Biochemical and Biophysical Research Communications
INT131 increases dendritic arborization and protects against Aβ toxicity by inducing mitochondrial changes in hippocampal neurons
Introduction
Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptors involved in energy homeostasis and include the PPARα, β/δ and γ isoforms. This type of receptor forms obligate heterodimers with the retinoid X receptor to modulate gene transcription [1], [2]. These receptors are activated by fatty acids, eicosanoids, fibrates and thiazolidinediones (TZD) [3]. PPARγ is a clinically validated target for the treatment of type 2 diabetes mellitus (T2DM) due to its critical roles in the functions of the liver, muscle, adipocytes and macrophages and has a direct impact on dyslipidemia, atherosclerosis, cardiovascular disease and insulin resistance [4]. In this regard, TZDs are small molecules that act as full PPARγ agonists, increasing insulin sensitivity and restoring insulin and glucose levels in hyperglycemic patients, and they have been clinically validated. However, the modulation of a wide spectrum of target genes also elicits undesirable effects, such as increased weight gain, cardiomegaly, hemodilution, bone fracture and plasma volume expansion [5], [6].
Recently, next-generation ligands called selective PPARγ modulators (SPPARMs), which exert partial agonist activity when compared with TZDs, have been described. INT131 is a potent, non-TZD SPPARM developed for the treatment of T2DM. A variety of biochemical and cell-based assays of INT131 have shown that over a 4 week treatment period, compared with placebo, INT131 was well tolerated and significantly improved insulin sensitivity and glucose tolerance without any undesirable effects in T2DM patients [5], [7].
For more than 25 years, the “amyloid cascade hypothesis” has dominated our understanding of the etiology and progression of Alzheimer's disease (AD), which is characterized by the extracellular deposition of amyloid-β peptide (Aβ) and the formation of intracellular neurofibrillary tangles (NFTs), triggering several molecular changes within the brain and leading to the development of the pathological and clinical hallmarks observed in AD [8].
Previously, we have shown that PPARγ at both the mRNA and protein levels is present in rat primary hippocampal neurons, and PPARγ full agonists, such as troglitazone and rosiglitazone (Rosi), but not the PPARγ antagonist GW-9662, prevent Aβ-dependent neurotoxicity [9], [10].
Concomitant activation of the PPARγ co-activator 1-alpha (PGC-1α), a cold-inducible co-activator of nuclear receptors that has been associated with mitochondrial biogenesis, might contribute to the modulation of neuronal mitochondrial density and functionality, enhancing the PPARγ-neuroprotective activity in AD [11].
The aim of our work was to evaluate the effects of INT131 and Rosi as PPARγ agonists in primary hippocampal neurons, including neuronal survival under Aβ challenge, PGC-1α protein expression level and the putative role in mitochondrial localization within synapses in the hippocampal CA1 region. Here, we report that INT131, a drug that has been shown to be safe, had better effects on neurons than other agonists such as Rosi, including increased dendritic branching, promotion of neuronal survival against Aβ amyloid toxicity, increased expression of PGC1-1α and modulation of neuronal mitochondrial dynamics.
Section snippets
Chemicals and reagents
Culture media, serum and supplements were from Sigma (St. Louis, MO) and Gibco BRL (Paisley, UK). Rosi, INT131 and GW-9662 (GW) were obtained from Cayman Chemical (Ann Arbor, MI). An anti-COX IV antibody was purchased from Santa Cruz Biotechnology (San Diego, CA). MitoTracker Orange was purchased from Molecular Probes (Carlsbad, CA). An anti-PGC-1α antibody was obtained from Abcam Inc. (Cambridge, MA). A BCA Protein Assay Kit was purchased from Pierce Chemical Co. (Rockford, IL). Western
INT131 treatment induces an increase in dendritic arborization
To study the complexity of the dendritic tree, a main feature of mature neurons, we used neuronal cultures transfected with EGFP and subjected them to Scholl analysis, enabling us to determine the number, length and complexity of neuronal processes. Primary hippocampal neurons were treated with increasing doses of the full PPARγ agonist Rosi (1–10 μM) or the specific agonist INT131 (1-10-100 nM) (Fig. 1A shows representative micrographs). Our results showed an increase in the complexity of
Discussion
AD is a neurodegenerative disorder with progressive dementia in the elderly and is accompanied by two main structural changes in the brain: senile plaque formation and intracellular protein deposits as neurofibrillary tangles. Consistent with the “amyloid cascade hypothesis”, we have previously shown that PPARγ agonists can activate PPARγ and reverse the morphological neurodegenerative changes in neurons exposed to Aβ. Moreover, we showed that the full agonists, such as troglitazone and Rosi,
Acknowledgments
*This work was supported by grants CONICYT-PFB 12/2007 from the Basal Centre for Excellence in Science and Technology and FONDECYT 1160724, both to NCI. A pre-doctoral fellowship was awarded to JAR from CONICYT. JAG is a PhD student from Universitat Pompeu Fabra, Barcelona, Spain.
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