Effects of chronic sleep deprivation on the extracellular signal-regulated kinase pathway in the temporomandibular joint of rats

Taurine Prevents Impairments in Skin Barrier Function and Dermal Collagen Synthesis Triggered by Sleep Deprivation-Induced Estrogen Circadian Rhythm Disruption

Sleep deprivation is a prevalent issue that disrupts the circadian rhythm of estrogen, particularly estradiol, thereby significantly affecting women's skin health and appearance. These disruptions can impair skin barrier functionality and decrease dermal collagen synthesis. In this study, our results demonstrate that topical taurine supplementation promotes the expression of tight junction (TJ)-related proteins and enhances collagen production, effectively restoring skin homeostasis in sleep-deprived female mice. Mechanistically, taurine upregulates the expression of TMEM38B, a gene encoding the TRIC-B trimeric cation channel, resulting in increased intracellular calcium ion levels. This, in turn, promotes the upregulation of TJ-related proteins, such as ZO-1, occludin, and claudin-11 in epidermal cells, while also enhancing the expression of type III collagen in fibroblasts, thus restoring skin homeostasis. These findings suggest that taurine may serve as an alternative to estradiol, effectively improving skin homeostasis disrupted by sleep deprivation while mitigating the potential risks associated with exogenous estrogen supplementation. Collectively, these results provide preliminary insights into the protective mechanisms of taurine against sleep deprivation-induced skin impairments and establish a foundation for its potential application in treating skin conditions related to estrogen imbalances, such as skin aging in menopausal women.

Signaling pathway mechanisms of circadian clock gene Bmal1 regulating bone and cartilage metabolism: a review

Circadian rhythm is ubiquitous in nature. Circadian clock genes such as Bmal1 and Clock form a multi-level transcription-translation feedback network, and regulate a variety of physiological and pathological processes, including bone and cartilage metabolism. Deletion of the core clock gene Bmal1 leads to pathological bone alterations, while the phenotypes are not consistent. Studies have shown that multiple signaling pathways are involved in the process of Bmal1 regulating bone and cartilage metabolism, but the exact regulatory mechanisms remain unclear. This paper reviews the signaling pathways by which Bmal1 regulates bone/cartilage metabolism, the upstream regulatory factors that control Bmal1, and the current Bmal1 knockout mouse models for research. We hope to provide new insights for the prevention and treatment of bone/cartilage diseases related to circadian rhythms.

Protective effect of Lavandula angustifolia essential oil inhalation on neuromodulators regulating the sleep/wake cycle in rats with total sleep deprivation

Objectives

This study aimed to investigate the potential effects of different doses of Lavender angustifolia essential oil (Lavender EO) administered by inhalation on sleep latency and neuromodulators regulating the sleep/wake cycle in rats with total sleep deprivation (TSD).

Materials and Methods

Forty-eight male Sprague-Dawley rats were divided into five groups: Control, Alprazolam (ALP, 0.25 mg/kg given intraperitoneally), L1 (Lavender EO, 0.3 ml given by inhalation), L2 (Lavender EO, 0.5 ml given by inhalation), and L3 (Lavender EO, 1 ml given by inhalation); TSD was applied to all groups. Rats in SD groups were kept on a platform surrounded by water for 18 hr for 20 days, and for the remaining time, the animals were exposed to Lavender EO for 1 hr (11:00-12:00) and then were kept in their home cage for 5 hr (12:00-17:00). Their brain and brainstem were removed for histopathological and immunohistochemical analyses (c-Fos, ChAT, GAD, and ADRB2 expression) in the locus coeruleus (LC), basal forebrain (BF), and preoptic area (PO).

Results

The groups ranked by the severity of edema, hyperemia, and neurodegeneration in LC, BF, and PO areas were control, L3, L1, L2, and ALP. c-Fos expression significantly decreased in all brain regions in all groups except the L1 group. ChAT and GAD expressions increased dramatically in all brain regions. ADRB2 significantly increased in LC in ALP and L2 groups; in the PO area in ALP, L1, and L2 groups; and in BF in all groups.

Conclusion

Lavender EO treatment ameliorated c-Fos, ChAT, GAD, and ADRB2 expression, similar to the effect of ALP.

Circadian rhythm disruption upregulating Per1 in mandibular condylar chondrocytes mediating temporomandibular joint osteoarthritis via GSK3β/β-CATENIN pathway

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) has a high incidence rate, but its pathogenesis remains unclear. Circadian rhythm is an important oscillation in the human body and influences various biological activities. However, it is still unclear whether circadian rhythm affects the onset and development of TMJOA.

METHODS

We disrupted the normal rhythm of rats and examined the expression of core clock genes in the mandibular condylar cartilage of the jaw and histological changes in condyles. After isolating rat mandibular condylar chondrocytes, we upregulated or downregulated the clock gene Per1, examined the expression of cartilage matrix-degrading enzymes, tested the activation of the GSK3β/β-CATENIN pathway and verified it using agonists and inhibitors. Finally, after downregulating the expression of Per1 in the mandibular condylar cartilage of rats with jet lag, we examined the expression of cartilage matrix-degrading enzymes and histological changes in condyles.

RESULTS

Jet lag led to TMJOA-like lesions in the rat mandibular condyles, and the expression of the clock gene Per1 and cartilage matrix-degrading enzymes increased in the condylar cartilage of rats. When Per1 was downregulated or upregulated in mandibular condylar chondrocytes, the GSK3β/β-CATENIN pathway was inhibited or activated, and the expression of cartilage matrix-degrading enzymes decreased or increased, which can be rescued by activator and inhibitor of the GSK3β/β-CATENIN pathway. Moreover, after down-regulation of Per1 in mandibular condylar cartilage in vivo, significant alleviation of cartilage degradation, cartilage loss, subchondral bone loss induced by jet lag, and inhibition of the GSK3β/β-CATENIN signaling pathway were observed. Circadian rhythm disruption can lead to TMJOA. The clock gene Per1 can promote the occurrence of TMJOA by activating the GSK3β/β-CATENIN pathway and promoting the expression of cartilage matrix-degrading enzymes. The clock gene Per1 is a target for the prevention and treatment of TMJOA.

Selective REM sleep restriction in mice using a device designed for tunable somatosensory stimulation

BACKGROUND

Sleep perturbation is widely used to investigate the physiological mechanisms that mediate sleep-wake dynamics, and to isolate the specific roles of sleep in health and disease. However, state-of-the-art methods to accomplish sleep perturbation in preclinical models are limited in their throughput, flexibility, and specificity.

NEW METHOD

A system was developed to deliver vibro-tactile somatosensory stimulation aimed at controlled, selective sleep perturbation. The frequency and intensity of stimulation can be tuned to target a variety of experimental applications, from sudden arousal to sub-threshold transitions between light and deep stages of NREM sleep. This device was activated in closed-loop to selectively interrupt REM sleep in mice.

RESULTS

Vibro-tactile stimulation effectively and selectively interrupted REM sleep - significantly reducing the average REM bout duration relative to matched, unstimulated baseline recordings. As REM sleep was repeatedly interrupted, homeostatic mechanisms prompted a progressively quicker return to REM sleep. These effects were dependent on the parameters of stimulation applied.

COMPARISON WITH EXISTING METHODS

Existing sleep perturbation systems often require moving parts within the cage and/or restrictive housing. The system presented is unique in that it interrupts sleep without invading the animal's space. The ability to vary stimulation parameters is a great advantage over existing methods, as it allows for adaptation in response to habituation and/or circadian/homeostatic changes in arousal threshold.

CONCLUSIONS

The proposed method of stimulation demonstrates feasibility in affecting mouse sleep within a standard home cage environment, thus limiting environmental stress. Furthermore, the ability to tune frequency and intensity of stimulation allows for graded control over the extent of sleep perturbation, which potentially expands the utility of this technology beyond applications related to sleep.

Effects of electroacupuncture on the ventral tegmental area- nucleus accumbens dopamine pathway in rats with chronic sleep deprivation

BACKGROUND

Insomnia is a well-recognized clinical sleep disorder in the adult population. It has been established that acupuncture has a clinical effects in the treatment of insomnia; however, research on the underlying neural circuits involved in these effects is limited.

METHODS

The modified multiple platform method (MMPM) was used to establish a rat model of chronic sleep deprivation (CSD). Forty rats were randomly divided into a control (Con) group, (untreated) CSD group, electroacupuncture-treated CSD group (CSD + EA) and estazolam-treated CSD group (CSD + Estazolam group) with n = 10 per group. In the CSD + EA group, EA was delivered at Yintang and unilateral HT7 (left and right treated every other day) with continuous waves (2 Hz frequency) for 30 min/day over 7 consecutive days. In the CSD + Estazolam groups, estazolam was administered by oral gavage (0.1 mg/kg) for 7 consecutive days. The open field test (OFT) was used to observe behavioral changes. Immunofluorescence assays and enzyme-linked immunosorbent assay (ELISA) were used to observe the effects of EA on the ventral tegmental area (VTA)-nucleus accumbens (NAc) dopamine (DA) pathway. We also assessed the effects of EA on the expression of dopamine D1 receptor (D1R) and dopamine D2 receptor (D2R) in the NAc, which are the downstream targets of the VTA-NAc DA pathway.

RESULTS

After CSD was established by MMPM, rats exhibited increased autonomous activity and increased excitability of the VTA-NAc DA pathway, with increased VTA and NAc DA content, increased D1R expression and decreased D2R expression in the NAc. EA appeared to reduce the autonomous ability of CSD rats, leading to lower DA content in the VTA and NAc, reduced expression of D1R in the NAc and increased expression of D2R. Most importantly, EA produced effects similar to estazolam with respect to the general condition of rats with CSD and regulation of the VTA-NAc DA pathway.

CONCLUSIONS

The therapeutic effect of EA in chronic insomnia may be mediated by reduced excitability of the VTA-NAc DA pathway, with lower DA content in the VTA and NAc, downregulated expression of D1R in the NAc and increased expression of D2R.

Sleep deprivation disturbs uterine contractility and structure in pregnant rats: role of matrix metalloproteinase 9 and transforming growth factor-β

Sleep deprivation (SD) during pregnancy can impact the delivery procedure, with prolongation of the labor duration. Matrix metalloproteinase-9 (MMP9) and transforming growth factor-β (TGF-β) are regulators of uterine remodeling. Their dysregulation is vital for abnormal placentation and uterine enlargement in complicated pregnancies. Therefore, this study aims to explore the outcome of SD throughout pregnancy on ex vivo uterine contractility, MMP9 and TGF-β, and uterine microscopic structure. A total of 24 pregnant rats were divided into two groups. From the first day of pregnancy, animals were exposed to partial SD/6 h/day. Uterine in vitro contractile responses to oxytocin, acetylcholine, and nifedipine were assessed. Additionally, uterine levels of superoxide dismutase and malondialdehyde and uterine mRNA expression of MMP9, TGF-β, and apoptotic biomarkers were analyzed. The results showed that SD significantly reduced uterine contractile responses to oxytocin and acetylcholine, while it augmented the relaxing effect of nifedipine. In addition, it significantly increased oxidative stress status, MMP9, TGF-β, and apoptotic biomarkers' mRNA expression. All were accompanied by degeneration of endometrial glands, vacuolization with apoptotic nuclei, and increased area% of collagen fibers. Finally, increased uterine MMP9 and TGF-β mRNA expression during SD clarified their potential role in modulating uterine contractility and structure.

The degeneration-pain relationship in the temporomandibular joint: Current understandings and rodent models

Temporomandibular disorders (TMD) represent a group of musculoskeletal conditions involving the temporomandibular joints (TMJ), the masticatory muscles and associated structures. Painful TMD are highly prevalent and conditions afflict 4% of US adults annually. TMD include heterogenous musculoskeletal pain conditions, such as myalgia, arthralgia, and myofascial pain. A subpopulations of TMD patients show structural changes in TMJ, including disc displacement or degenerative joint diseases (DJD). DJD is a slowly progressing, degenerative disease of the TMJ characterized by cartilage degradation and subchondral bone remodeling. Patients with DJD often develop pain (TMJ osteoarthritis; TMJ OA), but do not always have pain (TMJ osteoarthrosis). Therefore, pain symptoms are not always associated with altered TMJ structures, which suggests that a causal relationship between TMJ degeneration and pain is unclear. Multiple animal models have been developed for determining altered joint structure and pain phenotypes in response to various TMJ injuries. Rodent models of TMJOA and pain include injections to induce inflammation or cartilage destruction, sustained opening of the oral cavity, surgical resection of the articular disc, transgenic approaches to knockout or overexpress key genes, and an integrative approach with superimposed emotional stress or comorbidities. In rodents, TMJ pain and degeneration occur during partially overlapping time periods in these models, which suggests that common biological factors may mediate TMJ pain and degeneration over different time courses. While substances such as intra-articular pro-inflammatory cytokines commonly cause pain and joint degeneration, it remains unclear whether pain or nociceptive activities are causally associated with structural degeneration of TMJ and whether structural degeneration of TMJ is necessary for producing persistent pain. A thorough understanding of the determining factors of pain-structure relationships of TMJ during the onset, progression, and chronification by adopting novel approaches and models should improve the ability to simultaneously treat TMJ pain and TMJ degeneration.

Importance of Bmal1 in Alzheimer's disease and associated aging-related diseases: Mechanisms and interventions

With the aging world population, the prevalence of aging-related disorders is on the rise. Diseases such as Alzheimer's, type 2 diabetes mellitus (T2DM), Parkinson's, atherosclerosis, hypertension, and osteoarthritis are age-related, and most of these diseases are comorbidities or risk factors for AD; however, our understandings of molecular events that regulate the occurrence of these diseases are still not fully understood. Brain and muscle Arnt-like protein-1 (Bmal1) is an irreplaceable clock gene that governs multiple important physiological processes. Continuous research of Bmal1 in AD and associated aging-related diseases is ongoing, and this review picks relevant studies on a detailed account of its role and mechanisms in these diseases. Oxidative stress and inflammation turned out to be common mechanisms by which Bmal1 deficiency promotes AD and associated aging-related diseases, and other Bmal1-dependent mechanisms remain to be identified. Promising therapeutic strategies involved in the regulation of Bmal1 are provided, including melatonin, natural compounds, metformin, d-Ser2-oxyntomodulin, and other interventions, such as exercise, time-restricted feeding, and adiponectin. The establishment of the signaling pathway network for Bmal1 in aging-related diseases will lead to advances in the comprehension of the molecular and cellular mechanisms, shedding light on novel treatments for aging-related diseases and promoting aging-associated brain health.

Effect of bone marrow mesenchymal stem cell transplantation combined with lugua polypeptide injection on osteoarthritis in rabbit knee joint

PURPOSE

This study aimed to elucidate the effect of bone marrow mesenchymal stem cell (BMSC) transplantation combined with the administration of Lugua polypeptide injection into the knee joint cavity to treat knee osteoarthritis (KOA) in rabbits.

MATERIAL AND METHODS

Sixty white New Zealand rabbits were randomly divided into the blank, model, Lugua polypeptide, BMSC, and combined (Lugua polypeptide plus BMSC) groups, with 12 rabbits in each group. The mRNA and protein expression levels of cyclin D1, bcl-2, TIMP-1, p21, caspase-3, Bax, MMP-1, MMP-13, TLR-4, and NF-κB p65 in chondrocytes, and levels of IL-1, NO, TNF-α, and IL-6 in the synovial fluid were compared.

RESULTS

The severity of cartilage damage in the combined group was significantly less (P <0.01). Compared to the MG, the mRNA and protein expression levels of cyclin D1, bcl-2 and TIMP-1 in chondrocytes of the three other groups were significantly increased, while those of p21, caspase-3, Bax, MMP-1, MMP-13, TLR-4, and NF-κB p65 in the chondrocytes and levels of IL-1, NO, TNF-α, and IL-6 in the synovial fluid of the three other groups were significantly reduced (P <0.05). The aforementioned indicators in the combined group were significantly better than those of the Lugua polypeptide and BMSCs groups (P <0.05).

CONCLUSIONS

BMSC transplantation combined with Lugua polypeptide injection may improve KOA-related cartilage tissue damage in rabbits.

Similarities and differences of estrogen in the regulation of temporomandibular joint osteoarthritis and knee osteoarthritis

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) and knee osteoarthritis (knee OA) are two kinds of common osteoarthritis (OA) that are characterized by chronic degeneration of soft and hard tissues around joints. Their gender and age differences suggest that there are similarities and differences between the pathogenic mechanisms of TMJOA and knee OA.

OBJECTIVE

To review recent studies on the effect of estrogen on TMJOA and knee OA, and summarize their possible pathogenesis and molecular mechanisms.

SOURCES

Articles up to present reporting the relationship of estrogen and TMJOA or knee OA are included. An extensive electronic search was conducted of databases including PubMed, Web of science core collection.

CONCLUSION

According to epidemiological investigations, TMJOA primarily happens to females of puberty and childbearing age, while knee OA mainly affects postmenopausal women. Epidemiological investigation and experimental research suggest that estrogen may have a different effect on TMJ and on knee. Though estrogen regulates TMJOA and knee OA via estrogen-related receptors (ERR), their pathogenesis and pathway of estrogen regulation are different. To find out the accurate regulation of estrogen on TMJOA and knee OA, specific pathways and molecular mechanisms still need further exploration.

Cardioprotective effects of acute sleep deprivation on ischemia/reperfusion injury

OBJECTIVES

Modulation of sympathetic activity during acute sleep deprivation can produce various effects on body functions. We studied the effects of acute sleep deprivation before ischemia/reperfusion on myocardial injury in isolated rat hearts, and the role of sympathetic nervous system that may mediate these sleep deprivation induced effects.

METHODS

The animals were randomized into four groups (n = 11 per group): Ischemia- Reperfusion group (IR), Acute sleep deprivation group (SD), Control group for sleep deprivation (CON-SD) and Sympathectomy + ASD group (SYM-SD). In SD group, sleep deprivation paradigm was used 24 h prior to induction of ischemia/reperfusion. In SYM-SD group, the animals were chemically sympathectomized using 6-hydroxydopamine, 24 h before sleep deprivation. Then, the hearts of animals were perfused using Langendorff setup and were subjected to 30 min regional ischemia followed by 60 min of reperfusion. Throughout the experiment, the hearts were allowed to beat spontaneously and left ventricular developed pressure (LVDP) and rate pressure product (RPP) were recorded. At the end of study, infarct size and percentage of the area at risk were determined.

RESULTS

We found that SD increased LVDP and RPP, while reducing the myocardial infarct size. Moreover, sympathectomy reversed SD induced reduction in infarct size and showed no differences as compared to IR.

CONCLUSION

This study shows cardioprotective effects of acute sleep deprivation, which can be abolished by chemical sympathectomy in isolated hearts of rats.

Circadian Rhythm Protein Bmal1 Modulates Cartilage Gene Expression in Temporomandibular Joint Osteoarthritis via the MAPK/ERK Pathway

The purpose of this study was to elucidate the role of the circadian gene Bmal1 in human cartilage and its crosstalk with the MAPK/ERK signaling pathway in temporomandibular joint osteoarthritis (TMJ-OA). We verified the periodical variation of the circadian gene Bmal1 and then established a modified multiple platform method (MMPM) to induce circadian rhythm disturbance leading to TMJ-OA. IL-6, p-ERK, and Bmal1 mRNA and protein expression levels were assessed by real-time RT-PCR and immunohistochemistry. Chondrocytes were treated with an ERK inhibitor (U0126), siRNA and plasmid targeting Bmal1 under IL-6 simulation; then, the cells were subjected to Western blotting to analyze the relationship between Bmal1 and the MAPK/ERK pathway. We found that sleep rhythm disturbance can downregulate the circadian gene BMAL-1 and improve phosphorylated ERK (p-ERK) and IL-6 levels. Furthermore, Bmal1 siRNA transfection was sufficient to improve the p-ERK level and aggravate OA-like gene expression changes under IL-6 stimulation. Bmal1 overexpression relieved the alterations induced by IL-6, which was consistent with the effect of U0126 (an ERK inhibitor). However, we also found that BMAL1 upregulation can decrease ERK phosphorylation, whereas ERK downregulation did not change BMAL1 expression. Collectively, this study provides new insight into the regulatory mechanism that links chondrocyte BMAL1 to cartilage maintenance and repair in TMJ-OA via the MAPK/ERK pathway and suggests that circadian rhythm disruption is a risk factor for TMJ-OA.

Low-Intensity Pulsed Ultrasound Alleviates Hypoxia-Induced Chondrocyte Damage in Temporomandibular Disorders by Modulating the Hypoxia-Inducible Factor Pathway

Temporomandibular disorders are a common cause of chronic pain in the orofacial region and have a complex and multi-factorial pathophysiology. Mechanical loading or inflammatory conditions have been shown to decrease oxygen tension within the joint cartilage and activate the hypoxia-inducible factor (HIF) pathway, which in turn aggravates the pathological processes underlying temporomandibular joint (TMJ) disorders. We previously showed that low-intensity pulsed ultrasound (LIPUS) treatment effectively repairs TMJ injury induced by chronic sleep deprivation (CSD). Here, we explored the effects of LIPUS treatment on hypoxia-induced chondrocyte injury. We found that it effectively restored the proliferation capacity of mandibular chondrocytes under hypoxic conditions and lowered their rate of apoptosis. Chondrogenic capacity, as assessed by type II collagen levels, and mucin-positive areas were also significantly increased after LIPUS treatment. Levels of matrix metalloprotein-3 and interleukin-6 decreased in mandibular chondrocytes following this treatment, whereas the expression of tissue inhibitor of metalloproteinase-1 increased. We also found that HIF-1α expression was upregulated in mandibular chondrocytes under hypoxic conditions and was further enhanced by LIPUS treatment. Similarly, HIF-2α levels increased in mandibular chondrocytes under hypoxic conditions but decreased following LIPUS treatment. Subsequently, we established a CSD-induced TMJ injury model and found that LIPUS increased mucin-positive areas as well as HIF-1α expression and decreased HIF-2 level in the chondrocyte layer. Together, our results indicate that the protective effect of LIPUS on chondrocyte is partly associated with the HIF pathway.

The Optimal Regimen for the Treatment of Temporomandibular Joint Injury Using Low-Intensity Pulsed Ultrasound in Rats with Chronic Sleep Deprivation

Low-intensity pulsed ultrasound (LIPUS) is an emerging physical therapy for the treatment of early temporomandibular joint injury and has a good effect on promoting cartilage and subchondral bone tissue repair. However, the best LIPUS intensity and treatment duration remain unclear. This study is aimed at observing the preventive and therapeutic effects of different modes of LIPUS and at identifying the optimal LIPUS treatment regimen for temporomandibular joint injury. In the present study, rat models of temporomandibular joint injury were established using a chronic sleep deprivation (CSD) method, and the effect of LIPUS as intensities of 30, 45, and 60 mW/cm² was observed at 7, 14, and 21 days. After CSD, the condylar cartilage of the rats demonstrated variable degrees of surface roughening, collagen fiber disarrangement or even partial exfoliation, decreased proteoglycan synthesis and cartilage thickness, decreased chondrocyte proliferation, decreased type 2 collagen (COL-2) expression, and increased matrix metalloproteinase- (MMP-) 3 expression at all three time points. When the rats with CSD received different intensities of LIPUS treatment, the pathological changes were alleviated to various extents. The groups receiving 45 mW/cm² LIPUS showed the most significant relief of cartilage damage, and this significant effect was observed on days 14 and 21. These results demonstrated that LIPUS can effectively inhibit CSD-induced condylar cartilage damage in rats, and LIPUS treatment at an intensity of 45 mW/cm² for at least 2 weeks is the optimal regimen for temporomandibular joint injury.

Sleep deprivation and stress: a reciprocal relationship

Sleep is highly conserved across evolution, suggesting vital biological functions that are yet to be fully understood. Animals and humans experiencing partial sleep restriction usually exhibit detrimental physiological responses, while total and prolonged sleep loss could lead to death. The perturbation of sleep homeostasis is usually accompanied by an increase in hypothalamic–pituitary–adrenal (HPA) axis activity, leading to a rise in circulating levels of stress hormones (e.g. cortisol in humans, corticosterone in rodents). Such hormones follow a circadian release pattern under undisturbed conditions and participate in the regulation of sleep. The investigation of the consequences of sleep deprivation, from molecular changes to behavioural alterations, has been used to study the fundamental functions of sleep. However, the reciprocal relationship between sleep and the activity of the HPA axis is problematic when investigating sleep using traditional sleep-deprivation protocols that can induce stress per se. This is especially true in studies using rodents in which sleep deprivation is achieved by exogenous, and potentially stressful, sensory–motor stimulations that can undoubtedly confuse their conclusions. While more research is needed to explore the mechanisms underlying sleep loss and health, avoiding stress as a confounding factor in sleep-deprivation studies is therefore crucial. This review examines the evidence of the intricate links between sleep and stress in the context of experimental sleep deprivation, and proposes a more sophisticated research framework for sleep-deprivation procedures that could benefit from recent progress in biotechnological tools for precise neuromodulation, such as chemogenetics and optogenetics, as well as improved automated real-time sleep-scoring algorithms.

Estrogen-Related Receptor γ Induces Angiogenesis and Extracellular Matrix Degradation of Temporomandibular Joint Osteoarthritis in Rats

The main causes of cartilage destruction during temporomandibular joint osteoarthritis (TMJOA) are extracellular matrix degradation and angiogenesis, accompanied by an increased level of matrix-degrading enzymes and proangiogenic factors. Interleukin 6 and extracellular signal–regulated kinase (ERK) signaling pathways may play a critical role in these two processes simultaneously, but researchers have not clearly determined the mechanism. We hypothesized that estrogen-related receptor γ (ERRγ) is involved in both cartilage degeneration and angiogenesis in TMJOA. The interactions between ERRγ and the Mmp9 and Vegfa promoter regions were investigated using a chromatin immunoprecipitation (ChIP) assay. A chick embryo chorioallantoic membrane (CAM) assay was performed to investigate the inhibitory effects of U0126 and GSK5182 on angiogenesis. Western blotting, reverse transcription–quantitative PCR (RT-qPCR), immunofluorescence staining, toluidine blue staining, and transfection with cDNAs or small interfering RNAs (siRNAs) were performed on primary mandibular condylar chondrocytes (MCCs). Unilateral anterior crossbite–induced TMJOA models were established in rats, and Western blotting, RT-qPCR, immunohistochemistry, and Safranin O-Fast Green staining were performed to evaluate changes in vivo. ERK1/2 activated matrix metalloproteinase 9 (MMP9) and vascular endothelial growth factor A (VEGFA), which are involved in cartilage destruction, through ERRγ. Based on the ChIP assay results, ERRγ directly activated the transcription of the Mmp9 and Vegfa genes. In chick embryo CAM models, U0126 and GSK5182 significantly inhibited angiogenesis. In conclusion, ERRγ is a downstream transcription factor of ERK1/2, and its upregulation leads to extracellular matrix degradation and angiogenesis in TMJOA. This study identified a common factor between inflammation and vascularization in OA as well as a new therapeutic target for OA: ERRγ.

Trehalose enhances bone fracture healing in a rat sleep deprivation model

Background

The purpose of this study was to investigate whether sleep deprivation (SD) could delay bone fracture healing and evaluate the therapeutic effect of trehalose.

Methods

Eighteen 300-350 g female Sprague-Dawley rats were created a mid-femoral transverse osteotomy in the right thigh and divided into three groups (i.e., group 1: fracture; group 2: fracture + SD; and group 3: fracture + SD + trehalose). Seven days after surgery, the rats in group 2 and group 3 were started to get sleep-deprived for 18 h per day for 3 weeks. The rats in group 3 were injected with trehalose intraperitoneally at 1 g/kg/d for 3 weeks. Radiological and histological analyses were used to assess fracture healing quality. Circulating cytokines were detected by the end of the study. The expression of M1 and M2 macrophage markers were measured by quantitative real-time polymerase chain reaction (qPCR).

Results

X-rays showed group 2 experienced much poorer fracture healing. Micro CT demonstrated that the bone quality of the fracture callus site in group 2 was much worse than that in groups 1 and 3. Both haematoxylin eosin (H&E) and Masson staining revealed that the bone fracture of the group 2 healed worse. Elisa results demonstrated that the interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) of the rats in group 2 were significantly higher. In vitro study showed that 100 mM trehalose enhanced the expression of M2 macrophage markers (Arg-1 and IL-10), and decreased M1 macrophage polarization through the decreasing expression of IL-6.

Conclusions

The present study showed (SD) could delay bone fracture healing in a rat model. And, trehalose could promote the healing of delayed bone fracture union by down-regulating pro-inflammatory mediators and enhancing M2 polarization.

Therapeutic effect of low-intensity pulsed ultrasound on temporomandibular joint injury induced by chronic sleep deprivation in rats

Low-intensity pulsed ultrasound (LIPUS) treatment is an emerging physical therapy for treating bone, nerve, and muscle disorders. However, there have been no reports on the effectiveness of LIPUS for the treatment of temporomandibular joint injury, and the mechanisms of LIPUS remain unclear. The purpose of this study was to examine the therapeutic effects of LIPUS on temporomandibular joint injury in rats subjected to chronic sleep deprivation (CSD). In this study, after 2 weeks of chronic sleep deprivation in rats, the condylar cartilage exhibited rough surfaces, with a disorganized arrangement and partial sloughing of collagen fibers, decreased proliferation of chondrocytes, increased osteoclast activity in the calcified cartilage layer, and increased ratios of MMP-3/TIMP-1 and RANKL/OPG expression. After 4 weeks of LIPUS intervention in rats, the condylar cartilage displayed prominent reductions in these pathological changes, including noticeable repair of the injured cartilage structure, increased chondrocyte proliferation, a reduced number of osteoclasts, and marked reductions in the expression ratios of MMP-3/TIMP-1 and RANKL/OPG. These results demonstrated that LIPUS can effectively inhibit CSD-induced injury to condylar cartilage in rats. The therapeutic mechanism of LIPUS may involve promoting the repair function of chondrocytes and reducing the expression ratios of MMP-3/TIMP-1 and RANKL/OPG in condylar tissue, thus inhibiting the cleavage activity of MMP-3 on the condylar cartilage matrix and inhibiting osteoclast activation.

HIF-1-VEGF-Notch mediates angiogenesis in temporomandibular joint osteoarthritis

Angiogenesis has been reported participated in temporomandibular joint osteoarthritis (TMJ-OA). While the pathogenesis is unclear, recent studies indicate that hypoxia is important in TMJ-OA. In order to induce osteoarthritis-like lesions in mandibular condyles, rats were sleep deprived experimentally. An increased number of blood vessels were observed in the rats' condyles of SD and SR group compared with controls. Protein and mRNA levels of related factors including VEGF, HIF-1 and Notch were investigated by means of immunohistochemical staining, western blot and real-time PCR, which were highly expressed in the TMJ-OA rats. Furthermore, Cell test was designed to study effects of hypoxia on condylar chondrocytes. We found the expression of VEGF, HIF-1 and Notch were significantly increased in hypoxia group, indicating that HIF-1-Notch-VEGF signaling pathway were activated by hypoxia. The inhibitors of HIF-1 and Notch could suppress the expression of HIF-1, VEGF, Notch, suggesting the HIF-1-VEGF-Notch signaling pathway were bidirectional. Together, hypoxia played an important role in TMJ-OA and accelerates angiogenesis of condylar cartilage through HIF-1-VEGF-Notch signaling pathway. HIF-1α and Notch might be novel therapeutic targets in TMJ-OA.

Association between sleeping time and temporomandibular disorders in a sample of the South Korean population

Objective: This study investigated the relationship between sleeping time and temporomandibular disorders (TMDs).Methods: This study used data from the Fifth Korea National Health and Nutrition Examination Survey from 2010 to 2011. The final sample size consisted of 11,782 adults aged ≥19 years. Logistic regression analysis was performed to assess the relationship between sleeping time and TMD.Results: The adjusted odds ratios of the TMD group were 1.421 (1.067, 1.892) (Model 1), 1.388 (1.028, 1.873) (Model 2), and 1.360 (1.012, 1.826) (Model 3) for subjects with sleeping time ≤5 hours (p < 0.05) and 1.317 (0.992, 1.748) (Model 1), 1.358 (1.01, 1.827) (Model 2), and 1.352 (0.977, 1.872) (Model 3) for subjects with sleeping time ≥9 hours (p < 0.05).Conclusion: Sleeping time ≤5 hours and ≥9 hours were associated with an increased rate of TMD.

Sleep and Orofacial Pain

Sleep and pain share a bidirectional relationship. Therefore, it is important for practitioners managing patients experiencing either sleep and/or pain issues to recognize and understand this complex association from a neurobiological perspective involving neuroanatomic and neurochemical processes. Accounting for the influence of pain on the various aspects of sleep and understanding its impact on various orofacial pain disorders assists in developing a prudent management approach. Screening for sleep disorders benefits practitioners in identifying these individuals. Instituting evidence-based multidisciplinary management strategies using both behavioral and pharmacologic strategies enhances the delivery of appropriate care.

Cellular and Molecular Mechanisms of REM Sleep Homeostatic Drive: A Plausible Component for Behavioral Plasticity

Homeostatic regulation of REM sleep drive, as measured by an increase in the number of REM sleep transitions, plays a key role in neuronal and behavioral plasticity (i.e., learning and memory). Deficits in REM sleep homeostatic drive (RSHD) are implicated in the development of many neuropsychiatric disorders. Yet, the cellular and molecular mechanisms underlying this RSHD remain to be incomplete. To further our understanding of this mechanism, the current study was performed on freely moving rats to test a hypothesis that a positive interaction between extracellular-signal-regulated kinase 1 and 2 (ERK1/2) activity and brain-derived neurotrophic factor (BDNF) signaling in the pedunculopontine tegmentum (PPT) is a causal factor for the development of RSHD. Behavioral results of this study demonstrated that a short period (<90 min) of selective REM sleep restriction (RSR) exhibited a strong RSHD. Molecular analyses revealed that this increased RSHD increased phosphorylation and activation of ERK1/2 and BDNF expression in the PPT. Additionally, pharmacological results demonstrated that the application of the ERK1/2 activation inhibitor U0126 into the PPT prevented RSHD and suppressed BDNF expression in the PPT. These results, for the first time, suggest that the positive interaction between ERK1/2 and BDNF in the PPT is a casual factor for the development of RSHD. These findings provide a novel direction in understanding how RSHD-associated specific molecular changes can facilitate neuronal plasticity and memory processing.

VEGF promotes cartilage angiogenesis by phospho-ERK1/2 activation of Dll4 signaling in temporomandibular joint osteoarthritis caused by chronic sleep disturbance in Wistar rats

Chronic sleep disturbance (CSD) has been linked to the development of temporomandibular joint osteoarthritis (TMJ-OA). While the pathogenesis of TMJ-OA is unclear, recent studies indicate that osteochondral angiogenesis is important. We developed a rat model of CSD induced TMJ-OA to investigate the changes caused by sleep disturbance and to correlate them with vascular invasion in the TMJ. We found pathological alterations and an increased microvessel density in the rat TMJ following CSD. VEGF, Dll4 and p-ERK1/2, the expression of angiogenic factors, were highly expressed in the rat mandibular condylar cartilage and their expression increased with CSD. Furthermore, we show that VEGF-induce activation of ERK1/2, which in turn, increases Dll4 expression. Together, our results suggest that CSD can cause OA-like pathological alterations in the rat TMJ by increasing angiogenesis.

Lipo‑prostaglandin E1 modifies cognitive impairment in rats with vascular cognitive impairment by promoting angiogenesis via the VEGF/VEGFR pathway

The pathological mechanism of vascular cognitive impairment (VCI) involves ischemic lesions in the hippocampus. Prostaglandin E1 (PGE1) serves roles in the promotion of vascular endothelial growth factor (VEGF) expression, angiogenesis and enhances blood flow to ischemic regions. However, the effect of PGE1 on cognitive function in VCI rats and the underlying mechanism are unknown. In the current study, learning and memory function in VCI rats treated by lipo-PGE1 injection was assessed through Morris Water Maze test. Furthermore, the histological alterations, blood vessel numbers in the hippocampal CA1 region and relative VEGF protein and mRNA expression were researched. The results confirmed that VCI rats treated with lipo-PGE1 presented improved cognitive function, less neuronal cell loss, a greater number of blood vessels in the hippocampal region and higher VEGF protein and mRNA expression. However, the role of lipo-PGE1 in VCI rats can be inhibited by SU5416 (a specific VEGFR2 antagonist). The results indicated that lipo-PGE1 may alleviate cognitive deficits in VCI rats. The underlying mechanism may be associated with angiogenesis promoted by lipo-PGE1, which may involve the VEGF/VEGFR pathway. These findings may have therapeutic implications for cognitive impairment induced by hypoperfusion or chronic ischemic lesions.

Osteopontin stimulates matrix metalloproteinase expression through the nuclear factor-κB signaling pathway in rat temporomandibular joint and condylar chondrocytes

BACKGROUND

To examine the possible regulatory mechanisms of osteopontin (OPN) and the nuclear factor-κB (NF-κB) signaling pathway in the temporomandibular joint (TMJ) of rats subjected to chronic sleep deprivation (CSD).

METHODS

Rats were subjected to CSD using the modified multiple platform method. The histomorphology of the TMJ was observed by hematoxylin-eosin staining. OPN and NF-κB/p65 expression were detected by immunohistochemical and immunofluorescence staining together with western blotting. The condylar chondrocytes were isolated from the rat TMJ and treated with recombinant OPN (r-OPN) before detection for the expression of NF-κB/p65 and matrix metalloproteinases (MMPs). Western blotting and reverse transcription-polymerase chain reaction were performed to determine the expression of MMP-1, MMP-3, MMP-9, and MMP-13 in the TMJ and chondrocytes respectively.

RESULTS

There was a statistically significant difference in OPN and NF-κB/p65 expression between the CSD group and control (CON) group. OPN and NF-κB/p65 expression was increased in the CSD group as compared with in the CON group. NF-κB/p65 expression was significantly increased by r-OPN treatment in the chondrocytes. Furthermore, MMP-1, MMP-3, MMP-9, and MMP-13 production was also remarkably elevated in the CSD group as well as in the chondrocytes. Treatment with 1 μg/ml r-OPN for 48 h led to the highest production of inflammatory cytokines in chondrocytes.

CONCLUSIONS

CSD causes pathological alterations in the TMJ. OPN treatment activates the NF-κB signaling pathway and stimulates MMPs in the TMJ and condylar chondrocytes through NF-κB signaling pathway. Chondrocytes treated with 1 μg/ml r-OPN for 48 h produced the highest level of inflammatory cytokines.

Post-infarct sleep disruption and its relation to cardiac remodeling in a rat model of myocardial infarction

Sleep disruption after myocardial infarction (MI) by affecting ubiquitin-proteasome system (UPS) is thought to contribute to myocardial remodeling and progressive worsening of cardiac function. The aim of current study was to test the hypothesis about the increased risk of developing heart failure due to experience of sleep restriction (SR) after MI. Male Wistar rats (n = 40) were randomly assigned to four experimental groups: (1) Sham, (2) MI, (3) MI and SR (MI + SR) (4) Sham and SR (Sham + SR). MI was induced by permanent ligation of left anterior descending coronary artery. Twenty-four hours after surgery, animals were subjected to chronic SR paradigm. Blood sampling was performed at days 1, 8 and 21 after MI for determination of serum levels of creatine kinase-MB (CK-MB), corticosterone, malondialdehyde (MDA) and nitric oxide (NO). Finally, at 21 days after MI, echocardiographic parameters and expression of MuRF1, MaFBx, A20, eNOS, iNOS and NF-kB in the heart were evaluated. We used H&E staining to detect myocardial hypertrophy. We found out that post infarct SR increased corticosterone levels. Our results highlighted deteriorating effects of post-MI SR on NO production, oxidative stress, and echocardiographic indexes (p < 0.05). Moreover, its detrimental effects on myocardial damage were confirmed by overexpression of MuRF1, MaFBx, iNOS and NF-kB (p < 0.001) in left ventricle and downregulation of A20 and eNOS (p < 0.05). Furthermore, histological examination revealed that experience of SR after MI increased myocardial diameter as compared to Sham subjects (p < 0.05). Our data suggest that SR after MI leads to an enlargement of the heart within 21 days, marked by an increase in oxidative stress and NO production as well as an imbalance in UPS that ultimately results in cardiac dysfunction and heart failure.

Effects of chronic sleep deprivation on bone mass and bone metabolism in rats

BACKGROUND

This study aimed to assess the effects of chronic sleep deprivation (CSD) on bone mass and bone metabolism in rats.

METHODS

Twenty-four rats were randomly divided into CSD and control (CON) groups. Rats were subjected to CSD by using the modified multiple platform method (MMPM) to establish an animal model of CSD. Biochemical parameters such as levels of serum N-terminal propeptide of type I procollagen (PINP), N-terminal cross-linking telopeptide of type I collagen (NTX), growth hormone (GH), estradiol (E2), serum 25(OH)D, and calcium (Ca) were evaluated at 0, 1, 2, and 3 months. After 3 months, each fourth lumbar vertebra and the distal femoral metaphysis of the left extremity of rats were harvested for micro-computed tomography scans and histological analysis, respectively, after the rats were sacrificed under an overdose of pentobarbital sodium.

RESULTS

Compared with rats from the CON group, rats from the CSD group showed significant decreases in bone mineral density (BMD), bone volume over total volume, trabecular bone thickness, and trabecular bone number and significant increases in bone surface area over bone volume and trabecular bone separations (P < 0.05). Bone histomorphology studies showed that rats in the CSD group had decreased osteogenesis, impaired mineralization of newly formed bones, and deteriorative trabecular bone in the secondary spongiosa zone. In addition, they showed significantly decreased levels of serum PINP (1 month later) and NTX (3 months later) (P < 0.05). The serum 25(OH)D level of rats from the CSD group was lower than that of rats from the CON group after 1 month (P < 0.05).

CONCLUSIONS

CSD markedly affects bone health by decreasing BMD and 25(OH)D, deteriorating the bone microarchitecture, and decreasing bone formation and bone resorption markers.

Effects of chronic sleep deprivation on glucose homeostasis in rats

Epidemiological studies have shown that chronic sleep disturbances resulted in metabolic disorders. The purpose of this study was to assess the relationship between chronic sleep deprivation (CSD) and the glucose homeostasis in rats. Twenty-four rats were randomly divided into CSD group and control (CON) group. The CSD rats were intervened by a modified multiple platform method (MMPM) to establish an animal model of chronic sleep disturbances. After 3-month intervention, all rats were subjected to an intraperitoneal glucose tolerance test (IPGTT) and an insulin tolerance test (ITT), and the body weight, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatinine, lipid profile group, and homeostasis model assessment-IR (HOMA-IR) were measured. Both the CSD and CON groups had an attenuation of weight gain after 3-month intervention. The plasma glucose level of CSD group was higher than that of the CON group during the IPGTT (P < 0.01). The CSD rats showed a marked increase in HOMA-IR and ITT compared with the CON group (P < 0.01). There were no significant differences of AST, ALT, creatinine, and most lipid parameters between the CSD and CON groups (P > 0.05). The CSD has a marked effect on glucose homeostasis, comprising glucose intolerance and insulin resistance.

Effect of p38 Mitogen Activated Protein Kinase Inhibitor on Temporomandibular Joint Synovitis Induced by Occlusal Alteration

PURPOSE

To investigate the alteration in rat temporomandibular joint (TMJ) synovial membrane induced by increased occlusal vertical dimension (iOVD) and to determine whether the p38 mitogen activated protein kinase (MAPK) signaling cascade is involved.

MATERIALS AND METHODS

Thirty-six rats were randomly divided into 3 groups: control + normal saline (NS; controls), iOVD + NS, and iOVD + SB203580 (a potent p38 MAPK inhibitor). Morphologic changes of synovial tissues were observed and scored. Activation levels of p38 MAPK and activating transcription factor-2 (ATF2) were detected by immunohistochemistry. Expression levels of interleukin-1β (IL-1β) and matrix metalloproteinase-3 (MMP-3) were measured by quantitative real-time polymerase chain reaction and immunohistochemistry.

RESULTS

Obvious synovitis was found in the iOVD group. P38 and ATF2 were activated, and mRNA and protein expression levels of IL-1β and MMP-3 were upregulated after iOVD. However, decreased synovial tissue inflammation and lower mRNA and protein levels of IL-1β and MMP-3 were observed in the iOVD + SB203580 group.

CONCLUSION

iOVD can induce temporomandibular joint synovitis, and the p38 MAPK signaling cascade might participate in and aggravate the process of articular inflammation.