Biology subjects

Martinez, V. A.

Publications and source records attributed to Martinez, V. A..

4 recordsLinked to original sources

bioRxiv2025

MiR-23b Neutralization In Brain Endothelium Promotes Blood-Brain Barrier Repair Through Wnt/Beta-catenin Dependent And Independent Mechanisms

Blood-brain barrier (BBB) disruption drives stroke and other CNS disorders pathology, yet restoring its integrity remains challenging. Using an unbiased anti-miR lentiviral screen, miR-23b was identified as a critical negative regulator of BBB integrity in brain endothelial cells (BECs). Targeted inhibition of miR-23b using anti-miR-23b, validated by Wnt-reporter, Wnt-rescue, and eCLIP analysis, demonstrates that BEC miR-23b silencing in BECs, enhances junctional protein expression and strengthens barrier function while suppressing transcellular transport. Global multi-omics analysis reveals that miR-23b acts as a robust driver of angiogenesis-specific genes and proteins. Conversely, anti-miR-23b induces the expression of factors essential for BBB stabilization and repair. Notably, anti-miR-23b enhances these protective barrier properties through the multi-faceted regulation of Wnt/{beta}-catenin, TGF-{beta}, Notch, and VEGF signaling mechanisms. Using a 3D microfluidic platform, anti-miR-23b was shown to foster BBB repair by accelerating vessel maturation and enhancing resilience against ischemic injury. Proof-of-concept studies show that BEC specific AAVBR1-anti-miR-23b gene therapy reinforces BBB tight junctions, reduces BBB leakage, and improves outcome measures in a transient middle cerebral artery occlusion (t-MCAO) stroke model. Thus, miR-23b is a critical regulator of cerebrovascular integrity, positioning anti-miR-23b as a promising RNA-based therapy to enhance BBB stability and repair in stroke and other CNS disorders.

neuroscience↗

bioRxiv2021

Universal and Programmable Thinning and Thickening of Topologically-Active DNA Fluids

Understanding and controlling the rheology of polymeric complex fluids that are pushed out-of-equilibrium is a fundamental problem in both industry and biology. For example, to package, repair, and replicate DNA, cells use enzymes to constantly manipulate DNA topology, length, and structure. Inspired by this, here we engineer and study DNA-based complex fluids that undergo enzymatically-driven topological and architectural alterations via restriction endonuclease (RE) reactions. We show that these systems display time-dependent rheological properties that depend on the concentrations and properties of the comprising DNA and REs. Through time-resolved microrheology experiments and Brownian Dynamics simulations, we show that conversion of supercoiled to linear DNA topology leads to a monotonic increase in viscosity. On the other hand, the viscosity of entangled linear DNA undergoing fragmentation displays a universal decrease that we rationalize using living polymer theory. Finally, to showcase the tunability of these behaviours, we design a DNA fluid that exhibits a time-dependent increase, followed by a temporally-gated decrease, of its viscosity. Our results present a class of polymeric fluids that leverage naturally occurring enzymes to drive diverse time-varying rheology by performing architectural alterations to the constituents.

biophysics↗

bioRxiv2018

High-throughput characterisation of bull semen motility using differential dynamic microscopy

We report a high-throughput technique for characterising the motility of spermatozoa using differential dynamic microscopy. A large field of view movie (~ 10mm2) records thousands of cells (e.g. {approx} 5000 cells even at a low cell density of 20 x 106 cells/ml) at once and yields averaged measurements of the mean ({upsilon}) and standard deviation ({sigma}) of the swimming speed, a head oscillation amplitude (A0) and frequency (f0), and the fraction of motile spermatozoa (). Interestingly, the measurement of relies on the swimming spermatozoa enhancing the motion of the non-swimming population. We demonstrate the ease and rapidity of our method by performing on-farm characterisation of bull spermatozoa motility, and validate the technique by comparing laboratory measurements with tracking. Our results confirm the long-standing theoretical prediction that [Formula] for swimming spermatozoa.

biophysics↗

bioRxiv2018

Hook length of the bacterial flagellum is controlled to nanometer-scale for optimal motility performance

Most bacteria swim in liquid environments by rotating one or several flagella. The long external filament of the flagellum is connected to a membrane-embedded basal-body by a flexible universal joint, the hook, which allows the transmission of motor torque to the filament. The length of the hook is controlled on a nanometer-scale by a sophisticated molecular ruler mechanism. However, why its length is stringently controlled has remained elusive. We engineered and studied a diverse set of hook-length variants of Salmonella enterica. Measurements of plate-assay motility, single-cell swimming speed and directional persistence in quasi 2D and population-averaged swimming speed and body angular velocity in 3D revealed that the motility performance is optimal around the wild type hook-length. We conclude that too short hooks may be too stiff to function as a junction and too long hooks may buckle and create instability in the flagellar bundle. Accordingly, peritrichously flagellated bacteria move most efficiently as the distance travelled per body rotation is maximal and body wobbling is minimized. Thus, our results suggest that the molecular ruler mechanism evolved to control flagellar hook growth to the optimal length consistent with efficient bundle formation. The hook-length control mechanism is therefore a prime example of how bacteria evolved elegant, but robust mechanisms to maximize their fitness under specific environmental constraints.\n\nAuthor summaryMany bacteria use flagella for directed movement in liquid environments. The flexible hook connects the membrane-embedded basal-body of the flagellum to the long, external filament. Flagellar function relies on self-assembly processes that define or self-limit the lengths of major parts. The length of the hook is precisely controlled on a nanometer-scale by a molecular ruler mechanism. However, the physiological benefit of tight hook-length control remains unclear. Here, we show that the molecular ruler mechanism evolved to control the optimal length of the flagellar hook, which is consistent with efficient motility performance. These results highlight the evolutionary forces that enable flagellated bacteria to optimize their fitness in diverse environments and might have important implications for the design of swimming micro-robots.

microbiology↗