Glycosaminoglycans modulate long-range mechanical communication between cells in collagen networks

Senescent CAFs Mediate Immunosuppression and Drive Breast Cancer Progression

The tumor microenvironment (TME) profoundly influences tumorigenesis, with gene expression in the breast TME capable of predicting clinical outcomes. The TME is complex and includes distinct cancer-associated fibroblast (CAF) subtypes whose contribution to tumorigenesis remains unclear. Here, we identify a subset of myofibroblast CAFs (myCAF) that are senescent (senCAF) in mouse and human breast tumors. Utilizing the MMTV-PyMT;INK-ATTAC (INK) mouse model, we found that senCAF-secreted extracellular matrix specifically limits natural killer (NK) cell cytotoxicity to promote tumor growth. Genetic or pharmacologic senCAF elimination unleashes NK cell killing, restricting tumor growth. Finally, we show that senCAFs are present in HER2+, ER+, and triple-negative breast cancer and in ductal carcinoma in situ (DCIS) where they predict tumor recurrence. Together, these findings demonstrate that senCAFs are potently tumor promoting and raise the possibility that targeting them by senolytic therapy could restrain breast cancer development. Significance: senCAFs limit NK cell-mediated killing, thereby contributing to breast cancer progression. Thus, targeting senCAFs could be a clinically viable approach to limit tumor progression. See related article by Belle et al., p. 1324.

3D Traction Force Microscopy in Biological Gels: From Single Cells to Multicellular Spheroids

Cell traction force plays a critical role in directing cellular functions, such as proliferation, migration, and differentiation. Current understanding of cell traction force is largely derived from 2D measurements where cells are plated on 2D substrates. However, 2D measurements do not recapitulate a vital aspect of living systems; that is, cells actively remodel their surrounding extracellular matrix (ECM), and the remodeled ECM, in return, can have a profound impact on cell phenotype and traction force generation. This reciprocal adaptivity of living systems is encoded in the material properties of biological gels. In this review, we summarize recent progress in measuring cell traction force for cells embedded within 3D biological gels, with an emphasis on cell-ECM cross talk. We also provide perspectives on tools and techniques that could be adapted to measure cell traction force in complex biochemical and biophysical environments.

Structure-Mechanics Principles and Mechanobiology of Fibrocartilage Pericellular Matrix: A Pivotal Role of Type V Collagen

The pericellular matrix (PCM) is the immediate microniche surrounding resident cells in various tissue types, regulating matrix turnover, cell-matrix cross-talk and disease initiation. This study elucidated the structure-mechanical properties and mechanobiological functions of the PCM in fibrocartilage, a family of connective tissues that sustain complex tensile and compressive loads in vivo. Studying the murine meniscus as the model tissue, we showed that fibrocartilage PCM contains thinner, random collagen fibrillar networks that entrap proteoglycans, a structure distinct from the densely packed, highly aligned collagen fibers in the bulk extracellular matrix (ECM). In comparison to the ECM, the PCM has a lower modulus and greater isotropy, but similar relative viscoelastic properties. In Col5a1 +/- menisci, the reduction of collagen V, a minor collagen localized in the PCM, resulted in aberrant fibril thickening with increased heterogeneity. Consequently, the PCM exhibited a reduced modulus, loss of isotropy and faster viscoelastic relaxation. This disrupted PCM contributes to perturbed mechanotransduction of resident meniscal cells, as illustrated by reduced intracellular calcium signaling, as well as upregulated biosynthesis of lysyl oxidase and tenascin C. When cultured in vitro, Col5a1 +/- meniscal cells synthesized a weakened nascent PCM, which had inferior properties towards protecting resident cells against applied tensile stretch. These findings underscore the PCM as a distinctive microstructure that governs fibrocartilage mechanobiology, and highlight the pivotal role of collagen V in PCM function. Targeting the PCM or its molecular constituents holds promise for enhancing not only meniscus regeneration and osteoarthritis intervention, but also addressing diseases across various fibrocartilaginous tissues.

Identification of CD44 as a key mediator of cell traction force generation in hyaluronic acid-rich extracellular matrices

Mechanical properties of the extracellular matrix (ECM) critically regulate a number of important cell functions including growth, differentiation and migration. Type I collagen and glycosaminoglycans (GAGs) are two primary components of ECMs that contribute to mammalian tissue mechanics, with the collagen fiber network sustaining tension, and GAGs withstanding compression. The architecture and stiffness of the collagen network are known to be important for cell-ECM mechanical interactions via integrin cell surface adhesion receptors. In contrast, studies of GAGs in modulating cell-ECM interactions are limited. Here, we present experimental studies on the roles of hyaluronic acid (HA, an unsulfated GAG) in single tumor cell traction force generation using a recently developed 3D cell traction force microscopy method. Our work reveals that CD44, a cell surface adhesion receptor to HA, is engaged in cell traction force generation in conjunction with β1-integrin. We find that HA significantly modifies the architecture and mechanics of the collagen fiber network, decreasing tumor cells' propensity to remodel the collagen network, attenuating traction force generation, transmission distance, and tumor invasion. Our findings point to a novel role for CD44 in traction force generation, which can be a potential therapeutic target for diseases involving HA rich ECMs such as breast cancer and glioblastoma.

Effects of local incompressibility on the rheology of composite biopolymer networks

Fibrous networks such as collagen are common in biological systems. Recent theoretical and experimental efforts have shed light on the mechanics of single component networks. Most real biopolymer networks, however, are composites made of elements with different rigidity. For instance, the extracellular matrix in mammalian tissues consists of stiff collagen fibers in a background matrix of flexible polymers such as hyaluronic acid (HA). The interplay between different biopolymer components in such composite networks remains unclear. In this work, we use 2D coarse-grained models to study the nonlinear strain-stiffening behavior of composites. We introduce a local volume constraint to model the incompressibility of HA. We also perform rheology experiments on composites of collagen with HA. Theoretically and experimentally, we demonstrate that the linear shear modulus of composite networks can be increased by approximately an order of magnitude above the corresponding moduli of the pure components. Our model shows that this synergistic effect can be understood in terms of the local incompressibility of HA, which acts to suppress density fluctuations of the collagen matrix with which it is entangled.

Compositional, Structural, and Biomechanical Properties of Three Different Soft Tissue-Hard Tissue Insertions: A Comparative Review

Connective tissue attaches to bone across an insertion with spatial gradients in components, microstructure, and biomechanics. Due to regional stress concentrations between two mechanically dissimilar materials, the insertion is vulnerable to mechanical damage during joint movements and difficult to repair completely, which remains a significant clinical challenge. Despite interface stress concentrations, the native insertion physiologically functions as the effective load-transfer device between soft tissue and bone. This review summarizes tendon, ligament, and meniscus insertions cross-sectionally, which is novel in this field. Herein, the similarities and differences between the three kinds of insertions in terms of components, microstructure, and biomechanics are compared in great detail. This review begins with describing the basic components existing in the four zones (original soft tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone) of each kind of insertion, respectively. It then discusses the microstructure constructed from collagen, glycosaminoglycans (GAGs), minerals and others, which provides key support for the biomechanical properties and affects its physiological functions. Finally, the review continues by describing variations in mechanical properties at the millimeter, micrometer, and nanometer scale, which minimize stress concentrations and control stretch at the insertion. In summary, investigating the contrasts between the three has enlightening significance for future directions of repair strategies of insertion diseases and for bioinspired approaches to effective soft-hard interfaces and other tough and robust materials in medicine and engineering.

Age-dependent loss of HAPLN1 erodes vascular integrity via indirect upregulation of endothelial ICAM1 in melanoma

Melanoma, the most lethal form of skin cancer, often has worse outcomes in older patients. We previously demonstrated that an age-related decrease in the secreted extracellular matrix (ECM) protein HAPLN1 has a role in slowing melanoma progression. Here we show that HAPLN1 in the dermal ECM is sufficient to maintain the integrity of melanoma-associated blood vessels, as indicated by increased collagen and VE-cadherin expression. Specifically, we show that HAPLN1 in the ECM increases hyaluronic acid and decreases endothelial cell expression of ICAM1. ICAM1 phosphorylates and internalizes VE-cadherin, a critical determinant of vascular integrity, resulting in permeable blood vessels. We found that blocking ICAM1 reduces tumor size and metastasis in older mice. These results suggest that HAPLN1 alters endothelial ICAM1expression in an indirect, matrix-dependent manner. Targeting ICAM1 could be a potential treatment strategy for older patients with melanoma, emphasizing the role of aging in tumorigenesis.

Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. This study focuses on the GAG molecules chondroitin sulfate (CS), dermatan sulfate (DS), and hyaluronic acid (HA). CS and DS are stereoisomers while HA is the only non-sulfated GAG. We characterized and decoupled the effects of these GAG molecules on the stiffness, transport, and matrix microarchitecture properties of type I collagen hydrogels using mechanical indentation testing, microfluidics, and confocal reflectance imaging, respectively. We complement these biophysical measurements with turbidity assays to profile collagen aggregate formation. Surprisingly, only HA enhanced the ECM indentation modulus, while all three GAGs had no effect on hydraulic permeability. Strikingly, we show that CS, DS, and HA differentially regulate the matrix microarchitecture of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs define key physical properties of the ECM, this work shows new ways in which stiffness measurements, microfluidics, microscopy, and turbidity kinetics can be used complementarily to reveal details of collagen self-assembly and structure. STATEMENT OF SIGNIFICANCE: Collagen and glycosaminoglycans (GAGs) are integral to the structure, function, and bioactivity of the extracellular matrix (ECM). Despite widespread interest in collagen-GAG composite hydrogels, there is a lack of quantitative understanding of how different GAGs alter the biophysical properties of the ECM across tissue, cellular, and subcellular length scales. Here we show using mechanical, microfluidic, microscopy, and analytical methods and measurements that the GAG molecules chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially regulate the mechanical, transport, and microstructural properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. As such, these results will inform improved design and utilization of collagen-based scaffolds of tailored composition, mechanical properties, molecular availability due to mass transport, and microarchitecture.

Well-known polypeptides of deer antler velvet with key actives: modern pharmacological advances

Deer antler velvet, with kidney tonifying, promoting the production of essence and blood, strengthening tendons and bones, not only has a thousand-year medicinal history but also its modern pharmacology mainly focuses on its active polypeptides on motor, nerve, and immune systems. The purpose of this report is to fill the gap in the comprehensive, systematic, and detailed review of polypeptides during the recent 30 years (1992-2023). The research method was to review 53 pharmacological articles from the Public Medicine, Web of science, ACS, and Science Direct database sources by searching the keywords "pilose antler," "deer velvet," "Pilose Antler Peptide (PAP) and Velvet Antler Polypeptide (VAP)." The results showed that deer antler polypeptides (DAPs), by regulating EGF, EGFR, MAPK, P38, ERK, NF-κB, Wnt, PI3K, Akt, MMP, AMPK, Stir1, NLRP3, HO-1, Nrf, Rho, TLR, TGF-β, Smad, Ang II, etc., revealed their effects on seven system-related diseases and their mechanisms, including osteoarthritis, intervertebral disc degeneration, osteoporosis, Alzheimer's, Parkinson's, triple-negative breast cancer, liver injury, liver fibrosis, cardiovascular disease, acute lung injury, and late-onset hypogonadism. In conclusion, DAPs have good effects on motor and other system-related diseases, but the secondary and tertiary structures of DAPs (0.5-1800 KDa) need to be further elucidated, and the structure-activity relationship study is still unavailable and needs to be covered. It is expected that this review may provide the necessary literature support for further research. The activities and mechanisms of polypeptides from the past 30 years (1992-2023) are summarized covering seven systems, related diseases, and its regulatory genes and proteins.

A Comparative Analysis of Orthotopic and Subcutaneous Pancreatic Tumour Models: Tumour Microenvironment and Drug Delivery

Pancreatic ductal adenocarcinoma (PDAC) remains a challenging malignancy, mainly due to its resistance to chemotherapy and its complex tumour microenvironment characterised by stromal desmoplasia. There is a need for new strategies to improve the delivery of drugs and therapeutic response. Relevant preclinical tumour models are needed to test potential treatments. This paper compared orthotopic and subcutaneous PDAC tumour models and their suitability for drug delivery studies. A novel aspect was the broad range of tumour properties that were studied, including tumour growth, histopathology, functional vasculature, perfusion, immune cell infiltration, biomechanical characteristics, and especially the extensive analysis of the structure and the orientation of the collagen fibres in the two tumour models. The study unveiled new insights into how these factors impact the uptake of a fluorescent model drug, the macromolecule called 800CW. While the orthotopic model offered a more clinically relevant microenvironment, the subcutaneous model offered advantages for drug delivery studies, primarily due to its reproducibility, and it was characterised by a more efficient drug uptake facilitated by its collagen organisation and well-perfused vasculature. The tumour uptake seemed to be influenced mainly by the structural organisation and the alignment of the collagen fibres and perfusion. Recognising the diverse characteristics of these models and their multifaceted impacts on drug delivery is crucial for designing clinically relevant experiments and improving our understanding of pancreatic cancer biology.

Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. Here we characterized and decoupled the effects of the GAG molecules chondroitin sulfate (CS) dermatan sulfate (DS) and hyaluronic acid (HA) on the stiffness (indentation modulus), transport (hydraulic permeability), and matrix microarchitecture (pore size and fiber radius) properties of collagen-based hydrogels. We complement these biophysical measurements of collagen hydrogels with turbidity assays to profile collagen aggregate formation. Here we show that CS, DS, and HA differentially regulate the biophysical properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs play significant roles in defining key physical properties of the ECM, this work shows new ways in which stiffness measurements, microscopy, microfluidics, and turbidity kinetics can be used complementary to reveal details of collagen self-assembly and structure.

Extracellular Matrix-Derived Biophysical Cues Mediate Interstitial Flow-Induced Sprouting Angiogenesis

Sprouting angiogenesis is orchestrated by an intricate balance of biochemical and mechanical cues in the local tissue microenvironment. Interstitial flow has been established as a potent regulator of angiogenesis. Similarly, extracellular matrix (ECM) physical properties, such as stiffness and microarchitecture, have also emerged as important mediators of angiogenesis. However, the interplay between interstitial flow and ECM physical properties in the initiation and control of angiogenesis is poorly understood. Using a three-dimensional (3D) microfluidic tissue analogue of angiogenic sprouting with defined interstitial flow superimposed over ECM with well-characterized physical properties, we found that the addition of hyaluronan (HA) to collagen-based matrices significantly enhances sprouting induced by interstitial flow compared to responses in collagen-only hydrogels. We confirmed that both the stiffness and matrix pore size of collagen-only hydrogels were increased by the addition of HA. Interestingly, interstitial flow-potentiated sprouting responses in collagen/HA matrices were not affected when functionally blocking the HA receptor CD44. In contrast, enzymatic depletion of HA in collagen/HA matrices with hyaluronidase (HAdase) resulted in decreased stiffness, pore size, and interstitial flow-mediated sprouting to the levels observed in collagen-only matrices. Taken together, these results suggest that HA enhances interstitial flow-mediated angiogenic sprouting through its alterations to collagen ECM stiffness and pore size.

Hyperelastic characterization reveals proteoglycans drive the nanoscale strain-stiffening response in hyaline cartilage

Degenerative diseases such as osteoarthritis (OA) result in deterioration of cartilage extracellular matrix (ECM) components, significantly compromising tissue function. For measurement of mechanical properties at micron resolution, atomic force microscopy (AFM) is a leading technique in biomaterials research, including in the study of OA. It is common practice to determine material properties by applying classical Hertzian contact theory to AFM data. However, errors are consequential because the application of a linear elastic contact model to tissue ignores the fact that soft materials exhibit nonlinear properties even at small strains, influencing the biological conclusions of clinically-relevant studies. Additionally, nonlinear material properties are not well characterized, limiting physiological relevance of Young's modulus. Here, we probe the ECM of hyaline cartilage with AFM and explore the application of Hertzian theory in comparison to five hyperelastic models: NeoHookean, Mooney-Rivlin, Arruda-Boyce, Fung, and Ogden. The Fung and Ogden models achieved the best fits of the data, but the Fung model demonstrated robust sensitivity during model validation, demonstrating its ideal application to cartilage ECM and potentially other connective tissues. To develop a biological understanding of the Fung nonlinear parameter, we selectively degraded ECM components to target collagens (purified collagenase), hyaluronan (bacterial hyaluronidase), and glycosaminoglycans (chondroitinase ABC). We found significant differences in both Fung parameters in response to enzymatic treatment, indicating that proteoglycans drive the nonlinear response of cartilage ECM, and validating biological relevance of these phenomenological parameters. Our findings add value to the biomechanics community of using two-parameter material models for microindentation of soft biomaterials.

Micromechanical remodeling of the extracellular matrix by invading tumors: anisotropy and heterogeneity

Altered tissue mechanics is an important signature of invasive solid tumors. While the phenomena have been extensively studied by measuring the bulk rheology of the extracellular matrix (ECM) surrounding tumors, micromechanical remodeling at the cellular scale remains poorly understood. By combining holographic optical tweezers and confocal microscopy on in vitro tumor models, we show that the micromechanics of collagen ECM surrounding an invading tumor demonstrate directional anisotropy, spatial heterogeneity and significant variations in time as tumors invade. To test the cellular mechanisms of ECM micromechanical remodeling, we construct a simple computational model and verify its predictions with experiments. We find that collective force generation of a tumor stiffens the ECM and leads to anisotropic local mechanics such that the extension direction is more rigid than the compression direction. ECM degradation by cell-secreted matrix metalloproteinase softens the ECM, and active traction forces from individual disseminated cells re-stiffen the matrix. Together, these results identify plausible biophysical mechanisms responsible for the remodeled ECM micromechanics surrounding an invading tumor.

Does the Extracellular Matrix Support Cell-Cell Communication by Elastic Wave Packets?

The extracellular matrix (ECM) is a fibrous network supporting biological cells and provides them a medium for interaction. Cells modify the ECM by applying traction forces, and these forces can propagate to long ranges and establish a mechanism of mechanical communication between neighboring cells. Previous studies have mainly focused on analysis of static force transmission across the ECM. In this study, we explore the plausibility of dynamic mechanical interaction, expressed as vibrations or abrupt fluctuations, giving rise to elastic waves propagating along ECM fibers. We use a numerical mass-spring model to simulate the longitudinal and transversal waves propagating along a single ECM fiber and across a 2D random fiber network. The elastic waves are induced by an active contracting cell (signaler) and received by a passive neighboring cell (receiver). We show that dynamic wave propagation may amplify the signal at the receiver end and support up to an order of magnitude stronger mechanical cues and longer-ranged communication relative to static transmission. Also, we report an optimal impulse duration corresponding to the most effective transmission, as well as extreme fast impulses, in which the waves are encaged around the active cell and do not reach the neighboring cell, possibly due to the Anderson localization effect. Finally, we also demonstrate that extracellular fluid viscosity reduces, but still allows, dynamic propagation along embedded ECM fibers. Our results motivate future biological experiments in mechanobiology to investigate, on the one hand, the mechanosensitivity of cells to dynamic forces traveling and guided by the ECM and, on the other hand, the impact of ECM architecture and remodeling on dynamic force transmission and its spectral filtering, dispersion, and decay.

Cortical bone material / compositional properties in growing children and young adults aged 1.5-23 years, as a function of gender, age, metabolic activity, and growth spurt

Bone material / compositional properties are significant determinants of bone quality, thus strength. Raman spectroscopic analysis provides information on the quantity and quality of all three bone tissue components (mineral, organic matrix, and tissue water). The overwhelming majority of the published reports on the subject concern adults. We have previously reported on these properties in growing children and young adults, in the cancellous compartment. The purpose of the present study was to create normative reference data of bone material / compositional properties for children and young adults, in the cortical compartment. We performed Raman (Senterra (Bruker Optik GmbH), 50× objective, with an excitation of 785 nm (100 mW) and a lateral resolution of ~0.6 μm) microspectroscopic analysis of transiliac bone samples from 54 individuals between 1.5 and 23 years of age, with no known metabolic bone disease, and which have been previously used to establish histomorphometric, bone mineralization density distribution, and cancellous bone quality reference values. The bone quality indices that were determined were: mineral/matrix ratio (MM) from the integrated areas of the v₂PO₄ (410-460 cm^-1) and the amide III (1215-1300 cm^-1) bands, tissue water in nanopores approximated by the ratio of the integrated spectral area ~ 494-509 cm^-1 to Amide III band, the glycosaminoglycan (GAG) content (ratio of integrated area 1365-1390 cm^-1 to the Amide III band, the sulfated proteoglycan (sPG) content as the ratio of the integrated peaks ~1062 cm^-1 and 1365-1390 cm^-1, the pyridinoline (Pyd) content estimated from the ratio of the absorbance height at 1660 cm^-1 / area of the amide I (1620-1700 cm^-1) band, and the mineral maturity / crystallinity (MMC) estimated from the inverse of the full width at half height of the v₁PO₄ (930-980 cm^-1) band. Analyses were performed at the three distinct cortical surfaces (endosteal, osteonal, periosteal) at specific anatomical microlocations, namely the osteoid, and the three precisely known tissue ages based on the presence of fluorescence double labels. Measurements were also taken in interstitial bone, a much older tissue that has undergone extensive secondary mineralization. Overall, significant dependencies of the measured parameters on tissue age were observed, while at any given tissue age, sex and subject age were minimal confounders. The established Raman database in the cortical compartments complements the previously published one in cancellous bone, and provides healthy baseline bone quality indices that may serve as a valuable tool to identify alterations due to pediatric disease.

Effect of hyaluronic acid on microscale deformations of collagen gels

As fibrous collagen is the most abundant protein in mammalian tissues, gels of collagen fibers have been extensively used as an extracellular matrix scaffold to study how cells sense and respond to cues from their microenvironment. Other components of native tissues, such as glycosaminoglycans like hyaluronic acid, can affect cell behavior in part by changing the mechanical properties of the collagen gel. Prior studies have quantified the effects of hyaluronic acid on the mechanical properties of collagen gels in experiments of uniform shear or compression at the macroscale. However, there remains a lack of experimental studies of how hyaluronic acid changes the mechanical properties of collagen gels at the scale of a cell. Here, we studied how addition of hyaluronic acid to gels of collagen fibers affects the local field of displacements in response to contractile loads applied on length scales similar to those of a contracting cell. Using spherical poly(N-isopropylacrylamide) particles, which contract when heated, we induced displacement in gels of collagen and collagen with hyaluronic acid. Displacement fields were quantified using a combination of confocal microscopy and digital image correlation. Results showed that hyaluronic acid suppressed the distance over which displacements propagated, suggesting that it caused the network to become more linear. Additionally, hyaluronic acid had no statistical effect on heterogeneity of the displacement fields, but it did make the gels more elastic by substantially reducing the magnitude of permanent deformations. Lastly, we examined the effect of hyaluronic acid on fiber remodeling due to localized forces and found that hyaluronic acid partially - but not fully - inhibited remodeling. This result is consistent with prior studies suggesting that fiber remodeling is associated with a phase transition resulting from an instability caused by nonlinearity of the collagen gel.

Treatment of postmenopausal osteoporosis patients with teriparatide for 24 months reverts forming bone quality indices to premenopausal healthy control values

Postmenopausal osteoporosis (PMOP) therapies are frequently evaluated by bone mineral density (BMD) gains against patients receiving placebo (calcium and vitamin D supplementation, a mild bone turnover-suppressing intervention), which is not equivalent to either healthy or treatment-naive PMOP. The aim of the present observational study was to assess the effects of TPTD treatment in PMOP (20 μg, once daily) at 6 (TPTD 6m; n = 28, age 65 ± 7.3 years), and 24 (TPTD 24m; n = 32, age 67.4 ± 6.15 years) months on bone quality indices at actively forming trabecular surfaces (with fluorescent double labels). Data from the TPTD-treated PMOP patients were compared with those in healthy adult premenopausal women (HC; n = 62, age 40.5 ± 10.6 years), and PMOP receiving placebo (PMOP-PLC; n = 94, age 70.6 ± 4.5 years). Iliac crest biopsies were analyzed by Raman microspectroscopy at three distinct tissue ages: mid-distance between the second label and the bone surface, mid-distance between the two labels, and 1 μm behind the first label. Mineral to matrix ratio (MM), mineral maturity/crystallinity (MMC), tissue water (TW), glycosaminoglycan (GAGs), and pyridinoline (Pyd) content were determined. Outcomes were compared by ANCOVA with subject age and tissue age as covariates, and health status as a fixed factor, followed by Sidak's post-hoc testing (significance assigned to p < 0.05). Both TPTD groups increased MM compared to PMOP-PLC. While TPTD 6m had values similar to HC, TPTD 24m had higher values compared to either HC or TPTD 6m. Both TPTD groups had lower MMC values compared to PMOP-PLC and similar to HC. TPTD 6m patients had higher TW content compared to HC, while TPTD 24m had values similar to HC and lower than either PMOP-PLC or TPTD 6m. Both TPTD groups had lower GAG content compared to HC group, while TPTD 6m had higher values compared to PMOP-PLC. Finally, TPTD 6m patients had higher Pyd content compared to HC and lower compared to PMOP-PLC, while TPTD 24m had lower values compared to PMOP-PLC and TPTD 6m, and similar to HC group. The results of the present study indicate that effects of TPTD on forming trabecular bone quality indices depend on treatment duration. At the recommended length of 24 m, TPTD restores bone mineral and organic matrix quality indices (MMC, TW, Pyd content) to premenopausal healthy (HC) levels.