Tetanus toxin C fragment-conjugated nanoparticles for targeted drug delivery to neurons.

The use of nanoparticles for targeted drug delivery is often facilitated by specific conjugation of functional targeting molecules to the nanoparticle surface. We compared different biotin-binding proteins (avidin, streptavidin, or neutravidin) as crosslinkers to conjugate proteins to biodegradable nanoparticles prepared from poly(lactic-co-glycolic acid) (PLGA)-polyethylene glycol (PEG)-biotin polymers. Avidin gave the highest levels of overall protein conjugation, whereas neutravidin minimized protein non-specific binding to the polymer. The tetanus toxin C fragment (TTC), which is efficiently retrogradely transported in neurons and binds to neurons with high specificity and affinity, retained the ability to bind to neuroblastoma cells following amine group modifications. TTC was conjugated to nanoparticles using neutravidin, and the resulting nanoparticles were shown to selectively target neuroblastoma cells in vitro. TTC-conjugated nanoparticles have the potential to serve as drug delivery vehicles targeted to the central nervous system.

A porous photocurable elastomer for cell encapsulation and culture.

Encapsulating cells within a polymer matrix creates a three-dimensional (3D) scaffold that may more accurately represent the native microenvironment and cell organization. Here we report a porous scaffold prepared from a photocurable elastomer, poly(glycerolco-sebacate)-acrylate (PGSA). The scaffold porosity, swelling, mass loss, toxicity and mechanical properties, suggest that porous PGSA could be used to support the growth and differentiation of encapsulated cells. Neuroblastoma (NB) and human embryonic stem cells (hESCs) were encapsulated into the matrix and found to adhere to the material and interact with each other within 24h. After 7 days, encapsulated NB cells were found to grow, and form matrix fibrils and tissue. Undifferentiated hESCs proliferated and differentiated in the PGSA scaffold. In vivo experiments showed that both porous scaffolds have similar biocompatibility profiles as non-porous PGSA, but porous PGSA promotes tissue ingrowth, as compared to non-porous PGSA. We therefore propose that porous PGSA scaffolds can provide a logistical template for 3D growth of cells and tissue engineering.

Hyaluronic acid hydrogel for controlled self-renewal and differentiation of human embryonic stem cells.

Control of self-renewal and differentiation of human ES cells (hESCs) remains a challenge. This is largely due to the use of culture systems that involve poorly defined animal products and do not mimic the normal developmental milieu. Routine protocols involve the propagation of hESCs on mouse fibroblast or human feeder layers, enzymatic cell removal, and spontaneous differentiation in cultures of embryoid bodies, and each of these steps involves significant variability of culture conditions. We report that a completely synthetic hydrogel matrix can support (i) long-term self-renewal of hESCs in the presence of conditioned medium from mouse embryonic fibroblast feeder layers, and (ii) direct cell differentiation. Hyaluronic acid (HA) hydrogels were selected because of the role of HA in early development and feeder layer cultures of hESCs and the controllability of hydrogel architecture, mechanics, and degradation. When encapsulated in 3D HA hydrogels (but not within other hydrogels or in monolayer cultures on HA), hESCs maintained their undifferentiated state, preserved their normal karyotype, and maintained their full differentiation capacity as indicated by embryoid body formation. Differentiation could be induced within the same hydrogel by simply altering soluble factors. We therefore propose that HA hydrogels, with their developmentally relevant composition and tunable physical properties, provide a unique microenvironment for the self-renewal and differentiation of hESCs.

Critical role for the alpha-1B adrenergic receptor at the sympathetic neuroeffector junction.

The alpha-1 adrenergic receptors (alpha(1)ARs) are critical in sympathetically mediated vasoconstriction. The specific role of each alpha(1)AR subtype in regulating vasoconstriction remains highly controversial. Limited pharmacological studies suggest that differential alpha(1)AR responses may be the result of differential activation of junctional versus extrajunctional receptors. We tested the hypothesis that the alpha(1B)AR subtype is critical in mediating sympathetic junctional neurotransmission. We measured in vivo integrated cardiovascular responses to a hypotensive stimulus (induced via transient bilateral carotid occlusion [TBCO]) in alpha(1B)AR knockout (KO) mice and their wild-type (WT) littermates. In WT mice, after dissection of the carotid arteries and denervation of aortic baroreceptor buffering nerves, TBCO produced significant pressor and positive inotropic effects. Both responses were markedly attenuated in alpha(1B)AR KO mice (change systolic blood pressure 46+/-8 versus 11+/-2 mm Hg; percentage change in the end-systolic pressure-volume relationship [ESPVR] 36+/-7% versus 12+/-2%; WT versus KO; P<0.003). In vitro alpha(1)AR mesenteric microvascular contractile responses to endogenous norepinephrine (NE; elicited by electrical field stimulation 10 Hz) was markedly depressed in alpha(1B)AR KO mice compared with WT (12.4+/-1.7% versus 21.5+/-1.2%; P<0.001). In contrast, responses to exogenous NE were similar in alpha(1B)AR KO and WT mice (22.4+/-7.3% versus 33.4+/-4.3%; NS). Collectively, these results demonstrate a critical role for the alpha(1B)AR in baroreceptor-mediated adrenergic signaling at the vascular neuroeffector junction. Moreover, alpha(1B)ARs modulate inotropic responses to baroreceptor activation. The critical role for alpha(1B)AR in neuroeffector regulation of vascular tone and myocardial contractility has profound clinical implications for designing therapies for orthostatic intolerance.