MFN1 and MFN2 Are Dispensable for Sperm Development and Functions in Mice

MFN1 (Mitofusin 1) and MFN2 (Mitofusin 2) are GTPases essential for mitochondrial fusion. Published studies revealed crucial roles of both Mitofusins during embryonic development. Despite the unique mitochondrial organization in sperm flagella, the biological requirement in sperm development and functions remain undefined. Here, using sperm-specific Cre drivers, we show that either Mfn1 or Mfn2 knockout in haploid germ cells does not affect male fertility. The Mfn1 and Mfn2 double knockout mice were further analyzed. We found no differences in testis morphology and weight between Mfn-deficient mice and their wild-type littermate controls. Spermatogenesis was normal in Mfn double knockout mice, in which properly developed TRA98+ germ cells, SYCP3+ spermatocytes, and TNP1+ spermatids/spermatozoa were detected in seminiferous tubules, indicating that sperm formation was not disrupted upon MFN deficiency. Collectively, our findings reveal that both MFN1 and MFN2 are dispensable for sperm development and functions in mice.

Sex Differences in Behavior and Molecular Pathology in the 5XFAD Model

Background: The prevalence of Alzheimer’s disease (AD) is greater in women compared to men, but the reasons for this remain unknown. This sex difference has been widely neglected in experimental studies using transgenic mouse models of AD. Objective: Here, we studied behavior and molecular pathology of 5-month-old 5XFAD mice, which express mutated human amyloid precursor protein and presenilin-1 on a C57BL/6J background, versus their wild-type littermate controls, to compared both sex- and genotype-dependent differences. Methods: A novel behavioral paradigm was utilized (OF-NO-SI), comprising activity measures (Open Field, OF) arena, followed by Novel Object exploration (NO) and Social Interaction (SI) of a sex-matched conspecific. Each segment consisted of two repeated trials to assess between-trial habituation. Subsequently, brain pathology (amyloid load, stress response and inflammation markers, synaptic integrity, trophic support) was assessed using qPCR and western blotting. Results: Female 5XFAD mice had higher levels of human APP and amyloid-β and heightened inflammation versus males. These markers correlated with hyperactivity observed in both sexes, yet only female 5XFAD mice presented with deficits in object and social exploration. Male animals had higher expression of stress markers and neurotrophic factors irrespective of genotype, this correlated with cognitive performance. Conclusion: The impact of sex on AD-relevant phenotypes is in line with human data and emphasizes the necessity of appropriate study design and reporting. Differential molecular profiles observed in male versus female mice offer insights into possible protective mechanisms, and hence treatment strategies.

Müller glial responses compensate for degenerating photoreceptors in retinitis pigmentosa

Photoreceptor degeneration caused by genetic defects leads to retinitis pigmentosa, a rare disease typically diagnosed in adolescents and young adults. In most cases, rod loss occurs first, followed by cone loss as well as altered function in cells connected to photoreceptors directly or indirectly. There remains a gap in our understanding of retinal cellular responses to photoreceptor abnormalities. Here, we utilized single-cell transcriptomics to investigate cellular responses in each major retinal cell type in retinitis pigmentosa model (P23H) mice vs. wild-type littermate mice. We found a significant decrease in the expression of genes associated with phototransduction, the inner/outer segment, photoreceptor cell cilium, and photoreceptor development in both rod and cone clusters, in line with the structural changes seen with immunohistochemistry. Accompanying this loss was a significant decrease in the expression of genes involved in metabolic pathways and energy production in both rods and cones. We found that in the Müller glia/astrocyte cluster, there was a significant increase in gene expression in pathways involving photoreceptor maintenance, while concomitant decreases were observed in rods and cones. Additionally, the expression of genes involved in mitochondrial localization and transport was increased in the Müller glia/astrocyte cluster. The Müller glial compensatory increase in the expression of genes downregulated in photoreceptors suggests that Müller glia adapt their transcriptome to support photoreceptors and could be thought of as general therapeutic targets to protect against retinal degeneration.

The GhsrQ343X allele favors the storage of fat by acting on nutrient partitioning

The Growth Hormone Secretagogue Receptor (GHSR) mediates key properties of the gut hormone ghrelin on metabolism and behavior. Nevertheless, most recent observations also support that the GHSR is a constitutively active G protein-coupled receptor endowed of a sophisticated tuning involving a balance of endogenous ligands. Demonstrating the feasibility of shifting GHSR canonical signaling in vivo, we previously reported that a model with enhanced sensitivity to ghrelin (GhsrQ343X mutant rats) developed fat accumulation and glucose intolerance. Herein, we investigated the contribution of energy homeostasis to the onset of this phenotype, as well as behavioral responses to feeding or pharmacological challenges, by comparing GhsrM/M rats to wild-type littermate rats 1) as freely behaving animals and 2) in feeding and locomotor paradigms. Herein, GhsrM/M rats showed enhanced locomotor response to a GHSR agonist while locomotor or anorexigenic responses to amphetamine or cabergoline (dopamine receptor 2 agonist), respectively, were preserved. Ad libitum fed GhsrM/M rats consumed and conditioned for sucrose similarly to littermate control rats. In calorie-restricted conditions, GhsrM/M rats retained food anticipatory activity and maintained better their body weight and glycemia. Importantly, prior to fat accumulation, male GhsrM/M rats preferentially used carbohydrates as fuel substrate without alterations of energy intake, energy expenditure or physical activity and showed alterations of the GHSR system (i.e. enhanced ratio of GHSR hormones LEAP2:acyl-ghrelin and increased Ghsr expression in the hypothalamus). Overall, the present study provides proof of concept that shifted GHSR signaling can specifically alter nutrient partitioning resulting in modified balance of carbohydrate/lipid utilization.

Hematopoietic upstream stimulating factor 1 deficiency is associated with increased atherosclerosis susceptibility in LDL receptor knockout mice

Total body upstream stimulatory factor 1 (USF1) deficiency in mice is associated with brown adipose tissue activation and a marked protection against the development of obesity and atherosclerotic lesions. Functional expression of USF1 has also been detected in monocytes and monocyte-derived macrophages. In the current study we therefore tested whether selective hematopoietic USF1 deficiency can also beneficially impact the development of atherosclerosis. For this purpose, LDL receptor knockout mice were transplanted with bone marrow from USF1 knockout mice or their wild-type littermate controls and subsequently fed a Western-type diet for 20 weeks to stimulate atherosclerotic lesion development. Strikingly, absence of USF1 function in bone marrow-derived cells was associated with exacerbated blood leukocyte (+ 100%; P < 0.01) and peritoneal leukocyte (+ 50%; P < 0.05) lipid loading and an increased atherosclerosis susceptibility (+ 31%; P < 0.05). These effects could be attributed to aggravated hyperlipidemia, i.e. higher plasma free cholesterol (+ 33%; P < 0.001) and cholesteryl esters (+ 39%; P < 0.001), and the development of hepatosteatosis. In conclusion, we have shown that hematopoietic USF1 deficiency is associated with an increased atherosclerosis susceptibility in LDL receptor knockout mice. These findings argue against a contribution of macrophage-specific USF1 deficiency to the previously described beneficial effect of total body USF1 deficiency on atherosclerosis susceptibility in mice.

DJ-1 inhibits microglial activation and protects dopaminergic neurons in vitro and in vivo through interacting with microglial p65

Parkinson’s disease (PD), one of the most common neurodegenerative disorders, is characterized by progressive neurodegeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). DJ-1 acts essential roles in neuronal protection and anti-neuroinflammatory response, and its loss of function is tightly associated with a familial recessive form of PD. However, the molecular mechanism of DJ-1 involved in neuroinflammation is largely unclear. Here, we found that wild-type DJ-1, rather than the pathogenic L166P mutant DJ-1, directly binds to the subunit p65 of nuclear factor-κB (NF-κB) in the cytoplasm, and loss of DJ-1 promotes p65 nuclear translocation by facilitating the dissociation between p65 and NF-κB inhibitor α (IκBα). DJ-1 knockout (DJ-1−/−) mice exhibit more microglial activation compared with wild-type littermate controls, especially in response to lipopolysaccharide (LPS) treatment. In cellular models, knockdown of DJ-1 significantly upregulates the gene expression and increases the release of LPS-treated inflammatory cytokines in primary microglia and BV2 cells. Furthermore, DJ-1 deficiency in microglia significantly enhances the neuronal toxicity in response to LPS stimulus. In addition, pharmacological blockage of NF-κB nuclear translocation by SN-50 prevents microglial activation and alleviates the damage of DA neurons induced by microglial DJ-1 deficiency in vivo and in vitro. Thus, our data illustrate a novel mechanism by which DJ-1 facilitates the interaction between IκBα and p65 by binding to p65 in microglia, and thus repressing microglial activation and exhibiting the protection of DA neurons from neuroinflammation-mediated injury in PD.

Neutrophil Elastase-Regulated Macrophage Sheddome/ Secretome and Phagocytic Failure

Patients with cystic fibrosis (CF) have defective macrophage phagocytosis and efferocytosis. Several reports demonstrate that neutrophil elastase (NE) a major inflammatory protease in the CF airway, impairs macrophage phagocytic function. To date, NE-impaired macrophage phagocytic function has been attributed to cleavage of cell surface receptors or opsonins. We applied an unbiased proteomic approach to identify other potential macrophage targets of NE protease activity that may regulate phagocytic function. Using the murine macrophage cell line, RAW 264.7, human blood monocyte derived macrophages, and primary alveolar macrophages from Cftr-null and wild-type littermate mice, we demonstrated that NE exposure blocked phagocytosis of E. coli bio-particles. We performed LC-MS/MS proteomic analysis of the conditioned media from RAW264.7 treated either with active NE or inactive (boiled) NE as a control. Out of 840 proteins identified in the conditioned media, active NE upregulated 142 proteins and down-regulated 211 proteins. NE released not only cell surface proteins into the media but also released cytoskeletal, mitochondrial, cytosolic, and nuclear proteins that were detected in the conditioned media. At least 32 proteins were associated with the process of phagocytosis including 11 phagocytic receptors (including LRP1), 7 proteins associated with phagocytic cup formation, and 14 proteins involved in phagocytic maturation (including calpain-2) and phagolysosome formation. NE had a broad effect on the proteome required for regulation of all stages of phagocytosis and phagolysosome formation. Furthermore, the NE sheddome/ secretome included proteins from other macrophage cellular domains suggesting that NE may globally regulate macrophage structure and function.

PTX3 Deficiency Promotes Enhanced Accumulation and Function of CD11c+CD11b+ DCs in a Murine Model of Allergic Inflammation

PTX3 is a unique member of the long pentraxins family and plays an indispensable role in regulating the immune system. We previously showed that PTX3 deletion aggravates allergic inflammation via a Th17 -dominant phenotype and enhanced CD4 T cell survival using a murine model of ovalbumin (OVA) induced allergic inflammation. In this study, we identified that upon OVA exposure, increased infiltration of CD11c+CD11b+ dendritic cells (DCs) was observed in the lungs of PTX3-/- mice compared to wild type littermate. Further analysis showed that a short-term OVA exposure led to an increased number of bone marrow common myeloid progenitors (CMP) population concomitantly with increased Ly6Chigh CCR2high monocytes and CD11c+CD11b+ DCs in the lungs. Also, pulmonary CD11c+CD11b+ DCs from OVA-exposed PTX3-/- mice exhibited enhanced expression of maturation markers, chemokines receptors CCR2, and increased OVA uptake and processing compared to wild type controls. Taken together, our data suggest that PTX3 deficiency heightened lung CD11c+CD11b+DC numbers and function, hence exacerbating airway inflammatory response.

Knockout of Putative Tumor Suppressor Aldh1l1 in Mice Reprograms Metabolism to Accelerate Growth of Tumors in a Diethylnitrosamine (DEN) Model of Liver Carcinogenesis

Cytosolic 10-formyltetrahydrofolate dehydrogenase (ALDH1L1) is commonly downregulated in human cancers through promoter methylation. We proposed that ALDH1L1 loss promotes malignant tumor growth. Here, we investigated the effect of the Aldh1l1 mouse knockout (Aldh1l1−/−) on hepatocellular carcinoma using a chemical carcinogenesis model. Fifteen-day-old male Aldh1l1 knockout mice and their wild-type littermate controls (Aldh1l1+/+) were injected intraperitoneally with 20 μg/g body weight of DEN (diethylnitrosamine). Mice were sacrificed 10, 20, 28, and 36 weeks post-DEN injection, and livers were examined for tumor multiplicity and size. We observed that while tumor multiplicity did not differ between Aldh1l1−/− and Aldh1l1+/+ animals, larger tumors grew in Aldh1l1−/− compared to Aldh1l1+/+ mice at 28 and 36 weeks. Profound differences between Aldh1l1−/− and Aldh1l1+/+ mice in the expression of inflammation-related genes were seen at 10 and 20 weeks. Of note, large tumors from wild-type mice showed a strong decrease of ALDH1L1 protein at 36 weeks. Metabolomic analysis of liver tissues at 20 weeks showed stronger differences in Aldh1l1+/+ versus Aldh1l1−/− metabotypes than at 10 weeks, which underscores metabolic pathways that respond to DEN in an ALDH1L1-dependent manner. Our study indicates that Aldh1l1 knockout promoted liver tumor growth without affecting tumor initiation or multiplicity.

SIRT2 promotes murine melanoma progression through natural killer cell inhibition

SIRT2, an NAD+-dependent histone deacetylase, has been shown to play a pivotal role in various physiological processes, however, its role in cancer is currently controversial. In recent years, SIRT2 has been described as both a tumor suppressor and oncogene with divergent expression and function in various malignancies. Using murine allograft melanoma models, our results suggest increased systemic expression of SIRT2 promotes tumor progression. In this study, SIRT2-overexpressing mice exhibited enhanced tumor growth and larger tumor volumes compared to their wild-type littermates. Mechanistically, systemic overexpression of SIRT2 reduces the number of tumor-infiltrating natural killer (NK) cells and suppresses NK cell function and proliferation within the tumor microenvironment (TME). Furthermore, despite the enhancing effect of NK cell depletion on tumor volume and growth rate in wild-type littermate mice, this effect was diminished in SIRT2-overexpressing mice. Lastly, pharmacological inhibition of SIRT2 increases NK cell tumor infiltration and suppresses allograft melanoma tumor growth. The findings of this study identify a dynamic functional interaction between systemic SIRT2 and NK cell activity, which controls melanoma tumor progression. Given the recent renewed interest in NK-cell-mediated immunotherapy response, SIRT2 could present a new opportunity to mediate immunotherapy response and resistance.