Regenerative Medicine Approaches for Age-Related Muscle Loss and Sarcopenia: A Mini-Review.

Sarcopenia is a complex and multifactorial disease that includes a decrease in the number, structure and physiology of muscle fibers, and age-related muscle mass loss, and is associated with loss of strength, increased frailty, and increased risk for fractures and falls. Treatment options are suboptimal and consist of exercise and nutrition as the cornerstone of therapy. Current treatment principles involve identification and modification of risk factors to prevent the disease, but these efforts are of limited value to the elderly individuals currently affected by sarcopenia. The development of new and effective therapies for sarcopenia is challenging. Potential therapies can target one or more of the proposed multiple etiologies such as the loss of regenerative capacity of muscle, age-related changes in the expression of signaling molecules such as growth hormone, IGF-1, myostatin, and other endocrine signaling molecules, and age-related changes in muscle physiology like denervation and mitochondrial dysfunction. The present paper reviews regenerative medicine strategies that seek to restore adequate skeletal muscle structure and function including exogenous delivery of cells and pharmacological therapies to induce myogenesis or reverse the physiologic changes that result in the disease. Approaches that modify the microenvironment to provide an environment conducive to reversal and mitigation of the disease represent a potential regenerative medicine approach that is discussed herein.

Esophageal extracellular matrix hydrogel mitigates metaplastic change in a dog model of Barrett's esophagus.

Chronic inflammatory gastric reflux alters the esophageal microenvironment and induces metaplastic transformation of the epithelium, a precancerous condition termed Barrett's esophagus (BE). The microenvironmental niche, which includes the extracellular matrix (ECM), substantially influences cell phenotype. ECM harvested from normal porcine esophageal mucosa (eECM) was formulated as a mucoadhesive hydrogel, and shown to largely retain basement membrane and matrix-cell adhesion proteins. Dogs with BE were treated orally with eECM hydrogel and omeprazole (n = 6) or omeprazole alone (n = 2) for 30 days. eECM treatment resolved esophagitis, reverted metaplasia to a normal, squamous epithelium in four of six animals, and downregulated the pro-inflammatory tumor necrosis factor-α+ cell infiltrate compared to control animals. The metaplastic tissue in control animals (n = 2) did not regress. The results suggest that in vivo alteration of the microenvironment with a site-appropriate, mucoadhesive ECM hydrogel can mitigate the inflammatory and metaplastic response in a dog model of BE.

Biologic Scaffolds.

Biologic scaffold materials composed of allogeneic or xenogeneic extracellular matrix are commonly used for the repair and functional reconstruction of injured and missing tissues. These naturally occurring bioscaffolds are manufactured by the removal of the cellular content from source tissues while preserving the structural and functional molecular units of the remaining extracellular matrix (ECM). The mechanisms by which these bioscaffolds facilitate constructive remodeling and favorable clinical outcomes include release or creation of effector molecules that recruit endogenous stem/progenitor cells to the site of scaffold placement and modulation of the innate immune response, specifically the activation of an anti-inflammatory macrophage phenotype. The methods by which ECM biologic scaffolds are prepared, the current understanding of in vivo scaffold remodeling, and the associated clinical outcomes are discussed in this article.

Urinary bladder extracellular matrix hydrogels and matrix-bound vesicles differentially regulate central nervous system neuron viability and axon growth and branching.

Central nervous system neurons often degenerate after trauma due to the inflammatory innate immune response to injury, which can lead to neuronal cell death, scarring, and permanently lost neurologic function. Extracellular matrix bioscaffolds, derived by decellularizing healthy tissues, have been widely used in both preclinical and clinical studies to promote positive tissue remodeling, including neurogenesis, in numerous tissues, with extracellular matrix from homologous tissues often inducing more positive responses. Extracellular matrix hydrogels are liquid at room temperature and enable minimally invasive extracellular matrix injections into central nervous system tissues, before gelation at 37℃. However, few studies have analyzed how extracellular matrix hydrogels influence primary central nervous system neuron survival and growth, and whether central nervous system and non-central nervous system extracellular matrix specificity is critical to neuronal responses. Urinary bladder extracellular matrix hydrogels increase both primary hippocampal neuron survival and neurite growth to similar or even greater extents, suggesting extracellular matrix from non-homologous tissue sources, such as urinary bladder matrix-extracellular matrix, may be a more economical and safer alternative to developing central nervous system extracellular matrices for central nervous system applications. Additionally, we show matrix-bound vesicles derived from urinary bladder extracellular matrix are endocytosed by hippocampal neurons and positively regulate primary hippocampal neuron neurite growth. Matrix-bound vesicles carry protein and RNA cargos, including noncoding RNAs and miRNAs that map to the human genome and are known to regulate cellular processes. Thus, urinary bladder matrix-bound vesicles provide natural and transfectable cargoes which offer new experimental tools and therapeutic applications to study and treat central nervous system neuron injury.

Matrix-Bound Nanovesicles Recapitulate Extracellular Matrix Effects on Macrophage Phenotype.

The early macrophage response to biomaterials has been shown to be a critical and predictive determinant of downstream outcomes. When properly prepared, bioscaffolds composed of mammalian extracellular matrix (ECM) have been shown to promote a transition in macrophage behavior from a proinflammatory to a regulatory/anti-inflammatory phenotype, which in turn has been associated with constructive and functional tissue repair. The mechanism by which ECM bioscaffolds promote this phenotypic transition, however, is poorly understood. The present study shows that matrix-bound nanovesicles (MBV), a component of ECM bioscaffolds, are capable of recapitulating the macrophage activation effects of the ECM bioscaffold from which they are derived. MBV isolated from two different source tissues, porcine urinary bladder and small intestinal submucosa, were found to be enriched in miRNA125b-5p, 143-3p, and 145-5p. Inhibition of these miRNAs within macrophages was associated with a gene and protein expression profile more consistent with a proinflammatory rather than an anti-inflammatory/regulatory phenotype. MBV and their associated miRNA cargo appear to play a significant role in mediating the effects of ECM bioscaffolds on macrophage phenotype.

Regenerative Medicine: lessons from Mother Nature.

Regenerative medicine strategies for the restoration of functional tissue have evolved from the concept of ex vivo creation of engineered tissue toward the broader concept of in vivo induction of functional tissue reconstruction. Multidisciplinary approaches are being investigated to achieve this goal using evolutionarily conserved principles of stem cell biology, developmental biology and immunology, current methods of engineering and medicine. This evolution from ex vivo tissue engineering to the manipulation of fundamental in vivo tenets of development and regeneration has the potential to capitalize upon the incredibly complex and only partially understood ability of cells to adapt, proliferate, self-organize and differentiate into functional tissue.

Matrix-bound nanovesicles within ECM bioscaffolds.

Biologic scaffold materials composed of extracellular matrix (ECM) have been used in a variety of surgical and tissue engineering/regenerative medicine applications and are associated with favorable constructive remodeling properties including angiogenesis, stem cell recruitment, and modulation of macrophage phenotype toward an anti-inflammatory effector cell type. However, the mechanisms by which these events are mediated are largely unknown. Matrix-bound nanovesicles (MBVs) are identified as an integral and functional component of ECM bioscaffolds. Extracellular vesicles (EVs) are potent vehicles of intercellular communication due to their ability to transfer RNA, proteins, enzymes, and lipids, thereby affecting physiologic and pathologic processes. Formerly identified exclusively in biologic fluids, the presence of EVs within the ECM of connective tissue has not been reported. In both laboratory-produced and commercially available biologic scaffolds, MBVs can be separated from the matrix only after enzymatic digestion of the ECM scaffold material, a temporal sequence similar to the functional activity attributed to implanted bioscaffolds during and following their degradation when used in clinical applications. The present study shows that MBVs contain microRNA capable of exerting phenotypical and functional effects on macrophage activation and neuroblastoma cell differentiation. The identification of MBVs embedded within the ECM of biologic scaffolds provides mechanistic insights not only into the inductive properties of ECM bioscaffolds but also into the regulation of tissue homeostasis.