Pattern detection in the TGFß cascade controls the induction of long-term synaptic plasticity.

Transforming growth factor ß (TGFß) is required for long-term memory (LTM) for sensitization in Aplysia. When LTM is induced using a two-trial training protocol, TGFß inhibition only blocks LTM when administrated at the second, not the first trial. Here, we show that TGFß acts as a "repetition detector" during the induction of two-trial LTM. Secretion of the biologically inert TGFß proligand must coincide with its proteolytic activation by the Bone morphogenetic protein-1 (BMP-1/Tolloid) metalloprotease, which occurs specifically during trial two of our two-trial training paradigm. This paradigm establishes long-term synaptic facilitation (LTF), the cellular correlate of LTM. BMP-1 application paired with a single serotonin (5HT) pulse induced LTF, whereas neither a single 5HT pulse nor BMP-1 alone effectively did so. On the other hand, inhibition of endogenous BMP-1 activity blocked the induction of two-trial LTF. These results suggest a unique role for TGFß in the interaction of repeated trials: during learning, repeated stimuli engage separate steps of the TGFß cascade that together are necessary for the induction of long-lasting memories.

Mitochondrial ATP synthase c-subunit leak channel triggers cell death upon loss of its F1 subcomplex.

Mitochondrial ATP synthase is vital not only for cellular energy production but also for energy dissipation and cell death. ATP synthase c-ring was suggested to house the leak channel of mitochondrial permeability transition (mPT), which activates during excitotoxic ischemic insult. In this present study, we purified human c-ring from both eukaryotic and prokaryotic hosts to biophysically characterize its channel activity. We show that purified c-ring forms a large multi-conductance, voltage-gated ion channel that is inhibited by the addition of ATP synthase F1 subcomplex. In contrast, dissociation of F1 from FO occurs during excitotoxic neuronal death suggesting that the F1 constitutes the gate of the channel. mPT is known to dissipate the osmotic gradient across the inner membrane during cell death. We show that ATP synthase c-subunit knock down (KD) prevents the osmotic change in response to high calcium and eliminates large conductance, Ca2+ and CsA sensitive channel activity of mPT. These findings elucidate the gating mechanism of the ATP synthase c-subunit leak channel (ACLC) and suggest how ACLC opening is regulated by cell stress in a CypD-dependent manner.

ATP Synthase c-Subunit Leak Causes Aberrant Cellular Metabolism in Fragile X Syndrome.

Loss of the gene (Fmr1) encoding Fragile X mental retardation protein (FMRP) causes increased mRNA translation and aberrant synaptic development. We find neurons of the Fmr1-/y mouse have a mitochondrial inner membrane leak contributing to a "leak metabolism." In human Fragile X syndrome (FXS) fibroblasts and in Fmr1-/y mouse neurons, closure of the ATP synthase leak channel by mild depletion of its c-subunit or pharmacological inhibition normalizes stimulus-induced and constitutive mRNA translation rate, decreases lactate and key glycolytic and tricarboxylic acid (TCA) cycle enzyme levels, and triggers synapse maturation. FMRP regulates leak closure in wild-type (WT), but not FX synapses, by stimulus-dependent ATP synthase ß subunit translation; this increases the ratio of ATP synthase enzyme to its c-subunit, enhancing ATP production efficiency and synaptic growth. In contrast, in FXS, inability to close developmental c-subunit leak prevents stimulus-dependent synaptic maturation. Therefore, ATP synthase c-subunit leak closure encourages development and attenuates autistic behaviors.

Parkinson's disease protein DJ-1 regulates ATP synthase protein components to increase neuronal process outgrowth.

Familial Parkinson's disease (PD) protein DJ-1 mutations are linked to early onset PD. We have found that DJ-1 binds directly to the F1FO ATP synthase ß subunit. DJ-1's interaction with the ß subunit decreased mitochondrial uncoupling and enhanced ATP production efficiency while in contrast mutations in DJ-1 or DJ-1 knockout increased mitochondrial uncoupling, and depolarized neuronal mitochondria. In mesencephalic DJ-1 KO cultures, there was a progressive loss of neuronal process extension. This was ameliorated by a pharmacological reagent, dexpramipexole, that binds to ATP synthase, closing a mitochondrial inner membrane leak and enhancing ATP synthase efficiency. ATP synthase c-subunit can form an uncoupling channel; we measured, therefore, ATP synthase F1 (ß subunit) and c-subunit protein levels. We found that ATP synthase ß subunit protein level in the DJ-1 KO neurons was approximately half that found in their wild-type counterparts, comprising a severe defect in ATP synthase stoichiometry and unmasking c-subunit. We suggest that DJ-1 enhances dopaminergic cell metabolism and growth by its regulation of ATP synthase protein components.

TFII-I and AP2α Co-Occupy the Promoters of Key Regulatory Genes Associated with Craniofacial Development.

OBJECTIVES: The aim of this study is to define the candidate target genes for TFII-I and AP2α regulation in neural crest progenitor cells. DESIGN: The GTF2I and GTF2IRD1 genes encoding the TFII-I family of transcription factors are prime candidates for the Williams-Beuren syndrome, a complex multisystem disorder characterized by craniofacial, skeletal, and neurocognitive deficiencies. AP2α, a product of the TFAP2A gene, is a master regulator of neural crest cell lineage. Mutations in TFAP2A cause branchio-oculo-facial syndrome characterized by dysmorphic facial features and orofacial clefts. In this study, we examined the genome-wide promoter occupancy of TFII-I and AP2α in neural crest progenitor cells derived from in vitro-differentiated human embryonic stem cells. RESULTS: Our study revealed that TFII-I and AP2α co-occupy a selective set of genes that control the specification of neural crest cells. CONCLUSIONS: The data suggest that TFII-I and AP2α may coordinately control the expression of genes encoding chromatin-modifying proteins, epigenetic enzymes, transcription factors, and signaling proteins.