Publications

Restoration of mitophagy ameliorates cardiomyopathy in Barth syndrome
Jun Zhang, Xueling Liu, Jia Nie, Yuguang Shi
Autophagy. 2022 Jan 5;1-16. doi: 10.1080/15548627.2021.2020979. Online ahead of print.

Abstract:

Barth syndrome (BTHS) is an X-linked genetic disorder caused by mutations in the TAFAZZIN/Taz gene which encodes a transacylase required for cardiolipin remodeling. Cardiolipin is a mitochondrial signature phospholipid that plays a pivotal role in maintaining mitochondrial membrane structure, respiration, mtDNA biogenesis, and mitophagy. Mutations in the TAFAZZIN gene deplete mature cardiolipin, leading to mitochondrial dysfunction, dilated cardiomyopathy, and premature death in BTHS patients. Currently, there is no effective treatment for this debilitating condition. In this study, we showed that TAFAZZIN deficiency caused hyperactivation of MTORC1 signaling and defective mitophagy, leading to accumulation of autophagic vacuoles and dysfunctional mitochondria in the heart of Tafazzin knockdown mice, a rodent model of BTHS. Consequently, treatment of TAFAZZIN knockdown mice with rapamycin, a potent inhibitor of MTORC1, not only restored mitophagy, but also mitigated mitochondrial dysfunction and dilated cardiomyopathy. Taken together, these findings identify MTORC1 as a novel therapeutic target for BTHS, suggesting that pharmacological restoration of mitophagy may provide a novel treatment for BTHS.


LRG1 is an adipokine that mediates obesity-induced hepatosteatosis and insulin resistance
Sijia He, Jiyoon Ryu, Juanhong Liu, Hairong Luo, Ying Lv, Paul R Langlais, Jie Wen, Feng Dong, Zhe Sun, Wenjuan Xia, Jane L Lynch, Ravindranath Duggirala, Bruce J Nicholson, Mengwei Zang, Yuguang Shi, Fang Zhang, Feng Liu, Juli Bai, Lily Q Dong.
J Clin Invest. 2021;131(24):e148545. https://doi.org/10.1172/JCI148545

Abstract:

Dysregulation in adipokine biosynthesis and function contributes to obesity-induced metabolic diseases. However, the identities and functions of many of the obesity-induced secretory molecules remain unknown. Here, we report the identification of leucine-rich alpha-2-glycoprotein 1 (LRG1) as an obesity-associated adipokine that exacerbates high fat diet–induced hepatosteatosis and insulin resistance. Serum levels of LRG1 were markedly elevated in obese humans and mice compared with their respective controls. LRG1 deficiency in mice greatly alleviated diet-induced hepatosteatosis, obesity, and insulin resistance. Mechanistically, LRG1 bound with high selectivity to the liver and promoted hepatosteatosis by increasing de novo lipogenesis and suppressing fatty acid β-oxidation. LRG1 also inhibited hepatic insulin signaling by downregulating insulin receptor substrates 1 and 2. Our study identified LRG1 as a key molecule that mediates the crosstalk between adipocytes and hepatocytes in diet-induced hepatosteatosis and insulin resistance. Suppressing LRG1 expression and function may be a promising strategy for the treatment of obesity-related metabolic diseases.


The Insulin-Sensitizer Pioglitazone Remodels Adipose Tissue Phospholipids in Humans
Juan P. Palavicini, Alberto Chavez-Velazquez, Marcel Fourcaudot, Devjit Tripathy, Meixia Pan, Luke Norton, Ralph A. DeFronzo and Christopher E. Shannon
Frontiers in Physiology, 02 December 2021 | DOI: doi.org/10.3389/fphys.2021.784391

Abstract:

The insulin-sensitizer pioglitazone exerts its cardiometabolic benefits in type 2 diabetes (T2D) through a redistribution of body fat, from ectopic and visceral areas to subcutaneous adipose depots. Whereas excessive weight gain and lipid storage in obesity promotes insulin resistance and chronic inflammation, the expansion of subcutaneous adipose by pioglitazone is associated with a reversal of these immunometabolic deficits. The precise events driving this beneficial remodeling of adipose tissue with pioglitazone remain unclear, and whether insulin-sensitizers alter the lipidomic composition of human adipose has not previously been investigated. Using shotgun lipidomics, we explored the molecular lipid responses in subcutaneous adipose tissue following 6months of pioglitazone treatment (45mg/day) in obese humans with T2D. Despite an expected increase in body weight following pioglitazone treatment, no robust effects were observed on the composition of storage lipids (i.e., triglycerides) or the content of lipotoxic lipid species (e.g., ceramides and diacylglycerides) in adipose tissue. Instead, pioglitazone caused a selective remodeling of the glycerophospholipid pool, characterized by a decrease in lipids enriched for arachidonic acid, such as plasmanylethanolamines and phosphatidylinositols. This contributed to a greater overall saturation and shortened chain length of fatty acyl groups within cell membrane lipids, changes that are consistent with the purported induction of adipogenesis by pioglitazone. The mechanism through which pioglitazone lowered adipose tissue arachidonic acid, a major modulator of inflammatory pathways, did not involve alterations in phospholipase gene expression but was associated with a reduction in its precursor linoleic acid, an effect that was also observed in skeletal muscle samples from the same subjects. These findings offer important insights into the biological mechanisms through which pioglitazone protects the immunometabolic health of adipocytes in the face of increased lipid storage.


Pathogenic tau accelerates aging-associated activation of transposable elements in the mouse central nervous system.
Paulino Ramirez, Gabrielle Zuniga, Wenyan Sun, Adrian Beckmann, Elizabeth Ochoa, Sarah L. DeVos, Bradley Hyman, Gabriel Chiu, Ethan R. Roy, Wei Cao, Miranda Orr, Virginie Buggia-Prevot, William J. Ray, and Bess Frost.
Progress in Neurobiology. Available online 17 October 2021. https://doi.org/10.1016/j.pneurobio.2021.102181.

Abstract:

Transposable elements comprise almost half of the mammalian genome. A growing body of evidence suggests that transposable element dysregulation accompanies brain aging and neurodegenerative disorders, and that transposable element activation is neurotoxic. Recent studies have identified links between pathogenic forms of tau, a protein that accumulates in Alzheimer’s disease and related “tauopathies,” and transposable element-induced neurotoxicity. Starting with transcriptomic analyses, we find that age- and tau-induced transposable element activation occurs in the mouse brain. Among transposable elements that are activated at the RNA level in the context of brain aging and tauopathy, we find that the endogenous retrovirus (ERV) class of retrotransposons is particularly enriched. We show that protein encoded by Intracisternal A-particle, a highly active mouse ERV, is elevated in brains of tau transgenic mice. Using two complementary approaches, we find that brains of tau transgenic mice contain increased DNA copy number of transposable elements, raising the possibility that these elements actively retrotranspose in the context of tauopathy. Taken together, our study lays the groundwork for future mechanistic studies focused on transposable element regulation in the aging mouse brain and in mouse models of tauopathy and provides support for ongoing therapeutic efforts targeting transposable element activation in patients with Alzheimer’s disease.


Adult-onset CNS myelin sulfatide deficiency is sufficient to cause Alzheimer’s disease-like neuroinflammation and cognitive impairment.
Shulan Qiu, Juan Pablo Palavicini, Jianing Wang, Nancy S. Gonzalez, Sijia He, Elizabeth Dustin, Cheng Zou, Lin Ding, Anindita Bhattacharjee, Candice E. Van Skike, Veronica Galvan, Jeffrey L. Dupree & Xianlin Han.
Molecular Neurodegeneration, 2021 Sep 15;16(1):64. doi: 10.1186/s13024-021-00488-7.
PMID: 34526055 PMCID: PMC8442347

Abstract:

Background: Human genetic association studies point to immune response and lipid metabolism, in addition to amyloid-beta (Aβ) and tau, as major pathways in Alzheimer’s disease (AD) etiology. Accumulating evidence suggests that chronic neuroinflammation, mainly mediated by microglia and astrocytes, plays a causative role in neurodegeneration in AD. Our group and others have reported early and dramatic losses of brain sulfatide in AD cases and animal models that are mediated by ApoE in an isoform-dependent manner and accelerated by Aβ accumulation. To date, it remains unclear if changes in specific brain lipids are sufficient to drive AD-related pathology.

Methods: To study the consequences of CNS sulfatide deficiency and gain insights into the underlying mechanisms, we developed a novel mouse model of adult-onset myelin sulfatide deficiency, i.e., tamoxifen-inducible myelinating glia-specific cerebroside sulfotransferase (CST) conditional knockout mice (CSTfl/fl/Plp1-CreERT), took advantage of constitutive CST knockout mice (CST-/-), and generated CST/ApoE double knockout mice (CST-/-/ApoE-/-), and assessed these mice using a broad range of methodologies including lipidomics, RNA profiling, behavioral testing, PLX3397-mediated microglia depletion, mass spectrometry (MS) imaging, immunofluorescence, electron microscopy, and Western blot.

Results: We found that mild central nervous system (CNS) sulfatide losses within myelinating cells are sufficient to activate disease-associated microglia and astrocytes, and to increase the expression of AD risk genes (e.g., Apoe, Trem2, Cd33, and Mmp12), as well as previously established causal regulators of the immune/microglia network in late-onset AD (e.g., Tyrobp, Dock, and Fcerg1), leading to chronic AD-like neuroinflammation and mild cognitive impairment. Notably, neuroinflammation and mild cognitive impairment showed gender differences, being more pronounced in females than males. Subsequent mechanistic studies demonstrated that although CNS sulfatide losses led to ApoE upregulation, genetically-induced myelin sulfatide deficiency led to neuroinflammation independently of ApoE. These results, together with our previous studies (sulfatide deficiency in the context of AD is mediated by ApoE and accelerated by Aβ accumulation) placed both Aβ and ApoE upstream of sulfatide deficiency-induced neuroinflammation, and suggested a positive feedback loop where sulfatide losses may be amplified by increased ApoE expression. We also demonstrated that CNS sulfatide deficiency-induced astrogliosis and ApoE upregulation are not secondary to microgliosis, and that astrogliosis and microgliosis seem to be driven by activation of STAT3 and PU.1/Spi1 transcription factors, respectively.

Conclusion: Our results strongly suggest that sulfatide deficiency is an important contributor and driver of neuroinflammation and mild cognitive impairment in AD pathology.


The treatment of neurogenic lower urinary tract dysfunction in persons with spinal cord injury: An open label, pilot study of anticholinergic agent vs. mirabegron to evaluate cognitive impact and efficacy.
Michelle Trbovich, Terry Romo, Marsha Polk, Wouter Koek, Che Kelly, Sharon Stowe, Stephen Kraus, Dean Kellogg.
Spinal Cord Series and Cases. 2021 Jun 10;7(1):50. doi: 10.1038/s41394-021-00413-6.
PMID: 34112758 PMCID: PMC8192499 (available on 2022-06-10)

Abstract:

Study design: Pre-post intervention

Objectives: 1. To test whether replacement of oral anticholinergic (AC) agents with mirabegron for neurogenic lower urinary tract dysfunction (NLUTD) yields improved cognitive function in older persons with spinal cord injury (SCI). 2. To test whether mirabegron is safe and as efficacious as AC.

Settings: USA.

Methods: Pilot study: Twenty older (>60 y/o) persons with SCI taking chronic (>6 months) AC medication for NLUTD were enrolled. All participants were first studied on AC at baseline then switched to mirabegron for 6 months. Primary outcomes were cognitive tests of (1) executive function (TEXAS, SDMT); (2) attention (SCWT); and (3) memory (SLUMS and WMS-IV Story A/B). Secondary outcomes assessed efficacy and safety including Neurogenic Bladder Symptom Score (NBSS), bladder diary, neurogenic bowel dysfunction (NBD) survey, heart rate (HR), electrocardiogram (EKG), and mean arterial pressure (MAP).

Results: When switching from AC to mirabegron for NLUTD, older persons with SCI exhibited statistically significant improvements in immediate Story A recall (p = 0.01), delayed story A and B recall (p = 0.01, 0.004), and in TEXAS (p = 0.04). Three subscores within NBSS significantly improved (p = 0.001) and the frequency of incontinence decreased (p = 0.03) on mirabegron. NBD, HR, MAP, and EKGs were unchanged.

Conclusion: Older persons with SCI on AC for NLUTD demonstrated improved short-term and delayed memory (WMS-IV Story A/B) as well as executive function (TEXAS) when switched to mirabegron. Efficacy of mirabegron for NLUTD symptoms was superior to AC with no adverse effects on bowel or cardiovascular function.

Sponsorship: Claude D. Pepper Older Americans Independence Center.


In Vivo Generation of Lung and Thyroid Tissues from Embryonic Stem Cells Using Blastocyst Complementation.
Bingqiang Wen, Enhong Li, Vladimir Ustiyan, Guolun Wang, Minzhe Guo, Cheng-Lun Na, Gregory T Kalin, Veronica Galvan, Yan Xu, Timothy E Weaver, Tanya V Kalin, Jeffrey A Whitsett, Vladimir V Kalinichenko .
Am J Respir Crit Care Med. 2021 Feb 15;203(4):471-483. doi: 10.1164/rccm.201909-1836OC.

Abstract:

Rationale: The regeneration and replacement of lung cells or tissues from induced pluripotent stem cell- or embryonic stem cell-derived cells represent future therapies for life-threatening pulmonary disorders but are limited by technical challenges to produce highly differentiated cells able to maintain lung function. Functional lung tissue-containing airways, alveoli, vasculature, and stroma have never been produced via directed differentiation of embryonic stem cells (ESCs) or induced pluripotent stem cells. We sought to produce all tissue components of the lung from bronchi to alveoli by embryo complementation.

Objectives: To determine whether ESCs are capable of generating lung tissue in Nkx2-1-/- mouse embryos with lung agenesis.

Methods: Blastocyst complementation was used to produce chimeras from normal mouse ESCs and Nkx2-1-/- embryos, which lack pulmonary tissues. Nkx2-1-/- chimeras were examined using immunostaining, transmission electronic microscopy, fluorescence-activated cell sorter analysis, and single-cell RNA sequencing.

Measurements and Main Results: Although peripheral pulmonary and thyroid tissues are entirely lacking in Nkx2-1 gene-deleted embryos, pulmonary and thyroid structures in Nkx2-1-/- chimeras were restored after ESC complementation. Respiratory epithelial cell lineages in restored lungs of Nkx2-1-/- chimeras were derived almost entirely from ESCs, whereas endothelial, immune, and stromal cells were mosaic. ESC-derived cells from multiple respiratory cell lineages were highly differentiated and indistinguishable from endogenous cells based on morphology, ultrastructure, gene expression signatures, and cell surface proteins used to identify cell types by fluorescence-activated cell sorter.

Conclusions: Lung and thyroid tissues were generated in vivo from ESCs by blastocyst complementation. Nkx2-1-/- chimeras can be used as “bioreactors” for in vivo differentiation and functional studies of ESC-derived progenitor cells.


TREX2 Exonuclease Causes Spontaneous Mutations and Stress-Induced Replication Fork Defects in Cells Expressing RAD51K133A
Jun Ho Ko, Mi Young Son, Qing Zhou, Lucia Molnarova, Lambert Song, Jarmila Mlcouskova, Atis Jekabsons, Cristina Montagna, Lumir Krejci, Paul Hasty
Cell Reports. Volume 33, Issue 12, 22 December 2020, 108543. doi: 10.1016/j.celrep.2020.108543.

Summary:

DNA damage tolerance (DDT) and homologous recombination (HR) stabilize replication forks (RFs). RAD18/UBC13/three prime repair exonuclease 2 (TREX2)-mediated proliferating cell nuclear antigen (PCNA) ubiquitination is central to DDT, an error-prone lesion bypass pathway. RAD51 is the recombinase for HR. The RAD51 K133A mutation increased spontaneous mutations and stress-induced RF stalls and nascent strand degradation. Here, we report in RAD51K133A cells that this phenotype is reduced by expressing a TREX2 H188A mutation that deletes its exonuclease activity. In RAD51K133A cells, knocking out RAD18 or overexpressing PCNA reduces spontaneous mutations, while expressing ubiquitination-incompetent PCNAK164R increases mutations, indicating DDT as causal. Deleting TREX2 in cells deficient for the RF maintenance proteins poly(ADP-ribose) polymerase 1 (PARP1) or FANCB increased nascent strand degradation that was rescued by TREX2H188A, implying that TREX2 prohibits degradation independent of catalytic activity. A possible explanation for this occurrence is that TREX2H188A associates with UBC13 and ubiquitinates PCNA, suggesting a dual role for TREX2 in RF maintenance.


Early disruption of nerve mitochondrial and myelin lipid homeostasis in obesity-induced diabetes.
Juan P Palavicini, Juan Chen, Chunyan Wang, Jianing Wang, Chao Qin, Eric Baeuerle, Xinming Wang, Jung A Woo, David E Kang, Nicolas Musi, Jeffrey L Dupree, Xianlin Han.
JCI Insight. 2020 Nov 5;5(21):137286. doi: 10.1172/jci.insight.137286.

Abstract:

Diabetic neuropathy is a major complication of diabetes. Current treatment options alleviate pain but do not stop the progression of the disease. At present, there are no approved disease-modifying therapies. Thus, developing more effective therapies remains a major unmet medical need. Seeking to better understand the molecular mechanisms driving peripheral neuropathy, as well as other neurological complications associated with diabetes, we performed spatiotemporal lipidomics, biochemical, ultrastructural, and physiological studies on PNS and CNS tissue from multiple diabetic preclinical models. We unraveled potentially novel molecular fingerprints underlying nerve damage in obesity-induced diabetes, including an early loss of nerve mitochondrial (cardiolipin) and myelin signature (galactosylceramide, sulfatide, and plasmalogen phosphatidylethanolamine) lipids that preceded mitochondrial, myelin, and axonal structural/functional defects; started in the PNS; and progressed to the CNS at advanced diabetic stages. Mechanistically, we provided substantial evidence indicating that these nerve mitochondrial/myelin lipid abnormalities are (surprisingly) not driven by hyperglycemia, dysinsulinemia, or insulin resistance, but rather associate with obesity/hyperlipidemia. Importantly, our findings have major clinical implications as they open the door to novel lipid-based biomarkers to diagnose and distinguish different subtypes of diabetic neuropathy (obese vs. nonobese diabetics), as well as to lipid-lowering therapeutic strategies for treatment of obesity/diabetes-associated neurological complications and for glycemic control.


Pathogenic Tau Causes a Toxic Depletion of Nuclear Calcium.
Rebekah Mahoney, Elizabeth Ochoa Thomas, Paulino Ramirez, Henry E Miller, Adrian Beckmann, Gabrielle Zuniga, Radek Dobrowolski, Bess Frost.
Cell Reports. 2020 Jul 14;32(2):107900. doi: 10.1016/j.celrep.2020.107900.

Abstract:

Synaptic activity-induced calcium (Ca2+) influx and subsequent propagation into the nucleus is a major way in which synapses communicate with the nucleus to regulate transcriptional programs important for activity-dependent survival and memory formation. Nuclear Ca2+ shapes the transcriptome by regulating cyclic AMP (cAMP) response element-binding protein (CREB). Here, we utilize a Drosophila model of tauopathy and induced pluripotent stem cell (iPSC)-derived neurons from humans with Alzheimer’s disease to study the effects of pathogenic tau, a pathological hallmark of Alzheimer’s disease and related tauopathies, on nuclear Ca2+. We find that pathogenic tau depletes nuclear Ca2+ and CREB to drive neuronal death, that CREB-regulated genes are over-represented among differentially expressed genes in tau transgenic Drosophila, and that activation of big potassium (BK) channels elevates nuclear Ca2+ and suppresses tau-induced neurotoxicity. Our studies identify nuclear Ca2+ depletion as a mechanism contributing to tau-induced neurotoxicity, adding an important dimension to the calcium hypothesis of Alzheimer’s disease.


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