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Dry eye disease (DED) is a common multifactorial disorder characterized by a deficiency in the quality and/or quantity of tear fluid. Tear hyperosmolarity, the dysfunction of ion channel proteins, and eye inflammation are primarily responsible for the development and progression of DED. Alterations in the structure and/or function of ion channel receptors (transient receptor potential ankyrin 1 (TRPA1), transient receptor potential melastatin 8 (TRPM8), transient receptor potential vanilloid 1 and 4 (TRPV1 and TRPV4)), and consequent hyperosmolarity of the tears represent the initial step in the development and progression of DED. Hyperosmolarity triggers the activation of ion channel-dependent signaling pathways in corneal epithelial cells and eye-infiltrated immune cells, leading to the activation of transcriptional factors that enhance the expression of genes regulating inflammatory cytokine production, resulting in a potent inflammatory response in the eyes of DED patients. A persistent and untreated detrimental immune response further modifies the structure and function of ion channel proteins, perpetuating tear hyperosmolarity and exacerbating DED symptoms. Accordingly, suppressing immune cell-driven eye inflammation and alleviating tear hyperosmolarity through the modulation of ion channels in DED patients holds promise for developing new therapeutic strategies. Here, we summarize current knowledge about the molecular mechanisms responsible for the inflammation-induced modification of ion channels leading to tear hyperosmolarity and immune cell dysfunction in DED patients. We also emphasize the therapeutic potential of the newly designed immunomodulatory and hypo-osmotic solution d-MAPPS™ Hypo-Osmotic Ophthalmic Solution, which can activate TRPV4 in corneal epithelial cells, stabilize the tear film, enhance natural cytokine communication, and suppress detrimental immune responses, an important novel approach for DED treatment.

Dry eye disease (DED) is a multifactorial disorder of the lacrimal system and ocular surface, characterized by a deficiency in the quality and/or quantity of the tear fluid. The multifactorial nature of DED encompasses a number of interconnected underlying pathologies, including loss of homeostasis, instability and hyperosmolarity of the tears, and the induction and propagation of detrimental inflammatory responses in the eyes, which finally results in the development of neurosensory dysfunction and visual disruption. Dryness, grittiness, scratchiness, discomfort, inflammation, burning, watering, ocular fatigue, pain, and decreased functional visual acuity are common symptoms of DED. Eye dysfunction drastically attenuates patients' quality of life. Accordingly, a better understanding of the pathogenic processes that regulate the development and progression of DED is crucially important for the establishment of new and more effective DED-related treatment approaches, which would significantly improve the quality of life of DED patients. Since the process of osmoregulation, which guards the ocular surface epithelia and maintains normal vision, is affected when the osmolarity of the tears is greater than that of the epithelial cells, tear hyperosmolarity (THO) is considered an initial, important step in the development, progression, and aggravation of DED. In order to delineate the role of THO in the pathogenesis of DED, in this review article, we summarize current knowledge related to the molecular mechanisms responsible for the development of THO-induced pathological changes in the eyes of DED patients, and we briefly discuss the therapeutic potential of hypo-osmotic eye drops in DED treatment.

Due to their potent immunoregulatory and angio-modulatory properties, mesenchymal stem cells (MSCs) and their exosomes (MSC-Exos) have emerged as potential game-changers in regenerative ophthalmology, particularly for the personalized treatment of inflammatory diseases. MSCs suppress detrimental immune responses in the eyes and alleviate ongoing inflammation in ocular tissues by modulating the phenotype and function of all immune cells that play pathogenic roles in the development and progression of inflammatory eye diseases. MSC-Exos, due to their nano-sized dimension and lipid envelope, easily bypass all barriers in the eyes and deliver MSC-sourced bioactive compounds directly to target cells. Although MSCs and their exosomes offer a novel approach to treating immune cell-driven eye diseases, further research is needed to optimize their therapeutic efficacy. A significant number of experimental studies is currently focused on the delineation of intracellular targets, which crucially contribute to the immunosuppressive and anti-inflammatory effects of MSCs and MSC-Exos. The activation of NLRP3 inflammasome induces programmed cell death of epithelial cells, induces the generation of inflammatory phenotypes in eye-infiltrated immune cells, and enhances the expression of adhesion molecules on ECs facilitating the recruitment of circulating leukocytes in injured and inflamed eyes. In this review article, we summarize current knowledge about signaling pathways that are responsible for NLRP3 inflammasome-driven intraocular inflammation and we emphasize molecular mechanisms that regulate MSC-based modulation of NLRP3-driven signaling in eye-infiltrated immune cells, providing evidence that NLRP3 inflammasome should be considered a potentially new therapeutic target for MSCs and MSC-Exo-based treatment of inflammatory eye diseases.

There is growing evidence that mesenchymal stem cell (MSC)-based immunosuppression was mainly attributed to the effects of MSC-derived extracellular vesicles (MSC-EVs). MSC-EVs are enriched with MSC-sourced bioactive molecules (messenger RNA (mRNA), microRNAs (miRNAs), cytokines, chemokines, immunomodulatory factors) that regulate phenotype, function and homing of immune cells. In this review article we emphasized current knowledge regarding molecular mechanisms responsible for the therapeutic effects of MSC-EVs in attenuation of autoimmune and inflammatory diseases. We described the disease-specific cellular targets of MSC-EVs and defined MSC-sourced molecules, which were responsible for MSC-EV-based immunosuppression. Results obtained in a large number of experimental studies revealed that both local and systemic administration of MSC-EVs efficiently suppressed detrimental immune response in inflamed tissues and promoted survival and regeneration of injured parenchymal cells. MSC-EVs-based anti-inflammatory effects were relied on the delivery of immunoregulatory miRNAs and immunomodulatory proteins in inflammatory immune cells (M1 macrophages, dendritic cells (DCs), CD4+Th1 and Th17 cells), enabling their phenotypic conversion into immunosuppressive M2 macrophages, tolerogenic DCs and T regulatory cells. Additionally, through the delivery of mRNAs and miRNAs, MSC-EVs activated autophagy and/or inhibited apoptosis, necrosis and oxidative stress in injured hepatocytes, neurons, retinal cells, lung, gut and renal epithelial cells, promoting their survival and regeneration.

Galectin-3 regulates numerous biological processes in the gut. We investigated molecular mechanisms responsible for the Galectin-3-dependent regulation of colon inflammation and evaluated whether Galectin-3 may be used as biomarker for monitoring the progression of ulcerative colitis (UC). The differences in disease progression between dextran sodium sulphate-treated wild type and Galectin-3-deficient mice were investigated and confirmed in clinical settings, in 65 patients suffering from mild, moderate, and severe colitis. During the induction phase of colitis, Galectin-3 promoted interleukin-1β-induced polarization of colonic macrophages towards inflammatory phenotype. In the recovery phase of colitis, Galectin-3 was required for the immunosuppressive function of regulatory dendritic cells (DCs). Regulatory DCs in Galectin-3:Toll-like receptor-4:Kynurenine-dependent manner promoted the expansion of colon-infiltrated T regulatory cells (Tregs) and suppressed Th1 and Th17 cell-driven colon inflammation. Concentration of Galectin-3 in serum and stool samples of UC patients negatively correlated with clinical, endoscopic, and histological parameters of colitis. The cutoff serum values of Galectin-3 that allowed the discrimination of mild from moderate and moderate from severe colitis were 954 pg/mL and 580 pg/mL, respectively. Fecal levels of Galectin-3 higher than 553.44 pg/mL indicated attenuation of UC. In summing up, Galectin-3 regulates the cross-talk between colon-infiltrating DCs and Tregs and represents a new biomarker for monitoring the progression of UC.

Mesenchymal stem cell (MSC)-sourced secretome, defined as the set of MSC-derived bioactive factors (soluble proteins, nucleic acids, lipids and extracellular vesicles), showed therapeutic effects similar to those observed after transplantation of MSCs. MSC-derived secretome may bypass many side effects of MSC-based therapy, including unwanted differentiation of engrafted MSCs. In contrast to MSCs which had to be expanded in culture to reach optimal cell number for transplantation, MSC-sourced secretome is immediately available for treatment of acute conditions, including fulminant hepatitis, cerebral ischemia and myocardial infarction. Additionally, MSC-derived secretome could be massively produced from commercially available cell lines avoiding invasive cell collection procedure. In this review article we emphasized molecular and cellular mechanisms that were responsible for beneficial effects of MSC-derived secretomes in the treatment of degenerative and inflammatory diseases of hepatobiliary, respiratory, musculoskeletal, gastrointestinal, cardiovascular and nervous system. Results obtained in a large number of studies suggested that administration of MSC-derived secretomes represents a new, cell-free therapeutic approach for attenuation of inflammatory and degenerative diseases. Therapeutic effects of MSC-sourced secretomes relied on their capacity to deliver genetic material, growth and immunomodulatory factors to the target cells enabling activation of anti-apoptotic and pro-survival pathways that resulted in tissue repair and regeneration., Competing Interests: The authors declare no conflict of interest.