Signaling and other functions of lipids in autophagy: a review.

The process of autophagy is integral to cellular function. In this process, proteins, organelles, and metabolites are engulfed in a lipid vesicle and trafficked to a lysosome for degradation. Its central role in protein and organelle homeostasis has piqued interest for autophagy dysfunction as a driver of pathology for a number of diseases including cancer, muscular disorders, neurological disorders, and non-alcoholic fatty liver disease. For much of its history, the study of autophagy has centered around proteins, however, due to advances in mass spectrometry and refined methodologies, the role of lipids in this essential cellular process has become more apparent. This review discusses the diverse endogenous lipid compounds shown to mediate autophagy. Downstream lipid signaling pathways are also reviewed in the context of autophagy regulation. Specific focus is placed upon the Mammalian Target of Rapamycin (mTOR) and Peroxisome Proliferator-Activated Receptor (PPAR) signaling pathways as integration hubs for lipid regulation of autophagy.

Center of Biomedical Research Excellence in Matrix Biology: Building Research Infrastructure, Supporting Young Researchers, and Fostering Collaboration.

The Center of Biomedical Research Excellence in Matrix Biology strives to improve our understanding of extracellular matrix at molecular, cellular, tissue, and organismal levels to generate new knowledge about pathophysiology, normal development, and regenerative medicine. The primary goals of the Center are to i) support junior investigators, ii) enhance the productivity of established scientists, iii) facilitate collaboration between both junior and established researchers, and iv) build biomedical research infrastructure that will support research relevant to cell-matrix interactions in disease progression, tissue repair and regeneration, and v) provide access to instrumentation and technical support. A Pilot Project program provides funding to investigators who propose applying their expertise to matrix biology questions. Support from the National Institute of General Medical Sciences at the National Institutes of Health that established the Center of Biomedical Research Excellence in Matrix Biology has significantly enhanced the infrastructure and the capabilities of researchers at Boise State University, leading to new approaches that address disease diagnosis, prevention, and treatment. New multidisciplinary collaborations have been formed with investigators who may not have previously considered how their biomedical research programs addressed fundamental and applied questions involving the extracellular matrix. Collaborations with the broader matrix biology community are encouraged.

Cutting edge: IL-13Rα1 expression in dopaminergic neurons contributes to their oxidative stress-mediated loss following chronic peripheral treatment with lipopolysaccharide.

Inflammation and its mediators, including cytokines and reactive oxygen species, are thought to contribute to neurodegeneration. In the mouse brain, we found that IL-13Rα1 was expressed in the dopaminergic (DA) neurons of the substantia nigra pars compacta, which are preferentially lost in human Parkinson's disease. Mice deficient for Il13ra1 exhibited resistance to loss of DA neurons in a model of chronic peripheral inflammation using bacterial LPS. IL-13, as well as IL-4, potentiated the cytotoxic effects of t-butyl hydroperoxide and hydrogen peroxide on mouse DA MN9D cells. Collectively, our data indicate that expression of IL-13Rα1 on DA neurons can increase their susceptibility to oxidative stress-mediated damage, thereby contributing to their preferential loss. In humans, Il13ra1 lies on the X chromosome within the PARK12 locus of susceptibility to Parkinson's disease, suggesting that IL-13Rα1 may have a role in the pathogenesis of this neurodegenerative disease.

The Role of NAD+ and NAD+-Boosting Therapies in Inflammatory Response by IL-13.

The essential role of nicotinamide adenine dinucleotide+ (NAD+) in redox reactions during oxidative respiration is well known, yet the coenzyme and regulator functions of NAD+ in diverse and important processes are still being discovered. Maintaining NAD+ levels through diet is essential for health. In fact, the United States requires supplementation of the NAD+ precursor niacin into the food chain for these reasons. A large body of research also indicates that elevating NAD+ levels is beneficial for numerous conditions, including cancer, cardiovascular health, inflammatory response, and longevity. Consequently, strategies have been created to elevate NAD+ levels through dietary supplementation with NAD+ precursor compounds. This paper explores current research regarding these therapeutic compounds. It then focuses on the NAD+ regulation of IL-13 signaling, which is a research area garnering little attention. IL-13 is a critical regulator of allergic response and is associated with Parkinson's disease and cancer. Evidence supporting the notion that increasing NAD+ levels might reduce IL-13 signal-induced inflammatory response is presented. The assessment is concluded with an examination of reports involving popular precursor compounds that boost NAD+ and their associations with IL-13 signaling in the context of offering a means for safely and effectively reducing inflammatory response by IL-13.

FABP5-binding lipids regulate autophagy in differentiated SH-SY5Y cells.

The motor features of Parkinson's disease result from loss of dopaminergic neurons in the substantia nigra with autophagy dysfunction being closely linked to this disease. While a large body of work focusing on protein effectors of autophagy has been reported, regulation of autophagy by lipids has garnered far less attention. Therefore, we sought to identify endogenous lipid molecules that act as signaling mediators of autophagy in differentiated SH-SY5Y cells, a commonly used dopaminergic neuron-like cell model. In order to accomplish this goal, we assessed the role of a fatty acid-binding protein (FABP) family member on autophagy due to its function as an intracellular lipid chaperone. We focused specifically upon FABP5 due to its heightened expression in dopaminergic neurons within the substantia nigra and SH-SY5Y cells. Here, we report that knockdown of FABP5 resulted in suppression of autophagy in differentiated SH-SY5Y cells suggesting the possibility of an autophagic role for an interacting lipid. A lipidomic screen of FABP5-interacting lipids uncovered hits that include 5-oxo-eicosatetraenoic acid (5OE) and its precursor metabolite, arachidonic acid (AA). Additionally, other long-chain fatty acids were found to bind FABP5, such as stearic acid (SA), hydroxystearic acid (HSA), and palmitic acid (PA). The addition of 5OE, SA, and HSA but not AA or PA, led to potent inhibition of autophagy in SH-SY5Y cells. To identify potential molecular mechanisms for autophagy inhibition by these lipids, RNA-Seq was performed which revealed both shared and divergent signaling pathways between the lipid-treated groups. These findings suggest a role for these lipids in modulating autophagy through diverse signaling pathways and could represent novel therapeutic targets for Parkinson's disease.

Nonhistone Lysine Methylation as a Protein Degradation Signal.

Protein degradation is a fundamental feature of cellular life, and malfunction of this process is implicated in human disease. Ubiquitin tagging is the best characterized mechanism of targeting a protein for degradation; however, there are a growing number of distinct mechanisms which have also been identified that carry out this essential function. For example, covalent tagging of proteins with sequestosome-1 targets them for selective autophagy. Degradation signals are not exclusively polypeptides such as ubiquitin, NEDD8, and sequestosome-1. Phosphorylation, acetylation, and methylation are small covalent additions that can also direct protein degradation. The diversity of substrate sequences and overlap with other pleotrophic functions for these smaller signaling moieties has made their characterization more challenging. However, these small signals might be responsible for orchestrating a large portion of the protein degradation activity in the cell. As such, there has been increasing interest in lysine methylation and associated lysine methyltransferases (KMTs), beyond canonical histone protein modification, in mediating protein degradation in a variety of contexts. This review focuses on the current evidence for lysine methylation as a protein degradation signal with a detailed discussion of the class of enzymes responsible for this phenomenon.

Ccl22/MDC, is a prostaglandin dependent pyrogen, acting in the anterior hypothalamus to induce hyperthermia via activation of brown adipose tissue.

CC Chemokine ligand 22 (Ccl22) is a selective, high affinity ligand at the CC chemokine receptor 4 (Ccr4). We have identified cDNAs encoding both ligand and receptor of the Ccl22-Ccr4 pair in cDNA libraries of the anterior hypothalamus/pre-optic area (AH/POA) by PCR. The AH/POA is the key brain region where endogenous pyrogens have been shown to act on warm sensitive neurons to affect thermogenesis in brown adipose tissue (BAT) and other thermogenically responsive tissues. We show that functional Ccr4 receptors are present in the AH/POA neurons as injection of Ccl22 into the POA but not to other hypothalamic nuclei induces an increase in core body temperature as measured by radiotelemetry. Indomethacin (5 mg/kg s.c) pre-treatment markedly reduced the hyperthermia evoked by POA injection of Ccl22 (10 ng/0.5 ul) and thus suggests that this hyperthermia is mediated through cyclooxygenase activation and thus likely through the formation and action of the pyrogen prostaglandin E2. The temperature elevation involves a decrease in the respiratory exchange ratio and increased activation of the brown adipose tissue as demonstrated by ¹8F-FDG-PET imaging. We describe a novel role to the ligand Ccl22 and its receptor Ccr4 in the anterior hypothalamus in temperature regulation that depends on the synthesis of the endogenous pyrogen, prostaglandin E2.

Repurposing Drugs to Treat Heart and Brain Illness.

Drug development is a complicated, slow and expensive process with high failure rates. One strategy to mitigate these factors is to recycle existing drugs with viable safety profiles and have gained Food and Drug Administration approval following extensive clinical trials. Cardiovascular and neurodegenerative diseases are difficult to treat, and there exist few effective therapeutics, necessitating the development of new, more efficacious drugs. Recent scientific studies have led to a mechanistic understanding of heart and brain disease progression, which has led researchers to assess myriad drugs for their potential as pharmacological treatments for these ailments. The focus of this review is to survey strategies for the selection of drug repurposing candidates and provide representative case studies where drug repurposing strategies were used to discover therapeutics for cardiovascular and neurodegenerative diseases, with a focus on anti-inflammatory processes where new drug alternatives are needed.

Central nervous system and peripheral cell labeling by vascular endothelial cadherin-driven lineage tracing in adult mice.

Understanding the contribution of endothelial cells to the progenitor pools of adult tissues has the potential to inform therapies for human disease. To address whether endothelial cells transdifferentiate into non-vascular cell types, we performed cell lineage tracing analysis using transgenic mice engineered to express a fluorescent marker following activation by tamoxifen in vascular endothelial cadherin promoter-expressing cells (VEcad-CreERT2; B6 Cg-Gt(ROSA)26Sortm9(CAG-tdTomato)Hze). Activation of target-cell labeling following 1.5 months of ad libitum feeding with tamoxifen-laden chow in 4-5 month-old mice resulted in the tracing of central nervous system and peripheral cells that include: cerebellar granule neurons, ependymal cells, skeletal myocytes, pancreatic beta cells, pancreatic acinar cells, tubular cells in the renal cortex, duodenal crypt cells, ileal crypt cells, and hair follicle stem cells. As Nestin expression has been reported in a subset of endothelial cells, Nes-CreERT2 mice were also utilized in these conditions. The tracing of cells in adult Nes-CreERT2 mice revealed the labeling of canonical progeny cell types such as hippocampal and olfactory granule neurons as well as ependymal cells. Interestingly, Nestin tracing also labeled skeletal myocytes, ileal crypt cells, and sparsely marked cerebellar granule neurons. Our findings provide support for endothelial cells as active contributors to adult tissue progenitor pools. This information could be of particular significance for the intravenous delivery of therapeutics to downstream endothelial-derived cellular targets. The animal experiments were approved by the Boise State University Institute Animal Care and Use Committee (approval No. 006-AC15-018) on October 31, 2018.

Endothelial Cell Contributions to COVID-19.

Understanding of the clinical, histological and molecular features of the novel coronavirus 2019 (Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)) has remained elusive. Coronavirus disease 2019 (COVID-19) caused by this virus has unusual clinical presentation with regard to other related coronaviruses. Recent reports suggest that SARS-CoV-2, unlike other related viruses, infects and replicates within endothelial cells, which may explain a significant portion of the observed clinical pathology. Likewise, mounting evidence associates vascular and endothelial cell dysfunction with increased mortality. This review focuses on understanding how endothelial cell pathology is caused by SARS-CoV-2 at the molecular and cellular levels and how these events relate to COVID-19. A detailed examination of current knowledge regarding canonical inflammatory reaction pathways as well as alteration of endothelial cell-derived exosomes and transdifferentiation by SARS-CoV-2 is included in this assessment. Additionally, given an understanding of endothelial contributions to COVID-19, potential therapeutic aims are discussed, particularly as would affect endothelial function and pathology.

Enhanced Hyaluronan Signaling and Autophagy Dysfunction by VPS35 D620N.

The motor features of Parkinson's disease (PD) result from the loss of dopaminergic (DA) neurons in the substantia nigra with autophagy dysfunction being closely linked to this disease. A PD-causing familial mutation in VPS35 (D620N) has been reported to inhibit autophagy. In order to identify signaling pathways responsible for this autophagy defect, we performed an unbiased screen using RNA sequencing (RNA-Seq) of wild-type or VPS35 D620N-expressing retinoic acid-differentiated SH-SY5Y cells. We report that VPS35 D620N-expressing cells exhibit transcriptome changes indicative of alterations in extracellular matrix (ECM)-receptor interaction as well as PI3K-AKT signaling, a pathway known to regulate autophagy. Hyaluronan (HA) is a major component of brain ECM and signals via the ECM receptors CD44, a top RNA-Seq hit, and HA-mediated motility receptor (HMMR) to the autophagy-regulating PI3K-AKT pathway. We find that high (>950 kDa), but not low (15-40 kDa), molecular weight HA treatment inhibits autophagy. In addition, VPS35 D620N facilitated enhanced HA-AKT signaling. Transcriptomic assessment and validation of protein levels identified the differential expression of CD44 and HMMR isoforms in VPS35 D620N mutant cells. We report that knockdown of HMMR or CD44 results in upregulated autophagy in cells expressing wild-type VPS35. However, only HMMR knockdown resulted in rescue of autophagy dysfunction by VPS35 D620N indicating a potential pathogenic role for this receptor and HA signaling in Parkinson's disease.

Neuroprotection by histone deacetylase-related protein.

The expression of histone deacetylase-related protein (HDRP) is reduced in neurons undergoing apoptosis. Forced reduction of HDRP expression in healthy neurons by treatment with antisense oligonucleotides also induces cell death. Likewise, neurons cultured from mice lacking HDRP are more vulnerable to cell death. Adenovirally mediated expression of HDRP prevents neuronal death, showing that HDRP is a neuroprotective protein. Neuroprotection by forced expression of HDRP is not accompanied by activation of the phosphatidylinositol 3-kinase-Akt or Raf-MEK-ERK signaling pathway, and treatment with pharmacological inhibitors of these pathways fails to inhibit the neuroprotection by HDRP. Stimulation of c-Jun phosphorylation and expression, an essential feature of neuronal death, is prevented by HDRP. We found that HDRP associates with c-Jun N-terminal kinase (JNK) and inhibits its activity, thus explaining the inhibition of c-Jun phosphorylation by HDRP. HDRP also interacts with histone deacetylase 1 (HDAC1) and recruits it to the c-Jun gene promoter, resulting in an inhibition of histone H3 acetylation at the c-Jun promoter. Although HDRP lacks intrinsic deacetylase activity, treatment with pharmacological inhibitors of histone deacetylases induces apoptosis even in the presence of ectopically expressed HDRP, underscoring the importance of c-Jun promoter deacetylation by HDRP-HDAC1 in HDRP-mediated neuroprotection. Our results suggest that neuroprotection by HDRP is mediated by the inhibition of c-Jun through its interaction with JNK and HDAC1.

Contributions of VPS35 Mutations to Parkinson's Disease.

Parkinson's Disease (PD) is a multi-system neurodegenerative disease where approximately 90% of cases are idiopathic. The remaining 10% of the cases can be traced to a genetic origin and research has largely focused on these associated genes to gain a better understanding of the molecular and cellular pathogenesis for PD. The gene encoding vacuolar protein sorting protein 35 (VPS35) has been definitively linked to late onset familial PD following the identification of a point mutation (D620N) as the causal agent in a Swiss family. Since its discovery, numerous studies have been undertaken to characterize the role of VPS35 in cellular processes and efforts have been directed toward understanding the perturbations caused by the D620N mutation. In this review, we examine what is currently known about VPS35, which has pleiotropic effects, as well as proposed mechanisms of pathogenesis by the D620N mutation. A brief survey of other VPS35 polymorphisms is also provided. Lastly, model systems that are being utilized for these investigations and possible directions for future research are discussed.

A Fragment of Apolipoprotein E4 Leads to the Downregulation of a CXorf56 Homologue, a Novel ER-Associated Protein, and Activation of BV2 Microglial Cells.

Despite the fact that harboring the apolipoprotein E4 (APOE4) allele represents the single greatest risk factor for late-onset Alzheimer's disease (AD), the exact mechanism by which apoE4 contributes to disease progression remains unknown. Recently, we demonstrated that a 151 amino-terminal fragment of apoE4 (nApoE41-151) localizes within the nucleus of microglia in the human AD brain, suggesting a potential role in gene expression. In the present study, we investigated this possibility utilizing BV2 microglia cells treated exogenously with nApoE41-151. The results indicated that nApoE41-151 leads to morphological activation of microglia cells through, at least in part, the downregulation of a novel ER-associated protein, CXorf56. Moreover, treatment of BV2 cells with nApoE41-151 resulted in a 68-fold increase in the expression of the inflammatory cytokine, TNFα, a key trigger of microglia activation. In this regard, we also observed a specific binding interaction of nApoE41-151 with the TNFα promoter region. Collectively, these data identify a novel gene-regulatory pathway involving CXorf56 that may link apoE4 to microglia activation and inflammation associated with AD.

Class IIA HDACs in the regulation of neurodegeneration.

Neurodegenerative diseases affect millions of patients annually and are a significant burden on the health care systems around the world. While there are symptomatic remedies for patients suffering from various neurodegenerative diseases, there are no cures as of today. Cell death by apoptosis is a common hallmark of neurodegeneration. Therefore, deciphering the molecular pathways regulating this process is of significant value to scientists' endeavor to understand neurodegenerative disorders. Efforts along these lines have uncovered a number of molecular pathways that regulate neuronal apoptosis. Recently, a family of proteins known as histone deacetylases (HDACs) has been linked to regulation of cell survival as well as death. The focus of this review is to summarize our current understanding of the role of HDACs and in particular a subgroup of proteins in this family classified as class IIa HDACs in the regulation of neuronal cell death. It is apparent based on the information presented in this review that although very similar in their primary sequence, members of this family of proteins often have distinct roles in orchestrating apoptotic cell death in the brain.

Polydactyly in mice lacking HDAC9/HDRP.

Mice lacking histone deacetylase 9 (HDAC9) and its truncated variant, HDRP, exhibit post-axial polydactyly that manifests as an extra big toe on the right hind foot. Polydactyly in HDAC9/ HDRP knockout mice occurs with incomplete penetrance and affects both genders similarly. Because polydactyly can result from overactivity of sonic hedgehog (Shh) signaling, we investigated whether HDRP acted as a negative regulator of the Shh pathway. We find that Gli1, a transcription factor and downstream mediator of Shh signaling, is expressed at substantially higher levels in the feet of perinatal HDAC9/ HDRP-/- mice as compared with wild-type littermates. To more directly examine whether HDRP negatively-regulates Shh signaling we utilized cell lines that express components of the Shh pathway and that respond to the Shh agonist purmorphamine. We find that purmorphamine-mediated stimulation of Gli1 in the NIH 3T3 and HT22 cell lines is inhibited by the expression of HDRP. In HT22 cells, purmorphamine treatment leads to an increase in the rate of cell proliferation, which is also inhibited by HDRP. This inhibitory effect of HDRP on purmorphamine-mediated cell proliferation was also observed in primary cultures of glial cells. Although the mechanism by which it inhibits Gli1 induction and cell proliferation by purmorphamine is not clear, HDRP localizes to the nucleus suggesting it acts just upstream of Gli3 activation in the signaling cascade activated by Shh. Taken together our results suggest that HDRP acts as a negative regulator of the Shh pathway and that the absence of HDRP results in hyper-activation of this pathway resulting in polydactyly.

Chemokine-mediated recruitment of NK cells is a critical host defense mechanism in invasive aspergillosis.

Invasive aspergillosis is a severe pneumonia that is usually fatal despite currently available therapy. The disease disproportionately afflicts immunocompromised patients, indicating the critical importance of the immune status of the host in this infection, but the defense mechanisms against this pathogen remain incompletely understood. In the current study, we hypothesized that the chemokine ligand monocyte chemotactic protein-1, also designated CC chemokine ligand-2 (MCP-1/CCL2) is necessary for effective host defense against invasive aspergillosis in immunocompromised hosts. We found a rapid and marked induction of MCP-1/CCL2 in the lungs of neutropenic mice with invasive aspergillosis. Neutralizing MCP-1/CCL2 resulted in twofold greater mortality and greater than threefold increase in pathogen burden in the lungs. Neutralization of MCP-1/CCL2 also resulted in reduced recruitment of NK cells to the lungs at early time points, but did not affect the number of other leukocyte effector cells in the lungs. Ab-mediated depletion of NK cells similarly resulted in impaired defenses against the infection, resulting in a greater than twofold increase in mortality and impaired clearance of the pathogen from the lungs. These data establish MCP-1/CCL2-mediated recruitment of NK cells to the lungs as a critical early host defense mechanism in invasive aspergillosis and demonstrate NK cells to be an important and previously unrecognized effector cell in this infection.

Nigral dopaminergic neuron replenishment in adult mice through VE-cadherin-expressing neural progenitor cells.

The function of dopaminergic neurons in the substantia nigra is of central importance to the coordination of movement by the brain's basal ganglia circuitry. This is evidenced by the loss of these neurons, resulting in the cardinal motor deficits associated with Parkinson's disease. In order to fully understand the physiology of these key neurons and develop potential therapies for their loss, it is essential to determine if and how dopaminergic neurons are replenished in the adult brain. Recent work has presented evidence for adult neurogenesis of these neurons by Nestin+/Sox2- neural progenitor cells. We sought to further validate this finding and explore a potential atypical origin for these progenitor cells. Since neural progenitor cells have a proximal association with the vasculature of the brain and subsets of endothelial cells are Nestin+, we hypothesized that dopaminergic neural progenitors might share a common cell lineage. Therefore, we employed a VE-cadherin promoter-driven CREERT2:THlox/THlox transgenic mouse line to ablate the tyrosine hydroxylase gene from endothelial cells in adult animals. After 26 weeks, but not 13 weeks, following the genetic blockade of tyrosine hydroxylase expression in VE-cadherin+ cells, we observed a significant reduction in tyrosine hydroxylase+ neurons in the substantia nigra. The results from this genetic lineage tracing study suggest that dopaminergic neurons are replenished in adult mice by a VE-cadherin+ progenitor cell population potentially arising from an endothelial lineage.

Nuclear uptake of an amino-terminal fragment of apolipoprotein E4 promotes cell death and localizes within microglia of the Alzheimer's disease brain.

Although harboring the apolipoprotein E4 (APOE4) allele is a well known risk factor in Alzheimer's disease (AD), the mechanism by which it contributes to disease risk remains elusive. To investigate the role of proteolysis of apoE4 as a potential mechanism, we designed and characterized a site-directed cleavage antibody directed at position D151 of the mature form of apoE4 and E3. Characterization of this antibody indicated a high specificity for detecting synthesized recombinant proteins corresponding to the amino acid sequences 1-151 of apoE3 and E4 that would generate the 17 kDa (p17) fragment. In addition, this antibody also detected a ~17 kDa amino-terminal fragment of apoE4 following incubation with collagenase and matrix metalloproteinase-9 (MMP-9), but did not react with full-length apoE4. Application of this amino-terminal apoE cleavage-fragment (nApoECFp17) antibody, revealed nuclear labeling within glial cells and labeling of a subset of neurofibrillary tangles in the human AD brain. A quantitative analysis indicated that roughly 80% of labeled nuclei were microglia. To confirm these findings, cultured BV2 microglia cells were incubated with the amino-terminal fragment of apoE4 corresponding to the cleavage site at D151. The results indicated efficient uptake of this fragment and trafficking to the nucleus that also resulted in significant cell death. In contrast, a similarly designed apoE3 fragment showed no toxicity and primarily localized within the cytoplasm. These data suggest a novel cleavage event by which apoE4 is cleaved by the extracellular proteases, collagenase and MMP-9, generating an amino-terminal fragment that is then taken up by microglia, traffics to the nucleus and promotes cell death. Collectively, these findings provide important mechanistic insights into the mechanism by which harboring the APOE4 allele may elevate dementia risk observed in AD.

Discovery of nigral dopaminergic neurogenesis in adult mice.

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra. As a result, intensive efforts have focused upon mechanisms that facilitate the death of mature dopaminergic neurons. Unfortunately, these efforts have been unsuccessful in providing an effective treatment to address neurodegeneration in this disease. Therefore, alternative theories of pathogenesis are being explored. Adult neurogenesis of dopaminergic neurons is an attractive concept that would provide a possible mechanism of neurodegeneration as well as offer an endogenous means to replenish affected neurons. To determine whether dopaminergic neurons experience neurogenesis in adult mice we developed a novel cell lineage tracing model that permitted detection of neurogenesis without many of the issues associated with popular techniques. Remarkably, we discovered that dopaminergic neurons are replenished in adult mice by Nestin+/Sox2- progenitor cells. What's more, the rate of neurogenesis is similar to the rate of dopaminergic neuron loss reported using a chronic, systemic inflammatory response mouse model. This observation may indicate that neuron loss in Parkinson's disease results from inhibition of neurogenesis.