Integrin β3 regulates apical dendritic morphology of pyramidal neurons throughout hippocampal CA3

In excitatory hippocampal pyramidal neurons, integrin β3 is critical for synaptic maturation and plasticity in vitro. Itgb3 is a potential autism susceptibility gene that regulates dendritic morphology in the cerebral cortex in a cell-specific manner. However, it is unknown what role Itgb3 could have in regulating hippocampal pyramidal dendritic morphology in vivo, a key feature that is aberrant in many forms of autism and intellectual disability. We found that Itgb3 mRNA is expressed in the stratum pyramidale of CA3. We examined the apical dendritic morphology of CA3 hippocampal pyramidal neurons in conditional Itgb3 knockouts and controls, utilizing the Thy1-GFP-M line. We fully reconstructed the apical dendrite of each neuron and determined each neuron's precise location along the dorsoventral, proximodistal, and radial axes of the stratum pyramidale. We found a very strong effect for Itgb3 expression on CA3 apical dendritic morphology: neurons from conditional Itgb3 knockouts had longer and thinner apical dendrites than controls, particularly in higher branch orders. We also assessed potential relationships between pairs of topographic or morphological variables, finding that most variable pairs were free from any linear relationships to each other. We also found that some neurons from controls, but not conditional Itgb3 knockouts, had a graded pattern of overall diameter along the dorsoventral and proximodistal axes of the stratum pyramidale of CA3. Taken together, Itgb3 is essential for constructing normal dendritic morphology in pyramidal neurons throughout CA3.

Regulation of dendritic spine length in corticopontine layer V pyramidal neurons by autism risk gene β3 integrin

The relationship between autism spectrum disorder (ASD) and dendritic spine abnormalities is well known, but it is unclear whether the deficits relate to specific neuron types and brain regions most relevant to ASD. Recent genetic studies have identified a convergence of ASD risk genes in deep layer pyramidal neurons of the prefrontal cortex. Here, we use retrograde recombinant adeno-associated viruses to label specifically two major layer V pyramidal neuron types of the medial prefrontal cortex: the commissural neurons, which put the two cerebral hemispheres in direct communication, and the corticopontine neurons, which transmit information outside the cortex. We compare the basal dendritic spines on commissural and corticopontine neurons in WT and KO mice for the ASD risk gene Itgb3, which encodes for the cell adhesion molecule β3 integrin selectively enriched in layer V pyramidal neurons. Regardless of the genotype, corticopontine neurons had a higher ratio of stubby to mushroom spines than commissural neurons. β3 integrin affected selectively spine length in corticopontine neurons. Ablation of β3 integrin resulted in corticopontine neurons lacking long (> 2 μm) thin dendritic spines. These findings suggest that a deficiency in β3 integrin expression compromises specifically immature spines on corticopontine neurons, thereby reducing the cortical territory they can sample. Because corticopontine neurons receive extensive local and long-range excitatory inputs before relaying information outside the cortex, specific alterations in dendritic spines of corticopontine neurons may compromise the computational output of the full cortex, thereby contributing to ASD pathophysiology.

Integrin β3 organizes dendritic complexity of cerebral cortical pyramidal neurons along a tangential gradient

Dysfunctional dendritic arborization is a key feature of many developmental neurological disorders. Across various human brain regions, basal dendritic complexity is known to increase along a caudal-to-rostral gradient. We recently discovered that basal dendritic complexity of layer II/III cortical pyramidal neurons in the mouse increases along a caudomedial-to-rostrolateral gradient spanning multiple regions, but at the time, no molecules were known to regulate that exquisite pattern. Integrin subunits have been implicated in dendritic development, and the subunit with the strongest associations with autism spectrum disorder and intellectual disability is integrin β3 (Itgb3). In mice, global knockout of Itgb3 leads to autistic-like neuroanatomy and behavior. Here, we tested the hypothesis that Itgb3 is required for increasing dendritic complexity along the recently discovered tangential gradient among layer II/III cortical pyramidal neurons. We targeted a subset of layer II/III cortical pyramidal neurons for Itgb3 loss-of-function via Cre-loxP-mediated excision of Itgb3. We tracked the rostrocaudal and mediolateral position of the targeted neurons and reconstructed their dendritic arbors. In contrast to controls, the basal dendritic complexity of Itgb3 mutant neurons was not related to their cortical position. Basal dendritic complexity of mutant and control neurons differed because of overall changes in branch number across multiple branch orders (primary, secondary, etc.), rather than any changes in the average length at those branch orders. Furthermore, dendritic spine density was related to cortical position in control but not mutant neurons. Thus, the autism susceptibility gene Itgb3 is required for establishing a tangential pattern of basal dendritic complexity among layer II/III cortical pyramidal neurons, suggesting an early role for this molecule in the developing brain.

Quercitrin and taxifolin stimulate osteoblast differentiation in MC3T3-E1 cells and inhibit osteoclastogenesis in RAW 264.7 cells

Flavonoids are natural antioxidants that positively influence bone metabolism. The present study screened among different flavonoids to identify biomolecules for potential use in bone regeneration. For this purpose, we used MC3T3-E1 and RAW264.7 cells to evaluate their effect on cell viability and cell differentiation. First, different doses of chrysin, diosmetin, galangin, quercitrin and taxifolin were analyzed to determine the optimum concentration to induce osteoblast differentiation. After 48h of treatment, doses ≥100μM of diosmetin and galangin and also 500μM taxifolin revealed a toxic effect on cells. The same effect was observed in cells treated with doses ≥100μM of chrysin after 14 days of treatment. However, the safe doses of quercitrin (200 and 500μM) and taxifolin (100 and 200μM) induced bone sialoprotein and osteocalcin mRNA expression. Also higher osteocalcin secreted levels were determined in 100μM taxifolin osteoblast treated samples when compared with the control ones. On the other hand, quercitrin and taxifolin decreased Rankl gene expression in osteoblasts, suggesting an inhibition of osteoclast formation. Indeed, osteoclastogenesis suppression by quercitrin and taxifolin treatment was observed in RAW264.7 cells. Based on these findings, the present study demonstrates that quercitrin and taxifolin promote osteoblast differentiation in MC3T3-E1 cells and also inhibit osteoclastogenesis in RAW264.7 cells, showing a positive effect of these flavonoids on bone metabolism.