Metformin inhibition of mitochondrial ATP and DNA synthesis abrogates NLRP3 inflammasome activation and pulmonary inflammation.

Acute respiratory distress syndrome (ARDS), an inflammatory condition with high mortality rates, is common in severe COVID-19, whose risk is reduced by metformin rather than other anti-diabetic medications. Detecting of inflammasome assembly in post-mortem COVID-19 lungs, we asked whether and how metformin inhibits inflammasome activation while exerting its anti-inflammatory effect. We show that metformin inhibited NLRP3 inflammasome activation and interleukin (IL)-1ß production in cultured and alveolar macrophages along with inflammasome-independent IL-6 secretion, thus attenuating lipopolysaccharide (LPS)- and SARS-CoV-2-induced ARDS. By targeting electron transport chain complex 1 and independently of AMP-activated protein kinase (AMPK) or NF-κB, metformin blocked LPS-induced and ATP-dependent mitochondrial (mt) DNA synthesis and generation of oxidized mtDNA, an NLRP3 ligand. Myeloid-specific ablation of LPS-induced cytidine monophosphate kinase 2 (CMPK2), which is rate limiting for mtDNA synthesis, reduced ARDS severity without a direct effect on IL-6. Thus, inhibition of ATP and mtDNA synthesis is sufficient for ARDS amelioration.

EGR4 is critical for cell-fate determination and phenotypic maintenance of geniculate ganglion neurons underlying sweet and umami taste.

The sense of taste starts with activation of receptor cells in taste buds by chemical stimuli which then communicate this signal via innervating oral sensory neurons to the CNS. The cell bodies of oral sensory neurons reside in the geniculate ganglion (GG) and nodose/petrosal/jugular ganglion. The geniculate ganglion contains two main neuronal populations: BRN3A+ somatosensory neurons that innervate the pinna and PHOX2B+ sensory neurons that innervate the oral cavity. While much is known about the different taste bud cell subtypes, considerably less is known about the molecular identities of PHOX2B+ sensory subpopulations. In the GG, as many as 12 different subpopulations have been predicted from electrophysiological studies, while transcriptional identities exist for only 3 to 6. Importantly, the cell fate pathways that diversify PHOX2B+ oral sensory neurons into these subpopulations are unknown. The transcription factor EGR4 was identified as being highly expressed in GG neurons. EGR4 deletion causes GG oral sensory neurons to lose their expression of PHOX2B and other oral sensory genes and up-regulate BRN3A. This is followed by a loss of chemosensory innervation of taste buds, a loss of type II taste cells responsive to bitter, sweet, and umami stimuli, and a concomitant increase in type I glial-like taste bud cells. These deficits culminate in a loss of nerve responses to sweet and umami taste qualities. Taken together, we identify a critical role of EGR4 in cell fate specification and maintenance of subpopulations of GG neurons, which in turn maintain the appropriate sweet and umami taste receptor cells.

Classical and nonclassical effects of angiotensin-converting enzyme: How increased ACE enhances myeloid immune function.

As part of the classical renin-angiotensin system, the peptidase angiotensin-converting enzyme (ACE) makes angiotensin II which has myriad effects on systemic cardiovascular function, inflammation, and cellular proliferation. Less well known is that macrophages and neutrophils make ACE in response to immune activation which has marked effects on myeloid cell function independent of angiotensin II. Here, we discuss both classical (angiotensin) and nonclassical functions of ACE and highlight mice called ACE 10/10 in which genetic manipulation increases ACE expression by macrophages and makes these mice much more resistant to models of tumors, infection, atherosclerosis, and Alzheimer's disease. In another model called NeuACE mice, neutrophils make increased ACE and these mice are much more resistant to infection. In contrast, ACE inhibitors reduce neutrophil killing of bacteria in mice and humans. Increased expression of ACE induces a marked increase in macrophage oxidative metabolism, particularly mitochondrial oxidation of lipids, secondary to increased peroxisome proliferator-activated receptor α expression, and results in increased myeloid cell ATP. ACE present in sperm has a similar metabolic effect, and the lack of ACE activity in these cells reduces both sperm motility and fertilization capacity. These nonclassical effects of ACE are not due to the actions of angiotensin II but to an unknown molecule, probably a peptide, that triggers a profound change in myeloid cell metabolism and function. Purifying and characterizing this peptide could offer a new treatment for several diseases and prove potentially lucrative.

Testicular ACE regulates sperm metabolism and fertilization through the transcription factor PPARγ.

Testis angiotensin-converting enzyme (tACE) plays a critical role in male fertility, but the mechanism is unknown. By using ACE C-domain KO (CKO) mice which lack tACE activity, we found that ATP in CKO sperm was 9.4-fold lower than WT sperm. Similarly, an ACE inhibitor (ACEi) reduced ATP production in mouse sperm by 72%. Metabolic profiling showed that tACE inactivation severely affects oxidative metabolism with decreases in several Krebs cycle intermediates including citric acid, cis-aconitic acid, NAD, α-ketoglutaric acid, succinate, and L-malic acid. We found that sperms lacking tACE activity displayed lower levels of oxidative enzymes (CISY, ODO1, MDHM, QCR2, SDHA, FUMH, CPT2, and ATPA) leading to a decreased mitochondrial respiration rate. The reduced energy production in CKO sperms leads to defects in their physiological functions including motility, acrosine activity, and fertilization in vitro and in vivo. Male mice treated with ACEi show severe impairment in reproductive capacity when mated with female mice. In contrast, an angiotensin II receptor blocker (ARB) had no effect. CKO sperms express significantly less peroxisome proliferators-activated receptor gamma (PPARγ) transcription factor, and its blockade eliminates the functional differences between CKO and WT sperms, indicating PPARγ might mediate the effects of tACE on sperm metabolism. Finally, in a cohort of human volunteers, in vitro treatment with the ramipril or a PPARγ inhibitor reduced ATP production in human sperm and hence its motility and acrosine activity. These findings may have clinical significance since millions of people take ACEi daily, including men who are reproductively active.

Cryobanking of Human Distal Lung Epithelial Cells for Preservation of Their Phenotypic and Functional Characteristics.

The epithelium lining airspaces of the human lung is maintained by regional stem cells, including basal cells of pseudostratified airways and alveolar type 2 (AT2) pneumocytes of the gas-exchange region. Despite effective techniques for long-term preservation of airway basal cells, procedures for efficient preservation of functional epithelial cell types of the distal gas-exchange region are lacking. Here we detail a method for cryobanking of epithelial cells from either mouse or human lung tissue for preservation of their phenotypic and functional characteristics. Flow cytometric profiling, epithelial organoid-forming efficiency, and single-cell transcriptomic analysis were used to compare cells recovered from cryobanked tissue with those of freshly dissociated tissue. AT2 cells within single-cell suspensions of enzymatically digested cryobanked distal lung tissue retained expression of the pan-epithelial marker CD326 and the AT2 cell surface antigen recognized by monoclonal antibody HT II-280, allowing antibody-mediated enrichment and downstream analysis. Isolated AT2 cells from cryobanked tissue were comparable with those of freshly dissociated tissue both in their single-cell transcriptome and their capacity for in vitro organoid formation in three-dimensional cultures. We conclude that the cryobanking method described herein allows long-term preservation of distal human lung tissue for downstream analysis of lung cell function and molecular phenotype and is ideally suited for the creation of an easily accessible tissue resource for the research community.

Shift from androgen to estrogen action causes abdominal muscle fibrosis, atrophy, and inguinal hernia in a transgenic male mouse model.

Inguinal hernia develops primarily in elderly men, and more than one in four men will undergo inguinal hernia repair during their lifetime. However, the underlying mechanisms behind hernia formation remain unknown. It is known that testosterone and estradiol can regulate skeletal muscle mass. We herein demonstrate that the conversion of testosterone to estradiol by the aromatase enzyme in lower abdominal muscle (LAM) tissue causes intense fibrosis, leading to muscle atrophy and inguinal hernia; an aromatase inhibitor entirely prevents this phenotype. LAM tissue is uniquely sensitive to estradiol because it expresses very high levels of estrogen receptor-α. Estradiol acts via estrogen receptor-α in LAM fibroblasts to activate pathways for proliferation and fibrosis that replaces atrophied myocytes, resulting in hernia formation. This is accompanied by decreased serum testosterone and decreased expression of the androgen receptor target genes in LAM tissue. These findings provide a mechanism for LAM tissue fibrosis and atrophy and suggest potential roles of future nonsurgical and preventive approaches in a subset of elderly men with a predisposition for hernia development.

Role of muscle spindle feedback in regulating muscle activity strength during walking at different speed in mice.

Terrestrial animals increase their walking speed by increasing the activity of the extensor muscles. However, the mechanism underlying how this speed-dependent amplitude modulation is achieved remains obscure. Previous studies have shown that group Ib afferent feedback from Golgi tendon organs that signal force is one of the major regulators of the strength of muscle activity during walking in cats and humans. In contrast, the contribution of group Ia/II afferent feedback from muscle spindle stretch receptors that signal angular displacement of leg joints is unclear. Some studies indicate that group II afferent feedback may be important for amplitude regulation in humans, but the role of muscle spindle feedback in regulation of muscle activity strength in quadrupedal animals is very poorly understood. To examine the role of feedback from muscle spindles, we combined in vivo electrophysiology and motion analysis with mouse genetics and gene delivery with adeno-associated virus. We provide evidence that proprioceptive sensory feedback from muscle spindles is important for the regulation of the muscle activity strength and speed-dependent amplitude modulation. Furthermore, our data suggest that feedback from the muscle spindles of the ankle extensor muscles, the triceps surae, is the main source for this mechanism. In contrast, muscle spindle feedback from the knee extensor muscles, the quadriceps femoris, has no influence on speed-dependent amplitude modulation. We provide evidence that proprioceptive feedback from ankle extensor muscles is critical for regulating muscle activity strength as gait speed increases. NEW & NOTEWORTHY Animals upregulate the activity of extensor muscles to increase their walking speed, but the mechanism behind this is not known. We show that this speed-dependent amplitude modulation requires proprioceptive sensory feedback from muscle spindles of ankle extensor muscle. In the absence of muscle spindle feedback, animals cannot walk at higher speeds as they can when muscle spindle feedback is present.

A neuron autonomous role for the familial dysautonomia gene ELP1 in sympathetic and sensory target tissue innervation.

Familial dysautonomia (FD) is characterized by severe and progressive sympathetic and sensory neuron loss caused by a highly conserved germline point mutation of the human ELP1/IKBKAP gene. Elp1 is a subunit of the hetero-hexameric transcriptional elongator complex, but how it functions in disease-vulnerable neurons is unknown. Conditional knockout mice were generated to characterize the role of Elp1 in migration, differentiation and survival of migratory neural crest (NC) progenitors that give rise to sympathetic and sensory neurons. Loss of Elp1 in NC progenitors did not impair their migration, proliferation or survival, but there was a significant impact on post-migratory sensory and sympathetic neuron survival and target tissue innervation. Ablation of Elp1 in post-migratory sympathetic neurons caused highly abnormal target tissue innervation that was correlated with abnormal neurite outgrowth/branching and abnormal cellular distribution of soluble tyrosinated α-tubulin in Elp1-deficient primary sympathetic and sensory neurons. These results indicate that neuron loss and physiologic impairment in FD is not a consequence of abnormal neuron progenitor migration, differentiation or survival. Rather, loss of Elp1 leads to neuron death as a consequence of failed target tissue innervation associated with impairments in cytoskeletal regulation.

Axon Transport and Neuropathy: Relevant Perspectives on the Etiopathogenesis of Familial Dysautonomia.

Peripheral neuropathies are highly prevalent and are most often associated with chronic disease, side effects from chemotherapy, or toxic-metabolic abnormalities. Neuropathies are less commonly caused by genetic mutations, but studies of the normal function of mutated proteins have identified particular vulnerabilities that often implicate mitochondrial dynamics and axon transport mechanisms. Hereditary sensory and autonomic neuropathies are a group of phenotypically related diseases caused by monogenic mutations that primarily affect sympathetic and sensory neurons. Here, I review evidence to indicate that many genetic neuropathies are caused by abnormalities in axon transport. Moreover, in hereditary sensory and autonomic neuropathies. There may be specific convergence on gene mutations that disrupt nerve growth factor signaling, upon which sympathetic and sensory neurons critically depend.

Degradation of mouse locomotor pattern in the absence of proprioceptive sensory feedback.

Mammalian locomotor programs are thought to be directed by the actions of spinal interneuron circuits collectively referred to as "central pattern generators." The contribution of proprioceptive sensory feedback to the coordination of locomotor activity remains less clear. We have analyzed changes in mouse locomotor pattern under conditions in which proprioceptive feedback is attenuated genetically and biomechanically. We find that locomotor pattern degrades upon elimination of proprioceptive feedback from muscle spindles and Golgi tendon organs. The degradation of locomotor pattern is manifest as the loss of interjoint coordination and alternation of flexor and extensor muscles. Group Ia/II sensory feedback from muscle spindles has a predominant influence in patterning the activity of flexor muscles, whereas the redundant activities of group Ia/II and group Ib afferents appear to determine the pattern of extensor muscle firing. These findings establish a role for proprioceptive feedback in the control of fundamental aspects of mammalian locomotor behavior.

Egr3-dependent muscle spindle stretch receptor intrafusal muscle fiber differentiation and fusimotor innervation homeostasis.

Muscle stretch proprioceptors (muscle spindles) are required for stretch reflexes and locomotor control. Proprioception abnormalities are observed in many human neuropathies, but the mechanisms involved in establishing and maintaining muscle spindle innervation and function are still poorly understood. During skeletal muscle development, sensory (Ia-afferent) innervation induces contacted myotubes to transform into intrafusal muscle fibers that form the stretch receptor core. The transcriptional regulator Egr3 is induced in Ia-afferent contacted myotubes by Neuregulin1 (Nrg1)/ErbB receptor signaling and it has an essential role in spindle morphogenesis and function. Because Egr3 is widely expressed during development and has a pleiotropic function, whether Egr3 functions primarily in skeletal muscle, Ia-afferent neurons, or in Schwann cells that myelinate Ia-afferent axons remains unresolved. In the present studies, cell-specific ablation of Egr3 in mice showed that it has a skeletal muscle autonomous function in stretch receptor development. Moreover, using genetic tracing, we found that Ia-afferent contacted Egr3-deficient myotubes were induced in normal numbers, but their development was blocked to generate one to two shortened fibers that failed to express some characteristic myosin heavy chain (MyHC) proteins. These "spindle remnants" persisted into adulthood, remained innervated by Ia-afferents, and expressed neurotrophin3 (NT3), which is required for Ia-afferent neuron survival. However, they were not innervated by fusimotor axons and they did not express glial derived neurotrophic factor (GDNF), which is essential for fusimotor neuron survival. These results demonstrate that Egr3 has an essential role in regulating gene expression that promotes normal intrafusal muscle fiber differentiation and fusimotor innervation homeostasis.

Animal models of scleroderma: recent progress.

PURPOSE OF REVIEW: We discuss recent advances in evaluating and optimizing animal models of systemic sclerosis (SSc). Such models could be of value for illuminating etiopathogenesis using hypothesis-testing experimental approaches, for developing effective disease-modifying therapies, and for uncovering clinically relevant biomarkers. RECENT FINDINGS: We describe recent advances in previously reported and novel animal models of SSc. The limitations of each animal model and their ability to recapitulate the pathophysiology of recognized molecular subsets of SSc are discussed. We highlight attrition of dermal white adipose tissue as a consistent pathological feature of dermal fibrosis in mouse models, and its relevance to SSc-associated cutaneous fibrosis. SUMMARY: Several animal models potentially useful for studying SSc pathogenesis have been described. Recent studies highlight particular strengths and weaknesses of selected models in recapitulating distinct features of the human disease. When used in the appropriate experimental setting, and in combination, these models singly and together provide a powerful set of in-vivo tools to define underlying mechanisms of disease and to develop and evaluate effective antifibrotic therapies.

Cardiomyocytes induce macrophage receptor shedding to suppress phagocytosis.

BACKGROUND: Mobilization of the innate immune response to clear and metabolize necrotic and apoptotic cardiomyocytes is a prerequisite to heart repair after cardiac injury. Suboptimal kinetics of dying myocyte clearance leads to secondary necrosis, and in the case of the heart, increased potential for collateral loss of neighboring non-regenerative myocytes. Despite the importance of myocyte phagocytic clearance during heart repair, surprisingly little is known about its underlying cell and molecular biology. OBJECTIVE: To determine if phagocytic receptor MERTK is expressed in human hearts and to elucidate key sequential steps and phagocytosis efficiency of dying adult cardiomyocytes, by macrophages. RESULTS: In infarcted human hearts, expression profiles of the phagocytic receptor MER-tyrosine kinase (MERTK) mimicked that found in experimental ischemic mouse hearts. Electron micrographs of myocardium identified MERTK signal along macrophage phagocytic cups and Mertk-/- macrophages contained reduced digested myocyte debris after myocardial infarction. Ex vivo co-culture of primary macrophages and adult cardiomyocyte apoptotic bodies revealed reduced engulfment relative to resident cardiac fibroblasts. Inefficient clearance was not due to the larger size of myocyte apoptotic bodies, nor were other key steps preceding the formation of phagocytic synapses significantly affected; this included macrophage chemotaxis and direct binding of phagocytes to myocytes. Instead, suppressed phagocytosis was directly associated with myocyte-induced inactivation of MERTK, which was partially rescued by genetic deletion of a MERTK proteolytic susceptibility site. CONCLUSION: Utilizing an ex vivo co-cultivation approach to model key cellular and molecular events found in vivo during infarction, cardiomyocyte phagocytosis was found to be inefficient, in part due to myocyte-induced shedding of macrophage MERTK. These findings warrant future studies to identify other cofactors of macrophage-cardiomyocyte cross-talk that contribute to cardiac pathophysiology.

CD99-like 2 (CD99L2)-deficient mice are defective in the acute inflammatory response.

CD99-Like 2 (CD99L2) is a Type I glycoprotein expressed on leukocytes and endothelial cells as well as other cell types. It is related to CD99, although it shows only 38% sequence identity. CD99L2 has been shown to play a role in leukocyte extravasation in mice under various inflammatory conditions using anti-CD99L2 antibodies and, in one case by targeted deletion of CD99L2. We report here studies on an independently made CD99L2 "knockout mouse" that extend our knowledge of the role of CD99L2 in inflammation. CD99L2 deficiency did not affect the total or relative numbers of circulating leukocyte subsets, red blood cells, or platelets. Neither did CD99L2 deficiency affect the expression of ICAM-1, PECAM, or CD99 on endothelial cells. Mice lacking CD99L2 had a defective inflammatory response in the thioglycollate peritonitis model with a greater than 80% block in neutrophil infiltration and a nearly complete block in monocyte emigration into the peritoneal cavity measured 16h after the inflammatory challenge. The mice will be a useful resource to study the role of CD99L2 in various acute and chronic inflammatory diseases.

A sympathetic neuron autonomous role for Egr3-mediated gene regulation in dendrite morphogenesis and target tissue innervation.

Egr3 is a nerve growth factor (NGF)-induced transcriptional regulator that is essential for normal sympathetic nervous system development. Mice lacking Egr3 in the germline have sympathetic target tissue innervation abnormalities and physiologic sympathetic dysfunction similar to humans with dysautonomia. However, since Egr3 is widely expressed and has pleiotropic function, it has not been clear whether it has a role within sympathetic neurons and if so, what target genes it regulates to facilitate target tissue innervation. Here, we show that Egr3 expression within sympathetic neurons is required for their normal innervation since isolated sympathetic neurons lacking Egr3 have neurite outgrowth abnormalities when treated with NGF and mice with sympathetic neuron-restricted Egr3 ablation have target tissue innervation abnormalities similar to mice lacking Egr3 in all tissues. Microarray analysis performed on sympathetic neurons identified many target genes deregulated in the absence of Egr3, with some of the most significantly deregulated genes having roles in axonogenesis, dendritogenesis, and axon guidance. Using a novel genetic technique to visualize axons and dendrites in a subpopulation of randomly labeled sympathetic neurons, we found that Egr3 has an essential role in regulating sympathetic neuron dendrite morphology and terminal axon branching, but not in regulating sympathetic axon guidance to their targets. Together, these results indicate that Egr3 has a sympathetic neuron autonomous role in sympathetic nervous system development that involves modulating downstream target genes affecting the outgrowth and branching of sympathetic neuron dendrites and axons.

Early growth response 3 (Egr-3) is induced by transforming growth factor-ß and regulates fibrogenic responses.

Members of the early growth response (Egr) gene family of transcription factors have nonredundant biological functions. Although Egr-3 is implicated primarily in neuromuscular development and immunity, its regulation and role in tissue repair and fibrosis has not been studied. We now show that in normal skin fibroblasts, Egr-3 was potently induced by transforming growth factor-ß via canonical Smad3. Moreover, transient Egr-3 overexpression was sufficient to stimulate fibrotic gene expression, whereas deletion of Egr-3 resulted in substantially attenuated transforming growth factor-ß responses. Genome-wide expression profiling in fibroblasts showed that genes associated with tissue remodeling and wound healing were prominently up-regulated by Egr-3. Notably, <5% of fibroblast genes regulated by Egr-1 or Egr-2 were found to be coregulated by Egr-3, revealing substantial functional divergence among these Egr family members. In a mouse model of scleroderma, development of dermal fibrosis was accompanied by accumulation of Egr-3-positive myofibroblasts in the lesional tissue. Moreover, skin biopsy samples from patients with scleroderma showed elevated Egr-3 levels in the dermis, and Egr-3 mRNA levels correlated with the extent of skin involvement. These results provide the first evidence that Egr-3, a functionally distinct member of the Egr family with potent effects on inflammation and immunity, is up-regulated in scleroderma and is necessary and sufficient for profibrotic responses, suggesting important and distinct roles in the pathogenesis of fibrosis.

Angiotensin Converting Enzyme (ACE) expression in microglia reduces amyloid ß deposition and neurodegeneration by increasing SYK signaling and endolysosomal trafficking.

Genome-wide association studies (GWAS) have identified many gene polymorphisms associated with an increased risk of developing Late Onset Alzheimer's Disease (LOAD). Many of these LOAD risk-associated alleles alter disease pathogenesis by influencing microglia innate immune responses and lipid metabolism. Angiotensin Converting Enzyme (ACE), a GWAS LOAD risk-associated gene best known for its role in regulating systemic blood pressure, also enhances innate immunity and lipid processing in peripheral myeloid cells, but a role for ACE in modulating the function of myeloid-derived microglia remains unexplored. Using novel mice engineered to express ACE in microglia and CNS associated macrophages (CAMs), we find that ACE expression in microglia reduces Aß plaque load, preserves vulnerable neurons and excitatory synapses, and greatly reduces learning and memory abnormalities in the 5xFAD amyloid mouse model of Alzheimer's Disease (AD). ACE-expressing microglia show enhanced Aß phagocytosis and endolysosomal trafficking, increased clustering around amyloid plaques, and increased SYK tyrosine kinase activation downstream of the major Aß receptors, TREM2 and CLEC7A. Single microglia sequencing and digital spatial profiling identifies downstream SYK signaling modules that are expressed by ACE expression in microglia that mediate endolysosomal biogenesis and trafficking, mTOR and PI3K/AKT signaling, and increased oxidative phosphorylation, while gene silencing or pharmacologic inhibition of SYK activity in ACE-expressing microglia abrogates the potentiated Aß engulfment and endolysosomal trafficking. These findings establish a role for ACE in enhancing microglial immune function and they identify a potential use for ACE-expressing microglia as a cell-based therapy to augment endogenous microglial responses to Aß in AD.

Identification of retinal tau oligomers, citrullinated tau, and other tau isoforms in early and advanced AD and relations to disease status.

Importance: This study identifies and quantifies diverse pathological tau isoforms in the retina of both early and advanced-stage Alzheimer's disease (AD) and determines their relationship with disease status. Objective: A case-control study was conducted to investigate the accumulation of retinal neurofibrillary tangles (NFTs), paired helical filament (PHF)-tau, oligomeric tau (oligo-tau), hyperphosphorylated tau (p-tau), and citrullinated tau (Cit-tau) in relation to the respective brain pathology and cognitive dysfunction in mild cognitively impaired (MCI) and AD dementia patients versus normal cognition (NC) controls. Design setting and participants: Eyes and brains from donors diagnosed with AD, MCI (due to AD), and NC were collected (n=75 in total), along with clinical and neuropathological data. Brain and retinal cross-sections-in predefined superior-temporal and inferior-temporal (ST/IT) subregions-were subjected to histopathology analysis or Nanostring GeoMx digital spatial profiling. Main outcomes and measure: Retinal burden of NFTs (pretangles and mature tangles), PHF-tau, p-tau, oligo-tau, and Cit-tau was assessed in MCI and AD versus NC retinas. Pairwise correlations revealed associations between retinal and brain parameters and cognitive status. Results: Increased retinal NFTs (1.8-fold, p=0.0494), PHF-tau (2.3-fold, p<0.0001), oligo-tau (9.1-fold, p<0.0001), CitR 209 -tau (4.3-fold, p<0.0001), pSer202/Thr205-tau (AT8; 4.1-fold, p<0.0001), and pSer396-tau (2.8-fold, p=0.0015) were detected in AD patients. Retinas from MCI patients showed significant increases in NFTs (2.0-fold, p=0.0444), CitR 209 -tau (3.5-fold, p=0.0201), pSer396-tau (2.6-fold, p=0.0409), and, moreover, oligo-tau (5.8-fold, p=0.0045). Nanostring GeoMx quantification demonstrated upregulated retinal p-tau levels in MCI patients at phosphorylation sites of Ser214 (2.3-fold, p=0.0060), Ser396 (1.8-fold, p=0.0052), Ser404 (2.4-fold, p=0.0018), and Thr231 (3.3-fold, p=0.0028). Strong correlations were found between retinal tau forms to paired-brain pathology and cognitive status: a) retinal oligo-tau vs. Braak stage (r=0.60, P=0.0002), b) retinal PHF-tau vs. ABC average score (r=0.64, P=0.0043), c) retinal pSer396-tau vs. brain NFTs (r=0.68, P<0.0001), and d) retinal pSer202/Thr205-tau vs. MMSE scores (r= -0.77, P=0.0089). Conclusions and Relevance: This study reveals increases in immature and mature retinal tau isoforms in MCI and AD patients, highlighting their relationship with brain pathology and cognition. The data provide strong incentive to further explore retinal tauopathy markers that may be useful for early detection and monitoring of AD staging through noninvasive retinal imaging.

microRNA-21 regulates astrocytic response following spinal cord injury.

Astrogliosis following spinal cord injury (SCI) involves an early hypertrophic response that serves to repair damaged blood-brain barrier and a subsequent hyperplastic response that results in a dense scar that impedes axon regeneration. The mechanisms regulating these two phases of astrogliosis are beginning to be elucidated. In this study, we found that microRNA-21 (miR-21) increases in a time-dependent manner following SCI in mouse. Astrocytes adjacent to the lesion area express high levels of miR-21 whereas astrocytes in uninjured spinal cord express low levels of miR-21. To study the role of miR-21 in astrocytes after SCI, transgenic mice were generated that conditionally overexpress either the primary miR-21 transcript in astrocytes or a miRNA sponge designed to inhibit miR-21 function. Overexpression of miR-21 in astrocytes attenuated the hypertrophic response to SCI. Conversely, expression of the miR-21 sponge augmented the hypertrophic phenotype, even in chronic stages of SCI recovery when astrocytes have normally become smaller in size with fine processes. Inhibition of miR-21 function in astrocytes also resulted in increased axon density within the lesion site. These findings demonstrate a novel role for miR-21 in regulating astrocytic hypertrophy and glial scar progression after SCI, and suggest miR-21 as a potential therapeutic target for manipulating gliosis and enhancing functional outcome.

Sensorimotor function is modulated by the serotonin receptor 1d, a novel marker for gamma motor neurons.

Gamma motor neurons (MNs), the efferent component of the fusimotor system, regulate muscle spindle sensitivity. Muscle spindle sensory feedback is required for proprioception that includes sensing the relative position of neighboring body parts and appropriately adjust the employed strength in a movement. The lack of a single and specific genetic marker has long hampered functional and developmental studies of gamma MNs. Here we show that the serotonin receptor 1d (5-ht1d) is specifically expressed by gamma MNs and proprioceptive sensory neurons. Using mice expressing GFP driven by the 5-ht1d promotor, we performed whole-cell patch-clamp recordings of 5-ht1d::GFP⁺ and 5-ht1d::GFP⁻ motor neurons from young mice. Hierarchal clustering analysis revealed that gamma MNs have distinct electrophysiological properties intermediate to fast-like and slow-like alpha MNs. Moreover, mice lacking 5-ht1d displayed lower monosynaptic reflex amplitudes suggesting a reduced response to sensory stimulation in motor neurons. Interestingly, adult 5-ht1d knockout mice also displayed improved coordination skills on a beam-walking task, implying that reduced activation of MNs by Ia afferents during provoked movement tasks could reduce undesired exaggerated muscle output. In summary, we show that 5-ht1d is a novel marker for gamma MNs and that the 5-ht1d receptor is important for the ability of proprioceptive circuits to receive and relay accurate sensory information in developing and mature spinal cord motor circuits.