Innervation pattern of different cartilaginous tissues in the rat

The presence and degradation of nerve fibers in articular cartilage of neonatal rats

Purpose

To investigate the presence and change of nerve fibers and neuropeptide during early development of articular cartilage in neonatal rats.

Methods

Articular cartilage in distal-femoral epiphyses was collected from neonatal Sprague Dawley rats, which were 1-day, 5-day, and 10-day postnatal (P1, P5 and P10). Microscopy, immunofluorescence, transmission and scanning electron microscopy (TEM and SEM) were performed for detection of nerve fibers. Quantitative analysis for substance P (SP) and neuropeptide Y (NPY) was conducted using immunofluorescence and enzyme-linked immunosorbent assay (ELISA).

Results

TEM showed the existence of myelinated nerve fibers in the extracellular matrix of articular cartilage in both P1, P5 and P10 rats, and they formed synaptic contacts with chondrocytes. During this time, chondrocytes proceeded with their development, and the nerve fibers gradually degraded. The ELISA results showed significant increase of the sensory neuropeptide SP and the sympathetic neuropeptide NPY in the cartilage tissue. Immunofluorescence results showed the distribution of SP and NPY in the perichondrium, the cartilage canals, the plasma of chondrocytes, and extracellular matrix in the cartilage tissue.

Conclusions

Nerve fibers exist in the matrix of articular cartilage during early development of knee joints in neonatal rats. Nerve fibers form synaptic contacts with chondrocytes at the early stage and then degrade gradually in the course of chondrocyte development. SP and NPY significantly increase in articular cartilage during this very period. These results indicate that the nerve fibers and the neuropeptide they secrete may exert important effect on the development of articular cartilage.

Sympathectomy aggravates subchondral bone changes during osteoarthritis progression in mice without affecting cartilage degeneration or synovial inflammation

OBJECTIVE

Osteoarthritis (OA) pathogenesis involves the interaction of articular cartilage with surrounding tissues, which are innervated by tyrosine hydroxylase-positive (TH+) sympathetic nerve fibers suggesting a role of the sympathetic nervous system (SNS) during OA progression. We analyzed the effects of sympathectomy (Syx) in a murine OA model.

METHODS

Peripheral Syx was generated by 6-hydroxydopamine (6-OHDA) injections in male C57BL/6 mice. OA was induced in wild-type (WT) and Syx mice by destabilization of the medial meniscus (DMM). TH+ fibers and splenic NE were analyzed to evaluate Syx efficiency. OA progression was examined by OARSI and synovitis scores and micro-CT. Expression of TH, α2A- and β2-adrenergic receptors (AR), and activity of osteoblasts (ALP) and osteoclasts (TRAP) was investigated by stainings.

RESULTS

Syx resulted in synovial TH+ fiber elimination and splenic NE decrease. Cartilage degradation and synovitis after DMM were comparably progressive in both WT and Syx mice. Calcified cartilage (CC) and subchondral bone plate (SCBP) thickness and bone volume fraction (BV/TV) increased in Syx mice due to increased ALP and decreased TRAP activities compared to WT 8 weeks after DMMWT and Syx mice developed osteophytes and meniscal ossicles without any differences between the groups. AR numbers decreased in cartilage but increased in synovium and osteophyte regions after DMM in both WT and Syx mice.

CONCLUSION

Peripheral dampening of SNS activity aggravated OA-specific cartilage calcification and subchondral bone thickening but did not influence cartilage degradation and synovitis. Therefore, SNS might be an attractive target for the development of novel therapeutic strategies for pathologies of the subchondral bone.

Classification of four distinct osteoarthritis subtypes with a knee joint tissue transcriptome atlas

The limited molecular classifications and disease signatures of osteoarthritis (OA) impede the development of prediagnosis and targeted therapeutics for OA patients. To classify and understand the subtypes of OA, we collected three types of tissue including cartilage, subchondral bone, and synovium from multiple clinical centers and constructed an extensive transcriptome atlas of OA patients. By applying unsupervised clustering analysis to the cartilage transcriptome, OA patients were classified into four subtypes with distinct molecular signatures: a glycosaminoglycan metabolic disorder subtype (C1), a collagen metabolic disorder subtype (C2), an activated sensory neuron subtype (C3), and an inflammation subtype (C4). Through ligand-receptor crosstalk analysis of the three knee tissue types, we linked molecular functions with the clinical symptoms of different OA subtypes. For example, the Gene Ontology functional term of vasculature development was enriched in the subchondral bone-cartilage crosstalk of C2 and the cartilage-subchondral bone crosstalk of C4, which might lead to severe osteophytes in C2 patients and apparent joint space narrowing in C4 patients. Based on the marker genes of the four OA subtypes identified in this study, we modeled OA subtypes with two independent published RNA-seq datasets through random forest classification. The findings of this work contradicted traditional OA diagnosis by medical imaging and revealed distinct molecular subtypes in knee OA patients, which may allow for precise diagnosis and treatment of OA.

Defining the osteoarthritis patient: back to the future

The history of osteoarthritis (OA) is important because it can help broaden our perspective on past and present controversies. The naming of OA, beginning with Heberden's nodes, is itself a fascinating story. According to Albert Hoffa, R. Llewellyn Jones and Archibald Edward Garrod, the name OA was introduced in the mid-nineteenth century by surgeon Richard von Volkmann who distinguished it from rheumatoid arthritis and gout. Others preferred the terms 'chronical rheumatism', 'senile arthritis', 'hypertrophic arthritis' or 'arthritis deformans'. A similar narrative applies to the concept of OA affecting the whole joint vs the 'wear-and-tear' hypothesis, inflammation and the role of the central nervous system (CNS). In the late nineteenth and early twentieth centuries, the Garrods (father and son) and Hermann Senator argued that OA was a whole joint disease, and that inflammation played a major role in its progression. Garrod Jnr and John Spender also linked OA to a neurogenic lesion 'outside the joint'. The remaining twentieth century was no less dynamic, with major advances in basic science, diagnostics, treatments, surgical interventions and technologies. Today, OA is characterized as a multi-disease with inflammation, immune and CNS dysfunction playing central roles in whole joint damage, injury progression, pain and disability. In the current 'omics' era (genomics, proteomics and metabolomics), we owe a great debt to past physicians and surgeons who dared to think 'outside-the-box' to explain and treat OA. Over 130 years later, despite these developments, we still don't fully understand the underlying complexities of OA, and we still don't have a cure.

Peripheral Nerve Fibers and Their Neurotransmitters in Osteoarthritis Pathology

The importance of the nociceptive nervous system for maintaining tissue homeostasis has been known for some time, and it has also been suggested that organogenesis and tissue repair are under neuronal control. Changes in peripheral joint innervation are supposed to be partly responsible for degenerative alterations in joint tissues which contribute to development of osteoarthritis. Various resident cell types of the musculoskeletal system express receptors for sensory and sympathetic neurotransmitters, allowing response to peripheral neuronal stimuli. Among them are mesenchymal stem cells, synovial fibroblasts, bone cells and chondrocytes of different origin, which express distinct subtypes of adrenoceptors (AR), receptors for vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP). Some of these cell types synthesize and secrete neuropeptides such as SP, and they are positive for tyrosine-hydroxylase (TH), the rate limiting enzyme for biosynthesis of catecholamines. Sensory and sympathetic neurotransmitters are involved in the pathology of inflammatory diseases such as rheumatoid arthritis (RA) which manifests mainly in the joints. In addition, they seem to play a role in pathogenesis of priori degenerative joint disorders such as osteoarthritis (OA). Altogether it is evident that sensory and sympathetic neurotransmitters have crucial trophic effects which are critical for joint tissue and bone homeostasis. They modulate articular cartilage, subchondral bone and synovial tissue properties in physiological and pathophysiological conditions, in addition to their classical neurological features.

The role of peripheral nerve fibers and their neurotransmitters in cartilage and bone physiology and pathophysiology

The peripheral nervous system is critically involved in bone metabolism, osteogenesis, and bone remodeling. Nerve fibers of sympathetic and sensory origin innervate synovial tissue and subchondral bone of diathrodial joints. They modulate vascularization and matrix differentiation during endochondral ossification in embryonic limb development, indicating a distinct role in skeletal growth and limb regeneration processes. In pathophysiological situations, the innervation pattern of sympathetic and sensory nerve fibers is altered in adult joint tissues and bone. Various resident cell types of the musculoskeletal system express receptors for sensory and sympathetic neurotransmitters. Osteoblasts, osteoclasts, mesenchymal stem cells, synovial fibroblasts, and different types of chondrocytes produce distinct subtypes of adrenoceptors, receptors for vasointestinal peptide, for substance P and calcitonin gene-related peptide. Many of these cells even synthesize neuropeptides such as substance P and calcitonin gene-related peptide and are positive for tyrosine-hydroxylase, the rate-limiting enzyme for biosynthesis of catecholamines. Sensory and sympathetic neurotransmitters modulate osteo-chondrogenic differentiation of mesenchymal progenitor cells during endochondral ossification in limb development. In adults, sensory and sympathetic neurotransmitters are critical for bone regeneration after fracture and are involved in the pathology of inflammatory diseases as rheumatoid arthritis which manifests mainly in joints. Possibly, they might also play a role in pathogenesis of degenerative joint disorders, such as osteoarthritis. All together, accumulating data imply that sensory and sympathetic neurotransmitters have crucial trophic effects which are critical for proper limb formation during embryonic skeletal growth. In adults, they modulate bone regeneration, bone remodeling, and articular cartilage homeostasis in addition to their classic neurological actions.

Neural and psychosocial contributions to sex differences in knee osteoarthritic pain

People with osteoarthritis (OA) can have significant pain that interferes with function and quality of life. Women with knee OA have greater pain and greater reductions in function and quality of life than men. In many cases, OA pain is directly related to sensitization and activation of nociceptors in the injured joint and correlates with the degree of joint effusion and synovial thickening. In some patients, however, the pain does not match the degree of injury and continues after removal of the nociceptors with a total joint replacement. Growth of new nociceptors, activation of nociceptors in the subchondral bone exposed after cartilage degradation, and nociceptors innervating synovium sensitized by inflammatory mediators could all augment the peripheral input to the central nervous system and result in pain. Enhanced central excitability and reduced central inhibition could lead to prolonged and enhanced pain that does not directly match the degree of injury. Psychosocial variables can influence pain and contribute to pain variability. This review explores the neural and psychosocial factors that contribute to knee OA pain with an emphasis on differences between the sexes and gaps in knowledge.

Possible nociceptive structures in the sacroiliac joint cartilage: An immunohistochemical study

The sacroiliac joint (SI joint) is a known source of low back pain. In the absence of validated physical signs and imaging studies, the diagnosis of SI joint pain can be secured by positive response to SI joint intra-articular infiltration with local anesthetics. The current anatomical and histological knowledge concerning intra-articular structures of the sacroiliac joint is insufficient to explain the efficacy of this infiltration. Consequently, this study was undertaken to detect the intra-articular presence of substance P and calcitonin gene-related peptide (CGRP) positive nerve fibers, providing indirect evidence of nociceptive innervation of the SI joint. Free-floating sections, obtained from iliac and sacral cartilage and subchondral bone of the SI joint and adjacent ligamentous tissue, of 10 human cadavers were studied immunohistochemically. Tissue of nine human cadavers showed the presence of substance P and CGRP immunoreactivity in the superficial layer of sacral and iliac cartilage, and the surrounding ligamentous structures. Subchondral bone reacted weakly to the antisera used. These findings support the view that the SI joint may be capable of intra-articular nociception and may explain the positive response to the intra-articular deposition of local anesthetic.

Knee joint proprioception in ACL-deficient knees is related to cartilage injury, laxity and ageA retrospective study of 54 patients

BACKGROUND

ACL-deficient patients have been found to have proprioceptive defects, but the cause of these defects has not been identified nor has the relationship between proprioception and subjective function, laxity, activity level and age been adequately studied.

PATIENTS AND METHODS

Therefore, we analyzed proprioception, defined as the threshold to detect a slow passive motion (TTDPM), in relation to activity level, laxity, meniscal injuries, collateral ligament injuries, cartilage injuries, age and subjective function in 54 patients with a previous ACL rupture. We used multiple pair-wise correlation analyses, followed by a stepwise linear regression model.

RESULTS

We found that poorer proprioception was related to lateral cartilage lesions, increased laxity and older age while a high activity level before injury was related with better proprioception after injury. The results also suggest a relation between proprioception and subjective knee function.

INTERPRETATION

Anatomical injuy classification may need to be considered when discussing proprioceptive ability in patients with an ACL injury, laxity is related to proprioception and proprioception may decrease with age.

Anti-NGF therapy profoundly reduces bone cancer pain and the accompanying increase in markers of peripheral and central sensitization

Bone cancer pain can be difficult to control, as it appears to be driven simultaneously by inflammatory, neuropathic and tumorigenic mechanisms. As nerve growth factor (NGF) has been shown to modulate inflammatory and neuropathic pain states, we focused on a novel NGF sequestering antibody and demonstrated that two administrations of this therapy in a mouse model of bone cancer pain produces a profound reduction in both ongoing and movement-evoked bone cancer pain-related behaviors that was greater than that achieved with acute administration of 10 or 30 mg/kg of morphine. This therapy also reduced several neurochemical changes associated with peripheral and central sensitization in the dorsal root ganglion and spinal cord, whereas the therapy did not influence disease progression or markers of sensory or sympathetic innervation in the skin or bone. Mechanistically, the great majority of sensory fibers that innervate the bone are CGRP/TrkA expressing fibers, and if the sensitization and activation of these fibers is blocked by anti-NGF therapy there would not be another population of nociceptors, such as the non-peptidergic IB4/RET-IR nerve fibers, to take their place in signaling nociceptive events.

Biology of Fibrocartilage Cells

Fibrocartilage is an avascular tissue that is best documented in menisci, intervertebral discs, tendons, ligaments, and the temporomandibular joint. Several of these sites are of particular interest to those in the emerging field of tissue engineering. Fibrocartilage cells frequently resemble chondrocytes in having prominent rough endoplasmic reticulum, many glycogen granules, and lipid droplets, and intermediate filaments together with and actin stress fibers that help to determine cell organization in the intervertebral disc. Fibrocartilage cells can synthesize a variety of matrix molecules including collagens, proteoglycans, and noncollagenous proteins. All the fibrillar collagens (types I, II, III, V, and XI) have been reported, together with FACIT (types IX and XII) and network-forming collagens (types VI and X). The proteoglycans include large, aggregating types (aggrecan and versican) and small, leucine-rich types (decorin, biglycan, lumican, and fibromodulin). Less attention has been paid to noncollagenous proteins, although tenascin-C expression may be modulated by mechanical strain. As in hyaline cartilage, matrix metalloproteinases are important in matrix turnover and fibrocartilage cells are capable of apoptosis.