Low-intensity pulsed ultrasound delays the progression of osteoarthritis by regulating the YAP-RIPK1-NF-κB axis and influencing autophagy.

BACKGROUND: Osteoarthritis (OA) is a degenerative disease characterized by chronic inflammation of the joint. As the disease progresses, patients will gradually develop symptoms such as pain, physical limitations and even disability. The risk factors for OA include genetics, gender, trauma, obesity, and age. Unfortunately, due to limited understanding of its pathological mechanism, there are currently no effective drugs or treatments to suspend the progression of osteoarthritis. In recent years, some studies found that low-intensity pulsed ultrasound (LIPUS) may have a positive effect on osteoarthritis. Nonetheless, the exact mechanism by which LIPUS affects osteoarthritis remains unknown. It is valuable to explore the specific mechanism of LIPUS in the treatment of OA. METHODS: In this study, we validated the potential therapeutic effect of LIPUS on osteoarthritis by regulating the YAP-RIPK1-NF-κB axis at both cellular and animal levels. To verify the effect of YAP on OA, the expression of YAP was knocked down or overexpressed by siRNA and plasmid in chondrocytes and adeno-associated virus was injected into the knee joint of rats. The effect of LIPUS was investigated in inflammation chondrocytes induced by IL-1ß and in the post-traumatic OA model. RESULTS: In this study, we observed that YAP plays an important role in the development of osteoarthritis and knocking down of YAP significantly inhibited the inflammation and alleviated cartilage degeneration. We also demonstrated that the expression of YAP was increased in osteoarthritis chondrocytes and YAP could interact with RIPK1, thereby regulating the NF-κB signal pathway and influencing inflammation. Moreover, we also discovered that LIPUS decreased the expression of YAP by restoring the impaired autophagy capacity and inhibiting the binding between YAP and RIPK1, thereby delaying the progression of osteoarthritis. Animal experiment showed that LIPUS could inhibit cartilage degeneration and alleviate the progression of OA. CONCLUSIONS: These results showed that LIPUS is effective in inhibiting inflammation and cartilage degeneration and alleviate the progression of OA. As a result, our results provide new insight of mechanism by which LIPUS delays the development of osteoarthritis, offering a novel therapeutic regimen for osteoarthritis.

Exercise-induced modulation of myokine irisin on muscle-bone unit in the rat model of post-traumatic osteoarthritis.

BACKGROUND AND AIM: Post-traumatic osteoarthritis (PTOA) is a subtype of osteoarthritis (OA). Exercise may produce and release the myokine irisin through muscle fiber contraction. However, the effect of exercise-promoted irisin production on the internal interactions of the muscle-bone unit in PTOA studies remains unclear. METHODS: Eighteen 8-week-old Sprague-Dawley (SD) rats were randomly divided into three groups: Sham/sedentary (Sham/Sed), PTOA/sedentary (PTOA/Sed), and PTOA/treadmill-walking (PTOA/TW). The PTOA model was established by transection of anterior cruciate ligament (ACLT) and destabilization of medial meniscus (DMM). After 4 weeks of modeling, the PTOA/TW group underwent treadmill exercise (15 m/min, 30 min/d, 5 d/ week, 8 weeks), and the other two groups were free to move in the cage. Evaluation and correlation analysis of muscle, cartilage, subchondral bone and serological indexes were performed after euthanasia. RESULTS: Eight weeks of treadmill exercise effectively alleviated the trauma-induced OA phenotype, thereby maintaining cartilage and subchondral bone integrity in PTOA, and reducing quadriceps atrophy and myofibril degradation. Exercise reversed the down-regulated expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) and fibronectin type III structural domain protein 5 (FNDC5) in muscle tissue of PTOA rats, and increased the blood irisin level, and the irisin level was positively correlated with the expression of PGC-1α and FNDC5. In addition, correlation analysis showed that irisin metabolism level was strongly negatively correlated with Osteoarthritis Research Society International (OARSI) and subchondral bone loss, indicating that irisin may be involved in cartilage biology and PTOA-related changes in cartilage and subchondral bone. Moreover, the metabolic level of irisin was strongly negatively correlated with muscle fiber cross-sectional area (CSA), Atrogin-1 and muscle ring-finger protein-1(MuRF-1) expression, suggesting that irisin may alleviate muscle atrophy through autocrine action. CONCLUSION: Treadmill exercise can alleviate the atrophy and degeneration of muscle fibers in PTOA rats, reduce the degradation of muscle fibrin, promote the expression of serum irisin, and alleviate the degeneration of articular cartilage and subchondral bone loss in PTOA rats. These results indicate that treadmill exercise can affect the process of PTOA by promoting the expression of myokine irisin in rat muscle-bone unit.

Moderate mechanical strain and exercise reduce inflammation and excessive autophagy in osteoarthritis by downregulating mitofusin 2.

AIMS: The major pathological mechanisms of osteoarthritis (OA) progression include inflammation, autophagy, and apoptosis, etc. Moderate mechanical strain and exercise effectively improve chondrocyte degeneration by reducing these adverse factors. Mitofusin 2 (MFN2) is a crucial regulatory factor associated with inflammation, autophagy and apoptosis, and its expression is regulated by exercise. This study aims to elucidate the effects of moderate mechanical strain and exercise on MFN2 expression and its influence on OA progression. MAIN METHODS: Destabilization of the medial meniscus (DMM) surgery was performed on rats to induce an OA rat model. Subsequently, adeno-associated virus (overexpression/knockdown) intra-articular injection or moderate treadmill exercise was administered to evaluate the effects of these treatments on MFN2 expression and OA progression. Overexpressed plasmids and siRNA vectors were used to regulate MFN2 expression in chondrocytes. An inflammatory degeneration cell model was generated by IL-1ß stimulation. Moderate mechanical strain was applied to MFN2-overexpressing cells to explore their interactions. KEY FINDINGS: MFN2 overexpression aggravated inflammation by activating the NF-κB and P38 pathways and induced excessive autophagy by inhibiting the PI3K/AKT/mTOR pathway, thereby causing chondrocyte apoptosis and metabolic disorder. Moderate mechanical strain partially reversed these adverse effects. In the DMM rat model, MFN2 overexpression in articular cartilage exacerbated OA progression, whereas MFN2 knockdown and treadmill exercise alleviated cartilage degeneration, inflammation, and mechanical pain. SIGNIFICANCE: MFN2 is a critical factor mediating the association between inflammation and excessive autophagy in OA progression. Moderate mechanical strain and treadmill exercise may improve OA through downregulating MFN2 expression. This study may provide a theoretical basis for exercise therapy in OA treatment.

Injectable photocrosslinking spherical hydrogel-encapsulated targeting peptide-modified engineered exosomes for osteoarthritis therapy.

Osteoarthritis (OA) is a common degenerative joint disease urgently needing effective treatments. Bone marrow mesenchymal stromal cell-derived exosomes (Exo) are considered good drug carriers whereas they have limitations such as fast clearance and low retention. This study aimed to overcome the limitations of Exo in drug delivery using multiple strategies. Novel photocrosslinking spherical gelatin methacryloyl hydrogel (GelMA)-encapsulated cartilage affinity WYRGRL (W) peptide-modified engineered Exo were developed for OA treatment and the performance of the engineered Exo (W-Exo@GelMA) loaded with a small inhibitor LRRK2-IN-1 (W-Exo-L@GelMA) was investigated in vitro and in vivo. The W-Exo-L@GelMA showed an effective targeting effect on chondrocytes and a pronounced action on suppressing catabolism and promoting anabolism in vitro. Moreover, W-Exo-L@GelMA remarkably inhibited OA-related inflammation and immune gene expression, rescuing the IL-1ß-induced transcriptomic responses. With enhanced retention in the joint, W-Exo-L@GelMA demonstrated superior anti-OA activity and cartilage repair ability in the OA murine model. The therapeutic effect was validated in the cultured human OA cartilage. In conclusion, photocrosslinking spherical hydrogel-encapsulated targeting peptide-modified engineered Exo exhibit notable potential in OA therapy. Engineering Exo by a series of strategies enhanced the targeting ability and retention and cartilage-targeting and Exo-mediated drug delivery may offer a novel strategy for OA treatment.Clinical trial registration: Not applciable.

[Correlation between miR-21, miR-191 and Clinical Stage of Patients with Diffuse Large B-Cell Lymphoma].

OBJECTIVE: To analyze the relationship between microRNA (miR)-21, miR-191 and clinical stage of patients with diffuse large B-cell lymphoma (DLBCL). METHODS: 100 patients with DLBCL treated in Shanxi Fenyang Hospital from January 2019 to January 2021 were selected as the research subjects. All patients was divided into stage I, stage II, stage III and stage IV according to Ann-Arbor (Cotswolds) staging system at admission. The baseline data of patients at different clinical stages were counted and compared in detail. The relationship between the levels of miR-21 and miR-191 and the clinical stage of DLBCL patients was mainly analyzed. RESULTS: Among the 100 patients with DLBCL, there were 15 patients at stage I, 25 patients at stage II, 37 patients at stage III and 23 patients at stage IV. The levels of miR-21 and miR-191 in patients at stage Ⅰ, Ⅱ, Ⅲ and Ⅳ were increased gradually, which showed statistically significant differences (P<0.05). According to Kendall's tau-b correlation analysis, it was found that the levels of miR-21 and miR-191 were positively correlated with the clinical stage of DLBCL patients (r=0.566, 0.636). Multiple logistic regression analysis showed that the overexpression of serum miR-21 and miR-191 was a risk factor for high clinical stage in patients with DLBCL (OR>1, P<0.05). Bivariate Pearson correlation analysis showed that there was a positive correlation between miR-21 and miR-191 levels in patients with DLBCL (r=0.339). CONCLUSION: The overexpression of miR-21 and miR-191 in patients with DLBCL is related to high clinical stage.

Bone Deterioration in Response to Chronic High-Altitude Hypoxia Is Attenuated by a Pulsed Electromagnetic Field Via the Primary Cilium/HIF-1α Axis.

Chronic high-altitude hypoxia induces irreversible abnormalities in various organisms. Emerging evidence indicates that hypobaric hypoxia markedly suppresses bone mass and bone strength. However, few effective means have been identified to prevent such bone deficits. Here, we assessed the potential of pulsed electromagnetic fields (PEMFs) to noninvasively resist bone deterioration induced by hypobaric hypoxia. We observed that exogenous PEMF treatment at 15 Hz and 20 Gauss (Gs) improved the cancellous and cortical bone mass, bone microstructure, and skeletal mechano-properties in rats subjected to chronic exposure of hypobaric hypoxia simulating an altitude of 4500 m for 6 weeks by primarily modulating osteoblasts and osteoblast-mediated bone-forming activity. Moreover, our results showed that whereas PEMF stimulated the functional activity of primary osteoblasts in hypoxic culture in vitro, it had negligible effects on osteoclasts and osteocytes exposed to hypoxia. Mechanistically, the primary cilium was found to function as the major electromagnetic sensor in osteoblasts exposed to hypoxia. The polycystins PC-1/PC-2 complex was identified as the primary calcium channel in the primary cilium of hypoxia-exposed osteoblastic cells responsible for the detection of external PEMF signals, and thereby translated these biophysical signals into intracellular biochemical events involving significant increase in the intracellular soluble adenylyl cyclase (sAC) expression and subsequent elevation of cyclic adenosine monophosphate (cAMP) concentration. The second messenger cAMP inhibited the transcription of oxygen homeostasis-related hypoxia-inducible factor 1-alpha (HIF-1α), and thus enhanced osteoblast differentiation and improved bone phenotype. Overall, the present study not only advances our understanding of bone physiology at high altitudes, but more importantly, proposes effective means to ameliorate high altitude-induced bone loss in a noninvasive and cost-effective manner. © 2023 American Society for Bone and Mineral Research (ASBMR).

Swine wastewater treatment by combined process of iron carbon microelectrolysis-physical adsorption-microalgae cultivation.

Combined treatments were designed based on iron-carbon micro-electrolysis treatment (ICME), physical adsorption (PA) with zeolite (Z) or vermiculite (V) and microalgae cultivation (MC, Chlorella vulgaris) for removing pollutants from swine wastewater (SW): ICME + MC (IM), ICME + Z + MC (IZM) and ICME + V + MC (IVM). Results showed that the minimum total nitrogen (TN) of 43.66 mg L-1, NH4+-N of 1.33 mg-1 and total phosphorus (TP) of 0.14 mg-1 were obtained by IVM, while the minimum chemical oxygen demand (COD) was 105 mg-1 via IM. During the process of combined treatments, ICME contributed most to the removal of TN (84.52% by IZM), TP (97.78% by IVM and IZM) and COD (62.44% by IVM), and maximum NH4+-N removal (55.64%) was obtained by MC procedure in IM process. Vermiculite performed better than zeolite during all the combined treatments. Besides, the maximum cell dry weight (CDW, 0.74 g-1) of C. vulgaris was obtained by IM on day 13. The results provide an efficient integrated method for swine wastewater treatment.

[Effects of Magnolol combined with Gefitinib on A549 non-small cell lung cancer cells].

Objective: To investigate the synergistic effects of magnolol and gefitinib on non-small cell lung cancer A549 cells. Methods: A549 cells were treated with Magnolol (6.25～500 µmol/L) or gefitinib (6.25～500 µmol/L) for 24 h, respectively, and the cell viability was detected by cell counting Kit-8 (CCK-8) experiment (n=3). Magnolol 100 µmol/L and gefitinib 5 µmol/L were selected in the following experiments (n=3, 24 h). Control group, magnolol group, gefitinib group and magnolol+gefitinib group were set up for factorial analysis. Colony formation experiment was applied to detect the cell proliferation. Western blot was used to detect protein expressions. Flow cytometry was applied to test cell apoptosis and sorting CD44+ and CD133+ cells. Results: Compared with the control group, the colony formation rate of Magnolol or Gefitinib groups was decreased significantly (P＜0.05); the apoptosis rate was increased significantly (P＜0.05); the number of CD44+ and CD133+ cells was reduced significantly (P＜0.05); the expressions of Ki67, PCNA, and stem cell marker proteins SOX2 and OCT4 were down-regulated (P＜0.05); and the ratio of Bax/Bcl-2 was increased significantly (P＜0.05). Compared with the Magnolol group or Gefitinib group, the Magnolol+Gefitinib group further promoted the above changes (P＜0.05), and the apoptosis rate, the ratio of Bax/Bcl-2, SOX2 and OCT4 all showed interactions between magnolol and gefitinib (P＜0.05). Conclusion: Magnolol and gefitinib promote the apoptosis of A549 cells and inhibit its stem cell-like properties, and the effect of the two combined is better than separated administration. Magnolol and gefitinib have interactive effects on A549 cells.

Radiotherapy-induced bone deterioration is exacerbated in diabetic rats treated with streptozotocin.

Following radiotherapy, patients have decreased bone mass and increased risk of fragility fractures. Diabetes mellitus (DM) is also reported to have detrimental effects on bone architecture and quality. However, no clinical or experimental study has systematically characterized the bone phenotype of the diabetic patients following radiotherapy. After one month of streptozotocin injection, three-month-old male rats were subjected to focal radiotherapy (8 Gy, twice, at days 1 and 3), and then bone mass, microarchitecture, and turnover as well as bone cell activities were evaluated at 2 months post-irradiation. Micro-computed tomography results demonstrated that DM rats exhibited greater deterioration in trabecular bone mass and microarchitecture following irradiation compared with the damage to bone structure induced by DM or radiotherapy. The serum biochemical, bone histomorphometric, and gene expression assays revealed that DM combined with radiotherapy showed lower bone formation rate, osteoblast number on bone surface, and expression of osteoblast-related markers (ALP, Runx2, Osx, and Col-1) compared with DM or irradiation alone. DM plus irradiation also caused higher bone resorption rate, osteoclast number on bone surface, and expression of osteoclast-specific markers (TRAP, cathepsin K, and calcitonin receptor) than DM or irradiation treatment alone. Moreover, lower osteocyte survival and higher expression of Sost and DKK1 genes (two negative modulators of Wnt signaling) were observed in rats with combined DM and radiotherapy. Together, these findings revealed a higher deterioration of the diabetic skeleton following radiotherapy, and emphasized the clinical importance of health maintenance.

Effects of body weight-supported treadmill training on cartilage-subchondral bone unit in the rat model of posttraumatic osteoarthritis.

Posttraumatic osteoarthritis (PTOA) is a subset of osteoarthritis (OA) resulting from the integrated outcome of joint injury, accounting for more than 12% of the overall OA cases. Although current therapies restore joint kinematics and alleviate inflammation, more than 20% patients undergo the unexpected progression of PTOA. Exercise is widely recommended to patients with OA and treadmill training is effective in preventing osteoarthritic changes in PTOA animals. However, the understanding gap of modified treadmill exercise models with different exercise dose and loading weight still exists. To evaluate the effects of body weight-supported treadmill training on PTOA, 30 rats were divided into the sham group (n = 6) and the PTOA group (n = 24) which were further assigned into three subgroups including the sedentary, the treadmill walking (TW), and the body weight-supported treadmill training (BWSTT) groups. The training groups were subjected to 4-week treadmill training at the speed of 15 m/min for 30 min/d, 5 d/wk. Then the tibias were elevated by histological staining, immunohistochemical staining, and micro-computed tomography. In our results, the significant OA-relevant changes in cartilage-subchondral bone unit were observed in the PTOA groups after surgery, characterized by cartilage degradation and subchondral bone remodeling. After 4-week treadmill training, the OA-relevant changes in cartilage-subchondral bone unit were alleviated and BWSTT is more efficient to maintain cartilage integrity and attenuate the subchondral bone loss and remodeling than TW. In conclusion, BWSTT is a promising and favorable treatment of PTOA slowing down the development of PTOA by reprogramming the cartilage-subchondral unit.

Radiotherapy-induced bone deterioration is exacerbated in diabetic rats treated with streptozotocin

Following radiotherapy, patients have decreased bone mass and increased risk of fragility fractures. Diabetes mellitus (DM) is also reported to have detrimental effects on bone architecture and quality. However, no clinical or experimental study has systematically characterized the bone phenotype of the diabetic patients following radiotherapy. After one month of streptozotocin injection, three-month-old male rats were subjected to focal radiotherapy (8 Gy, twice, at days 1 and 3), and then bone mass, microarchitecture, and turnover as well as bone cell activities were evaluated at 2 months post-irradiation. Micro-computed tomography results demonstrated that DM rats exhibited greater deterioration in trabecular bone mass and microarchitecture following irradiation compared with the damage to bone structure induced by DM or radiotherapy. The serum biochemical, bone histomorphometric, and gene expression assays revealed that DM combined with radiotherapy showed lower bone formation rate, osteoblast number on bone surface, and expression of osteoblast-related markers (ALP, Runx2, Osx, and Col-1) compared with DM or irradiation alone. DM plus irradiation also caused higher bone resorption rate, osteoclast number on bone surface, and expression of osteoclast-specific markers (TRAP, cathepsin K, and calcitonin receptor) than DM or irradiation treatment alone. Moreover, lower osteocyte survival and higher expression of Sost and DKK1 genes (two negative modulators of Wnt signaling) were observed in rats with combined DM and radiotherapy. Together, these findings revealed a higher deterioration of the diabetic skeleton following radiotherapy, and emphasized the clinical importance of health maintenance.

Programmable Chemotherapy and Immunotherapy against Breast Cancer Guided by Multiplexed Fluorescence Imaging in the Second Near-Infrared Window.

Combined chemotherapy and immunotherapy have demonstrated great potential in cancer treatment. However, it is difficult to provide clear information of the pharmacokinetics and pharmacodynamics of chemodrugs and transplanted immune cells in vivo by traditional approaches, resulting in inadequate therapy. Here, a multiplexed intravital imaging strategy by using fluorescence in the second near-infrared window (NIR-II) is first developed to visualize the two events of chemotherapy and immunotherapy in vivo, so that a combinational administration is programed to improve the therapeutical effects against a mouse model of human breast cancer. In detail, Ag2 Se quantum dots (QDs) (λEm = 1350 nm) loaded with stromal-cell-derived factor-1α (SDF-1α) and chemodrug doxorubicin (DOX) are first administrated to deliver the SDF-1α and DOX to the tumor site. After their arrival, monitored by Ag2 Se QD fluorescence, natural killer (NK)-92 cells labeled with Ag2 S QDs (λEm = 1050 nm) are intravenously injected so that the cells are recruited to the tumor by the chemotaxis of SDF-1α, which is visualized by Ag2 S QD fluorescence. Such an imaging approach allows simultaneous evaluation of the behaviors of individual injections in vivo, and facilitates optimized administration regimens, resulting in enhanced tumor inhibition.

A miR-125b/CSF1-CX3CL1/tumor-associated macrophage recruitment axis controls testicular germ cell tumor growth.

Tumor growth is modulated by crosstalk between cancer cells and the tumor microenvironment. Recent advances have shown that miRNA dysfunction in tumor cells can modulate the tumor microenvironment to indirectly determine their progression. However, this process is poorly understood in testicular germ cell tumors (TGCTs). We reported here that miR-125b was repressed in TGCT samples by epigenetic modifications rather than genetic alternations. Furthermore, miR-125b overexpression significantly alleviated the tumor growth in two NCCIT human embryonic carcinoma xenograft models in vivo, whereas miR-125b did not stimulate autonomous tumor cell growth in vitro. Notably, forced expression of miR-125b in NCCIT embryonic carcinoma cells decreased the abundance of host tumor-associated macrophages (TAMs) within tumor microenvironment. Selective deletion of host macrophages by clodronate abolished the anti-tumoral ability of miR-125b in xenograft models. By RNA profiling, Western blot and luciferase reporter assay, we further observed that miR-125b directly regulated tumor cell-derived chemokine CSF1 and CX3CL1, which are known to control the recruitment of TAMs to tumor sites. Lastly, we found that one set of miRNAs, which are under the regulation of miR-125b, might convergently target CSF1/CX3CL1 in NCCIT cells using miRNA profiling. These findings uncover the anticancer effect of miR-125b via mediating tumor-stroma crosstalk in xenograft models of TGCTs and raise the possibility of targeting miR-125b as miRNA therapeutics.

Merotelic kinetochore attachment in oocyte meiosis II causes sister chromatids segregation errors in aged mice.

Mammalian oocyte chromosomes undergo 2 meiotic divisions to generate haploid gametes. The frequency of chromosome segregation errors during meiosis I increase with age. However, little attention has been paid to the question of how aging affects sister chromatid segregation during oocyte meiosis II. More importantly, how aneuploid metaphase II (MII) oocytes from aged mice evade the spindle assembly checkpoint (SAC) mechanism to complete later meiosis II to form aneuploid embryos remains unknown. Here, we report that MII oocytes from naturally aged mice exhibited substantial errors in chromosome arrangement and configuration compared with young MII oocytes. Interestingly, these errors in aged oocytes had no impact on anaphase II onset and completion as well as 2-cell formation after parthenogenetic activation. Further study found that merotelic kinetochore attachment occurred more frequently and could stabilize the kinetochore-microtubule interaction to ensure SAC inactivation and anaphase II onset in aged MII oocytes. This orientation could persist largely during anaphase II in aged oocytes, leading to severe chromosome lagging and trailing as well as delay of anaphase II completion. Therefore, merotelic kinetochore attachment in oocyte meiosis II exacerbates age-related genetic instability and is a key source of age-dependent embryo aneuploidy and dysplasia.

Selective deletion of Smad4 in postnatal germ cells does not affect spermatogenesis or fertility in mice.

SMAD4 is the central component of canonical signaling in the transforming growth factor beta (TGFß) superfamily. Loss of Smad4 in Sertoli cells affects the expansion of the fetal testis cords, whereas selective deletion of Smad4 in Leydig cells alone does not appreciably alter fetal or adult testis development. Loss of Smad4 in Sertoli and Leydig cells, on the other hand, leads to testicular dysgenesis, and tumor formation in mice. Within the murine testes, Smad4 is also expressed in germ cells of the seminiferous tubules. We therefore, crossed Ngn3-Cre or Stra8-Cre transgenic mice with Smad4-flox mice to generate conditional knockout animals in which Smad4 was specifically deleted in postnatal germ cells to further uncover cell type-specific requirement of Smad4. Unexpectedly, these germ-cell-knockout mice were fertile and did not exhibit any detectable abnormalities in spermatogenesis, indicating that Smad4 is not required for the production of sperm; instead, these data indicate a cell type-specific requirement of Smad4 primarily during testis development. Mol. Reprod. Dev. 83: 615-623, 2016. © 2016 Wiley Periodicals, Inc.

Androgen receptor in Sertoli cells regulates DNA double-strand break repair and chromosomal synapsis of spermatocytes partially through intercellular EGF-EGFR signaling.

Spermatogenesis does not progress beyond the pachytene stages of meiosis in Sertoli cell-specific AR knockout (SCARKO) mice. However, further evidence of meiotic arrest and underlying paracrine signals in SCARKO testes is still lacking. We utilized co-immunostaining of meiotic surface spreads to examine the key events during meiotic prophase I. SCARKO spermatocytes exhibited a failure in chromosomal synapsis observed by SCP1/SCP3 double-staining and CREST foci quantification. In addition, DNA double-strand breaks (DSBs) were formed but were not repaired in the mutant spermatocytes, as revealed by γ-H2AX staining and DNA-dependent protein kinase (DNA-PK) activity examination. The later stages of DSB repair, such as the accumulation of the RAD51 strand exchange protein and the localization of mismatch repair protein MLH1, were correspondingly altered in SCARKO spermatocytes. Notably, the expression of factors that guide RAD51 loading onto sites of DSBs, including TEX15, BRCA1/2 and PALB2, was severely impaired when either AR was down-regulated or EGF was up-regulated. We observed that some ligands in the epidermal growth factor (EGF) family were over-expressed in SCARKO Sertoli cells and that some receptors in the EGF receptor (EGFR) family were ectopically activated in the mutant spermatocytes. When EGF-EGFR signaling was repressed to approximately normal by the specific inhibitor AG1478 in the cultured SCARKO testis tissues, the arrested meiosis was partially rescued, and functional haploid cells were generated. Based on these data, we propose that AR in Sertoli cells regulates DSB repair and chromosomal synapsis of spermatocytes partially through proper intercellular EGF-EGFR signaling.