Biomedical subjects

Michelle M Aarts

Publications and source records attributed to Michelle M Aarts.

8 recordsLinked to original sources

PubMed2005

TRPMs and neuronal cell death.

Death of CNS neurons during acute injury occurs as a result of a complex combination of excitotoxicity, necrosis, apoptosis, oedema and inflammatory reactions. Neuroprotection via glutamate receptor blockade or antioxidant or anti-inflammatory therapy have not proven effective in the clinical treatment of brain damage due to narrow therapeutic windows, poor pharmacokinetics or blockade of the signalling essential for normal excitatory neurotransmission and neuronal survival. Recent work in neuronal biochemistry, genomics and proteomics has increased understanding of the molecular organization of the excitatory synapse and the neuronal postsynaptic density. Transient receptor potential (TRP) channels are an exciting new family of cation channels that are highly expressed in the brain. Several members can be induced by oxidative stress and oxygen free radicals, both of which play important roles in neurodegeneration. Recent work has indicated that members of the melastatin subfamily (TRPM) of TRP proteins, particularly TRPM7 and TRPM2, may play key roles in neuronal death that is activated by oxidative stress and downstream from excitotoxic signal pathways. This discovery provides an exiting new avenue for research into the pathophysiology and treatment of acute neurodegeneration.

Calcium↗

PubMed2005

TRPM7 and ischemic CNS injury.

Ischemic brain damage represents a major source of morbidity and mortality in westernized society and poses a significant financial burden on the health care system. To date, few effective therapies have been realized to treat stroke and once promising avenues such as antiexcitotoxic therapy with NMDA receptor antagonists have not proven clinically useful. Thus, we need to identify new targets for research and therapeutic intervention of the neurodegeneration caused by stroke. Transient receptor potential (TRP) channels are an exciting new family of cation channels that respond to intracellular and extracellular stimuli. Indeed, several members can be induced by oxidative stress and oxygen free radicals. We have recently demonstrated that one member, TRPM7, is an essential mediator of anoxic neuronal death that is activated by oxidative stress, in parallel to excitotoxic signal pathways. Thus, future treatment of ischemic brain injury may need to include strategies that inhibit or modulate TRPM7 activity. Further investigation of the physiology and pathophysiology of TRPM7 and other TRP family members is needed to provide both pharmacological targets and a better understanding of ischemic brain disorders.

Brain Ischemia↗

PubMed2004

Molecular mechanisms underlying specificity of excitotoxic signaling in neurons.

The central role of glutamate receptors in mediating excitotoxic neuronal death in stroke, epilepsy and trauma has been well established. Glutamate is the major excitatory amino acid transmitter within the CNS and it's signaling is mediated by a number of postsynaptic ionotropic and metabotropic receptors. Although calcium ions are considered key regulators of excitotoxicity, new evidence suggests that specific second messenger pathways rather than total Ca(2+) load, are responsible for mediating neuronal degeneration. Glutamate receptors are found localized at the synapse within electron dense structures known as the postsynaptic density (PSD). Localization at the PSD is mediated by binding of glutamate receptors to submembrane proteins such as actin and PDZ containing proteins. PDZ domains are conserved motifs that mediate protein-protein interactions and self-association. In addition to glutamate receptors PDZ-containing proteins bind a multitude of intracellular signal molecules including nitric oxide synthase. In this way PDZ proteins provide a mechanism for clustering glutamate receptors at the synapse together with their corresponding signal transduction proteins. PSD organization may thus facilitate the individual neurotoxic signal mechanisms downstream of receptors during glutamate overactivity. Evidence exists showing that inhibiting signals downstream of glutamate receptors, such as nitric oxide and PARP-1 can reduce excitotoxic insult. Furthermore we have shown that uncoupling the interaction between specific glutamate receptors from their PDZ proteins protects neurons against glutamate-mediated excitotoxicity. These findings have significant implications for the treatment of neurodegenerative diseases using therapeutics that specifically target intracellular protein-protein interactions.

Amino Acid Motifs↗

PubMed2003

Novel concepts in excitotoxic neurodegeneration after stroke.

Brain injury following cerebral ischaemia (stroke) involves a complex combination of pathological processes, including excitotoxicity and inflammation leading to necrotic and apoptotic forms of cell death. At the cellular level, excitotoxicity is mediated by glutamate and its cognate receptors, resulting in increased intracellular calcium and free radical production, and eventual cell death. Recent evidence suggests that scaffolding molecules that associate with glutamate receptors at the postsynaptic density allow coupling of receptor activity to specific second messengers capable of mediating excitotoxicity. These findings have important implications in the search for effective neuroprotective therapies in treating stroke.

Animals↗

PubMed2003

Novel treatment of excitotoxicity: targeted disruption of intracellular signalling from glutamate receptors.

Glutamate signalling plays key physiological roles in excitatory neurotransmission and CNS plasticity, but also mediates excitotoxicity, the process responsible for triggering neurodegeneration through glutamate receptor overactivation. Excitotoxicity is thought to be a key neurotoxic mechanism in neurological disorders, including brain ischemia, CNS trauma and epilepsy. However, treating excitotoxicity using glutamate receptor antagonists has not proven clinically viable, necessitating more sophisticated approaches. Increasing knowledge of the composition of the postsynaptic density at glutamatergic synapses has allowed us to extend our understanding of the molecular mechanisms of excitotoxicity and to dissect out the distinct signalling pathways responsible for excitotoxic damage. Key molecules in these pathways are physically linked to the cytoplasmic face of glutamate receptors by scaffolding proteins that exhibit binding specificity for some receptors over others. This imparts specificity to physiological and pathological glutamatergic signalling. Recently, we have capitalized on this knowledge and, using targeted peptides to selectively disrupt intracellular interactions linked to glutamate receptors, have blocked excitotoxic signalling in neurones. This therapeutic approach circumvents the negative consequences of blocking glutamate receptors, and may be a practical strategy for treating neurological disorders that involve excitotoxicity.

Animals↗

PubMed2003

Enhanced vulnerability to NMDA toxicity in sublethal traumatic neuronal injury in vitro.

Traumatic brain injury causes neuronal disruption and triggers secondary events leading to additional neuronal death. To study injuries triggered by secondary events, we exposed cultured cortical neurons to sublethal mechanical stretch, thus eliminating confounding death from primary trauma. Sublethally stretched neurons maintained cell membrane integrity, viability, and electrophysiological function. However, stretching induced in the cells a heightened vulnerability to subsequent challenges with L-glutamate or NMDA. This heightened vulnerability was specifically mediated by NMDA receptors (NMDARs), as stretched neurons did not become more vulnerable to either kainate toxicity or to that induced by the Ca(2+) ionophore A23187. Stretch-enhanced vulnerability to NMDA occurred independently of endogenous glutamate release, but required Ca(2+) and Na(+) influx through NMDARs. Stretch did not affect the electrophysiological properties of NMDARs nor excitatory synaptic activity, indicating that specificity of enhanced vulnerability to NMDA involves postsynaptic mechanisms downstream from NMDARs. To test whether this specificity requires physical interactions between NMDARs and cytoskeletal elements, we perturbed actin filaments and microtubules, both of which are linked to NMDARs. This had no effect on the stretch-induced vulnerability to NMDA, suggesting that sublethal stretch does not affect cell survival through the cytoskeleton. Our data illustrate that sublethal in vitro stretch injury triggers distinct signaling pathways that lead to secondary injury, rather than causing a generalized increase in vulnerability to secondary insults.

Animals↗

PubMed2003

Peptide action in stroke therapy.

Glutamate receptor antagonists, although effective in preventing in vitro excitotoxic death, also block the glutamatergic signalling that is essential for normal excitatory neurotransmission and neuronal survival. This has contributed to the failure of clinical trials employing glutamate receptor antagonists as stroke therapeutics. However, recent years have seen an increased understanding of the molecular organisation of glutamate receptors in the neuronal postsynaptic density. This and a dissection of their associated intracellular signalling cascades has allowed the identification of distinct pathways responsible for excitotoxicity. It has become possible to uncouple toxic signalling cascades from glutamate receptors by targeting the interactions of membrane receptors with downstream proteins. Toxic signalling can be effectively uncoupled from glutamate receptors using targeted, cell-permeable peptides to disrupt specific protein-protein interactions. This approach does not block essential excitatory neurotransmission, but attenuates neurotoxic signals specifically and reduces stroke damage. This novel approach to blocking excitotoxic signalling in cerebral ischaemia may constitute a practical approach to stroke therapy.

Animals↗

PubMed2002

1Alpha,25-dihydroxyvitamin D3 promotes vascularization of the chondro-osseous junction by stimulating expression of vascular endothelial growth factor and matrix metalloproteinase 9.

Vitamin D deficiency results in defects in endochondral bone development characteristic of rickets, which include elongation of the cartilaginous growth plates and disorganization of the primary spongiosa. These defects are caused in part by impaired cartilage mineralization and vascularization of the chondro-osseous junction. Blood vessel invasion of mineralized cartilage is an essential step in endochondral ossification, providing access for cells that degrade cartilage as well as those that form bone. Vascular endothelial growth factor (VEGF) was shown to be a key regulator of this process when infusion of a dominant negative VEGF receptor effectively blocked vascular invasion and endochondral ossification in the growth plates of juvenile mice. Here, we show that the active metabolite of vitamin D 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] directly stimulates transcription of mRNAs encoding VEGF121 and -165 isoforms in the CFK2 chondrogenic cell line. Enhanced VEGF expression also was evident in growth plate chondrocytes and osteoblasts in the tibia of juvenile mice treated systemically with 1alpha,25(OH)2D3. This was seen in conjunction with enhanced expression of matrix metalloproteinase (MMP) 9, which activates VEGF stored in the cartilage matrix, in osteoclastic cells adjacent to the chondro-osseous junction. The alterations in VEGF and MMP-9 expression were accompanied by enhanced vascular invasion of mineralized cartilage, as assessed by CD31 immunoreactivity. These results provide evidence that 1alpha,25(OH)2D3 signaling stimulates VEGF and MMP-9 gene expression and promotes neovascularization of the epiphyseal growth plate in vivo through increased availability of active growth factor.

Animals↗