Principles of Tendon Structure, Healing, and the Microenvironment.

Tendon is a strong viscoelastic tissue, responsible for conducting force from muscle to bone. In the hand, flexor tendons course through fibro-osseous sheaths, composed of an intricate tenosynovium and fibrocartilaginous pulley system. After flexor tendon laceration, changes occur in tendon force transduction as well as vascularity, affecting tendon healing on a tissue and cellular level. Tendon healing occurs through intrinsic and extrinsic mechanisms, which in combination with local anatomy, can predispose to adhesion formation. Understanding the relationship between microenvironmental cues and tendon healing on the cellular and tissue level will improve our knowledge and treatment of flexor tendon injuries.

Zone 1 Flexor Tendon Repairs: Laceration and Avulsion Injuries.

In contrast to other zones of the hand, zone 1 flexor tendon injuries include laceration as well as avulsion mechanisms. Although zone 1 tendon lacerations are treated similarly to other zones, with various suture configurations and techniques, zone 1 avulsion injuries often require repair of tendon to bone. Proximity of the repair site to the distal interphalangeal joint often results in persistent flexion contracture and stiffness. Despite these differences in injury mechanism and location, zone 1 flexor tendon repairs are well tolerated and often lead to fair-high patient satisfaction.

Role of Preoperative Nerve Conduction Studies for Penetrating Hand Injuries Involving the Median Palmar Cutaneous Nerve.

Penetrating lacerations to the hand are a common cause of nerve injury and can lead to debilitating pain and numbness in the distribution of the nerve affected. Owing to an overlap in the cutaneous innervation from different sensory nerves, clinically identifying the injured nerve can be difficult. We present a novel case of isolated injury to the palmar cutaneous nerve from a penetrating knife injury which was detected using 'comparison waveform' nerve conduction studies. Using this technique, we can isolate injuries to the palmar cutaneous branch of the median nerve (PCBmdn) from the median nerve, dorsal radial sensory nerve, and lateral antebrachial cutaneous nerve. In addition, sensory nerve testing identified conduction block as the mechanism of injury, which resolved after surgery at 8 weeks postoperatively. Preoperative nerve conduction study can discern the level of nerve injury to PCBmdn only, thus eliminating the need for median and radial nerve exploration at the forearm, unnecessary incisions, pain, and scarring. The objective of this case report is to illustrate the value of preoperative comparison waveform nerve conduction study, particularly the PCBmdn, in patients presenting with neurologic deficits who have sustained penetrating lacerations to the hand.

Aberrant chromatin reorganization in cells from diseased fibrous connective tissue in response to altered chemomechanical cues.

Changes in the micro-environment of fibrous connective tissue can lead to alterations in the phenotypes of tissue-resident cells, yet the underlying mechanisms are poorly understood. Here, by visualizing the dynamics of histone spatial reorganization in tenocytes and mesenchymal stromal cells from fibrous tissue of human donors via super-resolution microscopy, we show that physiological and pathological chemomechanical cues can directly regulate the spatial nanoscale organization and density of chromatin in these tissue-resident cell populations. Specifically, changes in substrate stiffness, altered oxygen tension and the presence of inflammatory signals drive chromatin relocalization and compaction into the nuclear boundary, mediated by the activity of the histone methyltransferase EZH2 and an intact cytoskeleton. In healthy cells, chemomechanically triggered changes in the spatial organization and density of chromatin are reversible and can be attenuated by dynamically stiffening the substrate. In diseased human cells, however, the link between mechanical or chemical inputs and chromatin remodelling is abrogated. Our findings suggest that aberrant chromatin organization in fibrous connective tissue may be a hallmark of disease progression that could be leveraged for therapeutic intervention.

Stem cell shape regulates a chondrogenic versus myogenic fate through Rac1 and N-cadherin.

Human mesenchymal stem cells (hMSCs) are multipotent cells that can differentiate into many cell types. Chondrogenesis is induced in hMSCs cultured as a micromass pellet to mimic cellular condensation during cartilage development, and exposed to transforming growth factor beta (TGFbeta). Interestingly, TGFbeta can also induce hMSC differentiation to smooth-muscle-like cell types, but it remains unclear what directs commitment between these two lineages. Our previous work revealed that cell shape regulates hMSC commitment between osteoblasts and adipocytes through RhoA signaling. Here we show that cell shape also confers a switch between chondrogenic and smooth muscle cell (SMC) fates. Adherent and well-spread hMSCs stimulated with TGF beta 3 upregulated SMC genes, whereas cells allowed to attach onto micropatterned substrates, but prevented from spreading and flattening, upregulated chondrogenic genes. Interestingly, cells undergoing SMC differentiation exhibited little change in RhoA, but significantly higher Rac1 activity than chondrogenic cells. Rac1 activation inhibited chondrogenesis and was necessary and sufficient for inducing SMC differentiation. Furthermore, TGF beta 3 and Rac1 signaling upregulated N-cadherin, which was required for SMC differentiation. These results demonstrate a chondrogenic-SMC fate decision mediated by cell shape, Rac1, and N-cadherin, and highlight the tight coupling between lineage commitment and the many changes in cell shape, cell-matrix adhesion, and cell-cell adhesion that occur during morphogenesis.

Cell shape, cytoskeletal tension, and RhoA regulate stem cell lineage commitment.

Commitment of stem cells to different lineages is regulated by many cues in the local tissue microenvironment. Here we demonstrate that cell shape regulates commitment of human mesenchymal stem cells (hMSCs) to adipocyte or osteoblast fate. hMSCs allowed to adhere, flatten, and spread underwent osteogenesis, while unspread, round cells became adipocytes. Cell shape regulated the switch in lineage commitment by modulating endogenous RhoA activity. Expressing dominant-negative RhoA committed hMSCs to become adipocytes, while constitutively active RhoA caused osteogenesis. However, the RhoA-mediated adipogenesis or osteogenesis was conditional on a round or spread shape, respectively, while constitutive activation of the RhoA effector, ROCK, induced osteogenesis independent of cell shape. This RhoA-ROCK commitment signal required actin-myosin-generated tension. These studies demonstrate that mechanical cues experienced in developmental and adult contexts, embodied by cell shape, cytoskeletal tension, and RhoA signaling, are integral to the commitment of stem cell fate.

Tendinosis develops from age- and oxygen tension-dependent modulation of Rac1 activity.

Age-related tendon degeneration (tendinosis) is characterized by a phenotypic change in which tenocytes display characteristics of fibrochondrocytes and mineralized fibrochondrocytes. As tendon degeneration has been noted in vivo in areas of decreased tendon vascularity, we hypothesized that hypoxia is responsible for the development of the tendinosis phenotype, and that these effects are more pronounced in aged tenocytes. Hypoxic (1% O2 ) culture of aged, tendinotic, and young human tenocytes resulted in a mineralized fibrochondrocyte phenotype in aged tenocytes, and a fibrochondrocyte phenotype in young and tendinotic tenocytes. Investigation of the molecular mechanism responsible for this phenotype change revealed that the fibrochondrocyte phenotype in aged tenocytes occurs with decreased Rac1 activity in response to hypoxia. In young hypoxic tenocytes, however, the fibrochondrocyte phenotype occurs with concomitant decreased Rac1 activity coupled with increased RhoA activity. Using pharmacologic and adenoviral manipulation, we confirmed that these hypoxic effects on the tenocyte phenotype are linked directly to the activity of RhoA/Rac1 GTPase in in vitro human cell culture and tendon explants. These results demonstrate that hypoxia drives tenocyte phenotypic changes, and provide a molecular insight into the development of human tendinosis that occurs with aging.

Total wrist arthroplasty.

This article reviews the history of total wrist arthroplasty as a treatment option for painful, nonfunctional wrists in disease states. Technologic advances in materials, wear properties, and manufacturing now account for increased implant longevity. They may also improve total wrist replacement design, survival, and hence patient function. Also, alternative surgical treatments such as distal radius hemiarthroplasty may serve as a treatment option for patients with higher activity levels and diffuse arthritis. With careful patient selection, soft tissue considerations, and novel implant designs, TWA may become a viable treatment staple for patients with functional wrist disability.

Factors affecting human IgE and IgG responses to allergen-like Schistosoma mansoni antigens: Molecular structure and patterns of in vivo exposure.

BACKGROUND: The human IgE response is associated with allergy and with host defence against parasitic worms. A response to Sm22.6, the dominant IgE antigen in adult Schistosoma mansoni worms, correlates with resistance to re-infection after treatment. Sm22.6 is one of a family of EF-hand containing parasite proteins with sequence similarity to dynein light chain (DLC) and with major non-parasite allergens. Here we compare human IgE and IgG responses to other family members, Sm20.8 and Sm21.7, as well as to SmDLC1, relating these to antigen structure and expression in parasite life stages. METHODS: Recombinant antigens were used in ELISA to measure antibody isotype responses in 177 cases from an endemic area, before and 7 weeks after treatment. Parasite antigen expression was assessed by RT-PCR and Western blotting. RESULTS: Levels of antibodies to Sm22.6 and Sm20.8 (but not to Sm21.7 or SmDLC1) showed posttreatment increases in all but young children. Many produced IgE to Sm22.6 and Sm20.8 (2 EF-hands), few to Sm21.7 (1 EF-hand) or SmDLC1 (no EF-hands). Sm21.7 was expressed in cercariae, adults and eggs, Sm22.6 and Sm20.8 were concentrated in the adult. CONCLUSIONS: These studies suggest that IgE antigens Sm22.6 and Sm20.8 are only released to boost antibodies when adult worms die, whilst Sm21.7 and SmDLC1 are released constantly from eggs dying in host tissue. IgE responses to these allergen-like molecules may be influenced by patterns of exposure and the number of EF-hand motifs.

Increased human IgE induced by killing Schistosoma mansoni in vivo is associated with pretreatment Th2 cytokine responsiveness to worm antigens.

In schistosomiasis endemic areas, children are very susceptible to postchemotherapy reinfection, whereas adults are relatively resistant. Different studies have reported that schistosome-specific IL-4 and IL-5 responses, or posttreatment worm-IgE levels, correlate with subsequent low reinfection. Chemotherapy kills i.v. worms providing an in vivo Ag challenge. We measured anti-worm (soluble worm Ag (SWA) and recombinant tegumental Ag (rSm22.6)) and anti-egg (soluble egg Ag) Ab levels in 177 Ugandans (aged 7-50) in a high Schistosoma mansoni transmission area, both before and 7 wk posttreatment, and analyzed these data in relation to whole blood in vitro cytokine responses at the same time points. Soluble egg Ag-Ig levels were unaffected by treatment but worm-IgG1 and -IgG4 increased, whereas worm-IgE increased in many but not all individuals. An increase in worm-IgE was mainly seen in >15-year-olds and, unlike in children, was inversely correlated to pretreatment infection intensities, suggesting this response was associated both with resistance to pretreatment infection, as well as posttreatment reinfection. The increases in SWA-IgE and rSm22.6-IgE positively correlated with pretreatment Th2 cytokines, but not IFN-gamma, induced by SWA. These relationships remained significant after allowing for the confounding effects of pretreatment infection intensity, age, and pretreatment IgE levels, indicating a link between SWA-specific Th2 cytokine responsiveness and subsequent increases in worm-IgE. An exceptionally strong relationship between IL-5 and posttreatment worm-IgE levels in < 15-year-olds suggested that the failure of younger children to respond to in vivo Ag stimulation with increased levels of IgE, is related to their lack of pretreatment SWA Th2 cytokine responsiveness.