Water-Dispersible Polydopamine-Coated Nanofibers for Stimulation of Neuronal Growth and Adhesion.

Hybrid nanomaterials have shown great potential in regenerative medicine due to the unique opportunities to customize materials properties for effectively controlling cellular growth. The peptide nanofiber-mediated auto-oxidative polymerization of dopamine, resulting in stable aqueous dispersions of polydopamine-coated peptide hybrid nanofibers, is demonstrated. The catechol residues of the polydopamine coating on the hybrid nanofibers are accessible and provide a platform for introducing functionalities in a pH-responsive polymer analogous reaction, which is demonstrated using a boronic acid modified fluorophore. The resulting hybrid nanofibers exhibit attractive properties in their cellular interactions: they enhance neuronal cell adhesion, nerve fiber growth, and growth cone area, thus providing great potential in regenerative medicine. Furthermore, the facile modification by pH-responsive supramolecular polymer analog reactions allows tailoring the functional properties of the hybrid nanofibers in a reversible fashion.

Serum Response Factor (SRF) Ablation Interferes with Acute Stress-Associated Immediate and Long-Term Coping Mechanisms.

Stress experience modulates behavior, metabolism, and energy expenditure of organisms. One molecular hallmark of an acute stress response is a rapid induction of immediate early genes (IEGs) such as c-Fos and Egr family members. IEG transcription in neurons is mediated by the neuronal activity-driven gene regulator serum response factor (SRF). We show a first role of SRF in immediate and long-lasting acute restraint stress (AS) responses. For this, we employed a standardized mouse phenotyping protocol at the German Mouse Clinic (GMC) including behavioral, metabolic, and cardiologic tests as well as gene expression profiling to analyze the consequences of forebrain-specific SRF deletion in mice exposed to AS. Adult mice with an SRF deletion in glutamatergic neurons (Srf; CaMKIIa-CreERT2 ) showed hyperactivity, decreased anxiety, and impaired working memory. In response to restraint AS, instant stress reactivity including locomotor behavior and corticosterone induction was impaired in Srf mutant mice. Interestingly, even several weeks after previous AS exposure, SRF-deficient mice showed long-lasting AS-associated changes including altered locomotion, metabolism, energy expenditure, and cardiovascular changes. This suggests a requirement of SRF for mediating long-term stress coping mechanisms in wild-type mice. SRF ablation decreased AS-mediated IEG induction and activity of the actin severing protein cofilin. In summary, our data suggest an SRF function in immediate AS reactions and long-term post-stress-associated coping mechanisms.

Proteomic analysis of SRF associated transcription complexes identified TFII-I as modulator of SRF function in neurons.

The serum response factor (SRF) is a neuronal activity regulated transcription factor (TF) mediating an immediate early (IEGs, e.g. cFos, Egr1) and actin cytoskeletal gene response. SRF activity is adjusted by two competing cofactor families, ternary complex factors (TCF; e.g. Elk-1) and myocardin related transcription factors (MRTF). We investigated mechanisms of SRF activation upon seizure associated neuronal activity in mice. SRF serine 103 phosphorylation or promoter binding was not obviously changed upon neuronal activation. In contrast, a SRF directed proteomic analysis uncovered established and potentially novel components of SRF associated protein complexes whose abundance was modified by neuronal activity. This included the general transcription factor TFII-I for which we provide a first functional analysis in neurons. TFII-I modulated neuronal SRF target gene expression, enhanced nerve fiber growth and modulated the shape of neuronal growth cones. Interestingly, TFII-I modulated two SRF cofactors, Elk-1 and MRTF-A, in opposite directions. TFII-I and Elk-1 co-expression enhanced SRF target gene abundance, SRF promoter binding and neurite growth, whereas TFII-I and MRTF-A resulted in opposite outcomes. In summary, we provide a first proteome wide analysis of SRF associated proteins. We characterized TFII-I as modulator of SRF activity by imposing differential impact on two SRF cofactors.

Neuronal expression of the transcription factor serum response factor modulates myelination in a mouse multiple sclerosis model.

In multiple sclerosis (MS), neurons in addition to inflammatory cells are now considered to mediate disease origin and progression. So far, molecular and cellular mechanisms of neuronal MS contributions are poorly understood. Herein we analyzed whether neuron-restricted signaling by the neuroprotective transcription factor serum response factor (SRF) modulates de- and remyelination in a rodent MS model. In the mouse cuprizone model, neuron- (Srf (flox/flox;CaMKCreERT2)) but not glia-specific (Srf (flox/flox;PlpCreERT2)) SRF depletion impaired demyelination suggesting impaired debris clearance by astrocytes and microglia. This supports an important role of SRF expression in neurons but not oligodendrocytes in de- and remyelination. During remyelination, NG2- and OLIG2-positive cells of the oligodendrocyte lineage as well as de novo mRNA synthesis of myelin genes were also reduced in neuron-specific Srf mutants. Using the stripe assay, we demonstrate that cortices of cuprizone-fed wild-type mice elicited astrocyte and microglia activation whereas this was abrogated in cuprizone-fed neuron-specific Srf mutants. We identified CCL chemokines (e.g. CCL2) as neuron-derived SRF-regulated paracrine signals rescuing immune cell activation upon neuronal SRF deletion. In summary, we uncovered important roles of neurons and neuronally expressed SRF in MS associated de- and remyelination.