Yaqian Duan

Impact of The Protective Renin-Angiotensin System (RAS) on The Vasoreparative Function of CD34+ CACs in Diabetic Retinopathy

PURPOSE Müller cells support retinal neurons with essential functions. Here, we aim to examine the impact of starvation and oxidative stress on glutamate uptake and mitochondrial function in Müller cells. METHODS Cultured human retinal Müller cells (MIO-M1) were exposed to H2O2 and additional starvation for 24 hours. Effects of starvation and H2O2 on glutamate uptake and mitochondrial function were assessed by kinetic glutamate uptake assays and Seahorse assays, respectively. Cell survival was evaluated by cell viability assays. mRNA and protein expressions were assessed by quantitative PCR and Western blot. RESULTS Starvation of Müller cells increased the glutamate uptake capacity as well as the expression of the most abundant glutamate transporter, EAAT1. Mitochondrial and glycolytic activity were diminished in starved Müller cells despite unaffected cell viability. Simultaneous starvation and exposure to oxidative stress resulted in a reduced glutamate uptake and a collapsed mitochondrial function. In Müller cells with intact energy supply, the glutamate uptake and mitochondrial function were unaffected after exposure to oxidative stress. CONCLUSIONS Here, we identify an increased susceptibility toward oxidative stress in starved Müller cells in spite of unaffected viability and an apparent decreased ability to transport glutamate. Solely exposure to oxidative stress did not affect Müller cell functions. Thus, our study suggests an increased susceptibility of Müller cells in case of more than one cellular stressor. Extrapolating these findings, age-related neurodegenerative retinal diseases may be the result of impaired Müller cell function.

Restructuring of the Gut Microbiome by Intermittent Fasting Prevents Retinopathy and Prolongs Survival in db/db Mice

Intermittent fasting (IF) protects against the development of metabolic diseases and cancer, but whether it can prevent diabetic microvascular complications is not known. In db/db mice, we examined the impact of long-term IF on diabetic retinopathy (DR). Despite no change in glycated hemoglobin, db/db mice on the IF regimen displayed significantly longer survival and a reduction in DR end points, including acellular capillaries and leukocyte infiltration. We hypothesized that IF-mediated changes in the gut microbiota would produce beneficial metabolites and prevent the development of DR. Microbiome analysis revealed increased levels of Firmicutes and decreased Bacteroidetes and Verrucomicrobia. Compared with db/db mice on ad libitum feeding, changes in the microbiome of the db/db mice on IF were associated with increases in gut mucin, goblet cell number, villi length, and reductions in plasma peptidoglycan. Consistent with the known modulatory effects of Firmicutes on bile acid (BA) metabolism, measurement of BAs demonstrated a significant increase of tauroursodeoxycholate (TUDCA), a neuroprotective BA, in db/db on IF but not in db/db on AL feeding. TGR5, the TUDCA receptor, was found in the retinal primary ganglion cells. Expression of TGR5 did not change with IF or diabetes. However, IF reduced retinal TNF-α mRNA, which is a downstream target of TGR5 activation. Pharmacological activation of TGR5 using INT-767 prevented DR in a second diabetic mouse model. These findings support the concept that IF prevents DR by restructuring the microbiota toward species producing TUDCA and subsequent retinal protection by TGR5 activation.

Electroacupuncture Promotes Central Nervous System-Dependent Release of Mesenchymal Stem Cells

Electroacupuncture (EA) performed in rats and humans using limb acupuncture sites, LI‐4 and LI‐11, and GV‐14 and GV‐20 (humans) and Bai‐hui (rats) increased functional connectivity between the anterior hypothalamus and the amygdala and mobilized mesenchymal stem cells (MSCs) into the systemic circulation. In human subjects, the source of the MSC was found to be primarily adipose tissue, whereas in rodents the tissue sources were considered more heterogeneous. Pharmacological disinhibition of rat hypothalamus enhanced sympathetic nervous system (SNS) activation and similarly resulted in a release of MSC into the circulation. EA‐mediated SNS activation was further supported by browning of white adipose tissue in rats. EA treatment of rats undergoing partial rupture of the Achilles tendon resulted in reduced mechanical hyperalgesia, increased serum interleukin‐10 levels and tendon remodeling, effects blocked in propranolol‐treated rodents. To distinguish the afferent role of the peripheral nervous system, phosphoinositide‐interacting regulator of transient receptor potential channels (Pirt)‐GCaMP3 (genetically encoded calcium sensor) mice were treated with EA acupuncture points, ST‐36 and LIV‐3, and GV‐14 and Bai‐hui and resulted in a rapid activation of primary sensory neurons. EA activated sensory ganglia and SNS centers to mediate the release of MSC that can enhance tissue repair, increase anti‐inflammatory cytokine production and provide pronounced analgesic relief. Stem Cells 2017;35:1303–1315

Electroacupuncture Promotes CNS-Dependent Release of Mesenchymal Stem Cells.

Electroacupuncture (EA) performed in rats and humans using limb acupuncture sites, LI‐4 and LI‐11, and GV‐14 and GV‐20 (humans) and Bai‐hui (rats) increased functional connectivity between the anterior hypothalamus and the amygdala and mobilized mesenchymal stem cells (MSCs) into the systemic circulation. In human subjects, the source of the MSC was found to be primarily adipose tissue, whereas in rodents the tissue sources were considered more heterogeneous. Pharmacological disinhibition of rat hypothalamus enhanced sympathetic nervous system (SNS) activation and similarly resulted in a release of MSC into the circulation. EA‐mediated SNS activation was further supported by browning of white adipose tissue in rats. EA treatment of rats undergoing partial rupture of the Achilles tendon resulted in reduced mechanical hyperalgesia, increased serum interleukin‐10 levels and tendon remodeling, effects blocked in propranolol‐treated rodents. To distinguish the afferent role of the peripheral nervous system, phosphoinositide‐interacting regulator of transient receptor potential channels (Pirt)‐GCaMP3 (genetically encoded calcium sensor) mice were treated with EA acupuncture points, ST‐36 and LIV‐3, and GV‐14 and Bai‐hui and resulted in a rapid activation of primary sensory neurons. EA activated sensory ganglia and SNS centers to mediate the release of MSC that can enhance tissue repair, increase anti‐inflammatory cytokine production and provide pronounced analgesic relief. Stem Cells 2017;35:1303–1315

Ataxia Telangiectasia Mutated Dysregulation Results in Diabetic Retinopathy

Ataxia telangiectasia mutated (ATM) acts as a defense against a variety of bone marrow (BM) stressors. We hypothesized that ATM loss in BM‐hematopoietic stem cells (HSCs) would be detrimental to both HSC function and microvascular repair while sustained ATM would be beneficial in disease models of diabetes. Chronic diabetes represents a condition associated with HSC depletion and inadequate vascular repair. Gender mismatched chimeras of ATM−/− on wild type background were generated and a cohort were made diabetic using streptozotocin (STZ). HSCs from the STZ‐ATM−/−chimeras showed (a) reduced self‐renewal; (b) decreased long‐term repopulation; (c) depletion from the primitive endosteal niche; (d) myeloid bias; and (e) accelerated diabetic retinopathy (DR). To further test the significance of ATM in hematopoiesis and diabetes, we performed microarrays on circulating angiogenic cells, CD34+ cells, obtained from a unique cohort of human subjects with long‐standing (>40 years duration) poorly controlled diabetes that were free of DR. Pathway analysis of microarrays in these individuals revealed DNA repair and cell‐cycle regulation as the top networks with marked upregulation of ATM mRNA compared with CD34+ cells from diabetics with DR. In conclusion, our study highlights using rodent models and human subjects, the critical role of ATM in microvascular repair in DR. Stem Cells 2016;34:405–417

Hematopoietic stem/progenitor involvement in retinal microvascular repair during diabetes: Implications for bone marrow rejuvenation.

&NA; The widespread nature of diabetes affects all organ systems of an individual including the bone marrow. Long‐term damage to the cellular and extracellular components of the bone marrow leads to a rapid decline in the bone marrow‐hematopoietic stem/progenitor cells (HS/PCs) compartment. This review will highlight the importance of bone marrow microenvironment in maintaining bone marrow HS/PC populations and the contribution of these key populations in microvascular repair during the natural history of diabetes. The autonomic nervous system can initiate and propagate bone marrow dysfunction in diabetes. Systemic pharmacological strategies designed to protect the bone marrow‐HS/PC population from diabetes induced‐oxidative stress and advanced glycation end product accumulation represent a new approach to target diabetic retinopathy progression. Protecting HS/PCs ensures their participation in vascular repair and reduces the risk of vasogdegeneration occurring in the retina.

Loss of Angiotensin‐Converting Enzyme 2 Exacerbates Diabetic Retinopathy by Promoting Bone Marrow Dysfunction

Angiotensin‐converting enzyme 2 (ACE2) is the primary enzyme of the vasoprotective axis of the renin angiotensin system (RAS). We tested the hypothesis that loss of ACE2 would exacerbate diabetic retinopathy by promoting bone marrow dysfunction. ACE2–/y were crossed with Akita mice, a model of type 1 diabetes. When comparing the bone marrow of the ACE2–/y‐Akita mice to that of Akita mice, we observed a reduction of both short‐term and long‐term repopulating hematopoietic stem cells, a shift of hematopoiesis toward myelopoiesis, and an impairment of lineage–c‐kit+ hematopoietic stem/progenitor cell (HS/PC) migration and proliferation. Migratory and proliferative dysfunction of these cells was corrected by exposure to angiotensin‐1‐7 (Ang‐1‐7), the protective peptide generated by ACE2. Over the duration of diabetes examined, ACE2 deficiency led to progressive reduction in electrical responses assessed by electroretinography and to increases in neural infarcts observed by fundus photography. Compared with Akita mice, ACE2–/y‐Akita at 9‐months of diabetes showed an increased number of acellular capillaries indicative of more severe diabetic retinopathy. In diabetic and control human subjects, CD34+ cells, a key bone marrow HS/PC population, were assessed for changes in mRNA levels for MAS, the receptor for Ang‐1‐7. Levels were highest in CD34+ cells from diabetics without retinopathy. Higher serum Ang‐1‐7 levels predicted protection from development of retinopathy in diabetics. Treatment with Ang‐1‐7 or alamandine restored the impaired migration function of CD34+ cells from subjects with retinopathy. These data support that activation of the protective RAS within HS/PCs may represents a therapeutic strategy for prevention of diabetic retinopathy. Stem Cells 2018;36:1430–1440

Erratum to: CX3CR1 deficiency accelerates the development of retinopathy in a rodent model of type 1 diabetes (Journal of Molecular Medicine, (2016), 94, 11, (1255-1265), 10.1007/s00109-016-1433-0)

The original version of this article unfortunately contains a mistake in Fig. 1a; the wrong figure panels were used. The correct Fig. 1a is shown in this paper.