Three vertebrate hyaluronan synthases are expressed during mouse development in distinct spatial and temporal patterns

Naked mole-rat hyaluronan

Naked mole rats (NMRs) are renowned for their exceptional longevity and remarkable maintenance of health throughout their lifetime. Their subterranean lifestyle has led to adaptations that have resulted in elevated levels of a very high molecular weight hyaluronan in their tissues. Hyaluronan, a glycosaminoglycan, is a key component of the extracellular matrix, which plays a critical role in maintaining tissue structure and regulating cell signaling pathways. This phenomenon in NMRs is attributed to a higher processing and production capacity by some of their hyaluronan synthases, along with lower degradation by certain hyaluronidases. Furthermore, this adaptation indirectly confers several advantages to NMRs, such as the preservation of skin elasticity and youthful appearance, accelerated wound healing, protection against oxidative stress, and resistance to conditions such as cancer and arthritis, largely attributable to CD44 signaling and other intricate mechanisms. Thus, the main objective of this study was to conduct a comprehensive study of the distinctive features of NMR hyaluronan, particularly emphasizing the currently known molecular mechanisms that contribute to its beneficial properties. Furthermore, this research delves into the potential applications of NMR hyaluronan in both cosmetic and therapeutic fields, as well as the challenges involved.

The significant role of glycosaminoglycans in tooth development

This review delves into the roles of glycosaminoglycans (GAGs), integral components of proteoglycans, in tooth development. Proteoglycans consist of a core protein linked to GAG chains, comprised of repeating disaccharide units. GAGs are classified into several types, such as hyaluronic acid, heparan sulfate, chondroitin sulfate, dermatan sulfate, and keratan sulfate. Functioning as critical macromolecular components within the dental basement membrane, these GAGs facilitate cell adhesion and aggregation, and play key roles in regulating cell proliferation and differentiation, thereby significantly influencing tooth morphogenesis. Notably, our recent research has identified the hyaluronan-degrading enzyme Transmembrane protein 2 (Tmem2) and we have conducted functional analyses using mouse models. These studies have unveiled the essential role of Tmem2-mediated hyaluronan degradation and its involvement in hyaluronan-mediated cell adhesion during tooth formation. This review provides a comprehensive summary of the current understanding of GAG functions in tooth development, integrating insights from recent research, and discusses future directions in this field.

Hyaluronic acid metabolism and chemotherapy resistance: recent advances and therapeutic potential

Hyaluronic acid (HA) is a major component of the extracellular matrix, providing essential mechanical scaffolding for cells and, at the same time, mediating essential biochemical signals required for tissue homeostasis. Many solid tumors are characterized by dysregulated HA metabolism, resulting in increased HA levels in cancer tissues. HA interacts with several cell surface receptors, such as cluster of differentiation 44 and receptor for hyaluronan-mediated motility, thus co-regulating important signaling pathways in cancer development and progression. In this review, we describe the enzymes controlling HA metabolism and its intracellular effectors emphasizing their impact on cancer chemotherapy resistance. We will also explore the current and future prospects of HA-based therapy, highlighting the opportunities and challenges in the field.

Loss of hyaluronan synthases impacts bone morphology, quality, and mechanical properties

Hyaluronan, a glycosaminoglycan synthesized by three isoenzymes (Has1, Has2, Has3), is known to play a role in regulating bone turnover, remodeling, and mineralization, which in turn can affect bone quality and strength. The goal of this study is to characterize how the loss of Has1 or Has3 affects the morphology, matrix properties, and overall strength of murine bone. Femora were isolated from Has1^-/-,Has3^-/-, and wildtype (WT) C57Bl/6 J female mice and were analyzed using microcomputed-tomography, confocal Raman spectroscopy, three-point bending, and nanoindentation. Of the three genotypes tested, Has1^-/- bones demonstrated significantly lower cross-sectional area (p = 0.0002), reduced hardness (p = 0.033), and lower mineral-to-matrix ratio (p < 0.0001). Has3^-/- bones had significantly higher stiffness (p < 0.0001) and higher mineral-to-matrix ratio (p < 0.0001) but lower strength (p = 0.0014) and bone mineral density (p < 0.0001) than WT. Interestingly, loss of Has3 was also associated with significantly lower accumulation of advanced glycation end-products than WT (p = 0.0478). Taken together, these results demonstrate, for the first time, the impact of the loss of hyaluronan synthase isoforms on cortical bone structure, content, and biomechanics. Loss of Has1 impacted morphology, mineralization, and micron-level hardness, while loss of Has3 reduced bone mineral density and affected organic matrix composition, impacting whole bone mechanics. This is the first study to characterize the effect of loss of hyaluronan synthases on bone quality, suggesting an essential role hyaluronan plays during the development and regulation of bone.

Hyaluronic Acid: A Review of the Drug Delivery Capabilities of This Naturally Occurring Polysaccharide

The inclusion of physiologically active molecules into a naturally occurring polymer matrix can improve the degradation, absorption, and release profile of the drug, thus boosting the therapeutic impact and potentially even reducing the frequency of administration. The human body produces significant amounts of polysaccharide hyaluronic acid, which boasts exceptional biocompatibility, biodegradability, and one-of-a-kind physicochemical features. In this review, we will examine the clinical trials currently utilizing hyaluronic acid and address the bright future of this versatile polymer, as well as summarize the numerous applications of hyaluronic acid in drug delivery and immunomodulation.

Revisiting the embryogenesis of lip and palate development

Clefts of the lip and palate (CLP), the major causes of congenital facial malformation globally, result from failure of fusion of the facial processes during embryogenesis. With a prevalence of 1 in 500-2500 live births, CLP causes major morbidity throughout life as a result of problems with facial appearance, feeding, speaking, obstructive apnoea, hearing and social adjustment and requires complex, multi-disciplinary care at considerable cost to healthcare systems worldwide. Long-term outcomes for affected individuals include increased mortality compared with their unaffected siblings. The frequent occurrence and major healthcare burden imposed by CLP highlight the importance of dissecting the molecular mechanisms driving facial development. Identification of the genetic mutations underlying syndromic forms of CLP, where CLP occurs in association with non-cleft clinical features, allied to developmental studies using appropriate animal models is central to our understanding of the molecular events underlying development of the lip and palate and, ultimately, how these are disturbed in CLP.

ROLE OF HYALURONAN IN PATHOPHYSIOLOGY OF VASCULAR1 ENDOTHELIAL AND SMOOTH MUSCLE CELLS

One of the main components of the extracellular matrix (ECM) of the blood vessel is hyaluronic acid or hyaluronan (HA). It is a ubiquitous polysaccharide belonging to the family of glycosaminoglycans, but, differently from other proteoglycan-associated glycosaminoglycans, it is synthesized on the plasma membrane by a family of three HA synthases (HAS). HA can be released as a free polymer in the extracellular space or remain associated with the membrane in the pericellular space via HAS or via binding proteins. In fact, several cell surface proteins can interact with HA working as HA receptors like CD44, RHAMM, and LYVE-1. In physiological conditions, HA is localized in the glycocalyx and in the adventitia and is responsible for the loose and hydrated vascular structure favoring flexibility and allowing the stretching of vessels in response to mechanical forces. During atherogenesis, ECM undergoes dramatic alterations which have a crucial role in lipoprotein retention and in triggering multiple signaling cascades that wake up cells from their quiescent status. HA becomes highly present in the media and neointima favoring smooth muscle cells dedifferentiation, migration, and proliferation that strongly contribute to vessel wall thickening. Further, HA is able to modulate immune cell recruitment both within the vessel wall and on the endothelial cell layer. This review is focused on the effects of HA on vascular cell behavior.

Hyaluronic Acid: Known for Almost a Century, but Still in Vogue

Hyaluronic acid (HA) has a special position among glycosaminoglycans. As a major component of the extracellular matrix (ECM). This simple, unbranched polysaccharide is involved in the regulation of various biological cell processes, whether under physiological conditions or in cases of cell damage. This review summarizes the history of this molecule’s study, its distinctive metabolic pathway in the body, its unique properties, and current information regarding its interaction partners. Our main goal, however, is to intensively investigate whether this relatively simple polymer may find applications in protecting against ionizing radiation (IR) or for therapy in cases of radiation-induced damage. After exposure to IR, acute and belated damage develops in each tissue depending upon the dose received and the cellular composition of a given organ. A common feature of all organ damage is a distinct change in composition and structure of the ECM. In particular, the important role of HA was shown in lung tissue and the variability of this flexible molecule in the complex mechanism of radiation-induced lung injuries. Moreover, HA is also involved in intermediating cell behavior during morphogenesis and in tissue repair during inflammation, injury, and would healing. The possibility of using the HA polymer to affect or treat radiation tissue damage may point to the missing gaps in the responsible mechanisms in the onset of this disease. Therefore, in this article, we will also focus on obtaining answers from current knowledge and the results of studies as to whether hyaluronic acid can also find application in radiation science.

Extracellular hyaluronate pressure shaped by cellular tethers drives tissue morphogenesis

How tissues acquire complex shapes is a fundamental question in biology and regenerative medicine. Zebrafish semicircular canals form from invaginations in the otic epithelium (buds) that extend and fuse to form the hubs of each canal. We find that conventional actomyosin-driven behaviors are not required. Instead, local secretion of hyaluronan, made by the enzymes uridine 5'-diphosphate dehydrogenase (ugdh) and hyaluronan synthase 3 (has3), drives canal morphogenesis. Charged hyaluronate polymers osmotically swell with water and generate isotropic extracellular pressure to deform the overlying epithelium into buds. The mechanical anisotropy needed to shape buds into tubes is conferred by a polarized distribution of actomyosin and E-cadherin-rich membrane tethers, which we term cytocinches. Most work on tissue morphogenesis ascribes actomyosin contractility as the driving force, while the extracellular matrix shapes tissues through differential stiffness. Our work inverts this expectation. Hyaluronate pressure shaped by anisotropic tissue stiffness may be a widespread mechanism for powering morphological change in organogenesis and tissue engineering.

Matters of size: Roles of hyaluronan in CNS aging and disease

Involvement of extracellular matrix (ECM) components in aging and age-related neurodegeneration is not well understood. The role of hyaluronan (HA), a major extracellular matrix glycosaminoglycan, in malignancy and inflammation is gaining new understanding. In particular, the differential biological effects of high molecular weight (HMW-HA) and low molecular weight hyaluronan (LMW-HA), and the mechanism behind such differences are being uncovered. Tightly regulated in the brain, HA can have diverse effects on cellular development, growth and degeneration. In this review, we summarize the homeostasis and signaling of HA in healthy tissue, discuss its distribution and ontogeny in the central nervous system (CNS), summarize evidence for its involvement in age-related neurodegeneration and Alzheimer Disease (AD), and assess the potential of HA as a therapeutic target in the CNS.

Fibroblasts as confederates of the immune system

Fibroblastic stromal cells are as diverse, in origin and function, as the niches they fashion in the mammalian body. This cellular variety impacts the spectrum of responses elicited by the immune system. Fibroblast influence on the immune system keeps evolving our perspective on fibroblast roles and functions beyond just a passive structural part of organs. This review discusses the foundations of fibroblastic stromal-immune crosstalk, under the scope of stromal heterogeneity as a basis for tissue-specific tutoring of the immune system. Focusing on the skin as a relevant immunological organ, we detail the complex interactions between distinct fibroblast populations and immune cells that occur during homeostasis, injury repair, scarring, and disease. We further review the relevance of fibroblastic stromal cell heterogeneity and how this heterogeneity is central to regulate the immune system from its inception during embryonic development into adulthood.

Molecular similarity between the mechanisms of epithelial fusion and fetal wound healing during the closure of the caudal neural tube in mouse embryos

BACKGROUND

Neural tube (NT) closure is a complex developmental process that takes place in the early stages of embryogenesis and that is a key step in neurulation. In mammals, the process by which the neural plate generates the NT requires organized cell movements and tissue folding, and it terminates with the fusion of the apposed ends of the neural folds.

RESULTS

Here we describe how almost identical cellular and molecular machinery is used to fuse the spinal neural folds as that involved in the repair of epithelial injury in the same area of the embryo. For both natural and wound activated closure of caudal neural tissue, hyaluronic acid and platelet-derived growth factor signaling appear to be crucial for the final fusion step.

CONCLUSIONS

There seems to be no general wound healing machinery for all tissues but rather, a tissue-specific epithelial fusion machinery that embryos activate when necessary after abnormal epithelial opening.

Balance Between Tooth Size and Tooth Number Is Controlled by Hyaluronan

While the function of proteins and genes has been widely studied during vertebrate development, relatively little work has addressed the role of carbohydrates. Hyaluronan (HA), also known as hyaluronic acid, is an abundant carbohydrate in embryonic tissues and is the main structural component of the extracellular matrix of epithelial and mesenchymal cells. HA is able to absorb large quantities of water and can signal by binding to cell-surface receptors. During organ development and regeneration, HA has been shown to regulate cell proliferation, cell shape, and migration. Here, we have investigated the function of HA during molar tooth development in mice, in which, similar to humans, new molars sequentially bud off from a pre-existing molar. Using an ex vivo approach, we found that inhibiting HA synthesis in culture leads to a significant increase in proliferation and subsequent size of the developing molar, while the formation of sequential molars was inhibited. By cell shape analysis, we observed that inhibition of HA synthesis caused an elongation and reorientation of the major cell axes, indicating that disruption to cellular orientation and shape may underlie the observed phenotype. Lineage tracing demonstrated the retention of cells in the developing first molar (M1) at the expense of the generation of a second molar (M2). Our results highlight a novel role for HA in controlling proliferation, cell orientation, and migration in the developing tooth, impacting cellular decisions regarding tooth size and number.

Diverse Roles for Hyaluronan and Hyaluronan Receptors in the Developing and Adult Nervous System

Hyaluronic acid (HA) plays a vital role in the extracellular matrix of neural tissues. Originally thought to hydrate tissues and provide mechanical support, it is now clear that HA is also a complex signaling molecule that can regulate cell processes in the developing and adult nervous systems. Signaling properties are determined by molecular weight, bound proteins, and signal transduction through specific receptors. HA signaling regulates processes such as proliferation, differentiation, migration, and process extension in a variety of cell types including neural stem cells, neurons, astrocytes, microglia, and oligodendrocyte progenitors. The synthesis and catabolism of HA and the expression of HA receptors are altered in disease and influence neuroinflammation and disease pathogenesis. This review discusses the roles of HA, its synthesis and breakdown, as well as receptor expression in neurodevelopment, nervous system function and disease.

Role of FGF and Hyaluronan in Choroidal Neovascularization in Sorsby Fundus Dystrophy

Sorsby's fundus dystrophy (SFD) is an inherited blinding disorder caused by mutations in the tissue inhibitor of metalloproteinase-3 (TIMP3) gene. The SFD pathology of macular degeneration with subretinal deposits and choroidal neovascularization (CNV) closely resembles that of the more common age-related macular degeneration (AMD). The objective of this study was to gain further insight into the molecular mechanism(s) by which mutant TIMP3 induces CNV. In this study we demonstrate that hyaluronan (HA), a large glycosaminoglycan, is elevated in the plasma and retinal pigment epithelium (RPE)/choroid of patients with AMD. Mice carrying the S179C-TIMP3 mutation also showed increased plasma levels of HA as well as accumulation of HA around the RPE in the retina. Human RPE cells expressing the S179C-TIMP3 mutation accumulated HA apically, intracellularly and basally when cultured long-term compared with cells expressing wildtype TIMP3. We recently reported that RPE cells carrying the S179C-TIMP3 mutation have the propensity to induce angiogenesis via basic fibroblast growth factor (FGF-2). We now demonstrate that FGF-2 induces accumulation of HA in RPE cells. These results suggest that the TIMP3-MMP-FGF-2-HA axis may have an important role in the pathogenesis of CNV in SFD and possibly AMD.

Requirement of Hyaluronan Synthase-2 in Craniofacial and Palate Development

Cleft palate is a common major birth defect resulting from disruption of palatal shelf growth, elevation, or fusion during fetal palatogenesis. Whereas the molecular mechanism controlling palatal shelf elevation is not well understood, a prevailing hypothesis is that region-specific accumulation of hyaluronan, a predominant extracellular glycosaminoglycan in developing palatal mesenchyme, plays a major role in palatal shelf elevation. However, direct genetic evidence for a requirement of hyaluronan in palate development is still lacking. In this study, we show that Has2, 1 of 3 hyaluronan synthases in mammals, plays a major role in hyaluronan synthesis in the neural crest-derived craniofacial mesenchyme during palatogenesis in mice. We analyzed developmental defects caused by tissue-specific inactivation of Has2 throughout the cranial neural crest lineage or specifically in developing palatal or mandibular mesenchyme, respectively, using Wnt1-Cre, Osr2-Cre, and Hand2-Cre transgenic mice. Inactivation of Has2 either throughout the neural crest lineage or specifically in the developing palatal mesenchyme caused reduced palatal shelf size and increased palatal mesenchyme cell density prior to the time of normal palatal shelf elevation. Whereas both Has2f/f;Wnt1-Cre and Has2f/f;Osr2-Cre mutant mice exhibit cleft palate at complete penetrance, the Has2f/f; Wnt1-Cre fetuses showed dramatically reduced mandible size and complete failure of palatal shelf elevation, whereas Has2f/f;Osr2-Cre fetuses had normal mandibles and delayed palatal shelf elevation. All Has2f/f;Hand2-Cre pups showed reduced mandible size and about 50% of them had cleft palate with disruption of palatal shelf elevation. Results from explant culture assays indicate that disruption of palatal shelf elevation in Has2f/f;Hand2-Cre mutant fetuses resulted from physical obstruction by the malformed mandible and tongue. Together, these data indicate that hyaluronan plays a crucial intrinsic role in palatal shelf expansion and timely reorientation to the horizontal position above the tongue as well as an important role in mandibular morphogenesis that secondarily affects palatal shelf elevation.

Hyaluronic acid is required for palatal shelf movement and its interaction with the tongue during palatal shelf elevation

Palatal shelf elevation is an essential morphogenetic process that results from palatal shelf movement caused by an intrinsic elevating force. The nature of the elevating force remains unclear, but the accumulation of hyaluronic acid (HA) in the extracellular matrix (ECM) of the palatal shelves may play a pivotal role in developing the elevating force. In mammals, HA is synthesized by hyaluronic acid synthases (HAS) that are encoded by three genes (Has1-3). Here, we used the Wnt1-Cre driver to conditionally disrupt hyaluronic acid synthase 2 (Has2) in cranial neural crest cell lineages. All Has2 conditional knockout (cko) mice had cleft palate due to failed shelf elevation during palate development. The HA content was significantly reduced in the craniofacial mesenchyme of Has2 cko mutants. Reduced HA content affected the ECM space and shelf expansion to result in a reduced shelf area and an increased mesenchymal cell density in the palatal shelves of Has2 cko mutants. We examined palatal shelf movement by removal of the tongue and mandible from unfixed E13.5 and early E14.5 embryonic heads. Reduced shelf expansion in Has2 cko mutants altered palatal shelf movement in the medial direction resulting in a larger gap between the palatal shelves than that of littermate controls. We further examined palatal shelf movement in the intact oral cavity by culturing explants containing the maxilla, palate, mandible and tongue (MPMT explants). The palatal shelves elevated alongside morphological changes in the tongue after 24-h culture in MPMT explants of early E14.5 wild type embryos. On the contrary, shelf elevation failed to occur in MPMT explants of age-matched Has2 cko mutants because the tongue obstructs palatal shelf movement, suggesting that reduced shelf expansion could be essential for the palatal shelves to interact with the tongue and overcome tongue obstruction during shelf elevation. Has2 cko mutants also showed micrognathia due to reduced HA content in the mandibular mesenchyme including Meckel's cartilage. Through 3D imaging and morphometric analysis, we demonstrate that mandibular growth results in a significant increase in the vertical dimension of the common oral-nasal cavity that facilitates palatal shelf movement and its interaction with the tongue during shelf elevation.

Dissecting the role of hyaluronan synthases in the tumor microenvironment

The tumor microenvironment is becoming a crucial factor in determining the aggressiveness of neoplastic cells. The glycosaminoglycan hyaluronan is one of the principal constituents of both the tumor stroma and the cancer cell surfaces, and its accumulation can dramatically influence patient survival. Hyaluronan functions are dictated by its ability to interact with several signaling receptors that often activate pro-angiogenic and pro-tumorigenic intracellular pathways. Although hyaluronan is a linear, non-sulfated polysaccharide, and thus lacks the ability of the other sulfated glycosaminoglycans to bind and modulate growth factors, it compensates for this by the ability to form hyaluronan fragments characterized by a remarkable variability in length. Here, we will focus on the role of both high and low molecular weight hyaluronan in controlling the hallmarks of cancer cells, including cell proliferation, migration, metabolism, inflammation, and angiogenesis. We will critically assess the multilayered regulation of HAS2, the most critical hyaluronan synthase, and its role in cancer growth, metabolism, and therapy.

Knockout of hyaluronan synthase 1, but not 3, impairs formation of the retrocalcaneal bursa

Hyaluronan (HA), a high molecular weight non-sulfated glycosaminoglycan, is an integral component of the extracellular matrix of developing and mature connective tissues including tendon. There are few published reports quantifying HA content during tendon growth and maturation, or detailing its effects on the mechanical properties of the tendon extracellular matrix. Therefore, the goal of the current study was to examine the role of HA synthesis during post-natal skeletal growth and maturation, and its influence on tendon structure and biomechanical function. For this purpose, the morphological, biochemical, and mechanical properties of Achilles tendons from wild type (WT) and hyaluronan synthase 1 and 3 deficient mouse strains (Has1-/- (Has1KO), Has3-/- (Has3KO), and Has1-/- 3-/- (Has1/3KO)) were determined at 4, 8, and 12 weeks of age. Overall, HAS-deficient mice did not show any marked differences from WT mice in Achilles tendon morphology or in the HA and chondroitin/dermatan sulfate (CS/DS) contents. However, HAS1-deficiency (in the single or Has1/3 double KO) impeded post-natal formation of the retrocalcaneal bursa, implicating HAS1 in regulating HA metabolism by cells lining the bursal cavity. Together, these data suggest that HA metabolism via HAS1 and HAS3 does not markedly influence the extracellular matrix structure or function of the tendon body, but plays a role in the formation/maintenance of peritendinous bursa. Additional studies are warranted to elucidate the relationship of HA and CS/DS metabolism to tendon healing and repair in vivo. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2622-2632, 2018.

Hyaluronic acid, CD44 and RHAMM regulate myoblast behavior during embryogenesis

Hyaluronic acid (HA) is an extracellular matrix (ECM) component that has been shown to play a significant role in regulating muscle cell behavior during repair and regeneration. For instance, ECM remodeling after muscle injury involves an upregulation in HA expression that is coupled with skeletal muscle precursor cell recruitment. However, little is known about the role of HA during skeletal muscle development. To gain insight into the way in which HA mediates embryonic myogenesis, we first determined the spatial distribution and gene expression of CD44, RHAMM and other HA related proteins in embryonic day (E)10.5 to E12.5 murine forelimbs. While HA and CD44 expression remained high, RHAMM decreased at both the protein (via immunohistochemistry) and RNA (via qPCR) levels. Next, we determined that 4-methylumbelliferone-mediated knockdown of HA synthesis inhibited the migration and proliferation of E11.5/E12.5 forelimb-derived cells. Then, the influence of CD44 and RHAMM on myoblast and connective tissue cell behavior was investigated using antibodies against these receptors. Anti-RHAMM, but not anti-CD44, significantly decreased the total distance myogenic progenitors migrated over 24 h, whereas both inhibited connective tissue cell migration. In contrast, anti-CD44 inhibited the proliferation of connective tissue cells and muscle progenitors, but anti-RHAMM had no effect. However, when myoblasts and connective tissue cells were depleted of CD44 and RHAMM by shRNA, motility and proliferation were significantly inhibited in both cells indicating that blocking cell surface-localized CD44 and RHAMM does not have as pronounced effect as global shRNA-mediated depletion of these receptors. These results show, for the first time, the distribution and activity of RHAMM in the context of skeletal muscle. Furthermore, our data indicate that HA, through interactions with CD44 and RHAMM, promotes myogenic progenitor migration and proliferation. Confirmation of the role of HA and its receptors in directing myogenesis will be useful for the design of regenerative therapies that aim to promote the restoration of damaged or diseased muscle.

Nppa and Nppb act redundantly during zebrafish cardiac development to confine AVC marker expression and reduce cardiac jelly volume

Atrial natriuretic peptide (nppa/anf) and brain natriuretic peptide (nppb/bnp) form a gene cluster with expression in the chambers of the developing heart. Despite restricted expression, a function in cardiac development has not been demonstrated by mutant analysis. This is attributed to functional redundancy; however, their genomic location in cis has impeded formal analysis. Using genome editing, we have generated mutants for nppa and nppb, and found that single mutants were indistinguishable from wild type, whereas nppa/nppb double mutants displayed heart morphogenesis defects and pericardial oedema. Analysis of atrioventricular canal (AVC) markers show expansion of bmp4, tbx2b, has2 and versican expression into the atrium of double mutants. This expanded expression correlates with increased extracellular matrix in the atrium. Using a biosensor for hyaluronic acid to measure the cardiac jelly (cardiac extracellular matrix), we confirmed cardiac jelly expansion in nppa/nppb double mutants. Finally, bmp4 knockdown rescued the expansion of has2 expression and cardiac jelly in double mutants. This definitively shows that nppa and nppb function redundantly during cardiac development to restrict gene expression to the AVC, preventing excessive cardiac jelly synthesis in the atrial chamber.

Tau Pathology Promotes the Reorganization of the Extracellular Matrix and Inhibits the Formation of Perineuronal Nets by Regulating the Expression and the Distribution of Hyaluronic Acid Synthases

Hyaluronic acid (HA) is the backbone of the extracellular matrix (ECM) and provides biochemical and physical support to aggrecan-based perineuronal nets (PNNs), which are associated with the selective vulnerability of neurons in Alzheimer's disease (AD). Here, we showed that HA synthases (HASs), including Has1, Has2, and Has3, were widely expressed in murine central nervous system. All types of HASs were localized to cell bodies of neurons; only Has1 existed in the membranes of neural axons. By using TauP301S transgenic (Tg) mouse model, we found that the axonal-localization of Has1 was abolished in TauP301S overexpressed mouse brain, and the redistribution of Has1 was also observed in human AD brains, suggesting that the localization of Has1 is dependent on intact microtubules which are regulated partially by the phosphorylation and dephosphorylation cycles of tau proteins. Furthermore, Has1 was reduced and Has3 was increased in TauP301S Tg mouse brain, resulting in the upregulation of shorter-chain HA in the ECM. These findings suggest that by abolishing the axonal-localization of Has1 and promoting the expression of Has3 and the synthesis of shorter-chain HA, the tau pathology breaks the balance of ECM components, promotes the reorganization of the ECM, and inhibits the formation of PNNs in the hippocampus, and then regulates neuronal plasticity during the progression of AD.

Brain extracellular space, hyaluronan, and the prevention of epileptic seizures

Mutant mice deficient in hyaluronan (HA) have an epileptic phenotype. HA is one of the major constituents of the brain extracellular matrix. HA has a remarkable hydration capacity, and a lack of HA causes reduced extracellular space (ECS) volume in the brain. Reducing ECS volume can initiate or exacerbate epileptiform activity in many in vitro models of epilepsy. There is both in vitro and in vivo evidence of a positive feedback loop between reduced ECS volume and synchronous neuronal activity. Reduced ECS volume promotes epileptiform activity primarily via enhanced ephaptic interactions and increased extracellular potassium concentration; however, the epileptiform activity in many models, including the brain slices from HA synthase-3 knockout mice, may still require glutamate-mediated synaptic activity. In brain slice epilepsy models, hyperosmotic solution can effectively shrink cells and thus increase ECS volume and block epileptiform activity. However, in vivo, the intravenous administration of hyperosmotic solution shrinks both brain cells and brain ECS volume. Instead, manipulations that increase the synthesis of high-molecular-weight HA or decrease its breakdown may be used in the future to increase brain ECS volume and prevent seizures in patients with epilepsy. The prevention of epileptogenesis is also a future target of HA manipulation. Head trauma, ischemic stroke, and other brain insults that initiate epileptogenesis are known to be associated with an early decrease in high-molecular-weight HA, and preventing that decrease in HA may prevent the epileptogenesis.

Hyaluronan Rich Microenvironment in the Limbal Stem Cell Niche Regulates Limbal Stem Cell Differentiation

Purpose

Limbal epithelial stem cells (LSCs), located in the basal layer of the corneal epithelium in the corneal limbus, are vital for maintaining the corneal epithelium. LSCs have a high capacity of self-renewal with increased potential for error-free proliferation and poor differentiation. To date, limited research has focused on unveiling the composition of the limbal stem cell niche, and, more important, on the role the specific stem cell niche may have in LSC differentiation and function. Our work investigates the composition of the extracellular matrix in the LSC niche and how it regulates LSC differentiation and function.

Methods

Hyaluronan (HA) is naturally synthesized by hyaluronan synthases (HASs), and vertebrates have the following three types: HAS1, HAS2, and HAS3. Wild-type and HAS and TSG-6 knockout mice-HAS1-/-;HAS3-/-, HAS2Δ/ΔCorEpi, TSG-6-/--were used to determine the importance of the HA niche in LSC differentiation and specification.

Results

Our data demonstrate that the LSC niche is composed of a HA rich extracellular matrix. HAS1-/-;HAS3-/-, HAS2Δ/ΔCorEpi, and TSG-6-/- mice have delayed wound healing and increased inflammation after injury. Interestingly, upon insult the HAS knock-out mice up-regulate HA throughout the cornea through a compensatory mechanism, and in turn this alters LSC and epithelial cell specification.

Conclusions

The LSC niche is composed of a specialized HA matrix that differs from that present in the rest of the corneal epithelium, and the disruption of this specific HA matrix within the LSC niche leads to compromised corneal epithelial regeneration. Finally, our findings suggest that HA has a major role in maintaining the LSC phenotype.

Hyaluronan and hyaluronan synthases expression and localization in embryonic mouse molars

Hyaluronan (HA) and hyaluronan synthases (HASs) have been shown to play critical roles in embryogenesis and organ development. However, there have not been any studies examining HA and HAS expression and localization during tooth development. The present study was designed to investigate the expression of HA and three isoforms of HASs (HAS1, 2, 3) in embryonic mouse molars. The first mandibular embryonic mouse molars were examined by immunohistochemistry at E11.5, E13.5, E14.5, E16.5, and E18.5. PCR and western blot analyses were performed on RNA and proteins samples from E13.5 to E18.5 tooth germs. At the initial stage (E11.5), HA and HASs were expressed in the dental epithelium but not the underlying dental mesenchyme. HA immunostaining gradually increased in the enamel organ from the bud stage (E13.5) to the late bell stage (E18.5), and HA and HASs were highly expressed in the stellate reticulum and stratum intermedium. HA immunostaining was also enhanced in the dental mesenchyme and its derived tissues, but it was not expressed in the ameloblast and odontoblast regions. The three HAS isoforms had distinct expression patterns, and they were expressed in the dental mesenchyme and odontoblast at various levels. Furthermore, HAS1 and HAS2 expression decreased, while HAS3 expression increased from E13.5 to E18.5. These results suggested that HA synthesized by different HASs is involved in embryonic mouse molar morphogenesis and cytodifferentiation.

An in situ hybridization study of Hyaluronan synthase (Has) mRNA in developing mouse molar and incisor tooth germs

Hyaluronan (HA) is a major constituent molecule in most extracellular matrices and is synthesized by Hyaluronan synthase (Has). In the present study, we examined expression patterns of Has1, -2, -3 mRNA in developing mouse molar and incisor tooth germs from embryonic day (E) 11.5 to postnatal day (P) 7, focusing on Hertwig's epithelial root sheath (HERS) and the apical bud in particular. Has1 mRNA expression was not detected in all tooth germs examined. Has2 mRNA was expressed in the surrounding mesenchyme from E12.0 to 18.0 in both molar and incisor tooth germs, but disappeared after birth. Meanwhile, Has3 mRNA was exclusively expressed within the enamel organ, especially in the inner enamel epithelium (IEE), stellate reticulum (SR), and stratum intermedium (SI) until the early bell stage at E16.0. Has3 mRNA disappeared as IEE differentiated into differentiating ameloblasts (dABs), but remained in SI until the root developmental stage of the molar tooth germ at P7. Has3 mRNA was also expressed in HERS until P7. In incisors, Has3 mRNA was expressed in the apical bud, especially in the transit-amplifying (TA) cell region from E16.0 to P7, and in the papillary layer (PL) adjacent to the mature enamel. These gene expression patterns suggested that Has3 is the main control factor for prenatal and postnatal HA synthesis of the tooth germ, and may in part regulate crown and root formation of the tooth germ, maintenance of stem cell niches in the apical bud as well as mineral transport in PL.

Regulation of synthesis and roles of hyaluronan in peritoneal dialysis

Hyaluronan (HA) is a ubiquitous extracellular matrix glycosaminoglycan composed of repeated disaccharide units of alternating D-glucuronic acid and D-N-acetylglucosamine residues linked via alternating β-1,4 and β-1,3 glycosidic bonds. HA is synthesized in humans by HA synthase (HAS) enzymes 1, 2, and 3, which are encoded by the corresponding HAS genes. Previous in vitro studies have shown characteristic changes in HAS expression and increased HA synthesis in response to wounding and proinflammatory cytokines in human peritoneal mesothelial cells. In addition, in vivo models and human peritoneal biopsy samples have provided evidence of changes in HA metabolism in the fibrosis that at present accompanies peritoneal dialysis treatment. This review discusses these published observations and how they might contribute to improvement in peritoneal dialysis.

Hyaluronan Synthase: The Mechanism of Initiation at the Reducing End and a Pendulum Model for Polysaccharide Translocation to the Cell Exterior

Hyaluronan (HA) biosynthesis has been studied for over six decades, but our understanding of the biochemical details of how HA synthase (HAS) assembles HA is still incomplete. Class I family members include mammalian and streptococcal HASs, the focus of this review, which add new intracellular sugar-UDPs at the reducing end of growing hyaluronyl-UDP chains. HA-producing cells typically create extracellular HA coats (capsules) and also secrete HA into the surrounding space. Since HAS contains multiple transmembrane domains and is lipid-dependent, we proposed in 1999 that it creates an intraprotein HAS-lipid pore through which a growing HA-UDP chain is translocated continuously across the cell membrane to the exterior. We review here the evidence for a synthase pore-mediated polysaccharide translocation process and describe a possible mechanism (the Pendulum Model) and potential energy sources to drive this ATP-independent process. HA synthases also synthesize chitin oligosaccharides, which are created by cleavage of novel oligo-chitosyl-UDP products. The synthesis of chitin-UDP oligomers by HAS confirms the reducing end mechanism for sugar addition during HA assembly by streptococcal and mammalian Class I enzymes. These new findings indicate the possibility that HA biosynthesis is initiated by the ability of HAS to use chitin-UDP oligomers as self-primers.

Size Matters: Molecular Weight Specificity of Hyaluronan Effects in Cell Biology

Hyaluronan signaling properties are unique among other biologically active molecules, that they are apparently not influenced by postsynthetic molecular modification, but by hyaluronan fragment size. This review summarizes the current knowledge about the generation of hyaluronan fragments of different size and size-dependent differences in hyaluronan signaling as well as their downstream biological effects.

Hyaluronan synthase 3 (HAS3) overexpression downregulates MV3 melanoma cell proliferation, migration and adhesion

Malignant skin melanoma is one of the most deadly human cancers. Extracellular matrix (ECM) influences the growth of malignant tumors by modulating tumor cells adhesion and migration. Hyaluronan is an essential component of the ECM, and its amount is altered in many tumors, suggesting an important role for hyaluronan in tumorigenesis. Nonetheless its role in melanomagenesis is not understood. In this study we produced a MV3 melanoma cell line with inducible expression of the hyaluronan synthase 3 (HAS3) and studied its effect on the behavior of the melanoma cells. HAS3 overexpression expanded the cell surface hyaluronan coat and decreased melanoma cell adhesion, migration and proliferation by cell cycle arrest at G1/G0. Melanoma cell migration was restored by removal of cell surface hyaluronan by Streptomyces hyaluronidase and by receptor blocking with hyaluronan oligosaccharides, while the effect on cell proliferation was receptor independent. Overexpression of HAS3 decreased ERK1/2 phosphorylation suggesting that inhibition of MAP-kinase signaling was responsible for these suppressive effects on the malignant phenotype of MV3 melanoma cells.

Regulation of hyaluronan synthesis in vascular diseases and diabetes

Cell microenvironment has a critical role determining cell fate and modulating cell responses to injuries. Hyaluronan (HA) is a ubiquitous extracellular matrix glycosaminoglycan that can be considered a signaling molecule. In fact, interacting with several cell surface receptors can deeply shape cell behavior. In vascular biology, HA triggers smooth muscle cells (SMCs) dedifferentiation which contributes to vessel wall thickening. Furthermore, HA is able to modulate inflammation by altering the adhesive properties of endothelial cells. In hyperglycemic conditions, HA accumulates in vessels and can contribute to the diabetic complications at micro- and macrovasculature. Due to the pivotal role in favoring atherogenesis and neointima formation after injuries, HA could be a new target for cardiovascular pathologies. This review will focus on the recent findings regarding the regulation of HA synthesis in human vascular SMCs. In particular, the effects of the intracellular HA substrates availability, adenosine monophosphate-activated protein kinase (AMPK), and protein O-GlcNAcylation on the main HA synthetic enzyme (i.e., HAS2) will be discussed.

Biological functions of hyaluronan and cytokine-inducible deubiquitinating enzymes

The modification of proteins through post-translation and degradation by the ubiquitin-proteasome system plays a pivotal role in a broad array of biological processes. Reversal of this process by deubiquitination is a central step in the maintenance and regulation of cellular homeostasis. It now appears that the regulation of ubiquitin pathways by deubiquitinating enzymes (DUBs) could be used as targets for anticancer therapy. Recent success in inducing apoptosis in cancerous cells by USP17, a cytokine-inducible DUB encoding two hyaluronan binding motifs (HABMs) showing direct interaction with hyaluronan (HA), could prove a promising step in the development of DUBs containing HABMs as agents in anticancer therapeutics. In this review, we summarize the importance of hyaluronan (HA) in cancer, the role played by DUBs in apoptosis, and a possible relationship between DUBs and HA in cancerous cells, suggesting new strategies for applying DUB enzymes as potential anticancer therapeutics.

Hyaluronan and RHAMM in wound repair and the "cancerization" of stromal tissues

Tumors and wounds share many similarities including loss of tissue architecture, cell polarity and cell differentiation, aberrant extracellular matrix (ECM) remodeling (Ballard et al., 2006) increased inflammation, angiogenesis, and elevated cell migration and proliferation. Whereas these changes are transient in repairing wounds, tumors do not regain tissue architecture but rather their continued progression is fueled in part by loss of normal tissue structure. As a result tumors are often described as wounds that do not heal. The ECM component hyaluronan (HA) and its receptor RHAMM have both been implicated in wound repair and tumor progression. This review highlights the similarities and differences in their roles during these processes and proposes that RHAMM-regulated wound repair functions may contribute to “cancerization” of the tumor microenvironment.

Tissue distribution and subcellular localization of hyaluronan synthase isoenzymes

Hyaluronan synthases (HAS) are unique plasma membrane glycosyltransferases secreting this glycosaminoglycan directly to the extracellular space. The three HAS isoenzymes (HAS1, HAS2, and HAS3) expressed in mammalian cells differ in their enzymatic properties and regulation by external stimuli, but clearly distinct functions have not been established. To overview the expression of different HAS isoenzymes during embryonic development and their subcellular localization, we immunostained mouse embryonic samples and cultured cells with HAS antibodies, correlating their distribution to hyaluronan staining. Their subcellular localization was further studied by GFP-HAS fusion proteins. Intense hyaluronan staining was observed throughout the development in the tissues of mesodermal origin, like heart and cartilages, but also for example during the maturation of kidneys and stratified epithelia. In general, staining for one or several HASs correlated with hyaluronan staining. The staining of HAS2 was most widespread, both spatially and temporally, correlating with hyaluronan staining especially in early mesenchymal tissues and heart. While epithelial cells were mostly negative for HASs, stratified epithelia became HAS positive during differentiation. All HAS isoenzymes showed cytoplasmic immunoreactivity, both in tissue sections and cultured cells, while plasma membrane staining was also detected, often in cellular extensions. HAS1 had brightest signal in Golgi, HAS3 in Golgi and microvillous protrusions, whereas most of the endogenous HAS2 immunoreactivity was localized in the ER. This differential pattern was also observed with transfected GFP-HASs. The large proportion of intracellular HASs suggests that HAS forms a reserve that is transported to the plasma membrane for rapid activation of hyaluronan synthesis.

Production Methods for Hyaluronan

Hyaluronan is a polysaccharide with multiple functions in the human body being involved in creating flexible and protective layers in tissues and in many signalling pathways during embryonic development, wound healing, inflammation, and cancer. Hyaluronan is an important component of active pharmaceutical ingredients for treatment of, for example, arthritis and osteoarthritis, and its commercial value far exceeds that of other microbial extracellular polysaccharides. Traditionally hyaluronan is extracted from animal waste which is a well-established process now. However, biotechnological synthesis of biopolymers provides a wealth of new possibilities. Therefore, genetic/metabolic engineering has been applied in the area of tailor-made hyaluronan synthesis. Another approach is the controlled artificial (in vitro) synthesis of hyaluronan by enzymes. Advantage of using microbial and enzymatic synthesis for hyaluronan production is the simpler downstream processing and a reduced risk of viral contamination. In this paper an overview of the different methods used to produce hyaluronan is presented. Emphasis is on the advancements made in the field of the synthesis of bioengineered hyaluronan.

The control and importance of hyaluronan synthase expression in palatogenesis

Development of the lip and palate involves a complex series of events that requires the close co-ordination of cell migration, growth, differentiation, and apoptosis. Palatal shelf elevation is considered to be driven by regional accumulation and hydration of glycosoaminoglycans, principally hyaluronan (HA), which provides an intrinsic shelf force, directed by components of the extracellular matrix (ECM). During embryogenesis, the extracellular and pericellular matrix surrounding migrating and proliferating cells is rich in HA. This would suggest that HA may be important in both shelf growth and fusion. TGFβ3 plays an important role in palatogenesis and the corresponding homozygous null (TGFβ3^−/−) mouse, exhibits a defect in the fusion of the palatal shelves resulting in clefting of the secondary palate. TGFβ3 is expressed at the future medial edge epithelium (MEE) and at the actual edge epithelium during E14.5, suggesting a role for TGFβ3 in fusion. This is substantiated by experiments showing that addition of exogenous TGFβ3 can “rescue” the cleft palate phenotype in the null mouse. In addition, TGFβ1 and TGFβ2 can rescue the null mouse palate (in vitro) to near normal fusion. In vivo a TGFβ1 knock-in mouse, where the coding region of the TGFβ3 gene was replaced with the full-length TGFβ1 cDNA, displayed complete fusion at the mid portion of the secondary palate, whereas the anterior and posterior regions failed to fuse appropriately. We present experimental data indicating that the three HA synthase (Has) enzymes are differentially expressed during palatogenesis. Using immunohistochemistry (IHC) and embryo sections from the TGFβ3 null mouse at days E13.5 and E14.5, it was established that there was a decrease in expression of Has2 in the mesenchyme and an increase in expression of Has3 in comparison to the wild-type mouse. In vitro data indicate that HA synthesis is affected by addition of exogenous TGFβ3. Preliminary data suggests that this increase in HA synthesis, in response to TGFβ3, is under the control of the PI3kinase/Akt pathway.

Pax6 interactions with chromatin and identification of its novel direct target genes in lens and forebrain

Pax6 encodes a specific DNA-binding transcription factor that regulates the development of multiple organs, including the eye, brain and pancreas. Previous studies have shown that Pax6 regulates the entire process of ocular lens development. In the developing forebrain, Pax6 is expressed in ventricular zone precursor cells and in specific populations of neurons; absence of Pax6 results in disrupted cell proliferation and cell fate specification in telencephalon. In the pancreas, Pax6 is essential for the differentiation of α-, β- and δ-islet cells. To elucidate molecular roles of Pax6, chromatin immunoprecipitation experiments combined with high-density oligonucleotide array hybridizations (ChIP-chip) were performed using three distinct sources of chromatin (lens, forebrain and β-cells). ChIP-chip studies, performed as biological triplicates, identified a total of 5,260 promoters occupied by Pax6. 1,001 (133) of these promoter regions were shared between at least two (three) distinct chromatin sources, respectively. In lens chromatin, 2,335 promoters were bound by Pax6. RNA expression profiling from Pax6^+/− lenses combined with in vivo Pax6-binding data yielded 76 putative Pax6-direct targets, including the Gaa, Isl1, Kif1b, Mtmr2, Pcsk1n, and Snca genes. RNA and ChIP data were validated for all these genes. In lens cells, reporter assays established Kib1b and Snca as Pax6 activated and repressed genes, respectively. In situ hybridization revealed reduced expression of these genes in E14 cerebral cortex. Moreover, we examined differentially expressed transcripts between E9.5 wild type and Pax6^−/− lens placodes that suggested Efnb2, Fat4, Has2, Nav1, and Trpm3 as novel Pax6-direct targets. Collectively, the present studies, through the identification of Pax6-direct target genes, provide novel insights into the molecular mechanisms of Pax6 gene control during mouse embryonic development. In addition, the present data demonstrate that Pax6 interacts preferentially with promoter regions in a tissue-specific fashion. Nevertheless, nearly 20% of the regions identified are accessible to Pax6 in multiple tissues.

Hyaluronan synthase 1 (HAS1) requires higher cellular UDP-GlcNAc concentration than HAS2 and HAS3

Mammals have three homologous genes encoding proteins with hyaluronan synthase activity (Has1-3), all producing an identical polymer from UDP-N-acetylglucosamine and UDP-glucuronic acid. To compare the properties of these isoenzymes, COS-1 cells, with minor endogenous hyaluronan synthesis, were transfected with human Has1-3 isoenzymes. HAS1 was almost unable to secrete hyaluronan or form a hyaluronan coat, in contrast to HAS2 and HAS3. This failure of HAS1 to synthesize hyaluronan was compensated by increasing the cellular content of UDP-N-acetyl glucosamine by ∼10-fold with 1 mm glucosamine in the growth medium. Hyaluronan synthesis driven by HAS2 was less affected by glucosamine addition, and HAS3 was not affected at all. Glucose-free medium, leading to depletion of the UDP-sugars, markedly reduced hyaluronan synthesis by all HAS isoenzymes while raising its concentration from 5 to 25 mm had a moderate stimulatory effect. The results indicate that HAS1 is almost inactive in cells with low UDP-sugar supply, HAS2 activity increases with UDP-sugars, and HAS3 produces hyaluronan at high speed even with minimum substrate content. Transfected Has2 and particularly Has3 consumed enough UDP-sugars to reduce their content in COS-1 cells. Comparison of different human cell types revealed ∼50-fold differences in the content of UDP-N-acetylhexosamines and UDP-glucuronic acid, correlating with the expression level of Has1, suggesting cellular coordination between Has1 expression and the content of UDP-sugars.

Therapeutic targeting of hyaluronan in the tumor stroma

The tumor stroma, consisting of non-malignant cells and the extracellular matrix, undergoes significant quantitative and qualitative changes throughout malignant transformation and tumor progression. With increasing recognition of the role of the tumor microenvironment in disease progression, stromal components of the tumor have become attractive targets for therapeutic intervention. Stromal accumulation of the glycosaminoglycan hyaluronan occurs in many tumor types and is frequently associated with a negative disease prognosis. Hyaluronan interacts with other extracellular molecules as well as cellular receptors to form a complex interaction network influencing physicochemical properties, signal transduction, and biological behavior of cancer cells. In preclinical animal models, enzymatic removal of hyaluronan is associated with remodeling of the tumor stroma, reduction of tumor interstitial fluid pressure, expansion of tumor blood vessels and facilitated delivery of chemotherapy. This leads to inhibition of tumor growth and increased survival. Current evidence shows that abnormal accumulation of hyaluronan may be an important stromal target for cancer therapy. In this review we highlight the role of hyaluronan and hyaluronan-mediated interactions in cancer, and discuss historical and recent data on hyaluronidase-based therapies and the effect of hyaluronan removal on tumor growth.

The murine allantois: a model system for the study of blood vessel formation

The allantois is the embryonic precursor of the umbilical cord in mammals and is one of several embryonic regions, including the yolk sac and dorsal aorta, that undergoes vasculogenesis, the de novo formation of blood vessels. Despite its importance in establishing the chorioallantoic placenta and umbilical circulation, the allantois frequently is overlooked in embryologic studies. Nonetheless, recent studies demonstrate that vasculogenesis, vascular remodeling, and angiogenesis are essential allantois functions in the establishment of the chorioallantoic placenta. Here, we review blood vessel formation in the murine allantois, highlighting the expression of genes and involvement of pathways common to vasculogenesis or angiogenesis in other parts of the embryo. We discuss experimental techniques available for manipulation of the allantois that are unavailable for yolk sac or dorsal aorta, and review how this system has been used as a model system to discover new genes and mechanisms involved in vessel formation. Finally, we discuss the potential of the allantois as a model system to provide insights into disease and therapeutics.

Hyaluronic acid, HAS1, and HAS2 are significantly upregulated during muscle hypertrophy

Hyaluronic acid (HA) is a component of the extracellular matrix (ECM) in most vertebrate tissues and is thought to play a significant role during development, wound healing, and regeneration. In vitro studies have shown that HA enhances muscle progenitor cell recruitment and inhibits premature myotube fusion, implicating a role for this glycosaminoglycan in functional repair. However, the spatiotemporal distribution of HA during muscle growth and repair was unknown. We hypothesized that inducing hypertrophy via synergist ablation would increase the expression of HA and the HA synthases (HAS1-HAS3). We found that HA and HAS1-HAS3 were significantly upregulated within the plantaris muscle in response to Achilles tenectomy. HA concentration significantly increased 2.8-fold after 2 days but decreased towards levels comparable to age-matched controls by 14 days. Using immunohistochemistry, we found the colocalization of HAS1-HAS3 with macrophages, blood vessel epithelia, and fibroblasts varied in response to time and/or tenectomy. At the level of gene expression, only HAS1 and HAS2 significantly increased with respect to both time and tenectomy. The profiles of additional genes that influence ECM composition during muscle repair, tenascin-C, type I collagen, the HA-degrading hyaluronidases (Hyal) and matrix metalloproteinases (MMP) were also investigated. Hyal1 and Hyal2 were highly expressed in skeletal muscle but did not change after tenectomy; however, indicators of hypertrophy, MMP-2 and MMP-14, were significantly upregulated from 2 to 14 days. These results indicate that HA levels dynamically change in response to a hypertrophic stimulus and various cells may participate in this mechanism of skeletal muscle adaptation.

The role of hyaluronan produced by Has2 gene expression in development of the spine

STUDY DESIGN

Histologic analysis of spine development in cartilage-specific knockout mice.

OBJECTIVE

To evaluate the role hyaluronan produced by hyaluronan synthase-2 (Has2) in spine development.

SUMMARY OF BACKGROUND DATA

The Has2 gene is responsible for most hyaluronan production throughout the body, including the skeleton. However, it is not possible to study the involvement of hyaluronan in skeletal development using constitutive Has2 knockout mice, as the embryonic mice die early before skeletal development has occurred. This problem can be overcome by the use of cartilage-specific knockout mice.

METHODS

Mice possessing floxed Has2 genes were crossed with mice expressing Cre recombinase under control of the type II collagen promoter to generate cartilage-specific Has2 knockout mice. Spine development was studied by histology.

RESULTS

Knockout mice died near birth and displayed severe abnormality in skeletal development. The spine showed defects in vertebral body size and the formation of the intervertebral discs. There was no evidence for the formation of an organized primary center of ossification within the vertebrae, and the appearance and organization of the hypertrophic chondrocytes was abnormal. Although no organized endochondral ossification appeared to be taking place, there was excessive bone formation at the center of the vertebrae. There was also a generalized increased cellularity of the vertebral cartilage and a corresponding decrease in the abundance of extracellular matrix. The nucleus pulposus of the intervertebral discs were less flattened than in the control mice and possessed an increased amount of large vacuolated cells. Remnants of the notochord could also be seen between adjacent discs.

CONCLUSION

Hyaluronan production by Has2 is essential for normal vertebral and intervertebral disc development within the spine, and the absence of this synthase impairs the organization of both soft and hard tissue elements.