Increased hyaluronan by naked mole-rat Has2 improves healthspan in mice.

Abundant high-molecular-mass hyaluronic acid (HMM-HA) contributes to cancer resistance and possibly to the longevity of the longest-lived rodent-the naked mole-rat1,2. To study whether the benefits of HMM-HA could be transferred to other animal species, we generated a transgenic mouse overexpressing naked mole-rat hyaluronic acid synthase 2 gene (nmrHas2). nmrHas2 mice showed an increase in hyaluronan levels in several tissues, and a lower incidence of spontaneous and induced cancer, extended lifespan and improved healthspan. The transcriptome signature of nmrHas2 mice shifted towards that of longer-lived species. The most notable change observed in nmrHas2 mice was attenuated inflammation across multiple tissues. HMM-HA reduced inflammation through several pathways, including a direct immunoregulatory effect on immune cells, protection from oxidative stress and improved gut barrier function during ageing. These beneficial effects were conferred by HMM-HA and were not specific to the nmrHas2 gene. These findings demonstrate that the longevity mechanism that evolved in the naked mole-rat can be exported to other species, and open new paths for using HMM-HA to improve lifespan and healthspan.

Downstream process intensification for biotechnologically generated hyaluronic acid: Purification and characterization.

Hyaluronic acid (HA), an anionic, non-sulfated glycosaminoglycan, has several clinical applications. This study examines several downstream methods for purifying HA with maximum recovery and purity. Following the fermentation of Streptococcus zooepidemicus MTCC 3523 to produce HA, the broth was thoroughly purified to separate cell debris and insoluble impurities using a filtration procedure and a variety of adsorbents for soluble impurities. Nucleic acids, proteins with high molecular weight, were successfully removed from the broth using activated carbons and XAD-7 resins. In contrast, insoluble and low molecular weight impurities were removed using diafiltration, with HA recovery of 79.16% and purity close to 90%. Different analytical and characterization procedures such as Fourier transform-infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy validated the presence, purity, and structure of HA. Microbial HA showed activity in tests for 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical-scavenging (4.87 ± 0.45 kmol TE/g), total antioxidant capacity (13.32 ± 0.52%), hydroxyl radical-scavenging (32.03 ± 0.12%), and reducing power (24.85 ± 0.45%). The outcomes showed that the precipitation, adsorption, and diafiltration processes are suitable for extracting HA from a fermented broth under the chosen operating conditions. The HA produced was of pharmaceutical grade for non-injectable applications.

Hyaluronic acid production and purification techniques: a review.

Hyaluronic acid (HA) is an exopolysaccharide extracted from several sources such as rooster combs, umbilical cords and microorganisms. A system that controls temperature, agitation and aeration of bacterial cultures could make the HA production autonomous. Therefore, HA of microbial origin is set to take over alternative methods of production. Furthermore, the use of different nutrient sources in the culture medium and the purification stage applied in the process can cause physicochemical alterations on the bioproduct. For instance, structural modifications that change the molecular weight of HA may alter its elastic and viscoelastic properties. As a result, HA synthesized by microbes has applications in pharmacology, biotechnology, and tissue engineering. Our aim here, is to show the vast range of applications by compiling articles and patents on the culture media or genetic modifications of microorganisms that synthesize HA.

JMJD3 activated hyaluronan synthesis drives muscle regeneration in an inflammatory environment.

Muscle stem cells (MuSCs) reside in a specialized niche that ensures their regenerative capacity. Although we know that innate immune cells infiltrate the niche in response to injury, it remains unclear how MuSCs adapt to this altered environment for initiating repair. Here, we demonstrate that inflammatory cytokine signaling from the regenerative niche impairs the ability of quiescent MuSCs to reenter the cell cycle. The histone H3 lysine 27 (H3K27) demethylase JMJD3, but not UTX, allowed MuSCs to overcome inhibitory inflammation signaling by removing trimethylated H3K27 (H3K27me3) marks at the Has2 locus to initiate production of hyaluronic acid, which in turn established an extracellular matrix competent for integrating signals that direct MuSCs to exit quiescence. Thus, JMJD3-driven hyaluronic acid synthesis plays a proregenerative role that allows MuSC adaptation to inflammation and the initiation of muscle repair.

3'UTR shortening of HAS2 promotes hyaluronan hyper-synthesis and bioenergetic dysfunction in pulmonary hypertension.

Pulmonary hypertension (PH) comprises a diverse group of disorders that share a common pathway of pulmonary vascular remodeling leading to right ventricular failure. Development of anti-remodeling strategies is an emerging frontier in PH therapeutics that requires a greater understanding of the interactions between vascular wall cells and their extracellular matrices. The ubiquitous matrix glycan, hyaluronan (HA), is markedly elevated in lungs from patients and experimental models with PH. Herein, we identified HA synthase-2 (HAS2) in the pulmonary artery smooth muscle cell (PASMC) layer as a predominant locus of HA dysregulation. HA upregulation involves depletion of NUDT21, a master regulator of alternative polyadenylation, resulting in 3'UTR shortening and hyper-expression of HAS2. The ensuing increase of HAS2 and hyper-synthesis of HA promoted bioenergetic dysfunction of PASMC characterized by impaired mitochondrial oxidative capacity and a glycolytic shift. The resulting HA accumulation stimulated pro-remodeling phenotypes such as cell proliferation, migration, apoptosis-resistance, and stimulated pulmonary artery contractility. Transgenic mice, mimicking HAS2 hyper-synthesis in smooth muscle cells, developed spontaneous PH, whereas targeted deletion of HAS2 prevented experimental PH. Pharmacological blockade of HAS2 restored normal bioenergetics in PASMC, ameliorated cell remodeling phenotypes, and reversed experimental PH in vivo. In summary, our results uncover a novel mechanism of HA hyper-synthesis and downstream effects on pulmonary vascular cell metabolism and remodeling.

Physicochemical characterization and in vitro antioxidant activity of hyaluronic acid produced by Streptococcus zooepidemicus CCT 7546.

Hyaluronic acid (HA) is a biopolymer with applications in different areas such as medicine and cosmetics. HA is currently either isolated from animal sources or produced by microbial fermentation. Animal HA presents some disadvantages such as high cost and risk of viral cross-species or another infectious agent. In the present study, we evaluated the physicochemical characteristics and in vitro antioxidant capacity of HA produced by Streptococcus zooepidemicus CCT 7546. In addition, commercial sodium hyaluronate (SH) from an animal source was used as control. The microbial HA yield after purification was 69.8 mg/L. According to Fourier transform infrared spectroscopy, it was seen that bacterial and animal HA spectra are overlapped. The thermogravimetric analysis revealed that microbial HA was more stable than its equivalent from the animal source. However, scanning electron microscopy indicates that the purification method used in the animal product was more effective. Microbial HA showed activity in total antioxidant capacity (14.02 ± 0.38%), reducing power (18.18 ± 6.43%), DPPH radical-scavenging (5.57 ± 0.23 kmol TE/g), and hydroxyl radical-scavenging (28.39 ± 2.40%) tests. Therefore, in vitro antioxidant tests demonstrated that the antioxidant action mechanism occurs through scavenging reactive oxygen species (ROS) and donating electrons/hydrogen atoms.

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.

The dilution effect of media culture on mixing time, Kla O2, and hyaluronic acid production in S. zooepidemicus fed-batch culture.

OBJECTIVES: Microbial production of biopolymers is typically associated with high viscosity and suitable mixing plays an important role in their production. Due to the nature of Streptococcus strains in high production of lactic acid and consequently high consumption of NaOH, which is associated with increased viscosity and reduced mixing caused by hyaluronic acid production, the injected NaOH accumulates and causes cells loss, and decreases in quantity and quality of the produced hyaluronic acid. RESULTS: In this study, the effect of increasing dilution of media culture of Streptococcus zooepidemicus fed-batch culture during pH control by NaOH on mixing time, volumetric oxygen transfer coefficient, and increasing hyaluronic acid production in a 2-L fermenter were studied. The results showed that significant increasing dilution causes reduction mixing time, remarkable improvement volumetric oxygen transfer coefficient, hyaluronic acid production enhancement from 6.6 to 8.4 g/L, and diminution the consumption of NaOH. CONCLUSION: Dilution of media culture of S. zooepidemicus fed-batch culture by the pH controlling agent achieved one of the highest amounts of hyaluronic acid that was reported recently. This method does not require any automatic control and can be used at a low cost to produce other soluble extracellular biopolymers.

4-Methylumbelliferone induces antitumor effects independently of hyaluronan synthesis inhibition in human acute leukemia cell lines.

AIMS: Despite continuous improvement in the treatment of acute leukemia, new therapies are still needed to overcome resistance and reduce adverse effects. The aim of this work was to study the tumor-suppressive effects of 4-methylumbelliferone (4MU) in human acute leukemia cell lines. In addition, we aimed to address the extent of these effects in relation to the inhibition of hyaluronic acid (HA) synthesis. MAIN METHODS: HA levels were measured by an ELISA-like assay. Human acute leukemia cell lines were treated with 4MU, HA or their combination. Cell proliferation was assessed by the [3H]-Tdr uptake assay, metabolic activity by the XTT assay and cell death was determined by DAPI, AO/EB and AnnexinV-PE/7-AAD staining. Senescence induction was evaluated by SA-ß-Gal and C12FDG staining. Total and surface RHAMM expression levels were assessed by flow cytometry and fluorescence microscopy. KEY FINDINGS: 4MU reduced metabolic activity and inhibited cell proliferation in all leukemia cells, and these effects were explained by the induction of senescence or cell death depending on the cell line evaluated. Exogenous HA failed to prevent most of the tumor-suppressive effects observed. Results from this work suggest that the tumor-suppressive effects exerted by 4MU would be explained by HA-synthesis-independent mechanisms. SIGNIFICANCE: These findings broaden the knowledge of 4MU as a potential treatment in acute leukemia. We report for the first time the existence of tumor-suppressive effects of 4MU on human acute leukemia cell lines that are independent of its role as HA-synthesis inhibitor.

Heterologous production of hyaluronic acid in Nicotiana tabacum hairy roots expressing a human hyaluronan synthase 2.

Hyaluronic acid (HA), a unique polysaccharide with excellent Physico-chemical properties, is broadly used in pharmaceutical, biomedical, and cosmetic fields. It is widely present in all vertebrates, certain bacterial strains, and even viruses while it is not found in plants, fungi, and insects. HA is naturally synthesized by a class of integral membrane proteins called Hyaluronic acid synthase (HAS). Thus far, industrial production of HA is carried out based on either extraction from animal sources or large-scale microbial fermentation. The major drawbacks to using these systems are contamination with pathogens and microbial toxins. Recently, the production of HA through recombinant systems has received considerable attention. Plants are eco-friendly ideal expression systems for biopharmaceuticals production. In this study, the optimized human hyaluronic acid synthase2 (hHAS2) sequence was transformed into Nicotiana tabacum using Agrobacterium rhizogenes. The highest rhHAS2 concentration of 65.72 ng/kg (wet weight) in transgenic tobacco hairy roots was measured by the human HAS2 ELISA kit. The HA production in the transgenic hairy roots was verified by scanning electron microscope (SEM) and quantified by the HA ELISA kit. The DPPH radical scavenging activity of HA with the highest concentration of 0.56 g/kg (wet weight) showed a maximum activity of 46%. Gel Permeation Chromatography (GPC) analyses revealed the high molecular weight HA (HMW-HA) with about > 0.8 MDa.

Roles of glomerular endothelial hyaluronan in the development of proteinuria.

Vascular endothelial cells are covered with glycocalyx comprising heparan sulfate, hyaluronan, chondroitin sulfate, and associated proteins. Glomerular endothelial glycocalyx is involved in protecting against induction of proteinuria and structural damage, but the specific components in glycocalyx that represent therapeutic targets remain unclear. Anti-vascular endothelial growth factor (VEGF) therapy is associated with an increased risk of glomerular endothelial injury. This study investigated whether hyaluronan could provide a therapeutic target to protect against proteinuria. We conducted ex vivo and in vivo experiments to explore the effects of degrading glomerular hyaluronan by administering hyaluronidase and of supplementation with hyaluronan. We investigated hyaluronan expression using biotin-labeled hyaluronan-binding protein (HABP) in human kidney specimens or serum hyaluronan in endothelial injuries under inhibition of VEGF signaling. We directly demonstrated hyaluronan in glomerular endothelial layers using HABP staining. Ex vivo and in vivo experiments showed the development of proteinuria after digestion of hyaluronan in glomerular capillaries. Supplementation with hyaluronan after hyaluronidase treatment suppressed proteinuria. Mice in the in vivo study developed albuminuria after intraperitoneal injection of hyaluronidase with decreased glomerular hyaluronan and increased serum hyaluronan. In human kidneys with endothelial cell dysfunction and proteinuria due to inhibition of VEGF, glomerular expression of hyaluronan was reduced even in normal-appearing glomeruli. Serum hyaluronan levels were elevated in patients with pre-eclampsia with VEGF signaling inhibition. Our data suggest that hyaluronan itself plays crucial roles in preventing proteinuria and preserving the integrity of endothelial cells. Hyaluronan could provide a therapeutic target for preventing glomerular endothelial glycocalyx damage, including VEGF signaling inhibition.

Current advances in the biosynthesis of hyaluronic acid with variable molecular weights.

Hyaluronic acid (HA) is a naturally formed acidic mucopolysaccharide, with excellent moisturising properties and used widely in the medicine, cosmetics, and food industries. The industrial production of specific molecular weight HA has become imperative. Different biological activities and physiological functions of HA mainly depend on the degree of polymerisation. This article reviews the research status and development prospects of the green biosynthesis and molecular weight regulation of HA. There is an application-based prerequisite of specific molecular weight of HA that could be regulated either during the fermentation process or via a controlled HA degradation process. This work provides an important theoretical basis for the downstream efficient production of diversified HA, which will further accelerate the research applications of HA and provide a good scientific basis and method reference for the study of the molecular weight regulation of similar biopolymers.

1-Ethyl-ß-N-acetylglucosaminide increases hyaluronan production in human keratinocytes by being converted to N-acetylglucosamine via ß-N-acetylglucosaminidase-dependent manner.

Regulation of hyaluronan (HA) is important for the maintenance of epidermal homeostasis. Here, we examined the mechanism by which 1-ethyl-ß-N-acetylglucosaminide (ß-NAG2), a newly developed N-acetylglucosamine (NAG) derivative, increases HA production in cultured human epidermal keratinocytes. When keratinocytes were treated with ß-NAG2, mRNA expression of HA synthase 3, which is responsible for HA production in human keratinocytes, was not influenced, but the intracellular level of UDP-NAG, a substrate used for HA synthesis, was increased. By using a synthetic substrate for ß-N-acetylglucosaminidase (ß-NAGase), keratinocytes were found to possess ß-NAGase activity, and treatment of o-(2-acetamido-2-deoxy-d-glucopyranosylidene) amino N-phenyl carbamate (PUGNAc), an inhibitor of ß-NAGase, abolished the release of NAG from ß-NAG2 in keratinocytes. Furthermore, PUGNAc attenuated the ß-NAG2-induced intracellular UDP-NAG and HA production in keratinocytes. These results suggest that ß-NAG2 is converted to NAG by endogenous ß-NAGase in keratinocytes, and the resulting NAG is further metabolized to UDP-NAG and utilized for HA production.

Hyaluronan Synthases' Expression and Activity Are Induced by Fluid Shear Stress in Bone Marrow-Derived Mesenchymal Stem Cells.

During biomineralization, the cells generating the biominerals must be able to sense the external physical stimuli exerted by the growing mineralized tissue and change their intracellular protein composition according to these stimuli. In molluscan shell, the myosin-chitin synthases have been suggested to be the link for this communication between cells and the biomaterial. Hyaluronan synthases (HAS) belong to the same enzyme family as chitin synthases. Their product hyaluronan (HA) occurs in the bone and is supposed to have a regulatory function during bone regeneration. We hypothesize that HASes' expression and activity are controlled by fluid-induced mechanotransduction as it is known for molluscan chitin synthases. In this study, bone marrow-derived human mesenchymal stem cells (hMSCs) were exposed to fluid shear stress of 10 Pa. The RNA transcriptome was analyzed by RNA sequencing (RNAseq). HA concentrations in the supernatants were measured by ELISA. The cellular structure of hMSCs and HAS2-overexpressing hMSCs was investigated after treatment with shear stress using confocal microscopy. Fluid shear stress upregulated the expression of genes that encode proteins belonging to the HA biosynthesis and bone mineralization pathways. The HAS activity appeared to be induced. Knowledge about the regulation mechanism governing HAS expression, trafficking, enzymatic activation and quality of the HA product in hMSCs is essential to understand the biological role of HA in the bone microenvironment.

Versatile strategies for bioproduction of hyaluronic acid driven by synthetic biology.

Owing to its outstanding water-retention ability, viscoelasticity, biocompatibility and non-immunogenicity, Hyaluronic acid (HA), a natural linear polymer alternating linked by d-glucuronic acid and N-acetylglucosamine, has been widely employed in cosmetic, medical and clinical applications. With the development of synthetic biology and bioprocessing optimization, HA production via microbial fermentation is an economical and sustainable alternative over traditional animal extraction methods. Indeed, recently Streptococci and other recombinant systems for HA synthesis has received increasing interests due to its technical advantages. This review summarizes the production of HA by microorganisms and demonstrates its synthesis mechanism, focusing on the current status in various production systems, as well as common synthetic biology strategies include driving more carbon flux into HA biosynthesis and regulating the molecular weight (MW), and finally discusses the major challenges and prospects.

Initial Identification of UDP-Glucose Dehydrogenase as a Prognostic Marker in Breast Cancer Patients, Which Facilitates Epirubicin Resistance and Regulates Hyaluronan Synthesis in MDA-MB-231 Cells.

UDP-glucose-dehydrogenase (UGDH) synthesizes UDP-glucuronic acid. It is involved in epirubicin detoxification and hyaluronan synthesis. This work aimed to evaluate the effect of UGDH knockdown on epirubicin response and hyaluronan metabolism in MDA-MB-231 breast cancer cells. Additionally, the aim was to determine UGDH as a possible prognosis marker in breast cancer. We studied UGDH expression in tumors and adjacent tissue from breast cancer patients. The prognostic value of UGDH was studied using a public Kaplan-Meier plotter. MDA-MB-231 cells were knocked-down for UGDH and treated with epirubicin. Epirubicin-accumulation and apoptosis were analyzed by flow cytometry. Hyaluronan-coated matrix and metabolism were determined. Autophagic-LC3-II was studied by Western blot and confocal microscopy. Epirubicin accumulation increased and apoptosis decreased during UGDH knockdown. Hyaluronan-coated matrix increased and a positive modulation of autophagy was detected. Higher levels of UGDH were correlated with worse prognosis in triple-negative breast cancer patients that received chemotherapy. High expression of UGDH was found in tumoral tissue from HER2--patients. However, UGDH knockdown contributes to epirubicin resistance, which might be associated with increases in the expression, deposition and catabolism of hyaluronan. The results obtained allowed us to propose UGDH as a new prognostic marker in breast cancer, positively associated with development of epirubicin resistance and modulation of extracellular matrix.

Inhibition of hyaluronan synthesis by 4-methylumbelliferone ameliorates non-alcoholic steatohepatitis in choline-deficient L-amino acid-defined diet-induced murine model.

Hyaluronan (HA) as a glycosaminoglycan can bind to cell-surface receptors, such as TLR4, to regulate inflammation, tissue injury, repair, and fibrosis. 4-methylumbelliferone (4-MU), an inhibitor of HA synthesis, is a drug used for the treatment of biliary spasms. Currently, therapeutic interventions are not available for non-alcoholic steatohepatitis (NASH). In this study, we investigated the effects of 4-MU on NASH using a choline-deficient amino acid (CDAA) diet model. CDAA diet-fed mice showed NASH characteristics, including hepatocyte injury, hepatic steatosis, inflammation, and fibrogenesis. 4-MU treatment significantly reduced hepatic lipid contents in CDAA diet-fed mice. 4-MU reversed CDAA diet-mediated inhibition of Ppara and induction of Srebf1 and Slc27a2. Analysis of serum ALT and AST levels revealed that 4-MU treatment protected against hepatocellular damage induced by CDAA diet feeding. TLR4 regulates low molecular weight-HA-induced chemokine expression in hepatocytes. In CDAA diet-fed, 4-MU-treated mice, the upregulated chemokine/cytokine expression, such as Cxcl1, Cxcl2, and Tnf was attenuated with the decrease of macrophage infiltration into the liver. Moreover, HA inhibition repressed CDAA diet-induced mRNA expression of fibrogenic genes, Notch1, and Hes1 in the liver. In conclusion, 4-MU treatment inhibited liver steatosis and steatohepatitis in a mouse model of NASH, implicating that 4-MU may have therapeutic potential for NASH.

Ganglioside GT1b increases hyaluronic acid synthase 2 via PI3K activation with TLR2 dependence in orbital fibroblasts from thyroid eye disease patients.

Thyroid eye disease (TED) is a complex autoimmune disease with a spectrum of signs. we previously reported that trisialoganglioside (GT)1b is significantly overexpressed in the orbital tissue of TED patients, and that exogenous GT1b strongly induced HA synthesis in orbital fibroblasts. However, the signaling pathway in GT1b-induced hyaluronic acid synthase (HAS) expression in orbital fibroblasts from TED patients have rarely been investigated. Here, we demonstrated that GT1b induced phosphorylation of Akt/mTOR in a dose-dependent manner in orbital fibroblasts from TED patients. Both co-treatment with a specific inhibitor for PI3K and siRNA knockdown of TLR2 attenuated GT1b-induced Akt phosphorylation. GT1b significantly induced HAS2 expression at both the transcriptional and translational level, which was suppressed by specific inhibitors of PI3K or Akt/mTOR, and by siRNA knockdown of TLR2. In conclusion, GT1b induced HAS2 in orbital fibroblasts from TED patients via activation of the PI3Krelated signaling pathway, dependent on TLR2. [BMB Reports 2021; 54(2): 136-141].

Melatonin alleviates d-galactose-decreased hyaluronic acid production in synovial membrane cells via Sirt1 signalling.

Hyaluronic acid (HA) exerts a critical role in the lubricating and buffering properties of synovial fluid in joints. The production of HA is regulated by growth factors, hormones, inflammatory cytokines and mechanical load. The reduction of HA contributes to the progression of osteoarthritis. Herein, we found that d-galactose (d-gal) induced the senescence of rabbit synovial membrane cells, accompanied by decreased HA production. The mRNA level of HA synthase 2 (HAS2) was downregulated by d-gal, as analysed by real-time polymerase chain reaction. Melatonin, an endocrine hormone, can regulate the homeostasis of bone and cartilage. We found that melatonin treatment attenuated d-gal-induced cell senescence and decreased the expression of p21, p16 and pp65 proteins. Melatonin could reverse HA production and maintain HAS2 expression. Furthermore, we revealed that Sirt1 signalling was required for melatonin effects. Sirt1 inhibitor could counteract melatonin-mediated HA production and HAS2 expression. Additionally, Sirt1 overexpression directly antagonized d-gal-induced cell aging and HA downregulation. Taken together, our results suggest that melatonin-Sirt1 signal has a protective effect on synovial membrane cells, enhancing HA synthesis and interrupting cell senescence.

The vitamin A ester retinyl propionate has a unique metabolic profile and higher retinoid-related bioactivity over retinol and retinyl palmitate in human skin models.

Human skin is exposed daily to environmental stressors, which cause acute damage and inflammation. Over time, this leads to morphological and visual appearance changes associated with premature ageing. Topical vitamin A derivatives such as retinol (ROL), retinyl palmitate (RPalm) and retinyl propionate (RP) have been used to reverse these changes and improve the appearance of skin. This study investigated a stoichiometric comparison of these retinoids using in vitro and ex vivo skin models. Skin biopsies were treated topically to compare skin penetration and metabolism. Treated keratinocytes were evaluated for transcriptomics profiling and hyaluronic acid (HA) synthesis and treated 3D epidermal skin equivalents were stained for epidermal thickness, Ki67 and filaggrin. A retinoic acid receptor-alpha (RARα) reporter cell line was used to compare retinoid activation levels. Results from ex vivo skin found that RP and ROL have higher penetration levels compared with RPalm. RP is metabolized primarily into ROL in the viable epidermis and dermis whereas ROL is esterified into RPalm and metabolized into the inactive retinoid 14-hydroxy-4,14-retro-retinol (14-HRR). RP treatment yielded higher RARα activation and HA synthesis levels than ROL whereas RPalm had a null effect. In keratinocytes, RP and ROL stimulated similar gene expression patterns and pathway theme profiles. In conclusion, RP and ROL show a similar response directionality whereas RPalm response was inconsistent. Additionally, RP has a consistently higher magnitude of response compared with ROL or RPalm.