Biology subjects

Huang, A. H.

Publications and source records attributed to Huang, A. H..

6 recordsLinked to original sources

bioRxiv2026

Seizures induce c-fos expression in a subset of astrocytes, termed fostrocytes, that dampen subsequent seizures

Objective: The original goal was to map neuronal circuits activated by spontaneous seizures in models of temporal lobe epilepsy. Studies used the c-fos driven TRAP2 system, which has been used successfully to label neurons after seizures. Unexpectedly, astrocytes were also labeled, then shown to express c-fos in a sustained manner after seizures. The role of these so-called fostrocytes in spontaneous seizures was studied using novel Cre-dependent AAVs. Methods: Studies used a homozygous mouse line produced by crossing TRAP2 Cre-driver mice with the Ai9 Cre-reporter line. Seizures were induced using electrical stimulation, kainic acid, or pilocarpine. Cre-dependent AAVs used the GFAP promoter to drive expression of either the catalytic A chain of diphtheria toxin (DTA), GFP, or empty vector. Spontaneous seizures were continuously recorded using EEG. Results: Discrete seizures in naive mice evoked transient c-fos expression in all astrocytes, while status epilepticus evoked a higher and sustained level of c-fos expression. Timing the activation of the TRAP2 system allowed specific labeling of the subset of astrocytes with high c-fos expression. These cells were colocalized with established astrocyte markers, showed reactive astrocyte morphology, and were selectively labeled by GFAP-driven Cre-dependent AAVs. Ablation of fostrocytes in spontaneously seizing mice increased seizure frequency. Significance: Next-generation sequencing studies have revealed a great diversity of astrocyte subtypes, identifying clusters with up-regulated c-fos expression in patients with neurological disorders. In conclusion, these studies suggest that therapies that augment the activity of c-fos expressing astrocytes would have anti-seizure activity.

neuroscience↗

bioRxiv2026

Mechanical cues from muscle contraction regulate TGFβ signaling and epitenon formation during embryonic tendon development.

Muscle loading is required for embryonic tendon growth; however, the underlying mechanisms that regulate tendon development downstream of mechanical cues remain unidentified. Although tendons in muscle paralysis models are structurally and functionally inferior, whether these differences arise from cell or matrix deficits remains unclear. Analysis of muscular dysgenesis embryos by atomic force microscopy showed that structural and functional deficits in paralyzed tendon arise in part from reduced proliferation and collagen fibril disorganization. Bulk and single cell transcriptional analyses reveal that both collagenous and non-collagenous extracellular matrix components, as well as cytoskeletal and actomyosin-associated proteins, are dysregulated in mdg tendons, whereas tendon markers remain unchanged. Surprisingly, we find that an arrest of TGF{beta} signaling occurs during normal embryonic tendon growth and that TGF{beta} signaling is abnormally prolonged in paralyzed embryos. We also show for the first time, that specification of the epitenon depends on muscle contraction. Together, these findings establish cell and molecular requirements for muscle contraction in embryonic tendon development. TeaserMuscle contraction is required for embryonic tendon development through regulation of TGF{beta} signaling, epitenon formation, and matrix organization.

developmental biology↗

bioRxiv2024

New Insights into Neuromuscular Contracture Reveals Myotendinous- SMAD4 Signaling Underlies Contracture Formation

Neuromuscular contractures (NC) are a prevalent cause of joint deformity in children suffering from neuromuscular disorders or nerve damage, leading to persistent disability. The role of tendon in the development of NC remains poorly understood, with current treatments predominantly targeting muscle. Here, we establish a surgical model of NC in the hindlimb that recapitulates functional deformity and transcriptomic changes observed in human disease. Our findings indicate that in NC, tendons dramatically elongate, undergoing changes in matrix and structural composition that reduce tensile stiffness. Contrary to expectations, we find that tendon elongation was principally driven by increased myotendon infiltration into muscle which restricted muscle elongation contributing to NC. Using lineage tracing, we show that myotendon elongation was due to increased infiltration of intrinsically derived tenocytes. Transcriptional profiling revealed BMP signaling as a key factor in myotendon elongation, corroborated by elevated myotendinous Smad4 activity in both our mouse model and in human NC tissues. Crucially, administration of a small molecule inhibitor of BMP-mediated Smad4 signaling not only restored joint mobility but also prevented myotendon elongation. These insights establish of a clinically relevant mouse model of NC and unveil a novel role for myotendon elongation in NC progression. Excitingly, our results suggest that targeting myotendon signaling could represent a new direction for tendon-focused therapies in NC management.

molecular biology↗

bioRxiv2024

Tendon Inversion Improves Tendon-to-Bone Healing in a Rat Bicep Tenodesis Model

PurposeTendon- or ligament-to-bone repair remains a surgical challenge. While bone tunnel fixation is a common surgical technique whereby soft tissue is expected to heal against a bone tunnel interface, contemporary methods have yet to recapitulate biomechanical similarity to the native enthesis. In this study, we aim to demonstrate that inside-out longitudinal tendon inversion may improve bone tunnel healing with the hypothesis that inversion removes the gliding epitenon surface from the healing interface thereby improving tunnel interface healing. Methods40 male Sprague-Dawley rats underwent either native tendon tenodesis (control group) or tendon inversion tenodesis (experimental group). Interface tissue was harvested 8 weeks post-operatively. Biomechanical testing was performed to assess tensile strength and modes of failure. Histology was performed to assess tissue architecture, and immunohistochemistry was used confirmed abrogation of epitendinous lubricin from interface tissue. ResultsNeither surgical intervention led to discernible adverse effects on animal health. Maximum tensile strength increased after tendon inversion compared to control surgery. The extracellular matrix protein lubricin was reduced with tendon inversion, and specimens with tendon inversion had greater healing scores and collagen fibril alignment at the healing interface. ConclusionsTendon inversion improves bone tunnel healing in rats. Clinical RelevanceOur findings suggest that longitudinal tendon inversion, or inverse tubularization, in a rat biceps tenodesis model improves tendon-to-bone healing in part due to disruption of the epitendinous surface at the bone healing interface. This work provides molecular insight into future improvements for tendon-to-bone repair surgical techniques.

physiology↗

bioRxiv2021

Reprogramming adult tendon healing using regenerative neonatal regulatory T cells

Tendinopathy is a common clinical problem leading to significant musculoskeletal disability. Using a neonatal mouse model of tendon regeneration compared to adult tendon fibrosis, we identified a unique immune profile in regeneration that is associated with type 2 macrophage polarization and regulatory T cell (Treg) infiltration. Neonatal Treg ablation resulted in a dysregulated immune response leading to failed tenocyte recruitment and loss of functional regeneration. Transcriptional profiling of adult and neonatal tendon Tregs revealed distinct type 1 and type 2 immune signatures that facilitate macrophage polarization following injury. Finally, adoptive transfer of mouse and human neonatal Tregs was sufficient to improve functional regeneration, in contrast to adult Treg transfer. Collectively, these studies uncover a critical role for neonatal Tregs in controlling immune polarization to promote an environment permissive for tendon regeneration. Our findings provide a basis for immune modulating therapies to facilitate regenerative adult tendon healing.

immunology↗

bioRxiv2019

TGFβ signaling is required for tenocyte recruitment and functional neonatal tendon regeneration

Tendon injuries are common with poor healing potential. The paucity of therapies for tendon is due to our limited understanding of the cells and molecules that drive tendon regeneration. Using a model of neonatal mouse tendon regeneration, we determined the molecular basis for regeneration and identify TGF{beta} signaling as a major pathway. Through targeted gene deletion, small molecule inhibition, and lineage tracing, we elucidated TGF{beta}-dependent and -independent mechanisms underyling tendon regeneration. Importantly, functional recovery depended on TGF{beta} signaling and loss of function is due to impaired tenogenic cell recruitment from both Scxlin and non-Scxlin sources. We show that TGF{beta} signaling is required directly in neonatal tenocytes for recruitment and that TGF{beta} is positively regulated in tendons. Collectively, these results are the first to show a functional role for TGF{beta} signaling in tendon regeneration and offer new insights toward the divergent cellular activities that may lead to regenerative vs fibrotic healing.

developmental biology↗