Cholesterol in the cargo membrane amplifies tau inhibition of kinesin-1-based transport

Intracellular cargos are often membrane-enclosed and transported by microtubule-based motors in the presence of microtubule-associated proteins (MAPs). Whereas increasing evidence reveals how MAPs impact the interactions between motors and microtubules, critical questions remain about the impact of the cargo membrane on transport. Here we combined in vitro optical trapping with theoretical approaches to determine the effect of a lipid cargo membrane on kinesin-based transport in the presence of MAP tau. Our results demonstrate that attaching kinesin to a fluid lipid membrane reduces the inhibitory effect of tau on kinesin. Moreover, adding cholesterol, which reduces kinesin diffusion in the cargo membrane, amplifies the inhibitory effect of tau on kinesin binding in a dosage-dependent manner. We propose that reduction of kinesin diffusion in the cargo membrane underlies the effect of cholesterol on kinesin binding in the presence of tau, and we provide a simple model for this proposed mechanism. Our study establishes a direct link between cargo membrane cholesterol and MAP-based regulation of kinesin-1. The cholesterol effects uncovered here may more broadly extend to other lipid alterations that impact motor diffusion in the cargo membrane, including those associated with aging and neurological diseases.

Population Health Innovations and Payment to Address Social Needs Among Patients and Communities With Diabetes

Policy Points Population health efforts to improve diabetes care and outcomes should identify social needs, support social needs referrals and coordination, and partner health care organizations with community social service agencies and resources. Current payment mechanisms for health care services do not adequately support critical up-front investments in infrastructure to address medical and social needs, nor provide sufficient incentives to make addressing social needs a priority. Alternative payment models and value-based payment should provide up-front funding for personnel and infrastructure to address social needs and should incentivize care that addresses social needs and outcomes sensitive to social risk.

CONTEXT

Increasingly, health care organizations are implementing interventions to improve outcomes for patients with complex health and social needs, including diabetes, through cross-sector partnerships with nonmedical organizations. However, fee-for-service and many value-based payment systems constrain options to implement models of care that address social and medical needs in an integrated fashion. We present experiences of eight grantee organizations from the Bridging the Gap: Reducing Disparities in Diabetes Care initiative to improve diabetes outcomes by transforming primary care and addressing social needs within evolving payment models.

METHODS

Analysis of eight grantees through site visits, technical assistance calls, grant applications, and publicly available data from US census data (2017) and from Health Resources and Services Administration Uniform Data System Resources data (2018). Organizations represent a range of payment models, health care settings, market factors, geographies, populations, and community resources.

FINDINGS

Grantees are implementing strategies to address medical and social needs through augmented staffing models to support high-risk patients with diabetes (e.g., community health workers, behavioral health specialists), information technology innovations (e.g., software for social needs referrals), and system-wide protocols to identify high-risk populations with gaps in care. Sites identify and address social needs (e.g., food insecurity, housing), invest in human capital to support social needs referrals and coordination (e.g., embedding social service employees in clinics), and work with organizations to connect to community resources. Sites encounter challenges accessing flexible up-front funding to support infrastructure for interventions. Value-based payment mechanisms usually reward clinical performance metrics rather than measures of population health or social needs interventions.

CONCLUSIONS

Federal, state, and private payers should support critical infrastructure to address social needs and incentivize care that addresses social needs and outcomes sensitive to social risk. Population health strategies that address medical and social needs for populations living with diabetes will need to be tailored to a range of health care organizations, geographies, populations, community partners, and market factors. Payment models should support and incentivize these strategies for sustainability.

Tuning ensemble-averaged cargo run length via fractional change in mean kinesin number

The number of motors carrying cargos in biological cells is not well-defined, instead varying from cargo to cargo about a statistical mean. Predictive understanding of motility in cells therefore requires quantitative insights into mixed ensembles of cargos. Toward this goal, here we employed Monte Carlo simulations to investigate statistical ensembles of cargos carried by a Poisson-distributed number of motors. Focusing on the key microtubule-based motor kinesin-1, our simulations utilized experimentally determined single-kinesin characteristics and alterations in kinesin's on- and off-rates caused by cellular factors and/or physical load. We found that a fractional increase in mean kinesin number enhances the ensemble-averaged cargo run length and amplifies run-length sensitivity to changes in single-kinesin on-rate and off-rate. These tuning effects can be further enhanced as solution viscosity increases over the range reported for cells. Together, our data indicate that the physiological range of kinesin number sensitively tunes the motility of mixed cargo populations. These effects have rich implications for quantitative and predictive understanding of cellular motility and its regulation.

Direct observation of the enzyme-intermediate complex of 5-enolpyruvylshikimate-3-phosphate synthase by 13C NMR spectroscopy

The interaction of 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase, 4,5-dideoxyshikimate 3-phosphate (ddS3P), and [2-13C]-and [3-13C]phosphoenolpyruvate (PEP) has been examined by 13C NMR spectroscopy. Although no resonances due to a dead-end intermediate complex could be detected, an enzyme active site specific formation of pyruvate was observed. The interaction of EPSP synthase with shikimate 3-phosphate (S3P) and [2-13C]- or [3-13C]PEP has been examined by 13C NMR spectroscopy. With [2-13C]PEP, in addition to the resonances due to [2-13C]PEP and [8-13C]EPSP, new resonances appeared at 164.8, 110.9, and 107.2 ppm. The resonance at 164.8 ppm has been assigned to enzyme-bound EPSP. The resonance at 110.9 ppm has been assigned to C-8 of an enzyme-free tetrahedral intermediate of the sort originally proposed by Levin and Sprinson [Levin, J. G., & Sprinson, D. B. (1964) J. Biol. Chem. 239, 1142-1150] and recently independently observed by Anderson et al. [Anderson, K. S., Sikorski, J. A., Benesi, A. J., & Johnson, K. A. (1988) J. Am. Chem. Soc. 110, 6577-6579]. The resonance at 107.2 ppm has been assigned to an enzyme-bound intermediate whose structure is closely related to that of the tetrahedral intermediate. With [3-13C]PEP, new resonances appeared at 88.9, 26.2, 25.5, and 24.5 ppm. The resonance at 88.9 ppm has been assigned to enzyme-bound EPSP. The resonance at 26.2 ppm, which was found to correlate with 1.48 ppm by isotope-edited multiple quantum coherence 1H NMR spectroscopy, has been assigned to the methyl group 4-hydroxy-4-methylketoglutarate.(ABSTRACT TRUNCATED AT 250 WORDS)

Decomposition of [ 14 C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using 14 C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain- 14 C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U- 14 C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [ 14 C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.