Infrapatellar Fat Pad Stem Cells Responsiveness to Microenvironment in Osteoarthritis: From Morphology to Function

The biphasic role of the infrapatellar fat pad in osteoarthritis

Osteoarthritis (OA) is a progressive degenerative disease resulting in joint deterioration. It is a whole organ disease characterized by cartilage degeneration and varying degrees of synovitis, involving pathological changes in all joint tissues, such as cartilage, subchondral bone, ligaments, meniscus, synovium, and infrapatellar fat pad (IPFP). IPFP is the largest adipose tissue structure in the knee joint and is composed of fat cells, immune cells and blood vessels. Moreover, IPFP is located close to the cartilage and bone surface so that it may reduce the impact of loading and absorb forces generated through the knee joint, and may have a protective role in joint health. IPFP has been shown to release various cytokines and adipokines that play pro-inflammatory and pro-catabolic roles in cartilage, promoting OA progression. Intra-articular injections of IPFP-derived mesenchymal stem cells and exosomes have been shown to reduce pain and prevent OA progression in patients with knee OA. Previous studies have shown that IPFP has a biphasic effect on OA progression. This article reviews the latest research progress of IPFP, discusses the role and mechanism of IPFP in OA, provide new intervention strategies for the treatment of OA. This article will also discuss the handling of IPFP during the procedure of total knee arthroplasty.

Removal of the infrapatellar fat pad and associated synovium benefits female guinea pigs in the Dunkin Hartley model of idiopathic osteoarthritis

Background

Several tissues contribute to the onset and advancement of knee osteoarthritis (OA). One tissue type that is worthy of closer evaluation, particularly in the context of sex, is the infrapatellar fat pad (IFP). We previously demonstrated that removal of the IFP had short-term beneficial effects for a cohort of male Dunkin-Hartley guinea pigs. The present project was designed to elucidate the influence of IFP removal in females of this OA-prone strain. It was hypothesized that resection of the IFP would reduce the development of OA in knees of a rodent model predisposed to the disease.

Methods

Female guinea pigs (n=16) were acquired at an age of 2.5 months. Surgical removal of the IFP and associated synovium complex (IFP/SC) was executed at 3 months of age. One knee had the IFP/SC resected; a comparable sham surgery was performed on the contralateral knee. All animals were subjected to voluntary enclosure monitoring and dynamic weight-bearing, as well as compulsory treadmill-based gait analysis monthly; baseline data was collected prior to surgery. Guinea pigs were euthanized at 7 months. Knees from eight animals were evaluated via histology, mRNA expression, and immunohistochemistry (IHC); knees from the remaining eight animals were allocated to microcomputed tomography (microCT), biomechanical analyses (whole joint testing and indentation relaxation testing), and atomic absorption spectroscopy (AAS).

Results

Fibrous connective tissue (FCT) replaced the IFP/SC. Mobility/gait data indicated that unilateral IFP/SC removal did not affect bilateral hindlimb movement. MicroCT demonstrated that osteophytes were not a significant feature of OA in this sex; however, trabecular thickness (TbTh) in medial femorae decreased in knees containing the FCT. Histopathology scores were predominantly influenced by changes in the lateral tibia, which demonstrated that histologic signs of OA were increased in knees containing the native IFP/SC versus those with the FCT. Similarly, indentation testing demonstrated higher instantaneous and equilibrium moduli in the lateral tibial articular cartilage of control knees with native IFPs. AAS of multiple tissue types associated with the knee revealed that zinc was the major trace element influenced by removal of the IFP/SC.

Conclusions

Our data suggest that the IFP/SC is a significant component driving knee OA in female guinea pigs and that resection of this tissue prior to disease has short-term benefits. Specifically, the formation of the FCT in place of the native tissue resulted in decreased cartilage-related OA changes, as demonstrated by reduced Osteoarthritis Research Society International (OARSI) histology scores, as well as changes in transcript, protein, and cartilage indentation analyses. Importantly, this model provides evidence that sex needs to be considered when investigating responses and associated mechanisms seen with this intervention.

Exosome miR-4738-3p-mediated regulation of COL1A2 through the NF-κB and inflammation signaling pathway alleviates osteoarthritis low-grade inflammation symptoms

This study aimed to elucidate the roles of microRNA (miR)-4738-3p and the collagen type I alpha 2 chain (COL1A2) gene in the pathogenesis of osteoarthritis (OA) through bioinformatics analysis and cellular assays. The GSE55235 dataset was analyzed using the weighted gene co-expression network analysis (WGCNA) method to identify gene modules associated with OA. Key overlapping genes were identified from these modules and the GSE55235-differential expressed genes (DEGs). The expression levels of selected genes were determined in C28/I2 cells using the quantitative real-time polymerase chain reaction (qRT-PCR). The interaction between miR-4738-3p and COL1A2 was examined in the context of interleukin 1 beta (IL-1β) induction. Exosome characterization was achieved through transmission electron microscopy (TEM), western blotting (WB), and other analyses. The study also investigated the functional relevance of miR-4738-3p in OA pathology through various molecular and cellular assays. Our findings revealed that the green module exhibited a strong correlation with the OA phenotype in the GSE55235 dataset, with COL1A2 emerging as a hub gene and miR-4738-3p as its key downstream target. IL-1β induction suggested that COL1A2 is involved in inflammation and apoptosis, while miR-4738-3p appeared to play an antagonistic role. The analysis of exosomes underscored the significance of miR-4738-3p in cellular communication, with an enhanced level of exo-miR-4738-3p antagonizing IL-1β-induced inflammation and promoting cell survival. Conversely, a reduction in exo-miR-4738-3p led to increased cell damage. This study established a clear regulatory relationship between miR-4738-3p and COL1A2, with the nuclear factor kappa B (NF-κB) signaling pathway playing a central role in this regulation. The miR-4738-3p significantly influences the OA-associated inflammation, primarily through modulation of COL1A2 and the NF-κB pathway. Therefore, targeting miR-4738-3p offers a potential therapeutic approach for OA, with exosome miR-4738-3p presenting a promising strategy.

The suprapatellar fat pad: A histotopographic comparative study

The suprapatellar fat pad is an adipose tissue located in the anterior knee whose role in osteoarthritis is still debated. Considering that anatomy drives function, the aim of this histotopographic study was to investigate the specific morphological features of the suprapatellar fat pad versus the infrapatellar fat pad in the absence of osteoarthritis, for a broad comparative analysis. Suprapatellar fat pad and infrapatellar fat pad tissue samples (n = 10/group) underwent microscopical/immunohistochemical staining and transmission electron microscopy analysis; thus, tissue-specific characteristics (i.e., vessels and nerve endings presence, lobuli, adipocytes features, septa), including extracellular matrix proteins prevalence (collagens, elastic fibers), were focused. Multiphoton microscopy was also adopted to evaluate collagen fiber orientation within the samples by Fast Fourier Transform (coherency calculation). The absence of inflammation was confirmed, and comparable counted vessels and nerve endings were shown. Like the infrapatellar fat pad, the suprapatellar fat pad appeared as a white adipose tissue with lobuli and septa of comparable diameter and thickness, respectively. Tissue main characteristics were also proved by both semithin sections and transmission electron microscopy analysis. The suprapatellar fat pad adipocytes were roundish and with a smaller area, perimeter, and major axis than that of the infrapatellar fat pad. The collagen fibers surrounding them showed no significant difference in collagen type I and significantly higher values for collagen type III in the infrapatellar fat pad group. Regarding the septa, elastic fiber content was statistically comparable between the two groups, even though more represented by the suprapatellar fat pad. Total collagen was significantly higher in the infrapatellar fat pad and comparing collagen type I and type III they were similarly represented in the whole cohort despite collagen type I appearing to be higher in the infrapatellar fat pad than in the suprapatellar fat pad and vice versa for collagen type III. Second harmonic generation microscopy confirmed through coherency calculation an anisotropic distribution of septa collagen fibers. From a mechanical point of view, the different morphological characteristics determined a major stiffness for the infrapatellar fat pad with respect to the suprapatellar fat pad. This study provides, for the first time, a topographic description of the suprapatellar fat pad compared to the infrapatellar fat pad; differences between the two groups may be attributed to a different anatomical location within the knee; the results gathered here may be useful for a more complete interpretation of osteoarthritis disease, involving not only cartilage but the whole joint.

Tendon stem/progenitor cells are promising reparative cell sources for multiple musculoskeletal injuries of concomitant articular cartilage lesions associated with ligament injuries

BACKGROUND

Trauma-related articular cartilage lesions usually occur in conjunction with ligament injuries. Torn ligaments are frequently reconstructed with tendon autograft and has been proven to achieve satisfactory clinical outcomes. However, treatments for the concomitant articular cartilage lesions are still very insufficient. The current study was aimed to evaluate whether stem cells derived from tendon tissue can be considered as an alternative reparative cell source for cartilage repair.

METHODS

Primary human tendon stem/progenitor cells (hTSPCs) were isolated from 4 male patients (32 ± 8 years) who underwent ACL reconstruction surgery with autologous semitendinosus and gracilis tendons. The excessive tendon tissue after graft preparation was processed for primary cell isolation with an enzyme digestion protocol. Decellularization cartilage matrix (DCM) was used to provide a chondrogenic microenvironment for hTSPCs. Cell viability, cell morphology on the DCM, as well as their chondrogenic differentiation were evaluated.

RESULTS

DAPI staining and DNA quantitative analysis (61.47 μg per mg dry weight before and 2.64 μg/mg after decellularization) showed that most of the cells in the cartilage lacuna were removed after decellularization process. Whilst, the basic structure of the cartilage tissue was preserved and the main ECM components, collagen type II and sGAG were retained after decellularization, which were revealed by DMMB assay and histology. Live/dead staining and proliferative assay demonstrated that DCM supported attachment, survival and proliferation of hTSPCs with an excellent biocompatibility. Furthermore, gene expression analysis indicated that chondrogenic differentiation of hTSPC was induced by the DCM microenvironment, with upregulation of chondrogenesis-related marker genes, COL 2 and SOX9, without the use of exogenous growth factors.

CONCLUSION

DCM supported hTSPCs attachment and proliferation with high biocompatibility. Moreover, TSPCs underwent a distinct chondrogenesis after the induction of a chondrogenic microenvironment provided by DCM. These results indicated that TSPCs are promising reparative cell sources for promoting cartilage repair. Particularly, in the cohort that articular cartilage lesions occur in conjunction with ligament injuries, autologous TSPCs can be isolated from a portion of the tendon autograph harvested for ligaments reconstruction. In future clinical practice, combined ligament reconstruction with TSPCs- based therapy for articular cartilage repair can to be considered to achieve superior repair of these associated injuries, in which autologous TSPCs can be isolated from a portion of the tendon autograph harvested for ligaments reconstruction.

Basic Properties of Adipose-Derived Mesenchymal Stem Cells of Rheumatoid Arthritis and Osteoarthritis Patients

Rheumatoid arthritis (RA) and osteoarthritis (OA) are destructive joint diseases, the development of which are associated with the expansion of pathogenic T lymphocytes. Mesenchymal stem cells may be an attractive therapeutic option for patients with RA or OA due to the regenerative and immunomodulatory abilities of these cells. The infrapatellar fat pad (IFP) is a rich and easily available source of mesenchymal stem cells (adipose-derived stem cells, ASCs). However, the phenotypic, potential and immunomodulatory properties of ASCs have not been fully characterised. We aimed to evaluate the phenotype, regenerative potential and effects of IFP-derived ASCs from RA and OA patients on CD4+ T cell proliferation. The MSC phenotype was assessed using flow cytometry. The multipotency of MSCs was evaluated on the basis of their ability to differentiate into adipocytes, chondrocytes and osteoblasts. The immunomodulatory activities of MSCs were examined in co-cultures with sorted CD4+ T cells or peripheral blood mononuclear cells. The concentrations of soluble factors involved in ASC-dependent immunomodulatory activities were assessed in co-culture supernatants using ELISA. We found that ASCs with PPIs from RA and OA patients maintain the ability to differentiate into adipocytes, chondrocytes and osteoblasts. ASCs from RA and OA patients also showed a similar phenotype and comparable abilities to inhibit CD4+ T cell proliferation, which was dependent on the induction of soluble factors The results of our study constitute the basis for further research on the therapeutic potential of ASCs in the treatment of patients with RA and OA.

Naturally derived injectable hydrogels with ROS-scavenging property to protect transplanted stem cell bioactivity for osteoarthritic cartilage repair

Intra-articular injection of adipose mesenchymal stem cells (ADSCs) is a potential alternative to the treatment of osteoarthritis (OA) and has aroused great interest of clinical researchers. However, the hostile microenvironment in the joint cavity, characterized by reactive oxygen species (ROS) accumulation and excessive inflammation, disturbs the bioactivity of the transplanted stem cells. The (-)-epigallocatechin-3-O-gallate (EGCG), a green tea catechin, has attracted the researchers' attention owing to its powerful ROS-scavenging and antioxidant properties. In this study, to avoid rapid degradation and/or depletion of EGCG, we prepare a long-lasting injectable hydrogel by EGCG and hyaluronic acid (HA). The naturally derived hydrogels with excellent biocompatibility and durable retention time can capture the redundant ROS continuously and efficiently, thus protecting ADSCs from ROS-mediated death and bioactivity inhibition, including cell survival, proliferation and chondrogenic differentiation. Intra-articular injection of this ADSCs loaded hydrogel significantly induced synovial macrophages polarization to M2 phenotype, decreased pro-inflammatory cytokines (e.g., IL-1β, MMP-13, and TNF-α) expression, promoted cartilage matrix formation, and repaired cartilage destruction in OA. This stem cell-protected hydrogel delivery strategy showed superior efficacy than ADSCs delivering or EGCG-HA injection singly, which providing a potential alternative strategy for OA management.

Preclinical and clinical orthotopic transplantation of decellularized/engineered tracheal scaffolds: A systematic literature review

Severe tracheal injuries that cannot be managed by mobilization and end-to-end anastomosis represent an unmet clinical need and an urgent challenge to face in surgical practice; within this scenario, decellularized scaffolds (eventually bioengineered) are currently a tempting option among tissue engineered substitutes. The success of a decellularized trachea is expression of a balanced approach in cells removal while preserving the extracellular matrix (ECM) architecture/mechanical properties. Revising the literature, many Authors report about different methods for acellular tracheal ECMs development; however, only few of them verified the devices effectiveness by an orthotopic implant in animal models of disease. To support translational medicine in this field, here we provide a systematic review on studies recurring to decellularized/bioengineered tracheas implantation. After describing the specific methodological aspects, orthotopic implant results are verified. Furtherly, the only three clinical cases of compassionate use of tissue engineered tracheas are reported with a focus on outcomes.

Influence of donor age and comorbidities on transduced human adipose-derived stem cell in vitro osteogenic potential

Human adipose-derived mesenchymal stem cells (ASCs) transduced with a lentiviral vector system to express bone morphogenetic protein 2 (LV-BMP-2) have been shown to reliably heal bone defects in animal models. However, the influence of donor characteristics such as age, sex, race, and medical co-morbidities on ASC yield, growth and bone regenerative capacity, while critical to the successful clinical translation of stem cell-based therapies, are not well understood. Human ASCs isolated from the infrapatellar fat pads in 122 ASC donors were evaluated for cell growth characteristics; 44 underwent additional analyses to evaluate in vitro osteogenic potential, with and without LV-BMP-2 transduction. We found that while female donors demonstrated significantly higher cell yield and ASC growth rates, age, race, and the presence of co-morbid conditions were not associated with differences in proliferation. Donor demographics or the presence of comorbidities were not associated with differences in in vitro osteogenic potential or stem cell differentiation, except that transduced ASCs from healthy donors produced more BMP-2 at day 2. Overall, donor age, sex, race, and the presence of co-morbid conditions had a limited influence on cell yield, proliferation, self-renewal capacity, and osteogenic potential for non-transduced and transduced (LV-BMP-2) ASCs. These results suggest that ASCs are a promising resource for both autologous and allogeneic cell-based gene therapy applications.

Recent advances in enzyme-related biomaterials for arthritis treatment

Arthritis is a group of highly prevalent joint disorders, and osteoarthritis (OA) and rheumatoid arthritis are the two most common types. The high prevalence of arthritis causes severe burdens on individuals, society and the economy. Currently, the primary treatment of arthritis is to relieve symptoms, but the development of arthritis cannot be effectively prevented. Studies have revealed that the disrupted balance of enzymes determines the pathological changes in arthritis. In particular, the increased levels of matrix metalloproteinases and the decreased expression of endogenous antioxidant enzymes promote the progression of arthritis. New therapeutic strategies have been developed based on the expression characteristics of these enzymes. Biomaterials have been designed that are responsive when the destructive enzymes MMPs are increased or have the activities of the antioxidant enzymes that play a protective role in arthritis. Here, we summarize recent studies on biomaterials associated with MMPs and antioxidant enzymes involved in the pathological process of arthritis. These enzyme-related biomaterials have been shown to be beneficial for arthritis treatment, but there are still some problems that need to be solved to improve efficacy, especially penetrating the deeper layer of articular cartilage and targeting osteoclasts in subchondral bone. In conclusion, enzyme-related nano-therapy is challenging and promising for arthritis treatment.

Aberrant Expression of COX-2 and FOXG1 in Infrapatellar Fat Pad-Derived ASCs from Pre-Diabetic Donors

Osteoarthritis (OA) is a degenerative joint disease resulting in limited mobility and severe disability. Type II diabetes mellitus (T2D) is a weight-independent risk factor for OA, but a link between the two diseases has not been elucidated. Adipose stem cells (ASCs) isolated from the infrapatellar fat pad (IPFP) may be a viable regenerative cell for OA treatment. This study analyzed the expression profiles of inflammatory and adipokine-related genes in IPFP-ASCs of non-diabetic (Non-T2D), pre-diabetic (Pre-T2D), and T2D donors. Pre-T2D ASCs exhibited a substantial decrease in levels of mesenchymal markers CD90 and CD105 with no change in adipogenic differentiation compared to Non-T2D and T2D IPFP-ASCs. In addition, Cyclooxygenase-2 (COX-2), Forkhead box G1 (FOXG1) expression and prostaglandin E2 (PGE2) secretion were significantly increased in Pre-T2D IPFP-ASCs upon stimulation by interleukin-1 beta (IL-1β). Interestingly, M1 macrophages exhibited a significant reduction in expression of pro-inflammatory markers TNFα and IL-6 when co-cultured with Pre-T2D IPFP-ASCs. These data suggest that the heightened systemic inflammation associated with untreated T2D may prime the IPFP-ASCs to exhibit enhanced anti-inflammatory characteristics via suppressing the IL-6/COX-2 signaling pathway. In addition, the elevated production of PGE2 by the Pre-T2D IPFP-ASCs may also suggest the contribution of pre-diabetic conditions to the onset and progression of OA.

Source and hub of inflammation: The infrapatellar fat pad and its interactions with articular tissues during knee osteoarthritis

Knee osteoarthritis, the most prevalent degenerative joint disorder worldwide, is driven by chronic low-grade inflammation and subsequent cartilage degradation. Clinical data on the role of the Hoffa or infrapatellar fat pad in knee osteoarthritis are, however, scarce. The infrapatellar fat pad is a richly innervated intracapsular, extrasynovial adipose tissue, and an abundant source of adipokines and proinflammatory and catabolic cytokines, which may contribute to chronic synovial inflammation, cartilage destruction, and subchondral bone remodeling during knee osteoarthritis. How the infrapatellar fat pad interacts with neighboring tissues is poorly understood. Here, we review available literature with regard to the infrapatellar fat pad's interactions with cartilage, synovium, bone, menisci, ligaments, and nervous tissue during the development and progression of knee osteoarthritis. Signaling cascades are described with a focus on immune cell populations, pro- and anti-inflammatory cytokines, adipokines, mesenchymal stromal cells, and molecules derived from conditioned media from the infrapatellar fat pad. Understanding the complex interplay between the infrapatellar fat pad and its neighboring articular tissues may help to better understand and treat the multifactorial pathogenesis of osteoarthritis.

Infrapatellar Fat Pad-Synovial Membrane Anatomo-Fuctional Unit: Microscopic Basis for Piezo1/2 Mechanosensors Involvement in Osteoarthritis Pain

The Infrapatellar Fat Pad (IFP) is a fibro-adipose tissue of the knee recently reconsidered as part of a single anatomo-functional unit (AFU) together with the synovial membrane (SM). Several evidence support the role of this unit in the mechanisms that trigger and perpetuate the onset and progression of osteoarthritis (OA) disease. Additionally, the contribution of IFP-SM AFU in OA-associated pain has also been supposed, but this assumption still needs to be fully elucidated. Within this context, the recent discovery of the mechanoceptive Piezo ion channels (i.e., Piezo1 and Piezo2) in mammals and consciousness on their role in mediating both mechanoceptive and inflammatory stimuli could shed some light on knee OA pain, as well as on the process leading from acute to chronic nociceptive responses. For this purpose, the IFP-SM AFUs of both healthy donors (non-OA IFP-SM AFUs, n = 10) and OA patients (OA IFP-SM AFUs, n = 10) were processed by histology and immunohistochemistry. After the attribution of a histopathological score to IFP-SM AFUs to confirm intrinsic differences between the two groups, the specimens were investigated for the expression and localization/distribution pattern of the mechanosensors Piezo1 and Piezo2. In addition, the presence of monocytes/macrophages (CD68), peripheral nerve endings (PGP9.5) and neoangiogenesis signs (YAP1) was evaluated for a broad tissue characterization. The study results lead to a better description of the IFP-SM AFU microscopic features in both healthy and pathological conditions, highlighting peculiar differences in the study cohort. Specifically, immunopositivity towards Piezo1/2, CD68 and YAP1 markers was detected at vessels level in the OA- IFP-SM AFUs compartments, differently from the non-OA-group. A correlation with pain was also inferred, paving the way for the identification of new and effective molecules in OA management.

Exploring Anatomo-Morphometric Characteristics of Infrapatellar, Suprapatellar Fat Pad, and Knee Ligaments in Osteoarthritis Compared to Post-Traumatic Lesions

Several studies have investigated cartilage degeneration and inflammatory subchondral bone and synovial membrane changes using magnetic resonance (MR) in osteoarthritis (OA) patients. Conversely, there is a paucity of data exploring the role of knee ligaments, infrapatellar fat pad (IFP), and suprapatellar fat pad (SFP) in knee OA compared to post-traumatic cohorts of patients. Therefore, the aim of this study was to analyze the volumetric and morphometric characteristics of the following joint tissues: IFP (volume, surface, depth, femoral and tibial arch lengths), SFP (volume, surface, oblique, antero−posterior, and cranio−caudal lengths), anterior (ACL) and posterior cruciate ligament (PCL) (volume, surface, and length), and patellar ligament (PL) (volume, surface, arc, depth, and length). Eighty-nine MR images were collected in the following three groups: (a) 32 patients with meniscal tears, (b) 29 patients with ACL rupture (ACLR), and (c) 28 patients affected by end-stage OA. Volume, surface, and length of both ACL and PCL were determined in groups a and c. A statistical decrease of IFP volume, surface, depth, femoral and tibial arch lengths was found in end-stage OA compared to patients with meniscal tear (p = 0.002, p = 0.008, p < 0.0001, p = 0.028 and p < 0.001, respectively) and patients with ACLR (p < 0.0001, p < 0.0001, p = 0.008 and p = 0.011, respectively). An increment of volume and surface SFP was observed in group b compared to both groups a and c, while no differences were found in oblique, antero−posterior, and cranio−caudal lengths of SFP among the groups. No statistical differences were highlighted comparing volume, surface, arc, and length of PL between the groups, while PL depth was observed to be decreased in end-OA patients compared with meniscal tear patients (p = 0.023). No statistical differences were observed comparing ACL and PCL lengths between patients undergoing meniscectomy and TKR. Our study confirms that IFP MR morphometric characteristics are different between controls and OA, supporting an important role of IFP in OA pathology and progression in accordance with previously published studies. In addition, PL depth changes seem to be associated with OA pathology. Multivariate analysis confirmed that OA patients had a smaller IFP compared to patients with meniscal tears, confirming its involvement in OA.

Adipose tissue derived stromal cells in a gelatin based 3D matrix with exclusive ascorbic acid signalling emerged as a novel neural tissue engineering construct – An innovative prototype for soft tissue

The current study investigated a triad, which comprises of adipose tissue derived stem cells isolated from infrapatellar fat pad and gelatin/polyvinyl alcohol (PVA)-based matrix with exclusive ascorbic acid signalling. Though, the bio-mechanical properties of the gelatin–PVA blended scaffolds in wet condition are equivalent to the ECM of soft tissues in general, in this study, the triad was tested as a model for neural tissue engineering. Apart from being cytocompatible and biocompatible, the porosity of the scaffold has been designed in such a manner that it facilitates the cell signalling and enables the exchange of nutrients and gases. The highly proliferative stem cells from Passage 2 were characterized using both, mesenchymal and embryonic stem cell markers. As an initial exploration the mesenchymal stem cells at Passage 4 were exposed to ascorbic acid and basic fibroblast growth factor signalling for neuronal differentiation in 2D environment independently. The MSCs successfully differentiated and acquired neuron specific markers related to cytoskeleton and synapses. Subsequently, three phases of experiments have been conducted on the 3D gelatin/PVA matrix to prove their efficacy, the growth of stem cells, growth of differentiated neurons and the in situ growth and differentiation of MSCs. The scaffold was conducive and directed MSCs to neuronal lineage under specific signalling. Overall, this organotypic model triad could open a new avenue in the field of soft tissue engineering as a simple and effective tissue construct.

The Corpus Adiposum Infrapatellare (Hoffa's Fat Pad)-The Role of the Infrapatellar Fat Pad in Osteoarthritis Pathogenesis

In recent years, the infrapatellar fat pad (IFP) has gained increasing research interest. The contribution of the IFP to the development and progression of knee osteoarthritis (OA) through extensive interactions with the synovium, articular cartilage, and subchondral bone is being considered. As part of the initiation process of OA, IFP secretes abundant pro-inflammatory mediators among many other factors. Today, the IFP is (partially) resected in most total knee arthroplasties (TKA) allowing better visualization during surgical procedures. Currently, there is no clear guideline providing evidence in favor of or against IFP resection. With increasing numbers of TKAs, there is a focus on preventing adverse postoperative outcomes. Therefore, anatomic features, role in the development of knee OA, and consequences of resecting versus preserving the IFP during TKA are reviewed in the following article.

Methodological Flaws in Meta-Analyses of Clinical Studies on the Management of Knee Osteoarthritis with Stem Cells: A Systematic Review

(1) Background: Conclusions of meta-analyses of clinical studies may substantially influence opinions of prospective patients and stakeholders in healthcare. Nineteen meta-analyses of clinical studies on the management of primary knee osteoarthritis (pkOA) with stem cells, published between January 2020 and July 2021, came to inconsistent conclusions regarding the efficacy of this treatment modality. It is possible that a separate meta-analysis based on an independent, systematic assessment of clinical studies on the management of pkOA with stem cells may reach a different conclusion. (2) Methods: PubMed, Web of Science, and the Cochrane Library were systematically searched for clinical studies and meta-analyses of clinical studies on the management of pkOA with stem cells. All clinical studies and meta-analyses identified were evaluated in detail, as were all sub-analyses included in the meta-analyses. (3) Results: The inconsistent conclusions regarding the efficacy of treating pkOA with stem cells in the 19 assessed meta-analyses were most probably based on substantial differences in literature search strategies among different authors, misconceptions about meta-analyses themselves, and misconceptions about the comparability of different types of stem cells with regard to their safety and regenerative potential. An independent, systematic review of the literature yielded a total of 183 studies, of which 33 were randomized clinical trials, including a total of 6860 patients with pkOA. However, it was not possible to perform a scientifically sound meta-analysis. (4) Conclusions: Clinicians should interpret the results of the 19 assessed meta-analyses of clinical studies on the management of pkOA with stem cells with caution and should be cautious of the conclusions drawn therein. Clinicians and researchers should strive to participate in FDA and/or EMA reviewed and approved clinical trials to provide clinically and statistically valid efficacy.

Characteristics of mesenteric adipose tissue attached to different intestinal segments and their roles in immune regulation

Mesenteric adipose tissue (MAT) plays a critical role in the intestinal physiological ecosystems. Small and large intestines have evidently intrinsic and distinct characteristics. However, whether there exist any mesenteric differences adjacent to the small and large intestines (SMAT and LMAT) has not been properly characterized. We studied the important facets of these differences, such as morphology, gene expression, cell components, and immune regulation of MATs, to characterize the mesenteric differences. The SMAT and LMAT of mice were used for comparison of tissue morphology. Paired mesenteric samples were analyzed by RNA-seq to clarify gene expression profiles. MAT partial excision models were constructed to illustrate the immune regulation roles of MATs, and 16S-seq was applied to detect the subsequent effect on microbiota. Our data show that different segments of mesenteries have different morphological structures. SMAT not only has smaller adipocytes but also contains more fat-associated lymphoid clusters than LMAT. The gene expression profile is also discrepant between these two MATs in mice. B-cell markers were abundantly expressed in SMAT, whereas development-related genes were highly expressed in LMAT. Adipose-derived stem cells of LMAT exhibited higher adipogenic potential and lower proliferation rates than those of SMAT. In addition, SMAT and LMAT play different roles in immune regulation and subsequently affect microbiota components. Finally, our data clarified the described differences between SMAT and LMAT in humans. There were significant differences in cell morphology, gene expression profiles, cell components, biological characteristics, and immune and microbiota regulation roles between regional MATs.NEW & NOTEWORTHY Our results change the paradigm of how we regard MAT as a contiguous and homogeneous tissue to an intensely heterogeneous tissue. Appreciation of the differences between regional MATs will guide future research to investigate the specialized roles of different MATs in intestinal health and disease.

Meniscus regeneration by 3D printing technologies: Current advances and future perspectives

Meniscal tears are a frequent orthopedic injury commonly managed by conservative strategies to avoid osteoarthritis development descending from altered biomechanics. Among cutting-edge approaches in tissue engineering, 3D printing technologies are extremely promising guaranteeing for complex biomimetic architectures mimicking native tissues. Considering the anisotropic characteristics of the menisci, and the ability of printing over structural control, it descends the intriguing potential of such vanguard techniques to meet individual joints’ requirements within personalized medicine. This literature review provides a state-of-the-art on 3D printing for meniscus reconstruction. Experiences in printing materials/technologies, scaffold types, augmentation strategies, cellular conditioning have been compared/discussed; outcomes of pre-clinical studies allowed for further considerations. To date, translation to clinic of 3D printed meniscal devices is still a challenge: meniscus reconstruction is once again clear expression of how the integration of different expertise (e.g., anatomy, engineering, biomaterials science, cell biology, and medicine) is required to successfully address native tissues complexities.

Cell and Cell Free Therapies in Osteoarthritis

Osteoarthritis (OA) is the most common articular disease in adults and has a current prevalence of 12% in the population over 65 years old. This chronic disease causes damage to articular cartilage and synovial joints, causing pain and leading to a negative impact on patients' function, decreasing quality of life. There are many limitations regarding OA conventional therapies-pharmacological therapy can cause gastrointestinal, renal, and cardiac adverse effects, and some of them could even be a threat to life. On the other hand, surgical options, such as microfracture, have been used for the last 20 years, but hyaline cartilage has a limited regeneration capacity. In recent years, the interest in new therapies, such as cell-based and cell-free therapies, has been considerably increasing. The purpose of this review is to describe and compare bioregenerative therapies' efficacy for OA, with particular emphasis on the use of mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP). In OA, these therapies might be an alternative and less invasive treatment than surgery, and a more effective option than conventional therapies.

Adipose-Derived Mesenchymal Stem Cells-Conditioned Medium Modulates the Expression of Inflammation Induced Bone Morphogenetic Protein-2, -5 and -6 as Well as Compared with Shockwave Therapy on Rat Knee Osteoarthritis

The dose-dependent effects of adipose-derived mesenchymal stem cell-conditioned medium (ADSC-CM) were compared with those of shockwave (SW) therapy in the treatment of early osteoarthritis (OA). Anterior cruciate ligament transaction (ACLT) with medial meniscectomy (MMx) was performed in rats divided into sham, OA, SW, CM1 (intra-articular injection of 100 μL ADSC-CM into knee OA), and CM2 (intra-articular injection of 200 μL ADSC-CM) groups. Cartilage grading, grading of synovium changes, and specific molecular analysis by immunohistochemistry staining were performed. The OARSI and synovitis scores of CM2 and SW group were significantly decreased compared with those of the OA group (p < 0.05). The inflammatory markers interleukin 1β, terminal deoxynucleotidyl transferase dUTP nick end labeling and matrix metalloproteinase 13 were significantly reduced in the CM2 group compared to those in the SW and CM1 groups (p < 0.001). Cartilage repair markers (type II collagen and SRY-box transcription factor 9, SOX9) expression were significantly higher in the CM2 group than in the other treatment groups (p < 0.001; p < 0.05). Furthermore, inflammation-induced growth factors such as bone morphogenetic protein 2 (BMP2), BMP5, and BMP6 were significantly reduced in the treatment groups, and the CM2 group showed the best results among the treatments (p < 0.05). In conclusion, ADSC-CM and SW ameliorated the expression of inflammatory cytokines and inflammation-induced BMPs to protect the articular cartilage of the OA joint.

The Use of Infrapatellar Fat Pad-Derived Mesenchymal Stem Cells in Articular Cartilage Regeneration: A Review

Cartilage is frequently damaged with a limited capacity for repair. Current treatment strategies are insufficient as they form fibrocartilage as opposed to hyaline cartilage, and do not prevent the progression of degenerative changes. There is increasing interest in the use of autologous mesenchymal stem cells (MSC) for tissue regeneration. MSCs that are used to treat articular cartilage defects must not only present a robust cartilaginous production capacity, but they also must not cause morbidity at the harvest site. In addition, they should be easy to isolate from the tissue and expand in culture without terminal differentiation. The source of MSCs is one of the most important factors that may affect treatment. The infrapatellar fat pad (IPFP) acts as an important reservoir for MSC and is located in the anterior compartment of the knee joint in the extra-synovial area. The IPFP is a rich source of MSCs, and in this review, we discuss studies that demonstrate that these cells have shown many advantages over other tissues in terms of ease of isolation, expansion, and chondrogenic differentiation. Future studies in articular cartilage repair strategies and suitable extraction as well as cell culture methods will extend the therapeutical application of IPFP-derived MSCs into additional orthopedic fields, such as osteoarthritis. This review provides the latest research concerning the use of IPFP-derived MSCs in the treatment of articular cartilage damage, providing critical information for the field to grow.

Harnessing adipose stem cell diversity in regenerative medicine

Since the first isolation of mesenchymal stem cells from lipoaspirate in the early 2000s, adipose tissue has been a darling of regenerative medicine. It is abundant, easy to access, and contains high concentrations of stem cells (ADSCs) exhibiting multipotency, proregenerative paracrine signaling, and immunomodulation-a winning combination for stem cell-based therapeutics. While basic science, preclinical and clinical findings back up the translational potential of ADSCs, the vast majority of these used cells from a single location-subcutaneous abdominal fat. New data highlight incredible diversity in the adipose morphology and function in different anatomical locations or depots. Even in isolation, ADSCs retain a memory of this diversity, suggesting that the optimal adipose source material for ADSC isolation may be application specific. This review discusses our current understanding of the heterogeneity in the adipose organ, how that heterogeneity translates into depot-specific ADSC characteristics, and how atypical ADSC populations might be harnessed for regenerative medicine applications. While our understanding of the breadth of ADSC heterogeneity is still in its infancy, clear trends are emerging for application-specific sourcing to improve regenerative outcomes.

The infrapatellar fat pad produces interleukin-6-secreting T cells in response to a proteoglycan aggrecan peptide and provides dominant soluble mediators different from that present in synovial fluid

OBJECTIVE

The purpose of this study was to investigate the effects of osteoarthritis (OA) peripheral blood mononuclear cell (PBMC) -stimulating proteoglycan aggrecan peptides on T cells present in infrapatellar fat pads (IPFPs) and synovial tissues, and to correlate these findings with mediators present in synovial fluid of OA patients.

METHODS

We tested for interleukin-6 (IL-6) -producing T cells in IPFPs of patients with knee OA using ELISPOT. Cytokine and cytotoxic mediator production from OA PBMCs, IPFPs, synovial tissues, and synovial fluids in response to proteoglycan aggrecan peptides were quantified by cytometric bead array. Patterns of cytokine and cytotoxic mediator production were analyzed and compared.

RESULTS

T cells from IPFPs elicited strong responses towards the p263-280 peptide by secreting IL-6. In addition, there was a trend that the p263-280 peptide stimulated higher production of cytokines/cytotoxic mediators than other proteoglycan aggrecan peptides, although this was not statistically significant. In patients with knee OA, a group of cytotoxic mediators (sFas, perforin, granzyme A, and granulysin) and IL-6 were detectable at high levels from the synovial fluid. In addition, inflammation in patients with knee OA was more pronounced in joint-surrounding tissues than levels in circulating peripheral blood.

CONCLUSION

Our data suggest that T cells responding to the p263-280 peptide contribute to the secretion of various soluble mediators that are found within the synovial fluid. We also identified potential new candidates that may serve as biomarkers of knee OA.

Age-Dependent Remodeling in Infrapatellar Fat Pad Adipocytes and Extracellular Matrix: A Comparative Study

The infrapatellar fat pad (IFP) is actively involved in knee osteoarthritis (OA). However, a proper description of which developmental modifications occur in the IFP along with age and in absence of joint pathological conditions, is required to adequately describe its actual contribution in OA pathophysiology. Here, two IFP sources were compared: (a) IFP from healthy young patients undergoing anterior-cruciate ligament (ACL) reconstruction for ACL rupture (n = 24); (b) IFP from elderly cadaver donors (n = 23). After histopathological score assignment to confirm the absence of inflammatory features (i.e., inflammatory infiltrate and increased vascularity), the adipocytes morphology was determined; moreover, extracellular matrix proteins were studied through histology and Second Harmonic Generation approach, to determine collagens content and orientation by Fast Fourier Transform and OrientationJ. The two groups were matched for body mass index. No inflammatory signs were observed, while higher area, perimeter, and equivalent diameter and volume were detected for the adipocytes in the elderly group. Collagen III displayed higher values in the young group and a lower total collagen deposition with aging was identified. However, collagen I/III ratio and the global architecture of the samples were not affected. A higher content in elastic fibers was observed around the adipocytes for the ACL-IFPs and in the septa cadaver donor-IFPs, respectively. Age affects the characteristics of the IFP tissue also in absence of a pathological condition. Variable mechanical stimulation, depending on age-related different mobility, could be speculated to exert a role in tissue remodeling.

Recent Updates of Diagnosis, Pathophysiology, and Treatment on Osteoarthritis of the Knee

Osteoarthritis (OA) is a degenerative and chronic joint disease characterized by clinical symptoms and distortion of joint tissues. It primarily damages joint cartilage, causing pain, swelling, and stiffness around the joint. It is the major cause of disability and pain. The prevalence of OA is expected to increase gradually with the aging population and increasing prevalence of obesity. Many potential therapeutic advances have been made in recent years due to the improved understanding of the underlying mechanisms, diagnosis, and management of OA. Embryonic stem cells and induced pluripotent stem cells differentiate into chondrocytes or mesenchymal stem cells (MSCs) and can be used as a source of injectable treatments in the OA joint cavity. MSCs are known to be the most studied cell therapy products in cell-based OA therapy owing to their ability to differentiate into chondrocytes and their immunomodulatory properties. They have the potential to improve cartilage recovery and ultimately restore healthy joints. However, despite currently available therapies and advances in research, unfulfilled medical needs persist for OA treatment. In this review, we focused on the contents of non-cellular and cellular therapies for OA, and briefly summarized the results of clinical trials for cell-based OA therapy to lay a solid application basis for clinical research.

The adenosinergic pathway in mesenchymal stem cell fate and functions

Mesenchymal stem cells (MSCs) play an important role in tissue homeostasis and damage repair through their ability to differentiate into cells of different tissues, trophic support, and immunomodulation. These properties made them attractive for clinical applications in regenerative medicine, immune disorders, and cell transplantation. However, despite multiple preclinical and clinical studies demonstrating beneficial effects of MSCs, their native identity and mechanisms of action remain inconclusive. Since its discovery, the CD73/ecto-5'-nucleotidase is known as a classic marker for MSCs, but its role goes far beyond a phenotypic characterization antigen. CD73 contributes to adenosine production, therefore, is an essential component of purinergic signaling, a pathway composed of different nucleotides and nucleosides, which concentrations are finely regulated by the ectoenzymes and receptors. Thus, purinergic signaling controls pathophysiological functions such as proliferation, migration, cell fate, and immune responses. Despite the remarkable progress already achieved in considering adenosinergic pathway as a therapeutic target in different pathologies, its role is not fully explored in the context of the therapeutic functions of MSCs. Therefore, in this review, we provide an overview of the role of CD73 and adenosine-mediated signaling in the functions ascribed to MSCs, such as homing and proliferation, cell differentiation, and immunomodulation. Additionally, we will discuss the pathophysiological role of MSCs, via CD73 and adenosine, in different diseases, as well as in tumor development and progression. A better understanding of the adenosinergic pathway in the regulation of MSCs functions will help to provide improved therapeutic strategies applicable in regenerative medicine.

CD38 and Regulation of the Immune Response Cells in Cancer

Cancer is a leading cause of death worldwide. Understanding the functional mechanisms associated with metabolic reprogramming, which is a typical feature of cancer cells, is key to effective therapy. CD38, primarily a NAD + glycohydrolase and ADPR cyclase, is a multifunctional transmembrane protein whose abnormal overexpression in a variety of tumor types is associated with cancer progression. It is linked to VEGFR2 mediated angiogenesis and immune suppression as it favors the recruitment of suppressive immune cells like Tregs and myeloid-derived suppressor cells, thus helping immune escape. CD38 is expressed in M1 macrophages and in neutrophil and T cell-mediated immune response and is associated with IFNγ-mediated suppressor activity of immune responses. Targeting CD38 with anti-CD38 monoclonal antibodies in hematological malignancies has shown excellent results. Bearing that in mind, targeting CD38 in other nonhematological cancer types, especially carcinomas, which are of epithelial origin with specific anti-CD38 antibodies alone or in combination with immunomodulatory drugs, is an interesting option that deserves profound consideration.

Excavating bioactivities of nanozyme to remodel microenvironment for protecting chondrocytes and delaying osteoarthritis

Osteoarthritis (OA) is the main cause of disability in the elderly. Effective intervention in the early and middle stage of osteoarthritis can greatly prevent or slow down the development of the disease, and reduce the probability of joint replacement. However, there is to date no effective intervention for early and middle-stage OA. OA microenvironment mainly destroys the balance of oxidative stress, extracellular matrix synthesis and degradation of chondrocytes under the joint action of biological and mechanical factors. Herein, hollow Prussian blue nanozymes (HPBzymes) were designed via a modified hydrothermal template-free method. The aim of this study was to investigate the effects of HPBzymes on chondrocytes and the progression of OA. The intrinsic bioactivities of HPBzymes were excavated in vitro and in vivo, remodeling microenvironment for significantly protecting chondrocytes and delaying the progression of traumatic OA by inhibiting reactive oxygen species (ROS) and Rac1/nuclear factor kappa-B (NF-κB) signaling in a rat model. HPBzyme significantly diminished interleukin (IL)-1β-stimulated inflammation, extracellular matrix degradation, and apoptosis of human chondrocytes. HPBzyme attenuated the expression of Rac1 and the ROS levels and prevented the release and nuclear translocation of NF-κB. Deeply digging the intrinsic bioactivities of nanozyme with single component to remodel microenvironment is an effective strategy for ROS-associated chronic diseases. This study reveals that excavating the bioactivities of nanomedicine deserves attention for diagnosis and treatment of severe diseases.

Infrapatellar Fat Pad Gene Expression and Protein Production in Patients with and without Osteoarthritis

Osteoarthritis (OA) is one of the most common joint disorders. Evidence suggests that the infrapatellar fat pad (IFP) is directly involved in OA pathology. However, a comparison between OA versus non-OA IFP is still missing. Thus, the aim of this study was to compare IFP molecular, adipocytes and extracellular matrix characteristics of patients affected by OA, and patients undergoing anterior cruciate ligament (ACL) reconstruction. We hypothesized that not only inflammation but also changes in adipocytes and extracellular matrix (ECM) composition might be involved in OA pathogenesis. Fifty-three patients were enrolled. IFP biopsies were obtained, evaluating: (a) lymphocytic infiltration and vascularization; (b) adipocytes area and number; (c) adipo-cytokines and extracellular matrix gene expression levels; (d) IL-6 and VEGF protein production; (e) collagen fibers distribution. OA IFP was more inflamed and vascularized compared to ACL IFP. OA IFP adipocytes were larger and numerically lower (1.3-fold) than ACL IFP adipocytes. An increase of gene expression of typical white adipose tissue genes was observed in OA compared to ACL IFP. Collagen-types distribution was different in the OA IFP group compared to controls, possibly explaining the change of the biomechanical characteristics found in OA IFP. Statistical linear models revealed that the adipocyte area correlated with BMI in the OA group. In conclusion, inflammation and fibrotic changes of OA IFP could represent novel therapeutic targets to counteract OA.

In vitro Evaluation of the Anti-inflammatory Effects of Thymoquinone in Osteoarthritis and in silico Analysis of Inter-Related Pathways in Age-Related Degenerative Diseases

Chronic inflammation is a common underlying factor in osteoarthritis (OA) and most age-related degenerative diseases. As conventional therapies help only in partial alleviation of symptoms in OA, stem cell-based therapies and herbal supplements are being widely explored. Thymoquinone (TQ), an active ingredient of Nigella sativa is reported to have immunomodulatory, anti-inflammatory and antioxidant properties. We evaluated the effects of TQ on bone marrow MSCs (BM-MSCs) derived from OA patients and its interrelated pathways in inflammation and age-related degenerative diseases using Ingenuity Pathway Analysis (IPA) as well as possible molecular targets using SwissTargetPrediction. BM-MSCs were derived from OA patients and their stemness properties were characterized by studying the MSCs related CD surface marker expression and differentiation into adipocytes, osteoblasts, and chondrocytes. Treatment with TQ (100 nM-5 μM) demonstrated cell death, especially at higher concentrations. MTT assay demonstrated a significant concentration-dependent decrease in cell viability which ranged from 20.04% to 69.76% with higher doses (300 nM, 1 μM, and 5 μM), especially at 48h and 72h. Additional cell viability testing with CellTiter-Blue also demonstrated a significant concentration-dependent decrease in cell viability which ranged from 27.80 to 73.67% with higher doses (300 nM, 1 μM, 3 μM, and 5 μM). Gene expression analysis following treatment of BM-MSCs with TQ (1 and 3 μM) for 48h showed upregulation of the anti-inflammatory genes IL-4 and IL-10. In contrast, the pro-inflammatory genes namely IFN-γ, TNF-α, COX-2, IL-6, IL-8, IL-16, and IL-12A although were upregulated, compared to the lower concentration of TQ (1 μM) they were all decreased at 3 μM. The pro-apoptotic BAX gene was downregulated while the SURVIVIN gene was upregulated. IPA of the molecular interaction of TQ in inflammation and age-related degenerative diseases identified canonical pathways directly related to synaptogenesis, neuroinflammation, TGF-β, and interleukin signaling. Further screening led to the identification of 36 molecules that are involved in apoptosis, cell cycle regulation, cytokines, chemokines, and growth factors. SwissTargetPrediction of TQ identified potential molecular targets with high probability. TQ exerted anti-inflammatory effects and therefore can be a useful adjuvant along with conventional therapies against inflammation in OA and other age-related degenerative diseases.