Biology subjects

Brown, B. L.

Publications and source records attributed to Brown, B. L..

5 recordsLinked to original sources

bioRxiv2025

A reversible feedback mechanism regulating mitochondrial heme synthesis

Proper heme biosynthesis is essential for numerous cellular functions across nearly all life forms. In humans, dysregulated heme metabolism is linked to multiple blood diseases, neurodegeneration, cardiovascular disease, and metabolic disorders. Erythroid heme production begins with the rate-limiting enzyme Aminolevulinic Acid Synthase (ALAS2) in the mitochondrion. Although prior studies discuss the regulation of ALAS2 in the nucleus and cytoplasm, its modulation as a mature mitochondrial matrix enzyme remains poorly understood. We report that heme binds mature human ALAS2 with high affinity, acting as a reversible mixed inhibitor that reduces enzymatic activity. Structure-based modeling reveals two flexible regions of ALAS2 interact with heme, locking the enzyme in an inactive conformation and occluding the active site. Our work reveals a negative feedback mechanism for heme synthesis, offering insights into the spatial regulation of ALAS2 and the maturation of the essential heme cofactor.

biochemistry↗

bioRxiv2022

Silencing long-descending inter-enlargement propriospinal neurons improves hindlimb stepping after contusive spinal cord injuries

Spinal locomotor circuitry is comprised of rhythm generating centers, one for each limb, that are interconnected by local and long-distance propriospinal neurons thought to carry temporal information necessary for interlimb coordination and gait control. We showed previously that conditional silencing of the long ascending propriospinal neurons (LAPNs) that project from the lumbar to the cervical rhythmogenic centers (L1/L2 to C6), disrupts right-left alternation of both the forelimbs and hindlimbs without significantly disrupting other fundamental aspects of interlimb and speed-dependent coordination (Pocratsky et al., 2020). Subsequently, we showed that silencing the LAPNs after a moderate thoracic contusive spinal cord injury (SCI) resulted in better recovered locomotor function (Shepard et al., 2021). In this research advance, we focus on the descending equivalent to the LAPNs, the long descending propriospinal neurons (LDPNs) that have cell bodies at C6 and terminals at L2. We found that conditional silencing of the LDPNs in the intact adult rat resulted in disrupted alternation of each limb pair (forelimbs and hindlimbs) and after a thoracic contusion SCI significantly improved locomotor function. These observations lead us to speculate that the LAPNs and LDPNs have similar roles in the exchange of temporal information between the cervical and lumbar rhythm generating centers, but that the partial disruption of the pathway after SCI limits the independent function of the lumbar circuitry. Silencing the LAPNs or LDPNs effectively permits or frees-up the lumbar circuitry to function independently.

neuroscience↗

bioRxiv2021

Silencing long ascending propriospinal neurons after spinal cord injury improves hindlimb stepping in the adult rat

Long ascending propriospinal neurons (LAPNs) are a subpopulation of spinal cord interneurons that directly connect the lumbar and cervical enlargements. In uninjured animals, conditionally silencing LAPNs resulted in disrupted left-right coordination of the hindlimbs and forelimbs in a context-dependent manner, demonstrating that LAPNs secure alternation of the fore- and hindlimb pairs during overground stepping in the adult rat. Given their ventrolateral location in the spinal cord white matter, many LAPN axons likely remain intact following thoracic spinal cord injury (SCI), suggesting a potential role in the recovery of stepping. Thus, we hypothesized that silencing LAPNs after SCI would result in diminished hindlimb locomotor function. We found instead that silencing of spared LAPNs post-SCI restored the left-right hindlimb coordination associated with alternating gaits that was lost as a result of SCI. Several other fundamental characteristics of hindlimb stepping were also improved and the number of abnormal steps were reduced. However, hindlimb-forelimb coordination was not restored. These data suggest that the temporal information carried between the enlargements by the LAPNs after SCI may be detrimental to hindlimb locomotor function. These observations have implications for our understanding of the relationship between injury severity and functional outcome, for the efforts to develop neuro- and axo-protective therapeutic strategies, and also for the clinical study/implementation of spinal stimulation and neuromodulation.

neuroscience↗

bioRxiv2019

Response relationships between CO2, CH4 and N2O emissions and microbial functional groups in wetland sediments after trace metal addition.

We investigated the effects of trace metal additions on microbial nitrogen and carbon cycling using freshwater wetland sediment microcosms amended with M concentrations of copper (Cu), molybdenum (Mo), iron (Fe), and all combinations. In addition to monitoring inorganic nitrogen transformations (NO3-, NO2-, N2O, NH4+) and carbon mineralization (CO2, CH4), we tracked changes in functional gene abundance associated with denitrification (nirS, nirK, nosZ), DNRA (nrfA), and methanogenesis (mcrA). Greater availability of Cu led to more complete denitrification (i.e., less N2O accumulation) and a higher abundance of the nirK and nosZ genes, which encode for Cu-dependent reductases. We found sparse evidence of DNRA activity and no consistent effect on CO2 production. Contrary, net CH4 production was stimulated by the trace metal amendments and the Mo additions, in particular, led to increased mcrA gene abundance. Taken together, these findings demonstrate that trace metal effects on microbial physiology, which have heretofore only been studied in pure culture, can impact community-level function. We observed direct and indirect effects on both nitrogen and carbon biogeochemistry that culminated in increased production of greenhouse gasses, and the shifts in functional group abundance that we documented suggest these responses may have been mediated through changes in microbial community composition. Overall, this work supports a more holistic consideration of metal effects on environmental microbial communities that recognizes the key role that metal limitation plays in microbial physiology.

ecology↗

bioRxiv2019

A simple and effective sampler to collect undisturbed cores from tidal marshes

Core sampling is a common procedure in wetland ecology. PVC tubes are widely used to collect soil cores; however several studies fail to describe even the most typical characteristics of their sampling auger. This work aims to fill this gap and provide a simple and standardized core sampler design. A simple and inexpensive sampler is described for field use. Its main advantages are: 1) extraction of undisturbed cores; 7.6 cm diameter and up to 100 cm depth, 2) it is light-weight, sturdy and reliable, 3) it is made from widely available PVC items and 4) it requires minimal skills to assemble. The sampler is introduced in the wetland soil, by rotation, to the desired depth; the tooth-like edge can cut and penetrate through the dense root systems. The sampler is capped with an industrial-type stopper, and pulled up. The core is held in the sampler by suction - negative pressure. A plunger is then used to slowly remove the soil - core and sub - samples are collected. Alternatively, both ends of sampler could be sealed and taken to the lab. An 8 cm long sub-sample was adequate for soil physical, biogeochemical and molecular analysis. The sampler has been tested for 2 years with more than 200 cores taken from tidal wetlands in Chesapeake Bay, Virginia, USA. A negative correlation between salinity and organic matter content at 3 - 5 and 8 - 10 cm was found. For the deeper samples (48 - 50 cm), a positive correlation between salinity and organic matter was observed. The sampler worked satisfactory and it required no maintenance besides cleaning.

ecology↗