Potential benefits of medium chain fatty acids in aging and neurodegenerative disease

Neurodegenerative diseases are a large class of neurological disorders characterized by progressive dysfunction and death of neurones. Examples include Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, and amyotrophic lateral sclerosis. Aging is the primary risk factor for neurodegeneration; individuals over 65 are more likely to suffer from a neurodegenerative disease, with prevalence increasing with age. As the population ages, the social and economic burden caused by these diseases will increase. Therefore, new therapies that address both aging and neurodegeneration are imperative. Ketogenic diets (KDs) are low carbohydrate, high-fat diets developed initially as an alternative treatment for epilepsy. The classic ketogenic diet provides energy via long-chain fatty acids (LCFAs); naturally occurring medium chain fatty acids (MCFAs), on the other hand, are the main components of the medium-chain triglyceride (MCT) ketogenic diet. MCT-based diets are more efficient at generating the ketone bodies that are used as a secondary energy source for neurones and astrocytes. However, ketone levels alone do not closely correlate with improved clinical symptoms. Recent findings suggest an alternative mode of action for the MCFAs, e.g., via improving mitochondrial biogenesis and glutamate receptor inhibition. MCFAs have been linked to the treatment of both aging and neurodegenerative disease via their effects on metabolism. Through action on multiple disease-related pathways, MCFAs are emerging as compounds with notable potential to promote healthy aging and ameliorate neurodegeneration. MCFAs have been shown to stimulate autophagy and restore mitochondrial function, which are found to be disrupted in aging and neurodegeneration. This review aims to provide insight into the metabolic benefits of MCFAs in neurodegenerative disease and healthy aging. We will discuss the use of MCFAs to combat dysregulation of autophagy and mitochondrial function in the context of “normal” aging, Parkinson’s disease, amyotrophic lateral sclerosis and Alzheimer’s disease

Plum modulates Myoglianin and regulates synaptic function in D. melanogaster

Alterations in the neuromuscular system underlie several neuromuscular diseases and play critical roles in the development of sarcopenia, the age-related loss of muscle mass and function. Mammalian Myostatin (MST) and GDF11, members of the TGF-β superfamily of growth factors, are powerful regulators of muscle size in both model organisms and humans. Myoglianin (MYO), the Drosophila homologue of MST and GDF11, is a strong inhibitor of synaptic function and structure at the neuromuscular junction in flies. Here, we identified Plum, a transmembrane cell surface protein, as a modulator of MYO function in the larval neuromuscular system. Reduction of Plum in the larval body-wall muscles abolishes the previously demonstrated positive effect of attenuated MYO signalling on both muscle size and neuromuscular junction structure and function. In addition, downregulation of Plum on its own results in decreased synaptic strength and body weight, classifying Plum as a (novel) regulator of neuromuscular function and body (muscle) size. These findings offer new insights into possible regulatory mechanisms behind ageing- and disease-related neuromuscular dysfunctions in humans and identify potential targets for therapeutic interventions

The BTB-zinc finger transcription factor abrupt acts as an epithelial oncogene in drosophila melanogaster through maintaining a progenitor-like cell state

The capacity of tumour cells to maintain continual overgrowth potential has been linked to the commandeering of normal self-renewal pathways. Using an epithelial cancer model in Drosophila melanogaster, we carried out an overexpression screen for oncogenes capable of cooperating with the loss of the epithelial apico-basal cell polarity regulator, scribbled (scrib), and identified the cell fate regulator, Abrupt, a BTB-zinc finger protein. Abrupt overexpression alone is insufficient to transform cells, but in cooperation with scrib loss of function, Abrupt promotes the formation of massive tumours in the eye/antennal disc. The steroid hormone receptor coactivator, Taiman (a homologue of SRC3/AIB1), is known to associate with Abrupt, and Taiman overexpression also drives tumour formation in cooperation with the loss of Scrib. Expression arrays and ChIP-Seq indicates that Abrupt overexpression represses a large number of genes, including steroid hormone-response genes and multiple cell fate regulators, thereby maintaining cells within an epithelial progenitor-like state. The progenitor-like state is characterised by the failure to express the conserved Eyes absent/Dachshund regulatory complex in the eye disc, and in the antennal disc by the failure to express cell fate regulators that define the temporal elaboration of the appendage along the proximo-distal axis downstream of Distalless. Loss of scrib promotes cooperation with Abrupt through impaired Hippo signalling, which is required and sufficient for cooperative overgrowth with Abrupt, and JNK (Jun kinase) signalling, which is required for tumour cell migration/invasion but not overgrowth. These results thus identify a novel cooperating oncogene, identify mammalian family members of which are also known oncogenes, and demonstrate that epithelial tumours in Drosophila can be characterised by the maintenance of a progenitor-like state

Troponin I and Tropomyosin regulate chromosomal stability and cell polarity

The Troponin-Tropomyosin (Tn-Tm) complex regulates muscle contraction through a series of Ca2+-dependent conformational changes that control actin-myosin interactions. Members of this complex in Drosophila include the actin-binding protein Troponin I (TnI), and two Tropomyosins (Tm1 and Tm2), which are thought to form heterodimers. We show here that precellular embryos of TnI, Tm1 and Tm2 mutants exhibit abnormal nuclear divisions with frequent loss of chromosome fragments. During cellularization, apico-basal polarity is also disrupted as revealed by the defective location of Discs large (Dlg) and its ligand Rapsynoid (Raps; also known as Partner of Inscuteable, Pins). In agreement with these phenotypes in early development, on the basis of RT-PCR assays of unfertilized eggs and germ line mosaics of TnI mutants, we also show that TnI is part of the maternal deposit during oogenesis. In cultures of the S2 cell line, native TnI is immunodetected within the nucleus and immunoprecipitated from nuclear extracts. SUMOylation at an identified site is required for the nuclear translocation. These data illustrate, for the first time, a role for TnI in the nucleus and/or the cytoskeleton of non-muscle cells. We propose that the Tn-Tm complex plays a novel function as regulator of motor systems required to maintain nuclear integrity and apico-basal polarity during early Drosophila embryogenesis.Peer Reviewe

Plum modulates Myoglianin and regulates synaptic function in D. melanogaster

Alterations in the neuromuscular system underlie several neuromuscular diseases and play critical roles in the development of sarcopenia, the age-related loss of muscle mass and function. Mammalian Myostatin (MST) and GDF11, members of the TGF-β superfamily of growth factors, are powerful regulators of muscle size in both model organisms and humans. Myoglianin (MYO), the Drosophila homologue of MST and GDF11, is a strong inhibitor of synaptic function and structure at the neuromuscular junction in flies. Here, we identified Plum, a transmembrane cell surface protein, as a modulator of MYO function in the larval neuromuscular system. Reduction of Plum in the larval body-wall muscles abolishes the previously demonstrated positive effect of attenuated MYO signalling on both muscle size and neuromuscular junction structure and function. In addition, downregulation of Plum on its own results in decreased synaptic strength and body weight, classifying Plum as a (novel) regulator of neuromuscular function and body (muscle) size. These findings offer new insights into possible regulatory mechanisms behind ageing- and disease-related neuromuscular dysfunctions in humans and identify potential targets for therapeutic interventions

The BTB-zinc Finger Transcription Factor Abrupt Acts as an Epithelial Oncogene in <i>Drosophila melanogaster</i> through Maintaining a Progenitor-like Cell State

<div><p>The capacity of tumour cells to maintain continual overgrowth potential has been linked to the commandeering of normal self-renewal pathways. Using an epithelial cancer model in <i>Drosophila melanogaster</i>, we carried out an overexpression screen for oncogenes capable of cooperating with the loss of the epithelial apico-basal cell polarity regulator, <i>scribbled</i> (<i>scrib</i>), and identified the cell fate regulator, Abrupt, a BTB-zinc finger protein. Abrupt overexpression alone is insufficient to transform cells, but in cooperation with <i>scrib</i> loss of function, Abrupt promotes the formation of massive tumours in the eye/antennal disc. The steroid hormone receptor coactivator, Taiman (a homologue of SRC3/AIB1), is known to associate with Abrupt, and Taiman overexpression also drives tumour formation in cooperation with the loss of Scrib. Expression arrays and ChIP-Seq indicates that Abrupt overexpression represses a large number of genes, including steroid hormone-response genes and multiple cell fate regulators, thereby maintaining cells within an epithelial progenitor-like state. The progenitor-like state is characterised by the failure to express the conserved Eyes absent/Dachshund regulatory complex in the eye disc, and in the antennal disc by the failure to express cell fate regulators that define the temporal elaboration of the appendage along the proximo-distal axis downstream of Distalless. Loss of <i>scrib</i> promotes cooperation with Abrupt through impaired Hippo signalling, which is required and sufficient for cooperative overgrowth with Abrupt, and JNK (Jun kinase) signalling, which is required for tumour cell migration/invasion but not overgrowth. These results thus identify a novel cooperating oncogene, identify mammalian family members of which are also known oncogenes, and demonstrate that epithelial tumours in <i>Drosophila</i> can be characterised by the maintenance of a progenitor-like state.</p></div

<i>ab</i> overexpression in <i>scrib</i> mutant clones promotes neoplastic overgrowth of eye/antennal epithelial tissue throughout an extended larval stage.

<p>Mosaic eye/antennal discs (anterior to the left in this and all subsequent figures) generated with <i>ey-FLP</i> and taken from larvae 5 days (A–H) or 9 days (I,J) AEL. Clones are positively marked by GFP (white, or green in merges). Tissue morphology is shown by F-actin (red in merges), and cell fate by Elav and Dll (white, or blue in merges – dark blue when overlaid with GFP). Brain lobes in I,J are marked by BL. GFP (panels A–J), Elav (panels A′,C′,E′,G′,I′), Dll (panel B′,D′,F′H′,J′) and merges (panels A″–J″). (A,B) Control mosaic eye/antennal discs show the normal pattern of Elav expression in developing photoreceptor cells, and Dll expression within the antenna. (C,D) <i>scrib¹</i> cells still express Elav and Dll, although the normal pattern of Elav-expressing photoreceptor cells is disrupted by alterations in tissue morphology. (E,F) <i>ab</i> overexpressing clones still express Elav and Dll, but are often larger than control clones within the antennal region, and in some discs ectopic domains of Dll expression are observed (F, arrowhead). (G,H) <i>scrib¹</i>+<i>ab</i> clones are larger than <i>scrib¹</i> clones, and do not express Elav (G, arrowhead), although Dll expression is maintained (H, arrowhead). (I,J) <i>scrib¹</i>+<i>ab</i> clones at day 9 are massively overgrown and the two eye/antennal discs fuse with each other and with the Elav-expressing brain lobes (I), whilst the Dll-expressing domain in the antennal disc is maintained (J). Yellow scale bar = 50 µm.</p

Model illustrating the pathways involved in <i>scrib</i>⁻+<i>ab</i> cooperative tumour overgrowth.

<p>Ab cooperates with the loss of <i>scrib</i> to form invasive tumours through modulating the expression of multiple genes involved in all aspects of tumour formation. Potential targets of Ab include genes involved with blocking apoptosis and promoting tumour overgrowth (eg. <i>hid</i>, <i>Buffy</i>, <i>ft</i>, <i>dm</i>, <i>Pten</i>), genes required for eye/antennal disc differentiation (eg. <i>ct</i>, <i>dac</i>, <i>eya</i>, <i>dan</i>), genes involved in promoting cell invasion (eg. <i>Mmp1</i>), and genes involved in the ecdysone-induced pupariation response (eg. <i>Blimp-1</i>, <i>br</i>, <i>Eip75E</i>, <i>Hr39</i>). Whilst not shown on the figure, the steroid hormone receptor coactivator Tai is both required for <i>ab</i>-driven tumour overgrowth and sufficient to cooperate with the loss of <i>scrib</i>, consistent with the possibility that Ab acts in concert with Tai to drive tumour formation. Loss of <i>scrib</i> activates JNK-mediated apoptosis, however, <i>ab</i> overexpression abrogates the apoptotic response, thereby unmasking a key role for JNK in promoting tumour cell migration and invasion through the expression of JNK-induced genes such as <i>Mmp1</i>. Loss of <i>scrib</i> also promotes aPKC-dependent Yki activity that is required and sufficient to cooperate with Ab by impairing differentiation and promoting tumour overgrowth. Other pathways deregulated in <i>scrib</i> mutants may participate in the tumour phenotype and promote the full spectrum of differentiation defects seen in <i>scrib</i>⁻+<i>ab</i> tumours (indicated by the dotted blocking arrow and question mark), such as Dac repression in the antenna. Green = downregulated genes, and red = upregulated genes.</p

Overexpression of <i>ab</i> in <i>scrib</i> mutant clones promotes the retention of a progenitor-like state in the eye and antennal disc.

<p><i>ey-FLP</i> induced eye/antennal disc clones at ∼5 days AEL. Clones are marked by GFP (white, or green in merges), and cell fate is shown by the expression of Dac, Dan and Hth (white, and magenta when overlaid with GFP in the merges) in wild type control clones (A,E,I), <i>scrib¹</i> clones (B,F,J), <i>ab</i> overexpressing clones (C,G,K), and <i>scrib¹</i>+<i>ab</i> clones (D,H,L). GFP (panels A–L), Dac (panels A′–D′), Dan (panels E′–H′), Hth (panels I′–L′) and merges (panels A″–L″). (A–D) Dac expression is only slightly reduced in <i>scrib¹</i> clones (B, yellow arrowhead), and unaffected in <i>ab</i> overexpressing clones in the eye disc, although ectopic Dac expressing antennal-like structures are sometimes observed in the antenna (C, arrowhead). <i>scrib¹</i>+<i>ab</i> clones do not express Dac (D, arrowhead; the magenta staining observed around some clones is derived from GFP bleed-through from underlying sections. (E–H) Dan levels are reduced in <i>scrib¹</i> clones both in the antennal and eye disc (F, arrowheads). <i>ab</i> overexpressing clones do not affect Dan levels in the eye disc (G, arrowhead), although Dan is slightly repressed in the antenna (G, arrow), albeit ectopically expressed in the ectopic antennal-like structures. Dan is repressed in <i>scrib¹</i>+<i>ab</i> clones (H, arrowhead). (I–L) Hth expression is generally unaffected in <i>scrib¹</i> clones (J). In <i>ab</i> overexpressing clones, levels of Hth are slightly reduced in the eye disc (K, arrow), and large clones in the antennal disc do not express Hth (K, arrowhead). In <i>scrib¹</i>+<i>ab</i> clones, Hth is expressed in some clones within the eye disc (L, arrowhead), but not all clones (L, arrow), and is generally reduced in antennal disc clones (L, and data not shown). (M) Diagram summarising the expression of cell fate markers in both wild type eye/antennal discs, as well as in eye/antennal disc <i>scrib</i>⁻+<i>ab</i> tumours (green). In the antenna, proximal refers to the outer circular domains of the tissue, whilst distal refers to the inner, central domains. See <b><a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003627#pgen.1003627.s013" target="_blank">Figures S9</a></b> and <b><a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003627#pgen.1003627.s014" target="_blank">S10</a></b> for immunohistochemical images of Tsh, Ey, Eya, Ato and Sens; and <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003627#pgen-1003627-t002" target="_blank"><b>Table 2</b></a> for a summary of these results. Yellow scale bar = 50 µm.</p

Identified <i>scrib⁻</i> cooperating oncogenes.

<p>Identified <i>scrib⁻</i> cooperating oncogenes.</p