Single-cell RNA sequencing analysis reveals the relationship of bone marrow and osteopenia in STZ-induced type 1 diabetic mice.

INTRODUCTION: Type 1 diabetes (T1D) is a multifactorial autoimmune disease. Broad knowledge about the genetics, epidemiology and clinical management of T1D has been achieved, but understandings about the cell varieties in the bone marrow during T1D remain limited. OBJECTIVES: We aimed to present a profile of the bone marrow cells and reveal the relationship of bone marrow and osteopenia in streptozotocin (STZ)-induced T1D mice. METHODS: The whole bone marrow cells from the femurs and tibias of healthy (group C) and STZ-induced T1D mice (group D) were collected for single-cell RNA sequencing analysis. Single-cell flow cytometry and immunohistochemistry were performed to confirm the proportional changes among bone marrow neutrophils (BM-neutrophils) (Cxcr2+, Ly6g+) and B lymphocytes (Cd19+). X-ray and micro-CT were performed to detect bone mineral density. The correlation between the ratio of BM-neutrophils/B lymphocytes and osteopenia in STZ-induced T1D mice was analyzed by nonparametric Spearman correlation analysis. RESULTS: The bone marrow cells in groups C and D were divided into 12 clusters, and 249 differentially expressed genes were found. The diversity of CD45+ immune cells between groups C and D were greatly affected: the proportion of BM-neutrophils showed a significant increase while the proportion of B lymphocytes in group D showed a significant decrease. X-ray and micro-CT analyses confirmed that osteopenia occurred in group D mice. In addition, the results of single-cell flow cytometry and correlation analysis showed that the ratio of BM-neutrophils/B lymphocytes negatively correlated with osteopenia in STZ-induced T1D mice. CONCLUSION: A single-cell RNA sequencing analysis revealed the profile and heterogeneity of bone marrow immune cells in STZ-induced T1D mice for the first time. The ratio of BM-neutrophils/B lymphocytes negatively correlated with osteopenia in STZ-induced T1D mice, which may enhance understanding for treating T1D and preventing T1D-induced osteopenia.

Macrophages induce cardiomyocyte ferroptosis via mitochondrial transfer.

INTRODUCTION: Mitochondrial transfer is a new cell-to-cell communication manner. Whether the mitochondrial transfer is also involved in the macrophage infiltration-induced cardiac injury is unclear. OBJECTIVES: This study aimed to determine whether macrophage mitochondria can be transferred to cardiomyocytes, and to investigate its possible role and mechanism. METHODS: Mitochondrial transfer between macrophages and cardiomyocytes was detected using immunofluorescence staining and flow cytometry. Cellular metabolites were analyzed using LC-MS technique. Differentially expressed mRNAs were identified using RNA-seq technique. RESULTS: (1) After cardiomyocytes were cultured with macrophage-conditioned medium (COND + group), macrophage-derived mitochondria have been found in cardiomyocytes, which could be blocked by dynasore (an inhibitor of clathrin-mediated endocytosis). (2) Compared with control (CM) group, there were 545 altered metabolites found in COND + group, most of which were lipids and lipid-like molecules. The altered metabolites were mainly enriched in the ß-oxidation of fatty acids and glutathione metabolism. And there were 4824 differentially expressed mRNAs, which were highly enriched in processes like lipid metabolism-associated pathway. (3) Both RNA-seq and qRT-PCR results found that ferroptosis-related mRNAs such as Ptgs2 and Acsl4 increased, and Gpx4 mRNA decreased in COND + group (P < 0.05 vs CM group). (4) The levels of cellular free Fe2+ and mitochondrial lipid peroxidation were increased; while GSH/GSSG ratio, mitochondrial aspect ratio, mitochondrial membrane potential, and ATP production were decreased in cardiomyocytes of COND + group (P < 0.05 vs CM group). All the above phenomena could be blocked by a ferroptosis inhibitor ferrostatin-1 (P < 0.05). CONCLUSION: Macrophages could transfer mitochondria to cardiomyocytes. Macrophage-derived mitochondria were internalized into cardiomyocytes through clathrin- and/or lipid raft-mediated endocytosis. Uptake of exogenous macrophage mitochondria induced cardiomyocyte injury via triggering ferroptosis.

Resveratrol suppresses microglial activation and promotes functional recovery of traumatic spinal cord via improving intestinal microbiota.

Spinal cord injury (SCI) can change the intestinal microbiota pattern and corresponding metabolites, which in turn affect the prognosis of SCI. Among many metabolites, short-chain fatty acids (SCFAs) are critical for neurological recovery after SCI. Recent research has shown that resveratrol exerts anti-inflammatory properties. But it is unknown if the anti-inflammatory properties of resveratrol are associated with intestinal microbiota and metabolites. We thus investigate the alteration in gut microbiota and the consequent change of SCFAs following resveratrol treatment. The SCI mouse models with retention of gut microbiota (donor) and depletion of gut microbiota (recipient) were established. Fecal microbiota transplantation from donors to recipients was performed with intragastrical administration. Spinal cord tissues of mice were examined by H&E, Nissl, and immunofluorescence stainings. The expressions of the inflammatory profile were examined by qPCR and cytometric bead array. Fecal samples of mice were collected and analyzed with 16S rRNA sequencing. The results showed that resveratrol inhibited the microglial activation and promoted the functional recovery of SCI. The analysis of intestinal microbiota and metabolites indicated that SCI caused dysbiosis and the decrease in butyrate, while resveratrol restored microbiota pattern, reversed intestinal dysbiosis, and increased the concentration of butyrate. Both fecal supernatants from resveratrol-treated donors and butyrate suppressed the expression of pro-inflammatory genes in BV2 microglia. Our result demonstrated that fecal microbiota transplantation from resveratrol-treated donors had beneficial effects on the functional recovery of SCI. One mechanism of resveratrol effects was to restore the disrupted gut microbiota and butyrate.

Single-cell transcriptome analysis reveals the immune heterogeneity and the repopulation of microglia by Hif1α in mice after spinal cord injury.

Neuroinflammation is regarded as a vital pathological process in spinal cord injury (SCI), which removes damaged tissue, secretes cytokines, and facilitates regeneration. Repopulation of microglia has been shown to favor recovery from SCI. However, the origin and regulatory factors of microglia repopulation after SCI remain unknown. Here, we used single-cell RNA sequencing to portray the dynamic transcriptional landscape of immune cells during the early and late phases of SCI in mice. B cells and migDCs, located in the meninges under physiological conditions, are involved in immune surveillance. Microglia quickly reduced, and peripheral myeloid cells infiltrated three days-post-injury (dpi). At 14 dpi, microglia repopulated, myeloid cells were reduced, and lymphocytes infiltrated. Importantly, genetic lineage tracing of nestin+ and Cx3cr1+ cells in vivo showed that the repopulation of microglia was derived from residual microglia after SCI. We found that residual microglia regress to a developmental growth state in the early stages after SCI. Hif1α promotes microglial proliferation. Conditional ablation of Hif1α in microglia causes larger lesion sizes, fewer axon fibers, and impaired functional recovery in the late stages after SCI. Our results mapped the immune heterogeneity in SCI and raised the possibility that targeting Hif1α may help in axon regeneration and functional recovery after SCI.

MCC950 Reduces Neuronal Apoptosis in Spinal Cord Injury in Mice.

BACKGROUND: Traumatic Spinal Cord Injury (SCI) is a severe condition usually accompanied by an inflammatory process that gives rise to uncontrolled local apoptosis and a subsequent unfavorable prognosis. One reason for this unfavorable outcome could be the activation of the NLRP3 inflammasome. OBJECTIVE: MCC950 is a specific inhibitor of NLRP3 that further inhibits the formation of the NLRP3 inflammasome. The purpose of this study was to determine whether the NLRP3 inflammasome was associated with the severity of local apoptosis and whether MCC950 could prevent neuronal apoptosis following SCI. METHODS: In this study, primary cortical neurons were cultured in vitro. With or without pretreatment/ posttreatment with MCC950, neurons were subjected to Oxygen-Glucose Deprivation (OGD) for 2 h and then reperfusion for 20 h. Immunofluorescence was used to determine the expression of NLRP3, ASC, and cleaved caspase-1 in neurons. In vivo, SCI model mice were established with a 5 g weight-drop method. MCC950 was intraperitoneally injected at 0, 2, 4, 6, 8, 10, and 12 days after SCI. Basso Mouse Scale (BMS) scores and footprint assays were used to assess motor function. Paw withdrawal threshold and tail-flick latency were used to assess somatosensory function. H&E, Nissl, and TUNEL staining were used to measure histological changes and apoptosis at 3 days after SCI, and scar formation was observed by Masson staining and GFAP immunohistochemical analysis at 28 days after SCI. RESULTS: Immunofluorescence analysis confirmed that MCC950 inhibited OGD-induced activation of the NLRP3 inflammasome in neurons. Behavioral tests, Masson staining, and GFAP immunohistochemical analysis showed that MCC950-treated mice had improved neuronal functional recovery and reduced scar formation at 28 days after SCI. H&E, Nissl, and TUNEL staining confirmed that there were more living neurons and fewer apoptotic neurons in MCC950-treated mice than control mice at 3 days after SCI. CONCLUSION: These results reveal that MCC950 exerts neuroprotective effects by reducing neuronal apoptosis, preserving the survival of the remaining neurons, attenuating the severity of the damage, and promoting the recovery of motor function after SCI.

Mitochondrial Unfolded Protein Response and Its Roles in Stem Cells.

The mitochondrial unfolded protein response (UPRmt) is a mitochondrial protein quality control mechanism that is involved in many pathophysiological activities and maintains cellular homeostasis. The UPRmt signaling pathway in both Caenorhabditis elegans and mammals has gained much attention in recent years. Many studies have reported the general function of UPRmt, including the relationship between UPRmt and longevity, survival, apoptosis, innate immunity, cancer growth, and neurodegenerative diseases. Stem cells are capable of self-renewing and differentiating, thus playing an important role in maintaining tissue homeostasis and tissue regeneration. Although the role and regulation of UPRmt in somatic cells have been widely studied, the regulatory mechanism of UPRmt in stem cells is not fully known. Thus, in this article, the regulatory role of UPRmt in stem cell proliferation, cellular differentiation, and aging is reviewed. This review aims to provide novel insights for UPRmt promoting stem cell rejuvenation and improving life span in mammals.