substrates of the neprilysin identified distinct peptides that regulate insulin-like peptide expression, feeding behavior, or both. The high functional conservation of neprilysins and their substrates renders the characterized principles applicable to numerous species, including higher eukaryotes and humans.

DOI:http://dx.doi.org/10.7554/eLife.19430.001

The hormone insulin and similar molecules called insulin-like peptides act as signals to control many processes in the body, including growth, stress responses and aging. Disrupting these signaling pathways can cause many diseases, with diabetes being the most common of these. Although the roles of the signaling pathways have been well studied, it is less clear how the body controls the production of insulin and insulin-like peptides.

Neprilysins are enzymes that can cut other proteins and peptides by a process known as hydrolysis. Their targets (known as “substrates”) include peptides that regulate a range of cell processes, and neprilysins have therefore been linked with many diseases. Fruit flies have at least five different neprilysin enzymes, but their substrates have not yet been identified. One of these, known as Nep4A, is produced in muscle tissue and appears to be important for muscles to work properly.

Hallier, Schiemann et al. reveal that Nep4A regulates the production of insulin-like peptides. The experiments used fruit fly larvae that had been genetically engineered so that the level of Nep4A could be altered in muscle tissue. Larvae with very high or very low levels of Nep4A eat less food, have smaller bodies and produce different amounts of insulin-like peptides compared to normal larvae.

Further experiments show that Nep4A can hydrolyze a number of peptides that regulate the production and the release of insulin-like peptides. This suggests that the enzymatic activity of neprilysins plays a direct role in controlling the production of insulin. The next challenge is to find out whether these findings apply to humans and other animals that also have neprilysins.

DOI:http://dx.doi.org/10.7554/eLife.19430.002

Sol narae (Sona) is a Drosophila ADAMTS involved in Wg signaling

ADAMTS (a disintegrin and metalloproteases with thrombospondin motif) family consists of secreted proteases, and is shown to cleave extracellular matrix proteins. Their malfunctions result in cancers and disorders in connective tissues. We report here that a Drosophila ADAMTS named Sol narae (Sona) promotes Wnt/Wingless (Wg) signaling. sona loss-of-function mutants are lethal and rare escapers had malformed appendages, indicating that sona is essential for fly development and survival. sona exhibited positive genetic interaction with wntless (wls) that encodes a cargo protein for Wg. Loss of sona decreased the level of extracellular Wg, and also reduced the expression level of Wg effector proteins such as Senseless (Sens), Distalless (Dll) and Vestigial (Vg). Sona and Wg colocalized in Golgi and endosomal vesicles, and were in the same protein complex. Furthermore, co-expression of Wg and Sona generated ectopic wing margin bristles. This study suggests that Sona is involved in Wg signaling by regulating the level of extracellular Wg.

Subcellular localisations of the CPTI collection of YFP-tagged proteins in Drosophila embryos

A key challenge in the post-genomic area is to identify the function of the genes discovered, with many still uncharacterised in all metazoans. A first step is transcription pattern characterisation, for which we now have near whole-genome coverage in Drosophila. However, we have much more limited information about the expression and subcellular localisation of the corresponding proteins. The Cambridge Protein Trap Consortium generated, via piggyBac transposition, over 600 novel YFP-trap proteins tagging just under 400 Drosophila loci. Here, we characterise the subcellular localisations and expression patterns of these insertions, called the CPTI lines, in Drosophila embryos. We have systematically analysed subcellular localisations at cellularisation (stage 5) and recorded expression patterns at stage 5, at mid-embryogenesis (stage 11) and at late embryogenesis (stages 15-17). At stage 5, 31% of the nuclear lines (41) and 26% of the cytoplasmic lines (67) show discrete localisations that provide clues on the function of the protein and markers for organelles or regions, including nucleoli, the nuclear envelope, nuclear speckles, centrosomes, mitochondria, the endoplasmic reticulum, Golgi, lysosomes and peroxisomes. We characterised the membranous/cortical lines (102) throughout stage 5 to 10 during epithelial morphogenesis, documenting their apico-basal position and identifying those secreted in the extracellular space. We identified the tricellular vertices as a specialized membrane domain marked by the integral membrane protein Sidekick. Finally, we categorised the localisation of the membranous/cortical proteins during cytokinesis.

Frazzled/DCC facilitates cardiac cell outgrowth and attachment during Drosophila dorsal vessel formation

Drosophila embryonic dorsal vessel (DV) morphogenesis is a highly stereotyped process that involves the migration and morphogenesis of 52 pairs of cardioblasts (CBs) in order to form a linear tube. This process requires spatiotemporally-regulated localization of signaling and adhesive proteins in order to coordinate the formation of a central lumen while maintaining simultaneous adhesion between CBs. Previous studies have shown that the Slit/Roundabout and Netrin/Unc5 repulsive signaling pathways facilitate site-specific loss of adhesion between contralateral CBs in order to form a luminal space. However, the concomitant mechanism by which attraction initiates CB outgrowth and discrete localization of adhesive proteins remains poorly understood. Here we provide genetic evidence that Netrin signals through DCC (Deleted in Colorectal Carcinoma)/UNC-40/Frazzled (Fra) to mediate CB outgrowth and attachment and that this function occurs prior to and independently of Netrin/UNC-5 signaling. fra mRNA is expressed in the CBs prior to and during DV morphogenesis. Loss-of-fra-function results in significant defects in cell shape and alignment between contralateral CB rows. In addition, CB outgrowth and attachment is impaired in both fra loss- and gain-of-function mutants. Deletion of both Netrin genes (NetA and NetB) results in CB attachment phenotypes similar to fra mutants. Similar defects are also seen when both fra and unc5 are deleted. Finally we show that Fra accumulates at dorsal and ventral leading edges of paired CBs, and this localization is dependent upon Netrin. We propose that while repulsive guidance mechanisms contribute to lumen formation by preventing luminal domains from coming together, site-specific Netrin/Frazzled signaling mediates CB attachment.

Ectodomain shedding and ADAMs in development

Proteolytic enzymes belonging to the A Disintegin And Metalloproteinase (ADAM) family are able to cleave transmembrane proteins close to the cell surface, in a process referred to as ectodomain shedding. Substrates for ADAMs include growth factors, cytokines, chemokines and adhesion molecules, and, as such, many ADAM proteins play crucial roles in cell-cell adhesion, extracellular and intracellular signaling, cell differentiation and cell proliferation. In this Review, we summarize the fascinating roles of ADAMs in embryonic and adult tissue development in both vertebrates and invertebrates.